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until Voyager arrived in the neptunian system this was the least understood of all the planets invisible to the naked eye Neptune was a World hidden from view even through the most powerful of telescopes it appeared as no more than a blurry ball of blue and green the fourth largest planet in the solar system by volume and the third largest by Mass from afar we knew nothing of its atmosphere or its structure and had only faintly observed two of the moons in its orbit Triton and
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narid this was a planet that had remained very firmly in the darkness a distant world that had clung on tightly to its secrets for over 140 years even the discovery of Neptune played out in the darkness the last of the planets to be discovered it is the only one whose existence we predicted before it was ever observed by the human eye for centuries we stared at it without knowing what we
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were looking at almost certainly Galileo was the first human to appear at Neptune directly during a series of observations at the end of 1612 in the beginning of 1613 the data he plotted with his newly invented telescope led him to believe this was a fixed star in the night sky not a planet over the next 200 years many astronomers must have fixed their Gaze on this dim star without
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realizing the significance of its bluish light but the first hint of its true nature would appear not in an eyepiece but in a set of astronomical tables in 1821 the French astronomer Alexi bvar published table astronomic a set of tables predicting the orbits of the three outer planets Jupiter Saturn and Uranus based on Newton's laws of motion and universal gravitation over the next few years
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bal's theoretical work would be tested against the movements in the night sky and his painstaking calculations were rewarded with the confirmation that actual observations of the movements of Jupiter and Saturn adhered precisely to his mathematical predictions however Uranus refused to behave quite so compliantly the movement of the then farthest planet deviated substantially from bv's predicted path and this led him to make a wild suggestion either Newton was wrong or
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perhaps there was an as yet undiscovered Planet lurking in the darkness distorting the passage of Uranus through its gravitational interaction a flurry of astronomers sped to find the hidden Planet the Ultimate Prize for any Stargazer as an acrimonious race kicked off between the British and French to predict the planet's location on the British side of the channel the Cornish astronomer
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and mathematician John couch Adams became obsessed with bv's hypothesis and was convinced he could use nothing more than pen and paper to determine the size position and orbit of this Hidden World by September 1845 Adams had at least partially completed his calculations but unknown to him almost simultaneously the French mathematician Urban ler in Paris was completing his own complex computations of Uranus's path and The elusive eighth planet by the summer of 1846 ler had played
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his hand and announced to the academy on the 31st of August that he had calculated a predicted location for the missing plan it revealing his work just 2 days before Adams secretly sent his own prediction in a letter to the Royal grenwich Observatory for verification in what must be one of the most close-run races in scientific history ler engaged the Berlin observatory in the search for his planet and at 0015 on the night of the 24th of September 1846 Yan Galla with the help
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of his assistant einrich Dar looked through his refracting telescope and and became the first person to knowingly gaze at the eighth and furthest planet in the solar system a planet that had taken decades to locate was found in less than an hour and within one degree of the position L had calculated even today the exact credit for the discovery of Neptune is still disputed but in the winner takes all world of astronomical Discovery it's ler whom history records as the discoverer
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of Neptune the man who discovered a planet with the point of his pen it took another 143 years before we would visit Leber's planet and witness a dynamic violent and volatile world as Voyager Drew closer it began to return a precious set of images that remained to date our only close- range record of this planetary system at first flying past nid the third largest of Neptune's moons Voyager
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captured our only image of this distant world traveling on its massively eccentric orbit around the planet but it was the images of Neptune itself that became increasingly astounding painted across the surface of the planet Voyager revealed Banks of methane clouds that were being whipped around by high altitude winds at speeds of over 2,000 km hour at least five times stronger than the most
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powerful winds ever measured on Earth these were the highest wind speeds we'd witnessed anywhere in the solar system it wasn't just violent winds that we saw through voyager's eyes great hurricane-like storms could be seen moving across its surface the largest being an earth-sized storm system similar to the Great Red Spot on Jupiter which became known as the Great Dark Spot Voyager took multiple
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images of this vast storm system as It sped past the planet skimming the cloud tops of the northern Pole from a distance of just 4,400 kilm as it reached its nearest approach on the 25th of August 1989 no one had expected such massive storms to be Brewing so far from the Sun but just 5 years later with the Hubble telescope up and running we peered back towards Neptune and found that the Great Dark
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Spot had disappeared unlike the giant storms on Jupiter which we've witnessed playing out for centuries it seems that the weather on Neptune is far more transient with the largest events coming and going within the space of a few years the intense weather systems that we witnessed on Neptune remain a tantilizing puzzle the planet is on average 50% further from the Sun than Uranus and receives just 40% of the sunlight that hits its sister world and the surface temperatures of
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both planets are equally intensely cold in fact the temperature of Neptune's outer atmosphere is one of the coldest places in the solar system with temperatures at its Cloud tops measuring aroundus 220° C orbiting this far out in the far Frozen reaches of the solar system explains the blandness of Uranus's weather but why would Neptune even further from the Sun be so active the answer we think lies in a mysterious and Powerful source of heat that we have detected
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coming from deep within the planet all of the planets including Uranus and Neptune have some residual heat locked deep inside them and much of this is the thermal energy that remains from the endless collisions of their creation as well as the heat releasing by the radioactive decay of certain elements in the core however this far out Uranus has rapidly lost this heat and today radiates just 1.1 times the energy it receives from the Sun so that the heat radiating from its
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core is too little to drive any kind of dynamic weather system through its atmosphere Neptune it seems has a far warmer heart and Voyager was able to reveal that the most distant planet radiates 2.61 times as much energy as it receives from the Sun sun it's these unexpectedly high temperatures that help to explain the violent storms we see in its atmosphere as the heat makes its way from the core of the planet and out into space it churns up the entire atmosphere creating Winds
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of extreme ferocity and once they start there is little to stop them Neptune like Uranus is an ice giant a planet composed of a rocky core and a mantle made up of water ammonia and methane ices surrounded by a cold gaseous atmosphere with no solid surface on the planet there are no mountains or continents to break up the flow of the atmospheric gases so this means the winds can whip around the planet picking up speed until they are quite literally supersonic all of this helps
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to give us a reason for Neptune's extreme weather but not an explanation Voyager 2 was unable to reveal why Neptune and Uranus are so different and we still don't know what it is about these planets its formation that left Neptune with far more residual heat making it the far more active of the two Neptune's active atmosphere was not the only surprise Voyager returned to us with the pictures from its two camera system in vibrant and Vivid detail the images also revealed the
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solar system to be home to not one but two blue planets Neptune is a bright blue world but with no liquid water on its surface we know that the origin of this color cannot be the same as here on Earth this deep Cobalt color must be produced by something else in Neptune's atmosphere and Voyager provided the answer using its onboard spectrometer Voyager was able to measure for the first time the
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composition of Neptune's atmosphere and found it to be comprised of 80% hydrogen 18.5% helium and 1.5% methane methane was by far the smallest component yet this is the key to understanding standing Neptune's blue hue the light of the sun contains all the colors of the rainbow but as it hits the surface of a planet it interacts in different ways depending on the molecules it Encounters in the case of the Earth the water that covers our planet absorbs all of the red light
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in sunlight so as the sun strikes the surface only the blue is reflected back it's the same with all the plants on our planet the chlorophyll absorbs the blue and red light so that only green is reflected back on Neptune there is no water to turn the planet blue instead it's the methane that absorbs the red light of the dim and distant Sun reflecting the blue light back out into the
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darkness but things aren't quite as simple as they first appear Uranus is also a blue world but just that bit paler and greener in shade compared with its more distant sibling and yet Uranus also has methane in its atmosphere in fact it has slightly more so Uranus not Neptune should be the darker shade of blue why is this well quite wonderfully we still don't know Voyager looked for other
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constituents in Neptune's atmosphere that could account for the deeper blue but it found nothing that could explain the discrepancy so for now the many differences between these two worlds remain a mystery after over 12 years of traveling Voyager 2 completed its grand tour of the solar system a tiny explorer that had set out from Earth and traveled across 7 billion kilometers of space on a single extraordinary journey to explore all of the outer worlds of the Solar System
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Jupiter Saturn Uranus and Neptune but before it began its long lonely journey into the darkness of interstellar space there was one more brief rendevu left on its itinerary while in the neptunian system syst Voyager had made endless discoveries including the detection of a faint ring system and the confirmation of six new moons in orbit but in those Final hours of close contact as it flew across the North Pole of the planet the mission scientists back at JPL had
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instructed the craft to make one last Intrepid maneuver a close flyby of Neptune's giant Moon Triton just 5 hours after nearly touching the cloud tops of Neptune Voyager traveled within 40,000 kilm of the neptunian Moon and returned the first pictures of this strange and distant world the British astronomer William lassle first spotted Triton on the 10th of October 1846 just 17 days after the discovery of Neptune as astronomers clamored to observe the newly identified Planet it
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was lassle with his homemade telescope who noticed the satellite first although not officially named until many years later Triton would remain the only known satellite of Neptune for over a 100 years until the discovery of narad by Gerard Kyper more of him later in 1949 as Voyager returned the first images of this distant Moon it immediately became apparent that just like Neptune Triton was
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far more active than we had ever imagined here in the furthest reaches of space the seventh largest moon in the solar system was far from a frozen inactive rock it was a geological active world with features unlike anything we had imagined able to image just 40% of its surface due to the fact that most of the northern hemisphere was in darkness Voyager revealed Triton to have a sparsely crated exterior with a strange network of ridges and valleys covering its entire surface
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including in the Western Hemisphere a region dumped the Canter Loop terrain because of its striking similarity to the skin of a melon all of this evidence pointed to the fact that the surface of Triton was young not battered and ancient like that of our moon a surface that even though it had been recorded by voyagers instruments as one of the coldest places in the solar system atus 235° C seemed to be being resurfaced by active volcanism occurring across the planet
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but this was not volcanism as we understand it here on Earth there is no molten rock beneath the surface of Triton this is an ice workm world with a surface covered in a frozen mixture of nitrogen water ice and carbon dioxide any volcano that exists here would be a cryo volcano erupting water ammonia and methane from below the surface cryo magma that would immediately solidify in the extreme low temperatures of the surface and as Voyager appeared closer at the surface of Triton
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it captured a series of images of the Southern polar region that appeared to provide evidence of such geological activity lurking amongst the flat volcanic Plains and rift valleys was a set of distinct features that at once caught the eye scattered across the surface were what appeared to be at least 50 dark plumes Voyager was traveling so fast and so far away from the Moon that it was unable to get close-ups of these intriguing plumes but we are certain that they are the evidence
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of ice geers and that the dark streaks of dust deposit it's left on the surface by the eruption of these geers according to planetary scientist Noah Hammond it was a big surpris to see active gas going on in Triton shooting 8 kilm into the air and we think these geas might be forming as a result of nitrogen ice which is being vaporized by the sun both of the gas that Voyager 2 observed which are currently blowing up are concentrated on the warmest part of Triton where the sunlight
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is striking the hardest and as the sunlight light pierces through the nitrogen ice it starts to turn that nitrogen ice back into a gas again and that gas builds up and builds up until it has enough energy to break through the ice and lift dust all the way up into the atmosphere further analysis of the images suggested that at least four of these geeses were active at the time of voyage's fly past belching clouds of ice and dust 8 kilomet up into the thin neptunian atmosphere
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before falling back down to the surface over 100 km downwind perhaps even more astonishingly we have been able to actually formulate a hypothesis for the mechanism that Lies Beneath them the key to understanding why this wondrous geological activity occurs in the most unlikely of places seems to involve their location on the surface of Triton from the Imaging data that Voyager 2 returned it seems the gas tend to erupt on the most sunlit part of Triton's surface from
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a distance of 4.5 billion kilm the Sun's rays are faint and the amount of thermal energy landing on the surface is low but combined with the specific chemistry on Triton surface the effect of the sun can still be dramatic what seems to be happening is that sunlight falling on the thin layer of nitrogen ice that covers Triton is penetrating the surface and heating up a layer of Darker methane
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particles a meter below the surface the methane acts as a subsurface greenhouse gas trapping the Heat below the surface and radiating that heat back up through the Frozen nitrogen even though this mechanism creates a temperature difference of just 4° C between the ambient surface temperature and that of the warmer interior this difference is enough to melt the Frozen nitrogen and create
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pockets of gas sitting beneath the nitrogen ice that gas is kept under pressure building up until ultimately it punches through the nitrogen ice creating the gers of Triton and carrying the dark ice particles up to 8 kilm into the sky although the faint light of the sun is just strong enough to power Triton's gas it's simply too weak to have driven the other geological processes that have
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created the network of valleys and crevasses we see all across the surface it seems that something in Triton's past must have heated the moon enough to drastically alter its terrain and a potential clue to the source of that ancient heat can be found in the Oddity of Triton's orbit unlike every other large moon in the solar system Triton orbits in the opposite direction to the spin of the planet traveling around Neptune in its tidily locked orbit with the same side facing inwards
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at all times Triton orbits in a clockwise Direction while Neptune spins on its axis every 16.11 hours anticlockwise such dissonance between planet and satellite suggests that it is very unlikely that Triton and Neptune formed at the same time a planet and moon system fashioned from an identical collapsing cloud of gas and dust at the same moment would tend to spin and orbit in the same direction as the spin of the initial dust cloud just like the overwhelming
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majority of moons we see in the solar system today so the most likely explanation is that Triton joined Neptune much later a visitor to the neptunian system that unlike Voyager never left like Uranus we don't know for certain the Deep history of Triton but all the evidence from its orbit and surface features point to the possibility that long ago Triton was not a moon at all to understand where it might have come from we need to look beyond the neptunian
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system and peer further out into the darkness it was only relatively recently that we confirmed the existence of a region of the solar system system now known as the Kyper belt a dis of millions of objects that stretches out from the orbit of Neptune to at least 50 AU from the Sun similar to the asteroid belt in structure but far larger in scale we had long speculated that such a region
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might exist but it wasn't until the discovery of an icy object known as 15760 albian in 1992 that we were able to put together a Body of Proof the discovery of this region was a turning point in our knowledge about our solar system according to Alan stern of the New Horizon's Mission the Kyer belt was so revolutionary because as it's so far from the Sun the temperatures out there are almost absolute zeros so everything is so well preserved it's an archaeological dig if you
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will into the early history of our solar system so it's a scientific Wonderland and you put all that together redrawing the map and putting it in our place about who's the Oddball now it's not Pluto it's the Earth or Jupiter that's the Oddball and then having this museum piece plac in the solar system where everything is so well preserved I can't think of a bigger discovery that we've made that's reshaped our thinking so profoundly in all the Decades of space exploration
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albian was the first trans neptunian object to be identified since the discovery of Pluto in its Moon Sharon and this finding launched a flurry of further Revelations that now put the number of identif objects in the Kyer Bel region at around 2,400 we think there are at least 100,000 objects bigger than 100 km wide in the Kyer belt just like the asteroid belt this dispersed region of debris is composed from the remnants of our solar systems formation but whereas the asteroid belt
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is a disc of Rocky fragments we think the Kyper belt is made up of icy objects with methane water and ammonia the major ingredients and it's that list of ingredients that leads us back to Triton and its strange history We Believe now that perhaps only Triton grew up out in the Kyper belt amongst the millions of other Frozen lumps of water ammonia and methane circling the sun before something such as a collision Disturbed its orbit and flung it inwards plucked from the Kyer
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belt Triton would be captured by the gravitational pull of Neptune and forever trapped in its strange orbit around the blue planet today Triton orbits in a nice regular circle around Neptune a bit like the way that our moon orbits around the Earth but to begin with this newly captured satellite would have almost certainly been in an a chaotic orbit glancing past the planet it would have started
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along a wide elliptical path around Neptune bringing it from far out to close in on every Revolution this would have meant that as Triton orbited Neptune the gravitational pull would be constantly changing stretching and squashing the moon just as Jupiter does to IO today with the result that the friction of these tidal forces would have heated up the interior of Triton creating far more activity than the erupting gas we see today through this process of tidal
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heating the ancient interior of ice would have become molten and volatile exploding up through cracks and faults in the moon's crust creating the Ragged surface we see today over time as the orbit adjusts into a more regular circular path the friction reduced the heating diminished and so what we're left with is an icy frozen Moon circling the wrong way around its Planet the subtle scars of its early life written across its surface All That Remains today of that dramatic
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violent past are the Geyers powered by The Faint light of the Sun Painting dark streaks across the now quiescent surface as Voyager 2 sped away from Triton and Neptune at over 60,000 kmph the Planetary Exploration phase of this extraordinary Mission finally came to an end its exploration would continue beyond even the furthest reaches of our solar system and would extend into the unknown depths of interstellar space but its time as a planetary explorer was over a tiny spacecraft
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built with a thousand human hands had Shone a light into the darkness revealing the secrets of Worlds that had been hidden in the night for over 4 billion years as yet we have not returned but while Neptune and Uranus have fallen back into the distance viewed only through the lenses of our most powerful telescopes another even more distant world was out there waiting for our first arrival on the night of the 23rd of January 1930 a 23-year-old Junior researcher at the
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Lowel observatory in Flagstaff Arizona took an image of the night sky using a 13-in astrograph a telescope designed for the sole purpose of astrophotography Clyde tomore had been at the observatory for just over a year when he took the image one of hundreds he had captured over previous months a keen amateur astronomer he had landed this first job after sending in a series of drawings he had made of Jupiter and Mars using telescopes he had built at his home every night at
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the Lowel tombor performed the same task using the astrograph to photograph a precise section of sky that he would then image again a few nights later the task was a little laborious but its purpose was profound because hiding within the near identical images Tombo was on the hunt for a new world the enigmatic Planet X unless we think hard our intellects are confined to the surface of the
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the Earth after Sunset Beyond cities the universe appears a destination for the imagination albe it separated by a seemingly unbridgeable Gulf this may be true for the stars but it is not so for the planets there are times when Mars Venus Jupiter and Saturn dominate the sky bright lights that shift position nightly against the fixed Stars commanding our attention even if we aren't certain
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what we're looking the distances are still vast by terrestrial standards but despite appearances the gulf is certainly not unbridgeable because we have visited all of these planets and taken our first steps into the outer reaches of the solar system Beyond and yet the wandering lights in the dark still feel detached from Human Affairs and the time and effort we've spent in visiting them might
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seem to be an Indulgence this assumption however is profoundly wrong the solar system is a system the sun and the eight major planets and countless billions of minor planets moons asteroids comets and unclassified lumps of ice and rock were formed back in the mids of time and they continue to evolve as one we rarely notice the dynamic interconnected nature of our system although asteroid strikes on our planet are not such a rare occurrence the cheliabinsk impact in February 2013
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injured 1500 people when a 12,000 ton asteroid broke up as it entered the Earth's atmosphere at 60 times the speed of sound and the tunguska air burst in Siberia in 1908 flattened 800 square mil of forest in an explosion comparable to that of the most powerful hydrogen bomb ever tested the surface of the Moon Bears Testament to a record of violence and destruction from the skies that the
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Earth has also endured but the Relentless eraser of craters by weathering and our good fortune that no major impacts have occurred in recorded human history are the reason for our misplaced sense of isolation from the heavens the interdependent nature of the solar system has become more evident as we've begun to understand its history it's tempting to imagine that the physical layout of
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the planets is a fossilized remnant of primordial patterns in the collapsing dust cloud around the newly ignited done 4.6 billion years ago but our exploration of the planets coupled with increasingly powerful computer simulations of the evolution of the solar system has revealed that this is not the case planetary orbits are prone to instability particularly so in the early more chaotic years when our solar system was young the details of precisely how the planetary orbits have
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shifted are still uncertain but we now suspect that mercury the innermost planet began life much further out and was deflected inwards to its present day seared orbit Jupiter and Saturn may have drifted inwards shortly after their formation before reversing their course and retreating but not before affecting the distribution of material out of which Mars and Earth would later form around the time that life began on Earth Neptune and Uranus may have been flung outwards disrupting
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the orbits of billions of smaller objects far from the Sun the record of this time of unprecedented violence known as the late heavy bombardment is written across the scarred surface of the Moon itself most likely formed in a glancing interplanetary collision between Earth and a mars-sized planet 4.5 billion years ago the planets are like snowflakes the detail of their structure their composition size Spin and climate are a frozen record of their past an understanding
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of the planets beyond Earth is therefore a prerequisite for understanding our home world and that in turn is a prerequisite for understanding ourselves Earth is unique in the solar system because it's a planet with a complex ecosystem the Genesis and subsequent 4 billion year evolution of life on Earth required planetary characteristics which are necessarily linked to the evolution of the system as a whole there had to be liquid water on the surface Surf and much of this water
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was delivered after the Earth's formation by Icy water-rich asteroids and comets possibly deflected inwards from the outer solar system by Jupiter these Rivers seas and lakes of extraterrestrial origin had to persist for the best part of 4 billion years which required a stable atmosphere to maintain surface temperatures and pressures within a limited range 4 billion years is a long time around a third of the age of the universe the sun has brightened by 25% since the Earth formed
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which makes the stability of our environment all the more difficult to understand in a chaotic system of planets around an evolving Star a planet with life-supporting properties and the remarkable stability enjoyed by Earth over billions of years may be extremely unusual the study of our sister worlds Mars and Venus has proved instructive in understanding just how fortunate we may have been
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and how delicate our position today might be 4 billion years ago as life began on Earth Mars was also earthlike it had oceans and rivers and active geology and complex surface chemistry the ingredients of life one of the primary goals of the fleet of spacecraft currently in orbit around and exploring the surface of Mars is to search for evidence of past or even present life and to understand why the red planet was transformed from a potential Eden at the dawn of the solar
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system to The Frigid desert world we observe today the story is complex but one of the most important differences between the two worlds is size Mars is just 1/10th the mass of Earth too small to hang on to its internal heat its protective magnetic field and its atmosphere for much more than a billion years after its formation yet Mars formed in a similar region of the solar system to Earth
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and Venus so why is it so small the answer May lie in the fast changing orbits of Jupiter and Saturn early in the Solar System's history the history of Venus is perhaps even more puzzling in part because of the immense difficulty of exploring the planet Venus is often described as a vision of Hell surface temperatures are high enough to melt lead and the atmospheric pressure is 90 times that on Earth sulfuric acid raindrops fall from its clouds and yet long ago Venus too
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may have been earthlike perhaps there were once venusians before a runaway greenhouse effect took hold and began destroying Venus's temperate climate about 2.5 billion years ago although this date is highly uncertain taken together the stories of the three large terrestrial planets are salutary if an alien astronomer observed our solar system from afar they would classify Mars Earth and Venus as potentially living worlds orbiting as they do inside the so-called habitable
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zone around the Sun the region within which if atmospheric conditions are right liquid water can exist on the surface of the planet all three worlds May once have been habitable and all three worlds May once have harbored life but now only Earth supports a complex ecosystem let alone a civilization understanding why Mars and Venus diverged so significantly from Earth over the last 4 billion years will provide great insight into the fragility of Worlds and perhaps suggest
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whether our own Good Fortune is near impossible to comprehend or merely outrageous planets change ours could change at any moment a stray Comet from the Frozen Kyper belt beyond the orbit of Neptune could put an end to our story we could also put an end to ourselves the study of Venus might help us avoid one of the ways by which we could destroy our civilization because it shows us what
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greenhouse gases can do to a world I think one of the reasons why anthropogenic climate change is so difficult for a certain type of person to accept is that atmospheres seem ethereal and tenuous and incapable of trapping enough heat to modify the temperatures on a planet significantly for such people I suggest to trip to Venus where they will be squashed and boiled and dissolved on the surface of Earth's twin the exploration of the planets then is not an Indulgence if
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we want to know how we came to be here we need to understand the histories of the planet that gave birth to us and the system that gave birth to it we are children of Earth and also Children of the solar system understanding our history is important because it places our existence in context the more we learn about the events that led to the emergence of humans on this planet only a few 100,000 years ago the more we are forced to Marvel at the sheer unlikeliness
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of it all we needed Jupiter and the comets and asteroids and countless collisions and mergers and near catastrophes stretching back 4.6 billion years there are valid objections to this way of thinking it is an objective fact that we are here and our future should be our primary concern that may be so but I argue that a deeper understanding of the evolution of the planets is essential for
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our continued prosperity and existence on this one the threat of catastrophic climate change is an obvious example but there are many other reasons why knowledge is important there is feedback in human Affairs our Collective State of Mind affects the decisions we make to confine our imaginations to the surface of the Earth is to ignore both our immense good fortune and the fragility of our
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position a wider knowledge of both will I believe help secure a safer and more prosperous future Earth sits a mere 150 million kilm from the Sun not too hot not too cold with surface temperatures ranging from -88 to + 58° C this goldilock location has created a stability of climate that despite the best efforts of ice ages and impacts has allowed life to maintain an unbroken chain for nearly 4 billion years and yet we know for certain that it cannot last our sun like every star in
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the universe is far from static stars have life cycles of their own and eventually the hydrogen fuel that powers the nucleus reactions within a star will begin to run out and the star will enter the final phases of its lifetime it will expand cool and change color to become a red giant small stars like har son will undergo a relatively peaceful and beautiful death which will see it pass through a planetary nebula phase to become a white dwarf which will cool down over time to
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leave a brown dwarf life on Earth has prospered through our Sun's middle years but these Optimum conditions are waning at first the changes will be invisible but a billion years from now they will be obvious to any life forms left on the planet an immense Sun filling the sky will warm and transform itself and the Earth that it shines upon the sun is both the giver and the taker of Life on our planet it is one of the great paradoxes of the universe that as the life of a star like
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ours begins to way its size and Luminosity will increase a rise in Luminosity of just 10% will see the average surface temperature on Earth rise to 47° C instead of the 15° C that it is today the effect of this rise in temperature manifests in a lifting of vast amounts of water vapor from the oceans into the atmosphere creating a greenhouse effect that could quickly and rapidly run out of
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control evaporating the ocean ions and sending the surface temperature skyrocketing astrobiologist David grinspoon explains the greenhouse effect is the name we give to the physical process by which planets heat up through the interaction of their atmospheres and solar radiation basically solar radiation comes in what we call the visible wavelengths primarily their wavelengths that we can see and most atmospheric gases are very transparent to visible radiation so so light from
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the sun comes through pretty much unimpeded by an atmosphere and reaches the surface of a planet then the surface of the planet radiates that radiation in infrared because planets are much cooler than the Sun and that means they radiate at much longer wavelengths what we call infrared or heat radiation that infrared radiation doesn't make it through an atmosphere so easily some of the atmospheric gases the ones we call greenhouse gases block infrared radiation and so therefore
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the more of those greenhouse gases that are in a planet's atmosphere the harder it is for that surface radiation to make it back out into space and the more that planet will heat up estimates of the time scale that we'll see our oceans disappear very massively and are heavily influenced by a multitude of factors but fewer in doubt that by the time our planet reaches its 8 billionth birthday in 3.5 billion years time the end will be in sight with temperatures heading above 1,000°
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life will have long disappeared from a surface that is beginning to melt under the burning Sun moving even further into the future the Outlook becomes Bleaker as the sun enters old age it will grow into a red giant engulfing the Earth within its expanding atmosphere moonless lifeless and perhaps reduced to its inner core our planet and the civilizations it once harbored will be nothing
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but a distant memory etched in the atoms that made us all as they are dispersed amongst the cosmos for planet Earth the clock is ticking and time is slowly running out but ours is far from the only world to enjoy its moment in the sun across the history of our solar system stretching deep into its ancient past and reaching far into its future we see stories of worlds in a constant battle with
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our everchanging star close in ancient worlds such as mercury which long ago lost their fight with the sun are taunted by views of earth and what might have been further out and even hotter Venus circles shrouded in a choking cloak of cloud and even further beyond the Earth Mars sits cold and Barren Beyond these Sun itss Frozen worlds await huddled In Perpetual hibernation anticipating the moment when the warmth of the Sun reaches out far enough with sufficient heat to trigger a
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first spring on that day mountains of ice will melt rivers of water will flow and where there was once only bleakness in the distant future on planets once Frozen and lifeless we might find a place that looks very much like home the story of our solar system is not as we once thought it Eternal and unchanging instead it is a place of endless transformation it is a narrative that repeats itself with a predictable Rhythm as one world passes another comes into the light only
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one planet has maintain stability for almost the entire life of the solar system the Earth has remained inh habitable for at least 4 billion years while change has played out all around it what makes the Earth so lucky compared to all of its terrestrial siblings to answer that question we need to look not just at our planet but at the whole of the solar system going right back to the very beginning for the first few million years after its birth there were no terrestrial worlds
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to see the sun rise and there were no no days no nights no circular tracks around it instead surrounding our infant star was a vast cloud of dust and gas a tiny fraction of the material left over from the sun's formation this swirling Cloud would one day coales to form the various planets of the solar system and many other smaller bodies but at this time 4.7 billion years ago there was nothing but tiny specks of dust reflecting back the light of our slowly growing star only time
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vast amounts of empty time would allow enough of this gas and dust to catch and cluster randomly forming the smallest of seeds most of these seeds would hardly get the chance to grow at all smashed apart and returned to the immense swirl of dust from when they arose just a few would grow big enough and survive long enough to capture and condense more of the cloud slowly increasing their
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mass and density we still do not fully understand the process by which grains of dust no thicker than a human hair can amass to become Rocky objects the size of a car and as yet no model exists to explain this part of the evolution of a planet but what we do know is that once that disc of gas and dust becomes populated with clumps of rock that make it past the meat meter sized barrier a powerful force comes into play to propel the process forward these newly formed
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planetesimals are big enough to allow the great sculpting force of gravity to draw the clumps together growing to sizes of over a kilometer in length swirling around the Sun thousands upon thousands of these objects live and die colliding and coalescing under the increasing gravitational forces of attraction and until eventually just a few emerge as planetary embryos moon-sized bodies known as protoplanets in the last violent stages of the process of planetary birth these
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protoplanets swirl around in crowded orbits and many are destroyed return to the dust of their Origins but occasionally when a collision brings two or more of these giant objects together the size of this mass of rock becomes big enough for Gravity to pull it in from all sides creating a sphere Fe of newly formed Rock a new world in that moment a planet is born each of the terrestrial planets in our solar system was born this way they are the survivors of a process that destroys
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far more worlds than it ever creates and which left just four rocky planets remaining starting closest to the Sun with Mercury then Venus Earth and finally farthest out the cold and dead world of M STS today these four worlds all look vastly different and yet all were created the same way made up of the same ingredients and orbiting the same star so why have they ended up so distinct from each other and with such starkly different environments and what makes this place the Earth
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so unique the only one of the rocks that has blossomed with life to understand we have to look deep into the past of our solar system to explore the unique history of each of the planets by means of amazing feats of human engineering across billions of miles and into environments of unknown and unimaginable extremes getting to the smallest planet in the solar system is anything but easy skirting past the Sun at a distance of just 46 million kilometers at the closest point in its
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orbit Mercury is a planet that is not only held deep in the gravitational grip of our massive star but is also moving at an average orbital speed of 48 km/s by far the fastest orbiting planet in the solar system and far outpacing the Earth more leisurely 30 km/s it needs to whip around this quickly otherwise it would have fallen into the sun's Embrace long ago but the combination of its speed and position make it a planet that's immensely difficult to get close to and even
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harder to get into orbit around in order to do so you have to travel fast enough to catch up with Mercury but not so fast that you cannot somehow slow down to prevent a headlong descent into the Sun and that challenge has meant that until relatively recently it was the least explored of all the terrestrial planets for many decades our first and only closeup glimpse of the innermost Rock orbiting the Sun came from the Mariner t spacecraft when on three separate occasions in
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1974 and 1975 it briefly flew past Mercury this was the first spacecraft to use another planet to slingshot itself into a different flight path using a fly by a Venus to bend its trajectory to allow it to enter an orbit that would bring it near enough to Mercury to photograph it close up clad in protection to ensure it could survive the intense solar radiation and immense extremes of temperature Marin 10 was able to send back the first detailed images of mercury as it flew past
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at just over 200 Mi above its surface it passed by the same sunlet side of mercury each time so it was only able to map 40 to 45% of Mercury's surface the spacecraft took over 2,800 photos which gave us never before seen views of the planet's cratered moonlike surface a surface that we had never previously been able to fully resolve through earth-based observation despite the beauty of the pictures taken it wasn't the images from Marin 10 that really surprised us
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it was the data the probe collected relating to Mercury's geology which pointed to a much more surprising history of the planet than had previously been imagined Mercury it seemed was far from being just a scorched husk marinina was able to sense the remains of an atmosphere consisting primarily of helium as well as a magnetic field and a large iron-rich core opening a mystery that
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would remain unexplored for another 30 years as it flew past Mercury for the last time on the 16th of March 1975 the transmitters were Switched Off and its contact with Earth silenced Mission completed Mariner 10 began a lonely orbit of the Sun that as far as We Know continues to this day at First Sight many things about Mercury simply don't make sense during its 88 day orbit around the sun it
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travels in a lopsided elliptical orbit which means it can be as far away from the Sun as 70 million kilm but occasionally as close as 46 million kilm this is by far the most irregular of orbits of all the planets but it is not the end of Mercury's Oddity temperatures at midday can rise to 430° C on the surface but at night because it's a small planet and it has no atmosphere temperatures fall
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to minus 170° giving it the greatest temperature swing of any known body in the solar system its rotation is also unusual gravitationally locked to the sun in what is known as a 3:2 spin orbital resonance this means the planet spins precisely three times on its axis for every two orbits which in turn means that its day is twice as long as its year in effect you could be traveling over its surface at walking pace and keep the Sun at the same point in the sky as you strolled through
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Eternal Twilight as planetary scientist Nancy shabo explains a day on Mercury is not like a day on Earth it has a very unusual orbit it has to go around the Sun twice to have one complete C solar day on the planet where the sun goes from directly overhead to directly overhead and this actually takes 176 Earth days because of the planet's orbit There Are Places on the mercurian surface where a
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hypothetical Observer would be able to see the 2 and 1 half times larger in the sky sun appear to rise and set twice during one mercurian day it rises then arcs across the sky stops moves back towards the rising Horizon stops again and finally restarts its Journey towards the setting Horizon most of Mercury's anomalies can be explained by the orbital mechanics of its Journey around the Sun except that is for the odd elliptical orbit that takes it on such an oval-shaped elongated
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course this irregularity has puzzled astronomers for centuries and hints at an ancient planet that was very different from the Mercury we see today to truly begin to understand Mercury's history we had to wait nearly 40 years before we could return to her on the 18th of March 2011 NASA's messenger spacecraft became the first to enter Mercury's orbit and over the next four years it succeeded
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in not only photographing 100% of the planet's surface but also collecting extensive data on its geology but before any of this could happen messenger had to take perhaps the most Securus route in the history of our exploration of the solar system just passing close to Mercury to take a few snaps as Marin attend did is hard enough but actually entering into its orbit was thought to be either too difficult to achieve or too costly to execute as Cosmo chemist on the
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messenger Mission Larry knitler explained there are two major challenges to getting a spacecraft into orbit around Mercury gravity and money when you go from Earth to Mercury you're falling into the gravitational well of the sun which makes you accelerate faster and faster as you get closer and if you were to go straight from Earth to Mercury this means that you would basically just zip right by the planet or you would need to bring an incredible amount of fuel to put the brakes
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on more than you could actually afford a number of missions never made it further than pencil and paper While others floundered and failed at the proposal stage it was only when Chen Juan Yen a NASA engineer from the jet propulsion laboratory JPL provided a trajectory that could not only get a craft into orbit but could do it at an estimated bargain bucket cost of $280 million that the messenger Mission could really begin to take flight taking off from Cape Canaveral on the
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3rd of August 2004 messenger began a 6-year 7mon 6 16-day journey to Mercury that would take it on a 7.9 billion kilm trajectory before it entered into orbit around the smallest of all the planets to arrive at Mercury with the right speed and on the right course would require a complex route that would entail a number of gravity assist Maneuvers around the earth Venus and Mercury itself to
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reduce the speed of the craft relative to Mercury so combined with the brief ing of its large rocket engine to finally insert it into orbit this Mission profile allowed Messenger to complete its Voyage without the need to carry the vast reserves of fuel required to slow its Passage through the firing of rockets this design made the craft lighter and cheaper but ultimately much slower almost 7 years was a long time to wait for the team patiently charting its progress across the
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Stars Larry knitler described mage pass's course as sneaking up on Mercury by taking a 7-year Journey flying around the Sun many times doing multiple flybys around Mercury and Venus and each time transferring some of the Craft's speed and energy to the planet so it could slow down so that when we finally got to Mercury after 7 years we were able to fire our engine just a little bit to slow down even more and get captured by the weak gravitational field of the planet appropriately
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when messenger finally entered into Mercury's orbit at 0045 UTC on the 18th of March 2011 the path it settled into was highly elliptical this orbit took it on a 12h hourly cycle from 200 km above the planet's surface to 10,000 km away from it it may seem like an odd orbit for a craft with the singular aim of getting as close to Mercury as possible but this was an essential part of the design Des of the mission vital to protect messenger from the fierce heat radiated by the
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scorching hot surface of mercury the sunlight reflected from the surface is so powerful it would have literally melted the solder holding the spacecraft together if it wasn't given time to cool down between its closest approaches to the planet protected by an enormous ceramic solar shield and its eccentric orbit messenger could begin its work for 2 years the spacecraft mapped pretty much every bit of the surface of mercury and the images beamed back to Earth revealed the
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planet that's been in the firing line for billions of years too small to hold on to an atmosphere that might protect it from meteorites and lacking any processes to recycle old terrain Mercury's ancient surface is the most crated place in the solar system the Mariner 10 Mission had enabled scientists to see about half of the planet so the first real glimpses into the terrain of mercury came from the flybys of Messenger as planetary scientist Nancy shabbo explains before messenger
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we had only seen 45% of the planet and we saw some stuff during the flybys before we went into orbit but after orbiting the planet we've now mapped 100% of the planet and seen nearly everywhere there are some permanently shadowed regions which are still mysterious but after mapping the full planet we have a good idea of what the surface looks like and craters are absolutely a dominant land form this planet has been sitting there for billions of years and been hit over and over and
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it hasn't had a lot of processes to destroy those craters amongst the thousands upon thousands of craters on Mercury the largest by far is caloris plena a lowland Basin 1,525 km in diameter that is thought to have formed in the early years of the solar system around 3.9 billion years ago it was first spotted as Mariner 10 sped past in 1974 but due to the trajectory and timing of The Craft
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only half of it was lit so the full character of this crater remained a mystery for another 30 years until messenger could photograph it in all of its Glory taking one of its very first photos messenger revealed caloris to be bigger than had been previously estimated encircled by a range of mountains Rising 2 km from the mercurian surface whose Peaks create a 1,000 km boundary around the lava Plains within on the other side of the mountains the vast amount of material that was
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lifted from the planet's surface at the moment of impact formed a series of concentric rings around the Basin stretching over 1,000 km from its Edge the Collision that created caloris hit Mercury with such force that it also had more Global consequences messenger photographed in great detail an area named in the not particularly scientific vernacular the weird terrain a region at the planet's diametrically opposite point the antipode to caloris this area of strange
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geological formations distinct from the rest of the surrounding terrain was likely created by the seismic shock wave of the caloris impact reverberating through the whole of the planet right up until the end of its mission in 2015 messenger continued to uncover many of Mercury's Secrets including a few very particular surprises using a combination of Photography spectroscopy and Laser topography messenger revealed tantalizing evidence that even this close to the
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Sun water ice can exist on the surface of a planet even though the sun blasts much of Mercury's surface the tilt of its rotational axis is almost zero so there are craters and features around the planet's poles that never see direct sunlight combined with the lack of atmosphere these regions are forever exposed to the freezing temperatures of space and it's in this environment that messenger was able to record the clear signature of water ice here in the Eternal Night of a polar
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crater it's cold enough for ice to survive for millions of years just meters away from the Savage ferocity of the Sun's light however messenger's most startling Discovery was still to come the mission objectives had been developed to explore the Deep history of mercury and provide data to test against our theories of the formation and early life of the planet messenger was equipped with a collection of spectrometers designed to analyze the composition of mercury at different
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depths the messenger team had worked on a detailed set of predictions outlining the chemistry of the planet but as the spacecraft began to sniff at the mercurian surface it soon became clear that our assumptions had not been quite right as the gamma ray and x-ray spectrometers analyzed the elements on Mercury's surface they began to measure the unexpected characteristic signature of a number of elements such as phosphorus potassium and sulfur at much higher levels than they were
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expecting up to this point the working hypothesis had been that during the formation of mercury and all the rocky planets as The Rock condensed and combined to form the planet the heavier elements like iron would sink towards the center forming the bulk of the core while the lighter elements such as phosphorus and sulfur would remain near the surface these more volatile elements would then be expected to be stripped away from the surface particularly on a planet like Mercury
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which is so close to the Sun and yet the messenger data confirmed high levels of potassium and sulfur was detected at 10 times the abundance of the element on Earth or the moon both are volatile elements easily vaporized and when this close to the Sun they simply should not have survived the planet's birth on top of that the messenger data confirmed what we had long suspected about the
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structure of mercury that it is the dense of all the planets with a massive iron core making up 75% of the planet's radius compared to just over 50% here on Earth the core creates a strange lopsided magnetic field indicating that the internal dynamics of the planet are different to anything we have seen before all of this adds up to making Mercury something of a mystery as nothing quite Accords The Eccentric orbit the abundance of volatile elements on the surface and the oversized
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iron core all point to the planet having a history far more complex than was first imagined and the only explanation to make sense of the messenger data is that mercury was not born in its current sun-scorched position it has long been supposedly known that the orbits of the planets are Eternal stable Loops that sustain the structure of the solar system in an endless Rhythm but everything we are learning now suggests that this is far from the whole story Mercury like all four of
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the rocky siblings was formed of molten rock a few million years later as the young Planet began to cool its crust solidified and its Journey around the Sun transformed from being part of a swirling Cloud into a clearly defined passage an orbit the path the infant Mercury traveled however was most probably far removed from the course it now holds the young Mercury was born not as the closest
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planet to the Sun but at a much greater distance far beyond the orbit of Venus beyond Earth perhaps even Beyond Mars This was a planet that came into being in the mildest region of the solar system it was far enough away from the Sun to allow volatile elements like sulfur potassium and phosphorus to be folded into its first rocks without being vaporized Away by the heat of the Sun but maybe
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near enough for its surface to be warmed perhaps even just the right amount for liquid water to settle on its surface this may well have been a planet big enough to hold an atmosphere a watery world upon which all the ingredients of Life Could well have existed Mercury it seems really did have its own moment in the Sun but these hopeful Beginnings were not to last today it's hard to imagine the planets in any orbit other than our night sky they feel Eternal permanent and
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so it's natural to think of the solar system as a piece of celestial Clockwork a mechanism running with perpetual and unchanging Precision marking out the passage of time in time frames that we can comprehend days weeks months and years the motion and trajectory of the planets is just that Clockwork we use these markers to plot out the 24 hours of a day 365 days of a year and the lunar cycle is of course intimately linked to our months beyond that Newton's Laws of universal
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gravitation first described in 1687 allow us to this day to plot out the trajectories of all the heavenly bodies far into the future and back into the distant past this predictability of motion is what allows us to plot great astronomical events such as eclipses and transits far into the future it's why for example we can predict that on the 14th of September 2099 the Sun Moon and Earth will be in precise alignment to create the final total solar eclipse of the 21st century across
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North America but 100 years ahead or behind us is nothing more than a proverbial blink in terms of the life of the solar system and over longer durations the Clockwork becomes a lot less reliable if there was only one planet orbiting one star for example if Mercury was the orphan child of the solar system we would be able to calculate precisely the gravitational force between Mercury and the Sun and to plot Mercury's orbit around the sun with essentially infinite Precision but add
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one more planet into our rather vacant imaginary solar system let's say we make it Jupiter so there is now a gravitational force between all three three objects the Sun Mercury and Jupiter and it's no longer possible to calculate exactly where they're all going to be in the future or where they were at some point in the past when there are more than two objects in play at any one time you have what physicists call a chaotic system it means the planets can push and
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pull one another moving entire orbits in ways we simply cannot predict so the further we look back in time the less certain we are of the position of any of the planets our mathematics fails so instead we have to rely on circumstantial evidence to piece together a picture of the past in the case of mercury it's the evidence from messenger detailing the levels of volatile elements like potassium and sulfur that enable us to begin to understand the early life of the planet and infer
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that mercury must have begun life further out in the solar system than it finds itself today so what happened next how did a planet that began its life in The Sweet Spot of the solar system end up in the scorched interior the answer lies in the other clue messenger confirmed for us Mercury's massive iron core relative to its size mercury has the most massive core of any of the rocky planets
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75% of its diameter and almost half of its mass is molten iron compared to around just a fifth of the mass of the Earth we've suspected the Oddity of Mercury's composition for well over 150 years and that's because of some brilliant deduction by a German astronomer called Yan France enker who determined the mass of mercury by measuring the gravitational effect it had on a passing Comet a comet that we now call unsurprisingly Comet anchor with an approximation of the planet's
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mass we are able to calculate the density of the planet and with that calculation approximate its composition so we've known for some time that mercury is odd but only with the arrival of messenger did we begin to reveal just how odd the smallest planet actually is by accurately measuring Mercury's magnetic field we've been able to confirm that far from being a geologically dead planet Mercury has a dynamic magnetic field driven by an internal Force indicating that
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the core is at least partially liquid this goes against the conventional thinking of planetary Dynamics because we would expect a planet as small as mercury to have lost its internal heat long ago just as Mars lost its heat because of its size we would have expected the core of mercury to have cooled and solidified but Messengers data proved otherwise by combining precise measurements of Mercury's gravity field with the extraordinary mapping of its surface messenger found that
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Mercury's structure is unique in the solar system it appears to have a solid silicate crust and mantle above a solid layer of ion sulfide which surrounds a deeper liquid core layer possibly with a solid inner core at the center of the planet this challenges all the theories about its formation 4 and A2 billion years ago we know that the inner solar system was in turmoil in the middle of it all the newly born Mercury found itself orbiting far out from today's intimate
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proximity with the sun surrounded by Rocky debris and scores of planetary embryos all jockeying for position the young solar system was still a place where planets could live or die but it wasn't just the rocky planets that found themselves Disturbed Jupiter the largest and oldest of all the planets was on the move and when a planet of that size shifts its position there are almost always
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casualties but for now all we need to know is that the evidence suggests that the juvenile Mercury was kicked by the gravitational force of Jupiter on an inward trajectory finding itself flung in towards the Sun and into the path of danger in the crowded orbits of the early solar system such a change of course was fraught with danger and all of the evidence indicated that this was the
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most violent and defining of turns in Mercury Ser history as the planet swerved inwards it collided with another embryonic world and shattered today we see the evidence of This ferocious Collision in the strange structure of this tiny planet a giant core has been left behind the exposed interior of a planet that had much of its outer layer its crust mantle Stripped Away and lost to space in the aftermath of the Collision this Collision not only trans formed the physical
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characteristics of the planet but also knocked Mercury further inwards on a lopsided trajectory that we see reflected in the most elliptical orbit of all the planets although we cannot be certain of these events it's a brilliant piece of scientific deduction to use the evidence we have to create a plausible scenario of events that happened unimaginably long ago events that drove the first Rock From the Sun from a position full of potential to a place much too close to the Sun
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to support any form of life an opportunity lost after four years of observation and its brilliant discovery of Mercury's ancient past messenger finally ran out of fuel on the 30th of April 2015 and added yet another crater to this tortured world that once held such promise shrouded in an unbroken blanket of cloud the next Rock From the Sun tells a very different story over 50 million kilometers Beyond Mercury lies a world that at first sight has the potential to be far more
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earthlike than her scorched inner companion Venus is perhaps the most mysterious of all the planets lying on the inner edge of the so-called habitable zone this is a planet that holds its Secrets close for centuries it has teased us with its brightness in the Earth early morning and early evening Sky it's so bright because it's a large planet about the same size as the Earth it's not too far away
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from as either and the clouds that shroud it are highly reflective reflecting 3/4 of the light that hits them that's the frustrating but tantalizing thing about Venus because even when you look at it through a big telescope it is featureless you never see the surface which means that until the 1950s scientists could only speculate about what lay beneath in the late 19th and early 20th centuries many thought that beneath her clouds Venus was hiding a mirror
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world to Earth if not home to complex sentient life then certainly hosting basic life forms faced with that impenetrable cloak our Collective imaginations fueled the idea of a living breathing World beneath the clouds a shroud that meant for the first half of the 20th century we lived convinced that we were far from alone in the solar system Nobel prizewinning chemists vant arenus was one of the most renowned scientists to fuel the mythology of what lurked behind Venus's cover
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like many of the scientists of his era arenus let his curiosity wander into many different Realms including astronomy and he hypothesized at length about the venusian environment assuming the clouds of Venus were composed of water he wrote in his book The Destinies of the stars that a very great part of the surface of Venus is no doubt covered with swamps creating an environment not unlike the
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tropical rainforests found here on earth expanding on this picture he suggested that the complete cloud cover of the planet created a uniformity totally unlike the extremes of weather that Define different parts of the Earth in aran's imagination this stable environment with a consistently uniform climate all over the planet meant that any life on Venus lived without the Evol uary pressures of changing environments that drive natural selection here on Earth leaving Venus in
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an evolutionary limbo akin to the Carboniferous period describing a world full of prehistoric swamps and dark forests Aran use created the perfect canvas for science fiction writers of the time to conjure up a managerie of curious life forms lurking beneath the clouds today arenus is far less known for his fertile imaginings on the wildlife of Venus than he is for his work on the climate of Earth in 1896 he was the first scientist to use basic principles of chemistry
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to demonstrate the impact that the atmosphere can have in particular levels of carbon dioxide on the surface temperature a process that was called the Aran use effect but is now known as the greenhouse effect an effect that would not only have profound consequences for our understanding of our impact on our own Planet but would also be vital in explaining the true nature of Venus beneath
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the clouds by the 1920s as groundbased technology improved we stopped painting the surface of Venus with our imaginations and started filling in the gaps with facts the first spectroscopic analysis of the planet's atmosphere suggested that it wasn't water or oxygen that filled the clouds of Venus so some thought this hinted at an arid desert land beneath others speculated that formaly filled the air leading to the belief that Venus was not only a dead Planet but a pickled
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one too but come the 1950s the true nature of Venus began to be revealed as more accurate earth-based observations suggested the presence of overwhelming levels of one defining gas in the venusian atmosphere this was not a planet shrouded in clouds of water and oxygen nor pickled in form alide this was a planet engulfed in a blanket of carbon dioxide and as a reuse had demonstrated on Earth this almost certainly meant that whatever lay beneath the clouds the heat would be beyond
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the limits of even the most resilient life forms on Earth as the first spacecraft were being built to explore our sister world it was becoming increasingly clear that visiting Venus would be far from easy and she would be far from welcoming in the early 1960s the Soviet Union began a series of missions under the program name name Venera which attempted to explore the atmosphere and surface of Venus directly for the first time the initial launches of the veneer program failed
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before they had even left Earth's orbit but within a couple of years the program began to slowly see some success vineer 1 was successfully launched on the 12th of February 1961 designed as a flyby Mission it is thought to have passed within 100,000 kilm of Venus but a total lemetry failure on the craft meant that no data was returned to Earth as far as we know Venera 1 is still in orbit around the Sun to this day Venera 3 attempted to go a step further and was designed to enter
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the venusian atmosphere to take the first direct measurements however on crossing the atmospheric boundary the probe systems failed and no data was returned as it plummeted towards the ground all that was left for Venera 3 was the historic position of was the first human-built object to crash into another planet's surface despite multiple failures the Soviets didn't give up and in October 1967 Venera 4 entered the atmosphere of Venus and sent back data supporting the
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earth-based observations revealing for the first time that the blanket of clouds surrounding Venus was made up of primarily carbon dioxide 90 to 95% 3% nitrogen and just Trace amount of oxygen and water vapor vineer 4 confirmed beyond all doubt that this was no second Earth as it descended through the thick clouds the temperature Rose to 262° C the atmospheric pressure increased to 22
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standard atmospheres 2,200 kPa and this was still 26 km above the surface as vineer 4 parachuted its way down to the surface it provided data to Earth where while confirming its own imminent death this was a spacecraft that was not designed to survive the intense pressures and temperatures it was measuring let alone the lack of the water landing it was designed for the craft failed during The
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Descent and was lost long before it reached the surface gradually through the following missions the Soviet scientists began to overcome each and every challenge Venus put in front of them vineer 7 was built to survive the most violent of Landings and even though its parachute failed it made it to the surface intact in 1970 and was able to use its damaged antenni to transmit limited temperature data for 23 minutes before it expired vinera 9 not only made it to the surface
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and operated for 53 minutes in October 1975 but was also the first craft to successfully deploy its camera on the ground and transmit an image back to Earth in the first ever picture taken from the surface of another planet the black and white fractured image revealed a rocky desolate landscape with measurements confirming it to be a blistering 485 de C with an atmospheric pressure of 90 ATM Crashing Down by the time Venera 13 launched on the 30th of October 1981
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the ambition of the missions and the confidence in delivering data from the surface had been radically transformed vineer 13 functioned for 127 minutes in recorded temperatures of 47° c and a pressure of 89 Earth atmospheres the probe's cameras deployed taking the first color image from the surface of Venus spring-loaded arms measured the compressibility of the soil while a mechanical drill arm took a sample of the venusian surface that was analyzed by an onboard spectrometer if
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that wasn't enough on board microphones were deployed to record The Vicious winds that were assumed to be whipping the surface of Venus the first ever recording of the sound of another planet as the vineer emissions came to a close in 1983 not even the smallest doubt remained of Venus's hostility far from the benign Water World we had once imagined the reality was that this was not a sister we recognized in our search of the heav for a place like home we'd found a toxic
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fiery hellscape Venus is an enigmatic World almost earthlike in size position and potential and yet as far from Paradise as it's possible to imagine if Mercury's story is one of catastrophic orbital change and Earth's of balance and stability the story of Venus is a tragedy a tale of subtle yet Relentless decline so why did it all go wrong for Venus why did a world born with such similarities
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to the Earth take such a different path to answer that we need to look beyond the tortured planet we see today and go back to a time when Venus was a young thriving Planet 4 billion years ago Venus was a familiar world a world created from the same dust as the earth born just about the same size and settled into an orbit that seemed just far enough away from the glare of the sun to allow
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a precious process to begin to take hold in almost every conceivable way Venus's early life mirrored that of our own world as its newly formed crust settled and cooled from the violent heat of its birth an atmosphere began to grow around the young Planet fed by gases bubbling up from the molten rock below its surface as well as was captured from the clouds of gas and dust it swept through
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on its orbit around the sun clinging to the young Venus this thin layer of gas would have certainly contained nitrogen oxygen and carbon dioxide but most intriguing of all we are certain it would have also contained large amounts of water vapor high in the venusian atmosphere this water vapor eventually cooled enough to change state from Vapor to liquid and with that transformation a process began that perhaps for the first time on any of the planets would have seen
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the conditions become just right for droplets of liquid water to take shape and begin falling from the venusian sky these were the first rains of the solar system showering down onto the dry Plains of Venus gradually these rains would have not just Fallen but flooded the surface Rivers would have flowed and shallow ocean taken hold of large SES of the planet's surface Venus perhaps before even the Earth became a water world a planet with Skies full of clouds and a surface
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full of oceans feeding the cycle of water around this young Planet how can we be certain this Blue version of Venus existed unlike Mars where we can see the evidence of its watery past etched onto its surface we have no such direct evidence of the presence of liquid with water on the surface of Venus the only physical evidence we have that suggests the planet's watery past comes from measurements taken by NASA's Pioneer Venus spacecraft back in 1978 one of its most surprising
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discoveries revealed an unexpected amount of dyum heavy water in the atmosphere compared with hydrogen this DH ratio is far smaller on Venus than it is on Earth and that's interesting because when the two planets formed the ratio would have almost certainly been the same because hydrogen is far more easily lost from an atmosphere than dyum this smaller ratio suggests that Venus has lost a
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lot more water than the earth over its lifetime the signature of a long-lost primordial ocean as cosmochemistry knitler explains scientists believe that Venus once had a lot of water in its oceans but lost it over time time and perhaps in oceans as recently as a billion years ago the reason we can tell this is from the isotopic composition of hydrogen measured in its atmosphere by spacecraft
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now hydrogen has two flavors of Isotopes whereas most hydrogen atoms are just a single proton in the nucleus some a small fraction are what we call dyum that have a proton and a neutron so they weigh twice as much as the regular hydrogen what happens when you have evaporation of water from a planet or the atmosphere is that the water molecules that contain hydrogen are much lighter than the water molecules that contain deuterium so they evaporate more easily and can be lost
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more easily so over time as you evaporate water dyum bearing molecules stay behind relatively to the regular ones and you build up a dyum to hydrogen ratio and by back calculating from the measured ratio today we can figure out how much water has been lost over the billions of years of evolution and on Venus it's quite a lot none of this is solid proof but it does begin to point us in One Direction and with no further exploration of the surface we've had to rely on
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an accumulation of indirect evidence to begin to paint a more detailed picture of Venus's watery past as with almost all of our understanding of the planets the evidence that built this picture has been accumulated through Decades of exploration starting with the veneer emissions first touchdown on the planet to the Pioneer Venus Orbiter and to the more recent melan Mission which not only relayed extraordinary raadar soundings of the surface of Venus but provided the First full
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topographical map of the planet collated over a period of 4 years in orbit combining all of the data that has been accumulated over Decades of exploration has allowed us to peer deep into the planet's past using the same tools that enable us to model the future of climate change here on Earth to create climate models of Venus in the past present and future the results of this analysis conducted most recently by a team from NASA's Godard Institute for space studies G all
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point to the same conclusion in the distant past Venus was a planet covered in Shallow primordial oceans some estimates suggest that this water world was far from fleeting a blue planet just like our own that could have been sustained for around 2 billion years and perhaps only disappeared some 700 million years ago it's a tantalizing thought that such a similar world to our own existed for so long with liquid water on its surface we know life took hold quickly on
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our own Blue Planet within half a billion years of the Earth being formed so there seems good reason to suspect that if Venus really was as wet as the models predict it too could have sprung into life exactly what went on in the long lost rivers and oceans of Venus is yet to be discovered hidden behind the clouds we have not yet been back to search for any signs that life ever took hold here
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our exploratory attentions have turned to Mars as a planet that not only has a fertile past but is also a possible Target for human colonization in the future we know for certain that no life at least no life we understand could exist on Venus today and perhaps even the evidence of any biology on that long lost water world has long ago vanished under the oppressive heat rampant volcanism and extreme pressures of the planet today today Venus has the slowest rotation of
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any planet in the solar system taking 243 Earth days to complete one rotation on its axxis this period is known as the siderial day which is different to a solar day the time it takes for the sun to return to the same point in the sky on Earth the siderial day at 23 hours 56 minutes and 4.1 seconds is very close to the solar day which lasts pretty much exactly 24 hours but on Venus the difference between these two periods is much greater even though the planet takes 243 days to
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rotate on its axis when combined with its orbit a solar day on Venus lasts for 116 16.75 Earth days it means every day on Venus lasts almost 4 months on Earth and not only that but Venus also rotates from east to west one of only two planets to do so along with Uranus so across this toxic World a sunrise would last literally for days as it inches across the sky this slow progression of the Sun in
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the venusian sky due to the planet's creeping rotation has raised many questions about how in the past the planet would have been heated and how the climate would have been affected by such a different rotation compared with the Earth's today the climate of Venus is what is known as isothermal there is a constant temperature between the day and night sides and between the Equator and the poles this is because the thick atmosphere literally acts like a blanket dissipating the heat
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of the Sun so that the only real variation in temperature on the venusian surface occurs due to differences in altitude in its past however this may have been very different with a more earthlike atmosphere so the sun would have been beating down on the planet's surface for days on end to make things even more complex we know the spin of a planet is intimately linked to its climate and we've got strong evidence to suggest that how fast a planet spins is directly related to its
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chance of habitability until very recently it was assumed that the slow rotation of Venus must have been caused by the presence of a thick atmosphere early on in its history that in effect acted as a break on the planet's spin however recent studies now suggest that the planet could have had a thin atmosphere like that of modern Earth and still have ended up with its slow rotation gradually
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as we start to build a picture of ancient Venus we begin to see beyond the cloud cover of today through to an ancient planet with an earthlike atmosphere and a day lasting over 200 Earth days as the sun beat down on the ocean covered surface to make sense of the climate of this earthlike Venus the team at The godart Institute needed to make another tweak or postulation to be more precise to the model with the Sun hitting the one side of the surface for so much longer than on the
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earth the evaporation rate of the oceans would be far greater and potentially incompatible with the water world we suspect existed but by simply adjusting the amount of dry land on the surface of Venus especially in the tropics the effect is dramatic with a higher percentage of land the models suggest that even the slow rotation would not dry out the planet and it could have held on to enough enough water to be ripe for supporting the emergence of Life by combining all of this
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data the G team have painted our most upto-date picture of early Venus and it's a beguiling image within the infant solar system it is a planet the size of Earth with similar atmosphere to the one we see today on Venus days lasted for months as the sun arked slowly across the sky from west to east rising and setting over a vast shallow ocean finally the data from radar measurements taken by NASA's melan mission in the 1990s was used to paint the last brush Strokes of this
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long lost world filling in the L lands with water the Topography of this ancient world emerges with the highlands exposed as the venusian continents it all points to the possibility that Venus could have been the first habitable World in our solar system so what changed to find out we need to look not just at the planet in isolation but also at the star around which it orbits no Planet lives out its life in isolation Venus like all the planets is not just part of a configuration
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of planets and moons asteroids and comets but is also part of a solar system A system that is driven more than anything else by the star at its center today the sun burns bright in our skies bathing our planet in just enough Starlight to keep the oceans from freezing but not too much to boil them away Earth lies in The Sweet Spot we call the goldilock Zone but as we have already seen in this chapter nothing in the solar system is forever and what we see today is not what we
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will see tomorrow nor what we would have seen yesterday as our sun gets older it's gradually burning hotter and hotter this is because as it ages the process of nuclear fusion the fusion of hydrogen into mainly helium gradually leads to an increase in the amount of helium in its core this rise in helium causes the sun's core to contract which in turn allows the whole star to shrink in on itself creating an increased pressure that results in a rise in the rate of fusion and so
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the energy output of the sun goes up if tomorrow the sun is burning hotter than today it of course makes sense that in the early days of the solar system our sun burned far less brightly it's a life cycle that is common to all main sequence Stars the category of star that includes our sun and as the most common type of star in the universe we've been able to study this life cycle in Intimate detail allowing us to make immensely detailed predictions about the characteristics of
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our son in the past and in the future winding back the clock the current consensus among astronomers is that 4 billion years ago the faint young sun was at least 30% dimmer than it is today this cooler Sun would have undoubtedly had a big impact on all of the terrestrial planets Earth would have been much colder and as it was receiving far less solar energy it remains something of a mystery as
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to why our planet wasn't frozen solid Instead at this time on Earth first life was just beginning in the liquid water that we are pretty certain covered its surface at the same time 3.5 to 4 billion years ago the young Sun would have bathed Venus in a warmer glow this ocean world found itself in its very own sweet spot a world held in a delicate balance with the sun weakened and restrained the earthlike atmosphere of Venus could act as a gentle blanket keeping the
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surface temperate and covered in an abundance of liquid water but even with this additional solar energy we we think Venus would still have been much cooler than the earth is today in fact we believe temperatures at that time would have been like a pleasant spring day here on Earth it wasn't to last slowly the young Sun grew brighter its increased energy output causing temperatures to gradually rise which in turn began to lift more and more water vapor into the air thickening the
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atmosphere and sealing the planet's fate although the oan of Venus may have persisted for billions of years as the surface warmed and the atmosphere thickened the destiny of this planet was already set driven by an Unstoppable process we have recently become very familiar with here on Earth the greenhouse effect is a process that has the power both to protect and to destroy a planet but
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despite this power it actually boils down to some pretty simple physics it's all about how sunlight solar radiation interacts with the constituent parts of an atmosphere in the case of the earth as solar radiation hits our atmosphere some of it is reflected straight back out into space some is absorbed by the atmosphere and clouds but most of the sunlight about 48% passes straight through the
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atmosphere and is absorbed by the Earth's surface where it is heated up the reason so much solar radiation makes it to the surface is because the gases in our atmosphere like water vapor and carbon dioxide are transparent to light in the visible spectrum when you think about it that's pretty obvious because there's a source of visible light in the sky the Sun and we can all see it but it's a different story when that sunlight heats the surface of the Earth and radiates back out
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not as visible light but as the longer wave infrared light thermal radiation we can't see this light but as it radiates back out out from the Earth's surface carbon dioxide and water vapor absorb the infrared trapping that energy and so the planet maintains a higher temperature that is intimately linked to the constituent parts of the atmosphere the higher its level of gases like water vapor carbon dioxide methane and ozone the greater the Greenhouse Effect and
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the bigger the uplift in temperature despite the very real threat that this now poses to the future of our planet the greenhouse effect on its own is not necessarily A Bad Thing the Earth would be at an average temperature of around -8° C without it but as we are currently witnessing here on Earth shift the balance of those gases and things can change very quickly at some point in Venus's past the levels of water vapor lifted into the atmosphere by the warming Sun pushed the
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greenhouse effect to become precariously more intense with less and less of the sun's energy escaping the ambient temperatures began to rise exponentially until the day came when the last raindrops fell onto the surface of the planet the heat evaporating the rains long before they could reach the ground Venus had reached a Tipping Point with the increasing temperatures feeding more and more water vapor into the atmosphere a runaway greenhouse effect took hold driving away
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the oceans this led to the surface of the planet getting so hot that carbon trapped in rocks was released into the atmosphere mixing with oxygen to form increasing amounts of another greenhouse gas carbon dioxide with no water left on the surface and no other means to remove it carbon dioxide built up in the atmosphere setting the planet on a course that would result in The Scorch body
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that we see today and so Venus's moment in the sun came to an end earthlings take note when it comes to the greenhouse effect there is a precariously thin line between keeping a planet warm and frying it of the four rocky worlds only one has managed to navigate through the instability and constant change of our solar system over the last 4 billion years and maintain the characteristics needed to
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support life Mercury lost its fight early as it was flung inwards towards the sun Venus flourished at first before slowly coming to the boil and Mars the runt of the litter became a frozen Wasteland long ago only Earth uniquely among the planets has persisted with an adequate stability over the last 4 billion years to allow liquid water to remain on its surface and an atmosphere just thick enough to keep its climate calm not too hot and not too cold events have rocked us and
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extremes of temperature have waxed and waned but never outside of the parameters needed to Harbor life in a chaotic solar system filled with planetary might have beans Earth is a shining example of stability and the evidence for this is to be found in every nook and cranny of the planet today Earth is dominating by life the land and seas are teeming with Millions upon millions of species with thousands of new life forms discovered each year somehow even when disaster
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threatened the Earth has remained a living world while endless species have come and gone life has always persisted it's woven into the fabric of the planet an integral part of every continent and every ocean life plays a crucial role in maintaining the balance of the atmosphere that keeps our planet temperate but we know for certain it cannot last the Kamchatka peninsula in eastern
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Siberia is one of the most inhospitable places on Earth a volcanic Wasteland peppered with thousands of Hot Springs it's here that we find some of the toughest living things extremophiles survive here that are able to withstand temperatures and pH levels higher than any other landbased life forms we have ever discovered Kamchatka is part of the Pacific Ring of Fire and despite its remoteness biologists have long been enticed here to explore its toxic bubbling cauldrons
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for signs of Life complex life animals and plants struggle to survive in temperatures about 50° C so searching for life here is all about searching for single celled life form WS bacteria and ARA ancient microorganisms that are somehow able to endure in this hostile environment life forms like acidilobus aticus an ARA that can be found in a hot spring where the water is so acidic it reaches a pH of two and where temperatures rise to 92° C in other parts of the hydrothermal field
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bacteria like desulfurella acetivorans have been discovered which happily live in pools that are touching 60 de C but it's these that are the real Hot Heads in one of the biggest and hottest pools investigated by scientists a large number of microbes have been found living in temperatures approaching 97° making it one of if not the hottest environment ever studied for signs of Life on land but to find the greatest hotthe heads on planet Earth you need to look not on land
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but deep Beneath the Sea in the furthest depth of the Atlantic around the black smoker hydrothermal vents blurting out of the ocean floor we found strains of ARA that can survive temperatures of 122° c and perhaps even higher these rare life forms live at the very edges of biology unique adaptations to their cellular chemistry enable the proteins and nucleic acids that create the structure of the microorganism to function while the membranes that are protecting the
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cells utilize different fatty acids and lipids to keep the cells stable at the higher temperatures perhaps there are even tougher life forms that we are yet to discover but the thermophilic microorganisms that we have so far identified and investigated in places like Kamchatka all point to the fact that life has its limits evolution by natural selection can only adapt so much and even though it's impossible to imagine what life on Earth will look like in a few 100 million or
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even a few billion years time we know that biology is constrained by thermodynamics and so we can say with some certainty that there will come a time when the earth is too hot for any living things to exist natural selection will eventually run out of options as the laws of physics outplay it and all life will come to an end when this will happen no one can be certain but as the sun ages and
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grows hotter temperatures on Earth will rapidly rise today the average surface temperature on the planet is 14.9 De C but with just a 10% rise in the sun's Luminosity the average temperature will rise to 47° C and climbing the increased temperatures will raise great storms across the planet the rains will remove carbon dioxide from the atmosphere and it will be locked away as newly formed sedimentary rock trees and plants will struggle as they are robbed of the gas that
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sustains them until eventually photosynthesis will cease the lungs of our planet will fail and the precious oxygen that green plants and algae produce will dwindle with the primary food source gone the food chain will collapse and the age of complex life on Earth will draw to a close heat loving extremophiles May flourish for millions of years more but eventually Nuclear Physics will have its work and as average temperatures race above 100° C the last pockets of life will
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be extinguished from the earth we can say with confidence this is going to happen because we can plot the future of our sun far more precisely than the future of the earth our understanding of nuclear physics allows us to predict what happens inside the cores of stars and thus we can see the past present and future of stars like ours written across the night sky the heavens are filled with
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shining examples of stars that give us a glimpse into the future of our sun Arcturus for example in the constellation bootes is one of the brightest stars in the northern hemisphere it's around the mass of the Sun perhaps a little bit heavier and so in the distant past would have had remarkably similar characteristics to our own star today though Arcturus is 6 to 8 billion years old
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potentially 3 billion years older than the Sun and as it is no longer a main sequence star it is now in the red giant phase it's fuel exhausted it has swollen up to 25 times its original diameter and is around 170 times as luminous despite the fact that as its core slowly burns out it is cooling to see even further into the future we need to look towards the brightest star in the northern
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sky Sirius the dog Star as it's commonly known is twice the mass of the Sun and still fully in the main sequence but obscured by the glare of Sirius a is a faint companion serious bee this is a star that has already burnt through its fuel swollen into a red giant and the outer layers have drifted off into space leaving the fading core of the star about the size of the Earth known as a white dwarf
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these stars are just two examples amongst many that point us towards the ultimate fate of our sun a fate that we believe will play out over the next 5 billion years or so just like Arcturus as the sun exhausts its hydrogen fuel its Outer Edge will inflate and it will enter a red giant phase expanding millions of kilometers out into space it will engulf Mercury first Venus's fate will be
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sealed next as the sun expands further some models predict that Earth may just escape the fiery end of its neighbors heated to 1,000° C but hanging on Beyond the Edge of the dying Star as its orbit extends out due to the lessening mass of the Sun dead but not destroyed Earth and Mars will orbit as burned out relics of their former selves the era of the four rocky inner planets will be over
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the billions of lives lived on the surface of one of them nothing but a distant memory but within our solar system lies another family of Rocky worlds whose moment in the sun may be to come far beyond the asteroid belt millions of miles away from the sundrenched planets of the inner solar system the gas giants of Jupiter and Saturn are home to another family of Rocky worlds Jupiter alone has 79 known moons orbiting it a managerie of satellites of multiple shapes and sizes we've
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been peering at these moons since Galileo galile spotted four of them IO Europa ganed and Kalisto known as the Galilean moons over 400 years ago with his telescope Transforming Our understanding of our place in the solar system today we have explored the Galilean moons not just from afar but close up and found them to be dynamic worlds IO is fiercely volcanic and Europa the ice Moon
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shows tantalizing evidence on its surface pointing to a subsurface ocean sitting below its icy crust ganid and Kalisto make up the final two Galilean moons and just like Europa they are rocky worlds with an abundance of water ice on their surfaces and perhaps their own oceans lurking beneath these three Rocky Frozen worlds are all sitting in the cold outreaches of our solar system touched by
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the distant Sun but barely warmed lying dormant until perhaps one day the Aging sun will reach out and turn these bodies into ocean worlds for the very first time the next planet out Saturn also has its ever growing family of moons amongst its collection of over 60 confirmed satellites are Titan the only known moon with a dense atmosphere and liquid Lakes on its surface though they are primarily methane not water and Enceladus a frozen ice Moon just like Europa with
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a liquid ocean deep beneath its ice until we go back and explore further we can't be certain what lies below its surface but the possibilities that the Cassini probe has so tantalizingly hinted at make it one of the most exciting places for us to visit within the next generation of interplanetary expeditions all these ice worlds sitting dormant in the Frozen reaches of the solar system offer
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the promise of of a very different future one in which the rocky worlds of the inner solar system have been reduced to Cinders and a new generation of Worlds waits to awaken ice worlds will become water worlds warmed by the expanding Sun until our dying star ultimately collapses into a white dwarf Mars is a mirror for our dreams and nightmares to the naked eye the planet exhibits a reddish Hue blood red in the imagination god of war star of judgment through a small telescope it
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is the most earthlike of planets with cinear deserts and white polar ice caps a world we could imagine visiting perhaps even settling in 19th century astronomers convinced themselves they saw ples and mountain ranges and canals delivering meltwater from high latitudes to arid equatorial cities some thought the Martians a peaceful civilization far in advance of our own others s threat across the Gulf of space minds that are to our minds as ours are to those of
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the beasts that perish intellects vast and cool and unsympathetic regarded this Earth with envious eyes wrote HG wells in his classic science fiction novel The War of the World in 1897 the nature of Mars remained a mystery until well into the 20th century because the planet is small and far away and therefore difficult to view with groundbased telescopes even the Hubble Space Telescope high
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above the distorting effects of Earth's atmosphere produces images which would not at first sight have prevented Wells from publishing with a little imagination the ice caps high clouds and dark regions circling the deserts could be mistaken for evidence of a water cycle feeding the seasonal advance and Retreat of vegetation photographs from the first flyby of Mars by NASA's Marin four spacecraft on the 15th of July 1965 abruptly laid to rest the Romantic notion of Mars
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as Earth's habitable twin or potential foe these images revealed an arid surface reminiscent not of our Blue Planet but of our desiccated Moon overnight we discovered for certain that Earth is the only planet in the solar system capable of supporting complex life and contemporary accounts of the impact of the Mariner for flyby suggest that this was a powerful realization in November 1965 the bulletin of the atomic scientists carried an article entitled the message from Marin four
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and the message was Bleak the shock of Marin 's photographic and radiometric reports is caused not only by their denial of the terrestrial image of Mars but by the Revelation that there is no second chance at least not in the solar system president lyen B Johnson was reported as commenting it may be it may just be that Life as We Know It with its humanity is more unique than many have thought the hesitation in the first few words is revealing here is Mars as a symbol of our
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Cosmic isolation it is as though deep or perhaps not so deep in the subconscious the 1960s power Brokers all the way up to the president suddenly understood that the Earth is far more fragile and precious than a dispassionate analysis of their Cold War brinkmanship might suggest or perhaps the perspective delivered by exploration is always shocking Apollo 8's earthrise the photograph that
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delivered such a positive end to a troubled 1968 by setting the Blue Earth against the gray moon was 3 years away but red Mars provided a foretaste in response Carl Sean co-authored a paper suggesting somewhat playfully that all was not lost Marin four took only 22 photographs with a resolution of over a kilometer in a strip crossing the region in which the astronomer peral LEL had sketched canals from his obser atory in Flagstaff Arizona at the turn of the 20th century from the
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warmth of the Arizona desert LEL wrote that Mars was Chile but no more so than the south of England which certainly supported a civilization of sorts using several thousand photographs of a similar resolution taken by meteorological satellites in Earth's orbit Sean and his co-authors found only a single feature that unambiguously indicated the presence of a civilization Interstate Highway 40
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in in Tennessee They concluded that Marin four would not have detected human civilization had it flown by Earth we do not expect intelligent life on Mars but if there were intelligent life on Mars comparable to that of Earth a photographic system considerably more sophisticated than Marin 4 would be required to detect it the non-existence of an extant Martian civilization was confirmed by The Marin 9 mission in November 1971 the first spacecraft to orbit another planet marinina 9
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achieved a photographic resolution of 100 m per pixel and no sign of intelligent life past or present was detected the twin Viking Landers in 1976 failed to detect even microbial life although the combined results of The Suite of microbiology experiments carried by the spacecraft are not considered to be unequivocal because Martian soil can chemistry is to coin a phrase from the official NASA report enigmatic and could conceivably have masked any biological
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activity in hindsight the fact that Mars is not teeming with life today is not so surprising Mars orbits 50 million miles further from the Sun than Earth and receives less than half the solar energy it is a small world with a tenuous atmosphere that provides little insulation or greenhouse warming NASA's Curiosity Rover in the Gale crater has measured midday temperatures above 20° C but in
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the early hours of the morning it is experienced minus 120 as Alfred Russell Wallace wrote in 1907 any attempt to transport water across the Martian surface today would be the work of Mad Men rather than of intelligent beings there are no canals no cities and no envious eyes the planet is a frozen hyper AR desert too far from the Sun to support complex life yet it hasn't always been this way observations from our Fleet of orbiting spacecraft and Landers have revealed a complex and
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varied past Once Upon a Time the red planet was glistening blue streams ran down hillsides and rivers wound their way through valleys carved by a water cycle from land to Sky and down again from mountains and Highlands to the Sea this presents a great challenge for planetary scientists put simply nobody would have been surprised if Mars had always been an inert Rock because it is a small planet far from its star but the geological evidence is unequivocal the surface
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tells a different story Mars then remains an enigma as a Wandering red star it stirred the imagination of the ancients as a telescopic image too small and shifting for visual or intellectual Clarity it became our twin When spacecraft flew by it shocked us into considering our Cosmic isolation the red planet was relegated in our Collective Consciousness to the status of just one more rock glistening in the night then we landed and discovered a world that was
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once habitable and could be again a map of Mars can be read like a history book unlike Earth where constant weathering tectonic activity and volcanism have erased the Deep geological past Mars has been relatively quiescent for most of its life the scars of collisions from the first turbulent billion years after the formation of the solar system can still be seen from orbit ancient cataclysms documented below a thin film of dust NASA's Mars Global surveyor spacecraft spent
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4 and a half years mapping Mars in the late 1990s and provided detailed maps with colors corresponding to differences in altitude just as on Earth there is significant variation but the geological features on our smaller sister world are much bigger and Bolder the highest elevations on Mars are found on the thsis rise a great volcanic plateau and home to the largest volcano in the solar system Olympus Mons at over twice the height of Everest Olympus Mons Towers 25 km
2:04:28
above the lowlands of amazonus plena to the west and its base would fit inside France just about cutting a deep scar across thsis to the southeast of Olympus Mons is Val marineris named after the Mariner 9 spacecraft that discovered it a canyon that dwarfs anything on Earth the Grand Canyon would fit into one of its side channels the lowest points on Mars are found in the helas impact Basin
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the largest clearly visible impact crater in the solar system from the highest points on the Crater Rim to the floor Hass is over 9 kilm deep it could contain Mount Everest the atmospheric pressure at the floor is twice that at The Rim high enough for liquid water to exist on the surface in a narrow range of temperatures these are extreme altitude differences for a small world over 30 km
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from the summit of Olympus Mons to the floor of helas on much larger Earth for comparison there is only 20 kilm difference between the summit of Everest and the Challenger Deep in the depths of the Mariana Trench the most striking and ancient elevation difference on Mars is that between the northern and southern hemispheres of the planet known as the global d otomy Mars is an asymmetric world the northern hemisphere is on average 5.5 km lower in altitude than the southern there is
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no consensus as to how the dichotomy formed other than that it was early in the planet's history and before the large impacts which created the Utopia and kryy basins around 4 billion years ago at some later time the northern L lands were resurfaced by volcanic activity in a similar fashion to the smooth lunar Seas which accounts for their lack of cratering relative to the much more ancient terrain to the South the oldest terrain on Mars is found in the nois Tera region of the
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Southern Highlands it is characterized by heavy cratering reminiscent of The Far Side of the Moon even small craters in the noan highlands are heavily eroded which suggests the regular if not persistent presence of liquid water there are dry river valleys and deltas and evidence of water pooling in the craters and overflowing their walls forming interconnected networks of lakes this is how we know Mars was once a warmer and wetter world at least occasionally the evidence
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is written across the land of Noah in contrast the younger terrain of Hesperia Plum displays much less evidence of regular erosion by water but Bears the scars of occasional catastrophic floods that cut deep valley over very short periods of time and may have formed temporary large lakes or Seas the amazonis plena region shows little sign of flowing water fewer impact craters and less evidence of active volcanism suggesting it was formed more recently when Mars was significantly
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less geologically active the Persistence of surface features over many billions of years in the noan Hesperian and Amazonian regions has led to the historical epochs of Mars being named after the distinctive terrains that still bear the characteristic marks of the climate and geological activity that formed and sculpted them the noan period was the earliest and wetest and coincided with the origin of life on Earth around 4 billion years ago when conditions on both worlds appear
2:08:10
to have been very similar the Martian atmosphere may have been denser than Earth's and dominated by carbon dioxide but significant questions remain about how such an atmosphere could have warmed Mars sufficiently to deliver the warm wet climate and how that atmosphere was lost the maven spacecraft currently in orbit around Mars aims to answer this question the noan period Ended as Mars became increasingly cold and arid around 3.5 billion years ago just as life was gaining a
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foothold on Earth the Hesperian period the time of catastrophic floods ran from the end of the noan to around 3 billion years ago when Mars entered its current Frozen arid phase punctuated by occasional volcanic activity and the large scale movement of ice but with very little evidence of flowing water the long three billion year Freeze from the end of the hesperion to the present day is known as the Amazonian this is a summary of what we know about STS the wise pose a significant
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challenge to planetary scientists given a warm wet and seemingly stable World early in its history what triggered the loss of atmosphere and descent into modern-day aridity what happened to the water on Mars was it lost to space or does it persist today as surface ice or in subsurface rocks or reservoirs if so how much water is still accessible could we exploit the ancient reservoirs of Mars to support a human colony and perhaps most significantly of all did life arise on the
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planet During the noan period coincident with the origin of life on Earth and could that life still be present on Mars today the current Fleet of spacecraft in orbit around Mars and roving across its surface has been designed mind to answer these questions Mars today is a planet buzzing with activity Communications to Earth and the Martian internet are managed by the Mars reconnaissance Orbiter M an orbiting bridge between worlds mro carries the high-rise instrument a camera with
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resolution high enough to see basketball-sized features on the Martian surface the Mars color imager Marque camera monitors Martian weather and the compact reconnaissance Imaging spectrometer for Mars crism identifies mineral deposits particularly those formed in the presence of surface water orbiting with the mro is the Mars atmosphere and volatile Evolution Mission Maven this cameralist spacecraft operates between 150 km and 6,000 km above the Martian surface measuring
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the composition of the atmosphere at different altitudes and observing how the tenuous gases are stripped from the planet by the solar wind Mars Odyssey is the veteran of the orbiting Fleet having arrived in 2001 and still being operational in a polar orbit searching primarily for water ice on the surface Mars Express is a European Space Agency mission that is delivering highresolution
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photographs menology data radar investigation of the near Subs surface and Atmospheric measurements including the search for methane a gas that on Earth is associated with biological activity India's Mangal Yan space probe is primarily a technology demonstrator but it carries a secondary scientific package capable of investigating atmospheric composition the newest arrival at Mars is the joint European Space Agency Russian exomars Trace gas Orbiter which will observe seasonal
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changes in the Martian atmosphere and search for subsurface water deposits the spacecraft will form the communications bridge for isa's exomars Rover due to land in 2021 the two most recent explorers of Mars are the opportunity and curiosity Rovers the opportunity Rover landed on the meridiani plum close to the Martian equator on the 25th of January 2004 with a planned lifetime of 90 Earth days in a spectacular Testament to the jet propulsion Laboratories engineering
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Excellence opportunity remained operational until a planet-wide dust storm covered its solar panels in June 2018 after over 14 years and a journey of 45 km on the surface of Mars exploring the endurance Victoria and Endeavor craters on the 13th of February 2019 opportunity was finally declared dead opportunities younger and far larger comp companion on Mars is curiosity the most massive and most capable spacecraft ever to touch down on a planet beyond Earth The
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Landing itself was a torer force of engineering Ingenuity and audacity the enormity of the mission is best described through the words of Alan Chen operations lead at Nasa for the Curiosity Mission at 1031 PDT on the 5th of August 2012 watching The Landing at the jet propulsion laboratory alongside the team the engineers described it as 7 Minutes of Terror 7 minutes to maneuver a spacecraft that
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had taken 8 years to design and build with a program cost of more than $2.5 billion from 13,000 mph at the top of the Martian atmosphere to a soft landing on the surface of the planet the tension reflected the high stakes the Mars science laboratory mission to give the landron Orbiter their full title was a high-risk Flagship science mission in the same category as Voyager the Hubble Space Telescope Viking and Cassini and was beset by cost and schedule overruns and
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controversy this is in many ways unsurprising new technologies and ambitious scientific objectives are difficult to implement and Achieve and in part because of this deliver great rewards in hindsight nobody would question the value of any of these missions which have delivered some of the greatest insights and most inspiring images in the history of exploration yet this never prevents Bean counters and rival scientists with agendas and more charitably
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budgetary challenges of their own winging and even considering cancellation this is naive funding for science is almost always grudging from a political class whose view of the acquisition of knowledge is utilitarian the far deeper value of exploration as a critical part of the internal Voyage of our species bringing us into direct confrontation with the mystery of our existence is lost on them at least until occasional johnsonian president not Alexander Boris
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tol moments it may be it may just be that Life as We Know It with its humanity is more unique than many have thought and we must remember this which means that a cancellation of one project does not mean an uplift in funds for another more likely the budget will be lost to science at the time of writing the same issues play another NASA Flagship Mission the James web Space Telescope as Robert D Bal wrote in an oped article for space news in December 2008 at the height of the Mars
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science laboratory controversy when implementing Flagship missions cost and shedule overruns are not uncommon but history shows that the mission return often eclipses the expend the Hubble Space Telescope experienced a development cost overrun several times its approved project budget and was launched much later than originally planned in hindsight would any rational space scientist not
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concede that the return from Hubble was worth the investment given the febr atmosphere however no amount of philosophy or Reason would mitigate the costs of failure of the Mars science laboratory Mission a landing accident was both possible and and Unthinkable delivering almost a ton of fragile Rover onto the surface of Mars with pinpoint accuracy is not trivial which is perhaps why the chosen engineering solution seemed not to put too fine a point on it daring Mars has a thin
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atmosphere so slowing down a spacecraft when it's traveling around 10 times faster than a bullet is hard and yet the atmosphere is thick enough to apply sufficient frictional heating to destroy a spacecraft without adequate protection and turbulent enough to cause significant uncertainty in the landing site of an un steered vehicle this renders the more obvious engineering Solutions redundant you can't simply deploy a parachute and Float to the surface the 1970s Viking Landers
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used a combination of heat shields during Arrow breaking parachutes and retro Rockets with success but the Curiosity engineering team dismissed this tried and tested solution it did not allow for high enough Precision or for the gentle Landing required for the pinpoint delivery of a large Rover with delicate Wheels the Viking Landers had legs built like tanks the Viking Landers also carried their heavy descent rocket systems with them to the ground which didn't matter because
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they stayed put curiosity would have had to Lug all this unnecessary Mass around Mars for years the opportunity Rover her sister Spirit and the earlier Mars Pathfinder employed a combination of Arrow breaking parachutes rockets and airbags to cushion the falling spacecraft but these previous Rovers were lightweight in comparison at just over a fifth of the mass of the gargantuan curiosity a Rover of this size and complexity bouncing over the surface in an airbag cocoon
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was not considered feasible primarily because of the sheer mass of the airbag system needed to cushion the impact the lightweight opportunity Rover's Landing system was almost twice the mass of the Rover itself The Chosen entry descent and Landing procedure edl for curiosity was described by Mission lead Adam steltzner as the result of reasoned engineering thought a beautiful example of the truism that reasoned engineering thought and Common Sense at least of the sort possessed
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by the average golf club bore do not always match up the curios edl appears to the untrained eye to be Bonkers or maybe over complicated but it wasn't and it worked tucked up inside a protective shell curiosity encountered the outer layers of the Martian atmosphere 125 km above the surface and traveling at around 20,000 kmph at 10:23 p.m. Pacific Daylight Time on the 5th of August 2012 the spacecraft at this stage cocooned inside a protective enclosure flew entirely under
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the control of its onboard computers with no input from mission control on Earth this was the first time an autonomous guided entry system was employed for an interplanetary Mission using a combination of thrusters and the ejection of balance masses to shift the center of mass and trajectory of the spaceship and guide it with a design accuracy of around 10 km towards the chosen l Landing site this guided rather than ballistic trajectory allowed for a much wider
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choice of Landing sites for curiosity than for the previous Landers which required around 100 km of flat safe land surrounding the nominal touchdown point but it also required the Rover to fly itself the roundtrip travel time for a radio signal to Mars was over 13 minutes when curiosity landed making control from the jet propulsion laboratory in California impossible during the first stage of
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descent a heat shield constructed from a unique material known as P phenolic impregnated carbon ablator protected curiosity from Peak temperatures of around 2000° C generated by friction in the thickening Martian atmosphere 4 minutes after beginning the entry phase slowed to just under 3,000 kmph curiosity's parachute deployed at an altitude of 11 mm above the surface the supersonic parachute is a vast and complex structure 80 suspension lines over 50 m long attached to a
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16 M canopy having slowed to a velocity of 700 km per hour with the help of the parachute the heat shield was jettisoned at an altitude of 8 km allowing the onboard radar to get a view of the ground and deliver High Precision altitude and velocity measurements with the the parachute fully unfolded in relatively dense low-level Martian atmosphere curiosity drifted in the Martian sky for 80 Seconds descending ever more slowly at an altitude of 1.8 km traveling at a sedate 280
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kmph the NASA timeline calls for a deep breath as curiosity separated from the parachute system and dropped in freefall towards Mars for engineers says the NASA website it's like jumping out of a plane for the first time the freefall drop was designed to allow curiosity to separate far enough from the parachute system so that it wouldn't accelerate back into it when 300 M further down its retro Rockets fired and the powered descent phase of the landing began for the Viking Landers
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this was the Final Phase but for curiosity after the Rockets had delivered the Rover to an altit itude of just 20 M with a descent velocity of less than 1 m/s almost a hover the audacious Final Phase of the landing protocol kicked into action the sky crane the Rover slowly Departed the rocket cradle attached by three nylon wires and an umbilical cord of electrical connections 7.5 m in length four of the Rockets angled away from the vertical so as not to damage the Rover
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continued to fire allowing the whole delicate system to approach the surface at walking pace at 5 M from the surface curiosity unfilled its Wheels stowed for the 8-month journey from Earth at 10:32 p.m. the Rover confirmed its Wheels were in contact with the Martian surface and issued one last command through the electrical umbilical up to the sky crane I'm down cut the cables and fly away after a half a billion kilometer Journey curiosity was delivered safely to Mars Just 2.4
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km from its nominal Landing point a Triumph of engineering Ingenuity and Brilliance curiosity was sent to Mars to explore Gale crater a 150 km wide impact crater formed during the late noan or early his beran period when liquid water would have been present at least occasionally on the surface in the great tradition of astronomy the crater is named after the Australian amateur astronomer planetary Observer comet hunter and occasional Banker Walter Frederick gaale who
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discovered a host of comets as well as a number of geological features on Mars at the turn of the 20th century using self-built telescopes in his backyard the primary reason for choosing gaale crater was the unusual Central structure m Mount sharp or aolis mons which Rises over 5 kilm above the crater floor there is still debate about precisely how Mount sharp formed but the layers visible from orbit along its flanks suggest that it is the weathered remains of sedimentary rocks
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which once filled the crater and were laid down over time after the impact subsequent erosion by the Relentless Martian winds removed much of the surrounding Rock to reveal the ancient crater floor once more while leaving the Towering Central structure intact deep exposed sedimentary layers are extremely enticing to geologists because a cross-section through Rock is a cross-section through time as surface and atmospheric conditions change different sorts of rock are laid down and
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chemically modified as curiosity ascends the slopes of Mount sharp it climbs forwards through Martian th and scientists are close behind Joy crisp the deputy project scientist from NASA's jet propulsion laboratory explained the choice of Landing site in the weeks before launch Mount sharp may be one of the thickest exposed sections of layered sedimentary rocks in the solar system The Rock record preserved in those layers holds stories that are billions of years old stories
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about whether when and for how long Mars might have been habitable just as the layers of exposed rock in the Grand Canyon on Earth reveal the story of our planet the exposed sedimentary layers of Mount sharp are a story book that the Winds of Mars have opened ready for curiosity to read at the time of writing Curiosity has traveled almost 19 kilometers from its Landing site on the flat Plains to the lower slopes of Mount sharp stopping along the way at each interesting
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site to characterize the geological environment curiosity's Suite of scientific instruments is the most sophisticated ever installed on a spacecraft the Rover is a mobile geological laboratory capable of analysis of the Martian surface and the layers just beneath NASA loves acronyms curiosity acquires samples using the SSS the surface sampling and science system it is made up of three parts the sasar sample acquisition process and handling subsystem Sam sample analysis at
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Mars instrument and Chemin chemistry and mineraly instrument the main components of sasar which is mounted at the end of curiosity's robot arm are an integrated scoop and Sample processing system Chimera and a drill for acquiring surface and subsurface samples the scoop and Sample processing system surely has one of the most inventive of all NASA acronyms C t h i m r a pronounced Chimera
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after the multi-headed creature of Greek mythology which stands for the collection and handling for insitu Martian Rock analysis tool someone deserves an award for that these are transferred into Sam which includes a gas chromatograph a mass spectrometer and a tunable laser spectrometer and Chemin the first x-ray defraction experiment ever flown in space and the most sophisticated modern
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technique for car characterizing mineral samples on Earth the science returned from curiosity is only just beginning as older data are analyzed and published and new data from its climb up the slopes of Mount sharp and through Martian geological time continues but current results are consistent with and greatly enhanced the detail of our picture of a planet that was warmer and wetter when gaale formed around 3.5 billion years ago in early October 2012 curiosity rolled to a
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halter to place the geologists christened Rock nest and scooped up a handful of Mars the sample of dust dirt and finely grained soil was fed into the Sam and heated to 835 de C the baking process revealed the presence of significant amounts of carbon dioxide oxygen and sulfur compounds Sam's analysis also suggested the presence of carbonates which form in the presence of water perhaps most
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surprising of all the soil from Rock Nest didn't just provide circumstantial evidence for ancient water around 3% of the sample's mass was water suspended as small ephemeral droplets of salty liquid curiosity is sitting on the floor of a Lost Lake a body of water that filled Gale at the noan Hesperian boundary the patterns of sedimentary deposits suggest the lake Ro Rose and fell in multiple Cycles over tens of millions of years a transient landscape of ancient streams deltas
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and ponds is bounded by the border of the crater when a lighting on Ancient riverbeds running down from the crater's rim Curiosity has found sulfur nitrogen hydrogen oxygen phosphorus and carbon all the necessary building blocks for Life summarizing the results in August 2017 Michael mayor NASA's lead scientist for the Mars exploration program said a fundamental question for this mission is whether Mars could have supported a habitable environment from what we know now the answer
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is yes in June 2018 two new discoveries strongly reinforced the idea that Mars was once a habitable world and maybe still is curiosity found complex organic molecules a few centimeters below the surface in rocks known as mudstone that form from silt deposited on Lake beds this means that all the ingredients for life were present at the time when Gail crater was filled with water detected
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molecules include Benzene toine propane and butane even more tantalizingly curiosity also observed a strong seasonal variation in methane levels in the Martian atmosphere today reaffirming and enhancing previous observations of methane spikes from orbit the important additional information from Curiosity was that the methane peaked repeatedly in the warm summer months and declined in the cooler winter which is what would be expected if the methane had a biological origin this is
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not irrefutable evidence of Life on Mars today by any means it's thought that geological processes may be able to account for such a seasonal variation although if this were Earth a biological explanation would be favored the appropriately cautious Michael Mayor had this to say in June 2018 are there Signs of Life on Mars we don't know but these results tell us we are on the right track science is a humble and cautious Pursuit and from the time of Viking we've known that Martian
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soil chemistry is notoriously complex and can easily catch out the uny scientist so we should leave it there Curiosity continues its journey through Martian geological history emboldened it is certainly driving across an ancient lake bed where for a reasonably extended period over 3 billion years ago conditions were favorable and all the ingredients for life were present while we shouldn't speculate or read too much into the results to date we can let our imaginations wander
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for a moment to picture what Gail crater might have been like during the late noan when life was gaining a foothold on her sister world we stand on the shores of a lake partially filling Gale fed by runoff from snow melt on the far Northern Rim where Mount sharp now stands a small island breaks the surface blue not the mountain of today but a small Central Peak left over from the impact a place of grand beauty where each marshan evening the pale sun sets in the west beyond
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the island rays glinting dimly off the Still Waters interrupted by the shadow of the peak out to the crater's edge a su dial marking the passing of time on a lake populated by microbial martians the crater counting techniques developed from our exploration of the Moon allow us to place our observations of Mars today in historical context they allow us to construct an absolute timeline if we see evidence that water once flowed across a surface or pooled within a
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crater and we can date the area using crater counting then we can estimate when the water flowed and when it disappeared as we've discussed curiosity is exploring Gale and painting a vivid picture of what happened there crater counting allows for an estimate of when independent from the Rover's ground base measurements a recent analysis using images from orbit taken by mro found 375 craters ranging in size from 88 M to 23 km inside Gale crater implying an age of 3.61
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billion years with an uncertainty of around 60 million years this places the formation of the crater and the geological events that played out inside it during the late noan early Hesperian and this time frame is consistent with observations of the presence of water at many other sites of a similar age consistency over a wide range of independent observations is extremely important in science one sight or set of observations alone may be tantalizing but rarely compelling multiple
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independent observations reduce the uncertainty and give scientists more confidence in their understanding when our goal is to understand the sequence of events on an ancient landscape far away that no human has ever visited caution and consistency are both vital Commodities since we have only one active Rover at present and landings are by their nature rare and confined to limited geographical regions orbital observations of much wider areas of the planet are a vital tool mro's
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high-rise camera has provided some of the most beautiful and detailed highresolution photographs in the history of space exploration covering over 99% of the Martian surface features as small as a meter wide can be seen in these images and the camera can also operate in the infrared allowing for the identification of different minerals at the surface there are many beautiful photographs in the mro library that reveal evidence of persistent lakes and river
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systems particularly across the no aian Terrain in the Southern Highlands sites such as the jezero crater clearly show Meandering River channels draining into deltas some images constructed using both visible light and data from the spacecraft spectrometer reveal well-defined River channels flowing out of the crater and the presence of carbonates and Clays that form where there is persistent liquid water for these reasons the jezero crater is one of the three prime targets
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for NASA's Mars 2020 Rover some of the more recent finds are associated with the Arabia Tera region which sits between the noaki and Southern Highlands and the great lowlands of the north where water could have flowed towards a possible Northern ocean researchers from University College London and the open University studied an area of Arabia Terror equivalent to the size of Brazil using highresolution imagery from mro the study mapped a network of over 177,000 kilm of ancient
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river channels not the usual excavated dry river valleys but rather a network of inverted channels raised lines of sand and gravel laid down on the riverbeds that persisted while the land around them eroded away long after the rivers dried similar ghost rivers are seen in desert environments on Earth in Utah Aman and Egypt where erosion rates are slow the identification of the ghost Rivers allows for Arabia Terror to be identified as a fossilized flood plane
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somewhat like the lower sections of the river Ganges on Earth the lowland interface between Mountain rivers and the Sea this is an important Discovery because it feeds into a long-standing and still unresolved scientific debate about the nature of the noan climate nobody disputes that Rivers once flowed on mars or that many impact craters were once home to Lakes the key question is one of longevity was Mars warm and wet for long periods of time or was it for the most part
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a Frozen planet on which water occasionally melted perhaps triggered by sporadic volcanic activity or shifts in the planet's orbit the tension arises because climate modelers find it very difficult to simulate an ancient Martian atmosphere thick enough to deliver a stable climate over hundreds of millions of years that would have been lost at a sufficiently fast rate to produce the Mars we see today in a recent review for example Robin woodsworth concludes the weight of geoc
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chemical and geomorphological evidence points towards a late noan hydrological cycle that was intermittent not permanently active and the latest state-of-the-art Martian climate simulations suggest a water-limited early Mars with episodic melting episodes may be a suitable Paradigm for much of the later noan and early Hesperian climate before the recent analysis of the Mars Global surveyor data it was thought that there was a relative absence of River channels on
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Arabia Terror and this was interpreted as support for a frozen episodically wet Mars ice may have been concentrated in the Southern Highlands and so lower elevations like Arabia Terror may have been generally more arid and therefore devoid of river channels this appears not to be the case Arabia Terror was once very wet indeed this debate has no consensus resolution at the time of writing
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which reminds us of important points about both our knowledge of Mars and Science in general we are describing and attempting to understand and contextualize events that happened over 3.5 billion years ago at or around the time that life on Earth began that is an immense span of time during which orbital parameters have changed solar output has varied and innumerable impact events have created the planets tracing the evolution of an atmosphere backwards through time
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from today's measurements anchored by geological and geochemical evidence from a few Landing sites and orbital imagery is extremely difficult suffice to say there remains an unresolved tension between Mars's small size and large distance from the Sun and the clear evidence of an ancient water cycle episodic or persistent as Wordsworth writes in the introduction to his review the nature of the early
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Martian climate is one of the major unanswered questions of planetary science the complexity and apparent intractability of the mystery is reason enough for many scientists to study Mars the character of The Scientist requires not only comfort with but attraction to the unknown an acceptance of and Delight in the complexity of nature there is no simple story of any Planet they are each too big and too old and some subject to too many variables we might reflect on what that
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means for our own existence as individuals and as a species the specific fact of our existence is inextricably linked with the evolution of our planet through an incomprehensible web of cause and effect stretching back via major and minor events many beyond Earth itself and filtered by the multi-dimensional Civ of evolution by natural selection this this connects us with every living thing that went before back to the origin of Life almost 4 billion years ago and the origin of our
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planet half a billion years before that and the origin of the solar system and the laws of nature who knows when perhaps during the Big Bang or perhaps infinitely far away in time there's a lot we can't know the search for certainty is a Fool's errand and the lesson is to find Delight in not knowing while simil multaneously committing to extending the domain of the known that's the key to science the key to happiness and the only reasonable response to the existential
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challenge of existence because it is the truth if you don't like that Comfort yourself with the fact that the domain of the knowable is vast possibly infinite and perhaps paradoxically the knowable things about Mars may exceed those about Earth because Mars has been in deep geological freeze for much of its life it is easier to research the Deep past than it is on Earth and that deep past may include the origin of Life traces of the geochemical alchemy that led to the emergence
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of self-replicating information carrying carbon molecules on Earth 4 billion years ago weathered away long ago although Clues may be found in the common structures and chemistry of living things today on Mars however geochemistry was frozen and archived in regions such as Arabia Tera if therefore life began or even still exists subsurface on Mars such a discovery May deliver insight into our own Origins that would simply not be possible by studying the weathered everchanging
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ecosystems of Earth this may be the gift of unknowable Mars she's less unknowable than Earth the eridania region of the Southern Highlands May provide the most compelling evidence yet of a warm wet early Mars with conditions not dissimilar to Earth at the time when life began the analysis we described below is a beautiful example of how the site of science instruments aboard multiple spacecraft in orbit around Mars can be combined with our knowledge of cratering rates on the moon
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to characterize an environment and Trace its history back through deep time it is also a beautiful example of the interconnected nature of science and the value of exploration we've already met the elevation maps from the Moler aboard the Mars Global surveyor this topological data in concert with visual data from Mr revealing the location of Valley networks suggests that the eridania Basin was once a giant Lake possibly the largest ever to exist on Mars 1.5 km deep
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in places and containing three times more water by volume than the Caspian Sea on Earth we know the terrain is late noan around 3.7 billion years old from crater counting the Chism spectrometer on board mro reveals the minerological composition of different areas of the eridania Basin and this can be used in conjunction with the topological and visual data to build a three-dimensional picture
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of the landscape and its chemical composition in the deepest areas of the eridania Basin magnesium and iron-rich clay minerals are common laid down as sheets of saponite talc Serpentine and so-called tot Clays these are characteristic of seafloor environments on earth materials known as iron rich philos silicates are also seen which are again characteristic of terrestrial seaf FL deposits the mineral jarosite is detected suggestive of the chemical weathering of sulfite
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deposits there are many different carbonate signatures containing ion manganese magnesium and calcium higher up the Basin walls chlorides are found which are indicative of evaporation in shallower water the most likely explanation for the origin of the deep clay carbonate and sulfite deposits it's argued is volcanic activity on the floor of a deep lake because very similar deposits are seen at hydrothermal sites on Earth the iron minerals detected are similar to those formed
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in the iron-rich early oceans of Earth prior to the release of large amounts of oxygen into our atmosphere by photosynthesis all this beautiful topological visual geophysical and geochemical data can be combined to produce a picture of what was happening in the eridania Basin around 3.7 billion years ago the geochemistry of the low-lying regions is indicative of a deep sea volcanically active hydrothermal environment with the salt-rich deposits at higher elevations
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suggestive of slow evaporation in shallower waters the Basin contained an iron and mineral Rich ocean energized by active volcanism deep below the waves a cauldron of complex geochemistry stirred by the constant flow of energy from the inner planet this is a striking conclusion because at the same time a few hundred million kilometers across the solar system on Earth many biologists believe believe
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that life began in similar deep sea volcanic environments the theory that life on Earth began in hydrothermal vent systems is mainstream although not universally accepted by any means the idea is partly based on the observation that all living organisms on Earth today share a chemistry associated with the establishment of gradients in the concentration of protons across membranes known as chemiosmosis proton gradients are also characteristic of the geochemistry of alkaline
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hydrothermal vent systems in acid oceans which were common on the young Earth and perhaps the young Mars an analysis published in 2017 claims to have detected evidence of biological activity in rocks laid down by hydrothermal activity at least 3.77 billion years ago in the Nua Guk crustal belt in Quebec near the Greenland ishua rocks the evidence comes from tube likee coils of the ion oxide mineral hematite similar in size and form to structures laid down by ion
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oxidizing bacteria in hydrothermal environments today it's possible that the rocks at Nook are much older a radiometric date using the samarium neodymium Decay process suggests an age of 4.28 billion years which would make them by far the oldest rocks on Earth and an astonishingly early date for biological activity these findings are controversial in part because of the difficulty of understanding how Earth's active geology has modified the samples over such vast time scales
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this is where Mars may have an advantage over Earth in helping us to understand the processes by which the chemistry of a planet became the chemistry of life the environment at eridania is far better preserved than that at nuu AOK it has been in sterile almost deep freeze conditions for over 3 billion years the ultimate laboratory for studying the origin of life if indeed life began on Mars the story of the eridania Basin and the possible scientific promise it holds was pieced
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together by using the results from different instruments on different spacecraft over many years spanning several scientific disciplines geology chemistry spectroscopy laser altitude ranging and photography the estimate of the age of the surface required the Apollo lunar Rock samples from 50 years ago and radiometric dating techniques which required an understanding of nuclear physics the estimate of the age of the surface requires a model of the entire solar
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system in order to interpret the measured crater density which illustrates another important idea the solar system is a system no planet is an island no planet can be understood in isolation just as the structure of any one living thing on Earth cannot be understood in isolation organisms are a product of evolution by natural selection the interaction of the expression of genetic mutations and mixing with other organisms in the ecosystem and The Wider environment
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the planets formed in a chaotic melstrom from motions as random as the impact of a cosmic ray on a strand of primordial DNA and whatever world worlds emerged from the chaos have had their histories shaped profoundly by their Mutual interactions throughout their evolution the late heavy bombardment is a beautiful example if indeed we discover that life began in the eridania Basin what a magnificent illustration of the unity of knowledge that would be understanding developed
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over centuries the life's work of thousands of explorers field geologists chemists biologists astronauts Engineers distilled into the discovery of a second Genesis but more than that because of the pristine nature of the ancient environments on Mars such a discovery would deliver an insight into our own Origins that may not be available to us here on Earth Mars is a time capsule containing
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the Frozen chemistry of an ancient world similar to the earth when life began but while Earth's deep past has been largely erased by 4 billion years of GE iology in the action of a complex Global living ecosystem which has transformed the planet and its atmosphere beyond all recognition Mars is a fossil from the deep past this raises the wonderful possibility that another world albe it an integral part of our system may be the key to decoding The Mystery of the origin of life
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here the reason we exist it's almost as if we have to leave the Cradle in order to truly understand it around 3.5 billion years ago change was underway on Mars the warmer wetter episodes that characterized the planet for millions of years during the noan became less frequent and the climate drifted imperceptibly at first towards the colder arid State we recognize today the water that flowed freely over the surface during the noan became locked away in
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giant reservoirs of ice Lakes turned solid and rivers ran dry the planet wasn't dying far from it the fireworks of the late heavy bombardment had faded but rumbles from the deep maintained the violence the shield volcanoes of thsis including the mighty Olympus Ms continued to build even as global temperatures plummeted and subsurface lava flows occasionally melted the reservoirs of ice leading to catastrophic floods that challenged the imagination in their scale and
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violence the age of Noah became the hesperion the age of floods or rather less portentously and more accurately the age of occasional floods the Hesperian period is named after the Hesperia Plum a giant lava field to the northeast of the helas Basin in the Southern Highlands the plane was resurfaced partly by the volcano at its Center Tyrus Mons and spans almost 2 million square kilm first photographed by Marin 9 in 1972 it's a relatively flat landscape with few visible rock
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formations the most prominent surface features are the craters that allow us to date it Tyrus mons is a very different volcano to Olympus Mons and the Giants of thsis it's much more ancient fully formed not long after the helis impact 4 billion years ago and it erupted through water or Frozen ground a process that produces large amounts of Ash rather than lava what geologists call a pyroclastic eruption as a result of its age and composition Tyrus was more prone to erosion
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than the Giants of thsis and today stands only 1.8 km above Hesperia Plum the Hesperian period was coincident with increased volcanic activity particularly at thsis but there's not necessarily A causal link between volcanic activity and the transition from the noan to the Hesperian what is clear is that volcanism became the dominant geological force on Mars as the long-lived water cycles waned and cratering rates declined after the late heavy bombardment around 3.5 billion
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years ago this is seen in both surface features and mineralogy Hesperian surfaces are richer in sulfates rather than the Clays and carbonates of the noan sulf form in the more acidic atmospheric conditions created by the release of sulfur dioxide from volcanoes while volcanic activity was the dominant Force sculpting the smoother Hesperian Landscapes there are spectacular and notable exceptions where water reasserted its dominance if only for a moment echos chasma is
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an unremarkable Valley today images taken by mro reveal a deep steep-sided depression lying to the north of the Marin Valley at 100 km long 10 km wide and between 1 and 4 km deep it would be impressive on Earth but is dwarfed by the Magnificent neighboring Valley system 3 and A2 billion years ago on Frozen Hesperian Mars however things were different high above on the thsis rise lava surged upwards through the crust and met great reservoirs of ancient ice releasing vast
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am PS of water that raged down from the Southern Highlands the meltwater was funneled towards echos chasma where it created one of the briefest and yet most spectacular wonders of the solar system The Waters from the highlands came tumbling over the cliffs roaring 4 km down into the valley below over the largest known waterfall in the history of the solar system around 350,000 cubic km of
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water cascaded through the valley the equivalent of a cube 70x 70x 70 kilm in less than 2 weeks this being Hesperian Mars the atmosphere was not substantial enough for the liquid to persist on the surface and the water disappeared as quickly as it came leaving scant evidence of the Great Falls etched into the canyon walls echos casma was unique in scale but the cycle of volcanic eruption followed by fleeting catastrophic floods was repeated in many locations across the planet
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throughout the Hesperian however in the thinning atmosphere the presence of liquid water was probably always fleeting increasingly so as time passed Hesperian became Amazonian around 3 billion years ago plus or minus half a billion years or so when a Mars expert is asked the question when did the Amazonian begin they will usually say depends who you ask but certainly by two billion years ago
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long before there was complex multicellular life on Earth Mars was pretty much indistinguishable from the planet we see today the red planet didn't die entirely volcanic eruptions persisted and have occurred in the very recent past at thses there may yet be eruptions in the future but we do know that Mars changed from a world that supported liquid water on the surface under a thick atmosphere via a period dominated by intense volcanic activity and episodic floods into a
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hyperarid frozen planet with a tenuous atmosphere more befitting its small size and place in the solar system this drama played out very roughly during the first 1.5 billion years of its life the challenge is to understand why the climate of a rocky planet is a complex dynamic system shaped by Myriad interactions feedbacks and instabilities and inevitably changes over geological time scales a thin envelope of atmospheric gases can be affected dramatically by volcanic and tectonic
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activity and impacts from space and on longer time scales by shifts in orbit and tilt and changes in solar output Earth seems to be a remarkable exception the most dramatic atmospheric change over the last 3 billion years has been the gentle introduction of oxygen by pH photosynthesis Mars today has a thin atmosphere composed primarily of carbon dioxide we know this atmosphere must have been significantly thicker in the past quite possibly at an even higher pressure than that
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of modern day Earth because there was once liquid water on the surface Mars must therefore have lost most of its original atmosphere and it's important to understand where it went and why the ancient atmospheric carbon dioxide molecules could have frozen out onto the surface in the polar ice caps become locked away in the subsurface as carbonate minerals or they could have been lost to space
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or some combination of all three to measure the composition of the Martian atmosphere today and understand how it evolved over time a dedicated Mission arrived in orbit in September 2014 Maven the Mars atmosphere and volatile Evolution mission has no highdefinition cameras and provides no dramatic photographs of the surface because the questions Maven was designed to answer are about the invisible envelope of gases surrounding the planet if curiosity is the extension of our hands
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and mro our eyes Maven is our nose sniffing the air for Clues to the past the spacecraft operates in a highly elliptical orbit bringing it as close as 150 km above the surface and out Beyond 6,000 km this eccentric path means that on every orbit Maven experiences a wide profile of the Martian upper atmosphere allowing it to build a three-dimensional picture of the gases that still remain and how their distribution changes with altitude and time maven's measurements show that
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Mars is losing atmospheric gases today at a rate of about 2 kg a second the question is is how is the atmosphere being lost and where is it going the maven team carried out an ingenious analysis based on observations of the concentrations of two different isotopes of the noble gas argon argon 36 and argon 38 argon 38 is chemically identical to argon 36 but it's heavier because it has two additional neutrons inside its nucleus the ratio of argon 38 to argon 36 is sensitive to
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the rate at which the atmosphere is being lost to space through a process known as sputtering high-speed electrically charged particles from the solar wind hit atoms in the upper atmosphere and literally knock them out into space because argon 36 is lighter than argon 38 the relative abundance of argon 36 in the upper atmosphere is enhanced in technical terminology argon 36 has a larger scale height than argon 38 this means that Argon 36 is preferentially lost to space
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through sputtering and the ratio of argon 38 to argon 36 increases since there's no other way that argon can be removed from the atmosphere it doesn't react with anything and it doesn't freeze it anywhere near the temperatures seen on Mars the Argon measurements provide a very clean indication of the way the Martian atmosphere is affected by the Solar Wind by using measurements from Maven at
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different altitudes during its elliptical orbit and surface measurements of the Argon isotope ratio from Curiosity this beautifully elegant experiment enabled the team to determine that 66% of the Argon in the Martian atmosphere has been lost over the planet's 4.5 billion-year life time once this rate of argon loss has been determined the rate of other atmospheric components can be calculated the published results concluded the evidence from Maven observations suggests that
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large fraction of the Martian volatile inventory has been removed to space and that loss to space has been an important process in the evolution of the Martian atmosphere through time in particular a large fraction of the dominant component of the Martian atmosphere the powerful greenhouse gas carbon dioxide has been lost to space through the interaction with the solar wind with a smaller fraction being locked away in subsurface carbonate deposits and an even smaller fraction
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stored as Frozen carbon dioxide in the polar ice caps these changes the authors conclude appear to be large enough to account for the change in the Martian climate inferred from the planet's geomorphology without declining levels of greenhouse gases in the atmosphere to keep in warmth and protect its lakes and oceans Mars was destined to become a frozen desert world but why has Earth not suffered the same fate we are after all closer to the Sun and
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bathed in a more violent solar wind why has our atmosphere survived the solar Onslaught for several billion years after the Martian atmosphere was stripped away the solar system is in fact a system although we might feel isolated on a ball of rock in the dark that is an illusion no planet is an island the system evolves as one draw a diagram of the food chain underpinning all complex life on on Earth today and at the base is a stream of photons generated
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150 million kilm away inside the Sun green plants are the interface between a star and civilization our understanding of Mars demonstrates that a planet's relationship with the sun is not all light and sweetness the star can provide the energy for life but the solar wind can also destroy life or prevent it from ever emerging through the damage it can cause to planetary atmospheres the solar wind emerges from the sun's atmosphere known as the
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corona the temperature at the sun's surface is 6,000 de C but the temperature of the corona is over a million de C heated by energy transferred from the surface by the powerful solar magnetic field twisted and coiled by the star's rotation at such high temperatures atoms cannot hold together electrons are ripped away from Atomic nuclei and matter exists in a fourth state not solid liquid
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or gas but a soup of negatively charged electrons and positive ions known as a plasma some of these particles are moving so fast that they escape the sun's Embrace completely streaming outwards across the solar system at velocities in excess of 800 km/s this is the solar wind when these high energy charged particles reach Earth most do not smash directly into atoms at the top of our atmosphere because we are protected by our magnetic field they are deflected harmlessly by
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stretching and distorting the field out on the night side of the planet the stretched field occasionally reconfigures accelerating electrically charged particles back down the magnetic field lines to the Earth's poles where they collide with atoms and molecules in the the upper atmosphere exciting them and causing them to emit light this is the Aurora the northern and southern lights from Earth the Aurora can be seen by those lucky enough to
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be far enough north or south on the right night when the sky is clear the sun is active and the interplanetary magnetic fields are favorably aligned from the lofty vantage point of the International Space Station the Aurora reveals itself as Halos dancing around the pole s it is an unforgettable site undoubtedly one of Nature's wonders but as is often the case in science and in life for that matter the experience is greatly enhanced by knowledge the lights dancing faster
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than the eye can see or perhaps the brain can comprehend are a direct result of the structure of atoms electrons shifting between allowed energy levels determined by the number of protons in the atomic nucleus that holds them captive high altitude oxygen glows red an atom is struck by a Charged particle accelerated down the Earth's magnetic field lines towards the pole the interaction shifts an electron into a longlived excited configuration if the atom is
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not involved in a collision in the thin air for around 100 seconds an eternity in atomic time the electron will shift down closer to the nucleus and a red Photon will be emitted at lower altitudes a different reconfiguration inside oxygen atoms causes the emission of green photons this time the atom must avoid Collision for around a second still an atomic eternity in the denser air excited nitrogen molecules add a deep red or pink to the lower edges of the Towering curtains
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of light during intense displays this is quantum mechanics written across the sky the structure of atoms revealed to calculate the colors physicists treat the electrons as waves trapped inside a deep well created by the electric charge of the protons particles imagined not as Tiny Flex of matter but as fields that can span great volumes of space the energy to drive the display comes from nuclear fusion reactions inside the Sun a factory a million times the volume of earth
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converting hydrogen into helium at a rate of 600 million tons per second the weak nuclear force acts slowly and grudgingly to convert protons into neutrons in the core nuclear alchemy that results in the creation of neutrinos which stream across 150 million kilm at close to the speed of light before passing unhindered through the entire planet on their Journey To Infinity thus 60 billion per square cm stream through your head every second without even a nudge because your
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head is almost entirely empty space and neutrinos hardly ever come close enough to interact with the all sparsely distributed molecules it might happen once in your lifetime the nuclear forces at work inside the Sun Also assembled the heavy elements that make up your body inside old Stars long ago from hydrogen and helium forged in the first few seconds after the big bang carbon oxygen nitrogen
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sulfur phosphorus and iron gravity assembled the Stars by forcing the collapse of of primordial interstellar clouds causing them to heat up in their centers and triggering the nuclear reactions that release the energy to Halt the collapse for a few billion years long enough for life to emerge in the gradient between the nuclear furnaces and the chill of the expanding Universe all of these thoughts are ignited in the imagination by the auroral display our experience is enhanced by
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knowledge a central component of the web of physical processes that make the Aurora shine is our magnetic field which deflects the solar wind harmlessly past our planet and allows it to return in a much subdued form to the poles without this the processes that Maven observes stripping the atmosphere of Mars would happen on Earth the magnetic field is one of the most important differences between our worlds Earth's magnetic field is generated by what is known as a Dynamo
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which is easy to explain in Broad brush terms but extremely complex and not fully understood in detail the basic physics is simple earth's core is composed largely of molten iron which is an electrically conducting fluid plumes of molten liquid rise and cool as they approach the mantle and the Earth's rotation swings these columns around into circulating rising and falling flows this circulating flow Act as a Dynamo and generates a magnetic field the stability of the
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Dynamo is related to the temperature gradient between the core and the mantle the radius of the core itself the rate of rotation of the planet and numerous other subtleties the rate of heat flow through the mantle is affected by geological processes including plate tectonics and volcanism the precise nature of the flows depends on the constituents of the core other than iron for example the SU content and distribution and so on it's
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fishlyn field gives every indication of being a delicate phenomenon it was certainly delicate on Mars we suspect there was once a martian Dynamo because the Martian crust is still partially magnetized in places particularly in the ancient Southern Highlands suggesting that these rocks cooled in the presence of a global magnetic field the helus impact Basin which formed around 4 billion years ago shows no sign of magnetization suggesting the Dynamo shut down
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before this impact impact basins that formed over 4.05 billion years ago do show signs of magnetization the Martian meteorite alh84001 dated at 4.1 billion years old also shows clear signs of having formed in the presence of a magnetic field these observations lead to the current Baseline view that Mars had a magnetic field not unlike Earth's which seems to have switched off just before the Hass impact from that point onwards the atmosphere was exposed to the full force of
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the solar wind and the maven results tell us that this was likely the key driver for the loss of the Martian atmosphere it would be tempting but wrong to suggest that the loss of the magnetic field was the trigger that drove the change from the noan to the hesperion the time scales probably don't match and in any case the loss of the magnetic field wouldn't have led to an immediate loss of the
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atmosphere sputtering as a gradual process which still continues today there have been speculative attempts to link the switch off of the Dynamo to the Hass impact or multiple impacts around the time of the late heavy bombardment the idea is that the heating of the mantle can disrupt the heat flow out from the core in turn disrupting the smooth convective Flows at the time of writing the sequence of events is reasonably well established but there is no consensus
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on how or even if they are causally linked a complicating factor is the relative instability of the Martian orbit the planet's obliquity the tilt of its spin axis varies by tens of degrees over time scales of a few hundred thousand years in response to gravitational interactions with the other planets and the Sun in comparison Earth's axis drifts gently between 22.1 and 24. 5° in a 41,000 year cycle and even this small change is responsible in part for Earth's periodic ice ages
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imagine what happened to the Martian climate when the polar regions with their reservoirs of carbon dioxide and water ice tilted towards the Sun by 20 or 30° the stability of Earth's spin axis is maintained by the damping effect of the Moon which is unusually large relative to our planet the Earth Moon system might almost be regarded Ed as a double Planet system the more we learn about other worlds the more fortunate our presence on Earth appears the red planet is
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simply too small it lost its heat more quickly than Earth from its smaller core and through its thinner mantle and crust geological activity fell markedly after reaching a peak during the hesperion and the planet faded the atmosphere held more tenuously than Earth because of the planet's lower Mass and gravitational pull and unprotect protected by a magnetic Shield was Stripped Away by the solar wind and the surface approached temperatures more in tune
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with an orbit far from the Sun Mars's fate was sealed during its formation 4.5 billion years ago it is too small and too far away from the Sun to have remained a vibrant active world today faint auroras still dance in the Martian Skies as photographed by isa's Mars Express spacecraft blue ghosts of a Martian past generated by localized magnetic hotspots scattered across the planet and the last traces of carbon dioxide in the atmosphere energized by the Relentless solar
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winds despite its three billion-year quesence Mars had a bright and active adolescence that Echoes down the ages and may yet have profound consequences for us confined for now on her planetary neighbor a solar systems lifetime away there may have been and may still be life on Mars we're looking hard and the next generation of spacecraft may find evidence for martians within the next decade the discovery of a second Genesis would have important philosophical scientific and
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cultural consequences it would mean that given the right conditions liquid water active geology and a sprinkling of Organics we would know that life emerges with the sense of inevitability through the entirely predictable action of the laws of nature it would be confirmation that we along with every living thing on our planet today are an outgrowth of the planet an extension of geology we
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would understand that whatever magic we perceive in the depths of our souls has its origins in the interface between water and heat and minerals and gas we are bubbling chemistry that thinks if it happened on two neighboring planets in a single solar system it happened everywhere we would understand that we are part of a grand living Universe we are not God's children but we are also not alone of even greater importance I think is the role that Mars must play in our future Mars
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is rich in potential it has reservoirs of Frozen or even liquid water below the surface and a great wealth of mineral resources all the things that are necessary to support a civilization because of its history this is a world in waiting a Treasure Island in stasis I think in my lifetime there will be martians the Martians will be us we will go to Mars and make it our home partly because there is
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nowhere else to go Mars is the only planet beyond Earth on which we could even contemplate a landing in the near future the message from Marin for was not interpreted correctly there is a second chance for us on Mars when we feel ready to take it I don't mean that we will leave Earth on mass for the new world this is Manifest nonsence the Earth is by far and a way the best planet we know
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of anywhere in the universe we were born of it and sculpted precisely and perfectly to flourish on it through the action of evolution by natural selection yet it is possible now to build a colony on Mars I imagine a group of pioneers on the new world living off the land and constructing the infrastructure necessary for tens hundreds and ultimately thousands of individuals to follow in their footsteps across the solar system and extend the human Frontier for the first time in many
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centuries Frontiers are important the intellectual Frontier is the domain of Science and where would we be without the Pioneers who felt drawn there the physical Frontier is the domain of adventurers engineers and dreamers and dreamers need somewhere to go in Vana herzog's film encounters at the end of the world a man named William jerser describes the sort of person who gravitates to Antarctica
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the last of Earth's Frontiers I like to say if you take everybody who's not tied down they all sort of fall down to the bottom of the planet so that's how we got here you know we're all at loose ends and here we are together I remember when I first got down here I sort of enjoyed the sensation of recognizing people with my travel markings I was like hey these are my people phds washing dishes
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and linguists on a continent with no languages Mars is the Step Beyond the Antarctic and perhaps we all need to take it in our imaginations our civilization feels untethered to me we're at a loose end huddled in a tiny corner of our system we watch the wandering planets and the Wheeling stars and the cycles of day and night and wonder what the hell we're doing we're all linguists on a continent with no languages as a consequence we Scrabble around eaing out the ever more precious
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resources on Earth trying to expand and build more stuff and grow in a thin shell of air on the two dimensional surface of a small rock giving little thought for the three-dimensional path marked by the lights in the night Robert Zubin the Visionary engineer whose work is inspired amongst others Elon Musk likes to say that ideas have consequences and the worst idea in the history of humanity is that we must compete for limited resources this is false the solar system contains
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raw materials beyond our needs or Desir s and they will become resources when we choose to access them the international tensions created by the competition for Earthbound resources are based on the entirely false and dangerous idea that resources are limited false false false we have the technology and perhaps as we drift ever more aimlessly we may discover the will to unlock the unlimited Treasures in the vast solar system of which we are aart we need to shift our
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Collective Consciousness we burn too bright for this world alone but that does not mean we should extinguish the flame we must Forge A New Path that transcends competition between nations that requires the wholesale rejection of the mindset that mistakenly compels us to retreat or fight over dwindling resources on a single groaning planet we must transform ourselves into a multiplanetary space fairing civilization and this begins with the colonization of Mars an achievable
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goal forged from the human desire to explore and expand without pushing up against someone else's border fence or damaging our planet Beyond repair Imagine The Magnificent intellectual and physical Vistas the new technologies the opportunities the excitement of creating a new new Society the joy of extending our collective experience and hopes and dreams to a new world and worlds Beyond Mars has a pivotal role to play in our future if we don't go there we'll never go
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anywhere and if we go nowhere we'll die here breathing new life into the old red planet will Breathe new life into us it will be our first Step Beyond the cradle and onwards to the Stars Earth before life 4.5 billion years ago was known nent Eden closer to the realm of Hades than the garden of God molten and smoldering cloaked in toxic clouds through which the young Sun could barely break to Signal the coming Dawn the Planet still trembled from the aftermath of a glancing
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collision with mars-sized Thea now fragmented into a ring of debris that given time coalesced with the ejected Rubble of Earth to form the moon 4 billion years later two people who owed their existence to the energetic geology of hadan Earth stepped onto the surface of the coales rubble and considered their position in the firmament from their Vantage Point Armstrong and Orrin viewed a peaceful pristine planet that has been many different worlds since its formation how
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do we know how can we speak with any authority of events that happened billions of years ago Beyond not only memory but also life on Earth itself how is such a timeline calibrated the answer lies in the Rocks Apollo delivered many Treasures countless engineering break throughs a generation inspired Earth rise from Apollo 8 the simple joy of exploration but scientifically speaking the treasure was Rock 382 kg of rock collected from six Landing sites on the moon as on Earth
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rocks can be dated with great accuracy using the natural clocks provided by the radioactive decay of certain atoms the chemical element rubidium for example occurs naturally and quite commonly in a form known as rubidium 87 which is found in many potassium rich minerals it is unstable with a halflife of 48 billion years this means that over a period of 48 billion years half of the rubidium 87 atoms that were present in a rock when it Formed will have decayed away transmuting
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into another sort of atom strontium 87 an older rock will have fewer rubidium 87 atoms and more strontium 87 atoms there is a little more to it than that of course how do we know how many rubidium and strontium atoms were present when the rock formed the clever part of the dating procedure is that we don't need to know the method called the isocon method relies on the fact that there is another naturally occurring form of strontium which is not
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produced by radioactive decay known as strontium 86 strontium 86 is stable and chemically identical to strum 887 the only difference is that it has one more Neutron inside its nucleus this means that any strontium 86 atoms inside a rock today were present when The Rock originally formed by counting the number of Rubidium 87 strontium 87 and strontium 86 atoms in a selection of samples taken from a rock it is possible to calculate the absolute time elapsed since the rock formed
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on Earth some of the oldest crustal rocks are found off the Southwest coast of Greenland at a place called ishua using ridium strontium dating we know these rocks were formed 3.66 billion years ago with an uncertainty of 0.06 billion years the oldest known rock on Earth was found in Jack Hills Western Australia it Formed 4.44 billion years ago with an uncertainty of 0.008 billion years all known samples from Earth's crust are younger than 4 billion years old because the seething
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surface of the hadan Earth meant that rocks were constantly being melted and reformed resetting the radiometric clocks the same analysis can be carried out on meteorites that have fallen to the surface of Earth from space the majority over a thousand known formed between 4.4 and 4.6 billion years ago which is consistent with independent estimates for the age of the solar system using
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for example Helio seismology measurements of the amount of helium in the sun's core the youngest of the moon rocks returned by the Apollo Astronauts were 3.2 billion years old and the oldest were 4.5 billion years old 12 of the samples were over 4.2 billion years old the variation in age of the moon rocks at the Apollo Landing site is extremely interesting and important and if forms the basis
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of the most accurate technique for dating areas of the Moon from which we have no Rock samples we can make a graph showing the age of the Rocks collected from each Apollo Landing site and also the Russian Luna 24 robotic sample return Mission plotted against the number of craters per square kilometer at the site the dark blobs around the labels of the various missions will represent the uncertainty of the measurements of the ages of the rocks and the crater counts two very low
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and uncertain points from the craters cernus and Tao are from rocks collected by Apollo that are thought to have been thrown into the landing SES by the impacts that created these two distinctive lunar craters in the much more recent past two solid lines curve up across the plot bounding the measured points older sites have more craters which is easy to understand because there's been more time for meteorite impacts to build up surfaces that were created in the more
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recent past such as the Copernicus crater have experienced many fewer subsequent impacts imagine now that there's an area of the Moon from which we have no samples but we do have photographs of that location from space we count the number of craters per square kilometer let's say we get an average of 0.2 craters above a diameter of 4 km per square kilm this allows us to say that the surface formed somewhere between around 3.2 and 4 billion years ago similar in age to the Apollo 17
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Landing site this is one of the simplest uses of the graph more importantly for our purposes we can extrapolate the graph from the Moon to Mars we have to make some model dependent estimates of how the number of impacts changes because Mars is a larger planet with a stronger gravitational pole and to account for from Mars's different place in the solar system closer to the asteroid belt the
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source of most of the impacting objects we can do this with some confidence and this is the primary way we estimate the absolute age of the different regions of Mars the noan terrain is the oldest and has the highest density of craters followed by the Hesperian and the Amazonian the northern lowlands have been resurfaced by volcanic activity in the more recent past which we know because they're
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relatively devoid of at much like the lunar seas in this way the absolute dates we quote for events on Mars are all ultimately tied to the radioactive dating of moon rocks and this is one of the main reasons why the Apollo Rock samples from different Landing sites are so valuable scientifically there's another key line on the graph a dashed line will call constant production rate the number of craters plotted against age would follow this line if the moon had been subjected to a
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constant rate of impacts throughout its history the measurements follow this line until we get to the surfaces around 3.8 to4 billion years old when the number of craters increases dramatically implying that in the early history of the solar system there was a time when the rate of impacts was much greater than today that's not surprising we might expect that the young solar system would
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have been filled with leftover rubble from the formation of planets and so a more violent place but there is a complication if we assume that the impact rates seen on the oldest lunar terrains such as the Apollo 16 Landing site in the decart highlands were sustained all the way back to the moon's formation then the impact rate would have been impossibly high the amount of mass falling on the surface of the Moon would have been similar to the mass of the Moon itself we
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know that didn't happen so the assumption is that the rise of the impact rate curve on the graph is in fact a spike that peaked around 3.9 billion years ago and then returned to the much lower impact rate from earlier times this violent spike in the rate of impacts from space is known as the late heavy bombardment the cause of the late heavy bombardment is not known but a leading theory is that Neptune changed its orbit from inside to outside that of Uranus and the resulting
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gravitational disturbance deflected a malstrom of icy objects in the distant Kyper belt towards the planets of the inner solar system we might reflect on the interconnected nature of knowledge and of the solar system exploration of the Moon provided us with the intellectual tools to date the surface of Mars using the scars delivered by objects deflected into the inner solar system by events that occurred far away in space and time beyond the orbit of either world it's a story that
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began before the solar system even truly existed 5 billion years ago a vast Interstellar cloud of dust and gas at least 65 light years across that's 6.1 * 10 ^ 14 in kilom began to collapse and coales under its own enormous weight fragmenting into a collection of smaller dense cores one of these gigantic clumps formed what is known as the pre-solar nebula the embryo from which every part
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of our solar system would develop in this dense cloud of gas comprised almost entirely of hydrogen and helium hung every atom that would go on to form the Sun the planets and every element that would define the character of each of these worlds including the ingredients of Life the components of you and me what triggered This Cloud Beyond The Tipping Point and onto the next stage of its
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stellar evolution is lost in the eons of time but astonishingly we have been able to pull together scraps of evidence to guide us by studying some of the oldest meteorites ever discovered on the surface of the Earth we've been able to get a glimpse of the time when it All Began locked away inside these ancient meteorites are the unmistakable signatures of rare forms of iron that we believe can only have been created under a very specific set of conditions the only place in the
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universe where these rare Isotopes can be formed is at the heart of giant short-lived Stars at the very moment they explode in other words they are the product of supern noi this clear chemical fingerprint from rocks dating back to the earliest days of the solar system over 4.5 billion years ago suggests that our solar system emerged among a cluster of thousands of stars in a large Stellar Nursery perhaps not unlike the Orion Nebula the star forming region that lies closest to the
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earth at 1,500 light years away which can even be spotted with the naked eye in the night sky
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