Enigmas of the Solar System | Documentary Boxset | Knowing the Planets

by the 1920s as ground-based 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 formaldehyde filled the air leading to the belief that venus was not only a dead planet but a pickled 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 formaldehyde this was a planet engulfed in a blanket of carbon dioxide and as a reinducer demonstrated on earth this almost certainly meant that whatever lay beneath the clouds the heat would be beyond 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 programme named vignera which attempted to explore the atmosphere and surface of venus directly for the first time the initial launches of the venera program failed before they had even left earth's orbit but within a couple of years the program began to slowly see some success vignero 1 was successfully launched on the 12th of february 1961. designed as a flyby mission it is thought to have passed within 100 000 kilometers of venus but a total telemetry 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 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 iii was the historic position as the first human-built object to crash into another planet's surface nobel prize-winning chemist svante erianus was one of the most renowned scientists to fuel the mythology of what lurked behind venus's cover like many of the scientists of his era arianus 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 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 defined different parts of the earth in arenas imagination this stable environment with a consistently uniform climate all over the planet meant that any life on venus lived without the evolutionary pressures of changing environments that drive natural selection here on earth leaving venus in an evolutionary limbo akin to the carboniferous period describing a world full of prehistoric swamps and dark forests ariendus created the perfect canvas for science fiction writers of the time to conjure up a menagerie of curious life forms lurking beneath the clouds today arianus 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 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 area 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 the clouds 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 chabot explains before messenger we had only seen 45 percent 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 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 plunicia a lowland basin 1525 kilometers 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 spread past in 1974 but due to the trajectory and timing of the craft 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 colorist to be bigger than had been previously estimated encircled by a range of mountains rising two kilometers from the mercurian surface whose peaks create a one thousand kilometer boundary around the lava plains within on the other side of the mountains the vast amount of material that was lifted from the planet's surface at the moment of impact formed a series of concentric rings around the basin stretching over one thousand kilometers 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 coloris this area of strange geological formations distinct from the rest of the surrounding terrain was likely created by the seismic shock wave of the coloris 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 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 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 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 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 which is so close to the sun and yet the messenger data confirmed high levels of potassium and sulfur was detected at ten 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 structure of mercury that it is the densest of all the planets with a massive iron core making up 75 percent of the planet's radius compared to just over 50 percent 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 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 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 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 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 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 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 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 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 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 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 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 75 percent 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 a hundred and fifty years and that's because of some brilliant deduction by a german astronomer called joanne franz 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 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 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 messenger's data proved otherwise by combining precise measurements of mercury's gravity field with the extraordinary mapping of its surface messenger found that mercury's structure is unique in the solar system it appears to have a solid silicate crust and mantle above a solid layer of iron 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 four and a half 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 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 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 most violent and defining of turns in mercury's 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 transformed the physical 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 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 earth-like 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 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 from us either and the clouds that shroud it are highly reflective reflecting three quarters 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 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 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 magellan mission which not only relayed extraordinary radar soundings of the surface of venus but provided the first full topographical map of the planet collated over a period of four 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 goddard institute for space studies gis all 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 two 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 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 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 despite multiple failures the soviets didn't give up and in october 1967 venera iv entered the atmosphere of venus and sent back data supporting the 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 percent three percent nitrogen and just trace amounts of oxygen and water vapor veneer iv confirmed beyond all doubt that this was no second earth as it descended through the thick clouds the temperature rose to 262 degrees celsius the atmospheric pressure increased to 22 standard atmospheres 2200 kpa and this was still 26 kilometers above the surface as veneer iv parachuted its way down to the surface it provided data to earth 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 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 venera 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 antennae to transmit limited temperature data for 23 minutes before it expired vignera 9 not only made it to the surface 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 degrees celsius with an atmospheric pressure of 90 atm crashing down by the time veneer 13 launched on the 30th of october 1981 the ambition of the missions and the confidence in delivering data from the surface had been radically transformed venera 13 functioned for 127 minutes in recorded temperatures of 457 degrees celsius 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 that wasn't enough onboard 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 veneer 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 heavens for a place like home we'd found a toxic fiery hellscape venus is an enigmatic world almost earth-like 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 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 four 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 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 captured from the clouds of gas and dust it swept through on its orbit around the sun [Music] 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 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 oceans taken hold of large swathes 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 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 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 discoveries revealed an unexpected amount of deuterium 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 deuterium this smaller ratio suggests that venus has lost a lot more water than the earth over its lifetime the signature of a long-lost primordial ocean as cosmochemist larry nitler explains scientists believe that venus once had a lot of water in its oceans but lost it over 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 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 deuterium 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 more easily so over time as you evaporate water deuterium bearing molecules stay behind relatively to the regular ones and you build up a deuterium 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 an accumulation of indirect evidence to begin to paint a more detailed picture of venus's watery past 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 a liquid ocean deep beneath its eyes 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 [Music] all these ice worlds sitting dormant in the frozen reaches of the solar system offer the promise 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 today venus has the slowest rotation of any planet in the solar system taking 243 earth days to complete one rotation on its axis this period is known as the sidereal 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 sidereal 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 rotate on its axis when combined with its orbit a solar day on venus lasts for 116.75 earth days it means every day on venus lasts almost four 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 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 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 earth-like 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 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 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 earth-like 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 earth-like venus the team at the goddard 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 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 onto enough water to be ripe for supporting the emergence of life by combining all of this data the gist team have painted our most up-to-date picture of early venus and it's a big guiding 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 arced 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 magellan mission in the 1990s was used to paint the last brush strokes of this long lost world filling in the lowlands 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 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 goldilocks zone but as we've already seen in this chapter nothing in the solar system is forever and what we see today is not what we 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 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 our sun in the past and in the future winding back the clock the current consensus among astronomers is that four billion years ago the faint young sun was at least 30 percent 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 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 based 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 earth-like atmosphere of venus could act as a gentle blanket keeping the surface temperate and covered in an abundance of liquid water but even with this additional solar energy 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 atmosphere and sealing the planet's fate although the oceans 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 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 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 re-radiates back out 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 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 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 minus 18 degrees celsius 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 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 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 scorched body 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 four billion years and maintain the characteristics needed to 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 four 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 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 of beings 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 dominated 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 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 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 land-based 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 for signs of life complex life animals and plants struggle to survive in temperatures above 50 degrees celsius so searching for life here is all about searching for single-celled life forms bacteria and archaea ancient microorganisms that are somehow able to endure in this hostile environment life forms like acidibus aceticus an archaea 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 degrees celsius in other parts of the hydrothermal field bacteria like desulfarella acetovoranz have been discovered which happily live in pools that are touching 60 degrees celsius 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 degrees making it one of if not the hottest environment ever studied for signs of life on land but to find the greatest hotheads on planet earth you need to look not on land but deep beneath the sea in the furthest depths of the atlantic around the black smoker hydrothermal vents blurting out of the ocean floor we found strains of archaea that can survive temperatures of 122 degrees celsius 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 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 hundred million or 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 grows hotter temperatures on earth will rapidly rise today the average surface temperature on the planet is 14.9 degrees celsius but with just a 10 rise in the sun's luminosity the average temperature will rise to 47 degrees celsius 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 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 way and as average temperatures race above 100 degrees celsius the last pockets of life will 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 cause 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 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 six to eight billion years old potentially three billion years older than the sun and as it is no longer a main sequence star it is now in the red giant phase its 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 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 sirius b 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 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 five 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 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 degrees celsius 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 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 sun-drenched 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 menagerie of satellites of multiple shapes and sizes we've been peering at these moons since galileo galilei spotted four of them io europa ganymede and callisto 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 shows tantalizing evidence on its surface pointing to a subsurface ocean sitting below its icy crust ganymede and callisto 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 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 in early october 2012 curiosity rolled to a halter to place the geologist's christened rock nest and scooped up a handful of mars the sample of dust dirt and finely grained soil was fed into the sand and heated to 835 degrees celsius 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 surprising of all the soil from rock nest didn't just provide circumstantial evidence for ancient water around three percent of the samples 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 noachian hesperian boundary the patterns of sedimentary deposits suggest the lake rose and fell in multiple cycles over tens of millions of years a transient landscape of ancient streams deltas 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 mayer 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 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 gale crater was filled with water detected molecules include benzene toluene 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 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 mayer 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 soil chemistry is notoriously complex and can easily catch out the unwary 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 three 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 for a moment to picture what gale crater might have been like during the late nowakian 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 snowmelt 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 martian evening the pale sun sets in the west beyond the island rays glinting dimly off the still waters interrupted by the shadow of the peak out to the crater's edge a sundial marking the passing of time on a lake populated by microbial martians 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 is the most earth-like of planets with cinnabar deserts and white polar ice caps a world we could imagine visiting perhaps even settling in 19th century astronomers convinced themselves they saw planes and mountain ranges and canals delivering melt water from high latitudes to arid equatorial cities some thought the martian's a peaceful civilization far in advance of our own others saw threat across the gulf of space minds that are to our minds as ours are to those of the beasts that perish intellects vast and cool and unsympathetic regarded this earth with envious eyes wrote h.g wells in his classic science fiction novel the war of the worlds 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 ground-based telescopes even the hubble space telescope high 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 mariner 4 spacecraft on the 15th of july 1965 abruptly laid to rest the romantic notion of mars 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 4 flyby suggest that this was a powerful realization in november 1965 the bulletin of the atomic scientists carried an article entitled the message from mariner 4 and the message was bleak the shock of mariners 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 lyndon 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 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 delivered such a positive end to a troubled 1968 by setting the blue earth against the grey moon was three years away but red mars provided a foretaste in response carl sagan co-authored a paper suggesting somewhat playfully that all was not lost mariner 4 took only 22 photographs with a resolution of over a kilometer in a strip crossing the region in which the astronomer percival lowell had sketched canals from his observatory in flagstaff arizona at the turn of the 20th century from the warmth of the arizona desert lowell wrote that mars was chilly 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 sagan and his co-authors found only a single feature that unambiguously indicated the presence of a civilization interstate highway 40 in tennessee they concluded that mariner 4 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 mariner 4 would be required to detect it the non-existence of an extant martian civilization was confirmed by the mariner 9 mission in november 1971 the first spacecraft to orbit another planet mariner 9 achieved a photographic resolution of 100 meters 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 chemistry is to coin a phrase from the official nasa report enigmatic and could conceivably have masked any biological 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 sonar 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 degrees celsius but in the early hours of the morning it has experienced -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-arid 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 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 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 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 four and a half years mapping mars in the late 1990s and provided detailed maps with colours 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 farces 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 kilometers above the lowlands of amazonas planitia to the west and its base would fit inside france just about cutting a deep scar across this to the southeast of olympus mons is valet's marinaris 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 hellas impact basin the largest clearly visible impact crater in the solar system from the highest points on the crater rim to the floor halas is over nine kilometers 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 kilometers from the summit of olympus mons to the floor of helas on much larger earth for comparison there is only 20 kilometers difference between the summit of everest and the challenger deep in the depths of the mariana trench [Music] the most striking and ancient elevation difference on mars is that between the northern and southern hemispheres of the planet known as the global dichotomy mars is an asymmetric world the northern hemisphere is on average 5.5 kilometers lower in altitude than the southern there is 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 crisey basins around 4 billion years ago at some later time the northern lowlands 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 noecus terra region of the southern highlands it is characterized by heavy cratering reminiscent of the far side of the moon even small craters in the nowakian 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 is written across the land of noah in contrast the younger terrain of hesperia planum displays much less evidence of regular erosion by water but bears the scars of occasional catastrophic floods that cut deep valleys over very short periods of time and may have formed temporary large lakes or seas the amazonis planitia 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 less geologically active the persistence of surface features over many billions of years in the no achievement 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 noekian period was the earliest and wettest and coincided with the origin of life on earth around four billion years ago when conditions on both worlds appear 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 noikian period ended as mars became increasingly cold and arid around 3.5 billion years ago just as life was gaining a foothold on earth the hesperian period the time of catastrophic floods ran from the end of the noachian to around three 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 hesperian to the present day is known as the amazonian this is a summary of what we know about mars the whys pose a significant 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 planet during the nowakian 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 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 mro an orbiting bridge between worlds mro carries the high rise instrument a camera with resolution high enough to see basketball-sized features on the martian surface the mars color imager marquee monitors martian weather and the compact reconnaissance imaging spectrometer for mars chrism 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 cameraless spacecraft operates between 150 kilometers and 6000 kilometers above the martian surface measuring 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 high resolution photographs mineralogy data radar investigation of the near subsurface and atmospheric measurements including the search for methane a gas that on earth is associated with biological activity india's mangalyaan 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 changes in the martian atmosphere and search for subsurface water deposits the spacecraft will form the communications bridge for esa'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 meridian planum 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 laboratory's engineering 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 kilometers on the surface of mars exploring the endurance victoria and endeavour craters on the 13th of february 2019 opportunity was finally declared dead opportunities younger and far larger companion on mars is curiosity the most massive and most capable spacecraft ever to touch down on a planet beyond earth the landing itself was a tour de 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 10 31 pdt on the 5th of august 2012 watching the landing at the jet propulsion laboratory alongside the team the engineers described it as seven minutes of terror seven minutes to maneuver a spacecraft that had taken eight years to design and build with a program cost of more than 2.5 billion dollars from 13 000 miles per hour 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 lander an 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 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 budgetary challenges of their own whinging 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 to prefer 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 plague another nasa flagship mission the james webb space telescope as robert d baum wrote in an op-ed article for space news in december 2008 at the height of the mars science laboratory controversy when implementing flagship missions cost and schedule overruns are not uncommon but history shows that the mission return often eclipses the expenditure 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 concede that the return from hubble was worth the investment given the febrile 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 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 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 unsteered 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 used a combination of heat shields during aerobraking 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 they stayed put curiosity would have had to lug all this unnecessary mass around mars for years the opportunity rover her sistership spirit and the earlier mars pathfinder employed a combination of aerobraking 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 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 stelzner 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 by the average golf club boar do not always match up the curiosity 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 kilometers above the surface and traveling at around 20 000 kilometers per hour at 10 23 pm pacific daylight time on the 5th of august 2012. the spacecraft at this stage cocooned inside a protective enclosure flew entirely under the control of its on-board 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 kilometers towards the chosen landing site this guided rather than ballistic trajectory allowed for a much wider choice of landing sites for curiosity than for the previous landers which required around 100 kilometers of flat safe land surrounding the nominal touchdown point but it also required the rover to fly itself the round-trip 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 descent a heat shield constructed from a unique material known as pica phenolic impregnated carbon ablator protected curiosity from peak temperatures of around 2000 degrees celsius generated by friction in the thickening martian atmosphere four minutes after beginning the entry phase slowed to just under three thousand kilometers per hour curiosity's parachute deployed at an altitude of 11 kilometers above the surface the supersonic parachute is a vast and complex structure 80 suspension lines over 50 meters long attached to a 16 meter canopy having slowed to a velocity of 700 kilometers per hour with the help of the parachute the heat shield was jettisoned at an altitude of eight kilometers allowing the onboard radar to get a view of the ground and deliver high precision altitude and velocity measurements with 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 kilometers traveling at a sedate 280 kilometers per hour the nasa timeline calls for a deep breath as curiosities separated from the parachute system and dropped in free freefall towards mars for engineers says the nasa website it's like jumping out of a plane for the first time the free-fall 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 meters further down its retro rockets fired and the powered descent phase of the landing began for the viking landers this was the final phase but for curiosity after the rockets had delivered the rover to an altitude of just 20 meters with the descent velocity of less than one meter per second 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 meters in length four of the rockets angled away from the vertical so as not to damage the rover continued to fire allowing the whole delicate system to approach the surface at walking pace at five meters from the surface curiosity unfurled its wheels stowed for the eight month journey from earth at 10 32 pm 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 kilometers from its nominal landing point a triumph of engineering ingenuity and brilliance curiosity was sent to mars to explore gale crater a 150 kilometer wide impact crater formed during the late no achievement or early hesperian 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 gale who 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 gale crater was the unusual central structure mount sharp or aolis mons which rises over five kilometers 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 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 chemically modified as curiosity ascends the slopes of mount sharp it climbs forwards through martian time 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 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 storybook 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 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 saspar sample acquisition processing and handling subsystem sam sample analysis at mars instrument and chemin chemistry and mineralogy instrument the main components of sas bar which is mounted at the end of curiosity's robot arm are an integrated scope 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-h-i-m-r-a pronounced chimera after the multi-headed creature of greek mythology which stands for the collection and handling for in-situ 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 diffraction experiment ever flown in space and the most sophisticated modern technique for 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 enhance the detail of our picture of a planet that was warmer and wetter when gale formed around 3.5 billion years ago [Music] [Music] [Music] [Music]

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Length: 95min 39sec (5739 seconds)

Published: Wed Nov 18 2020