Carl Sagan Christmas lecture 2 - The Outer Solar System and Life

[Music] hey um [Music] [Applause] thank you very much i'm very pleased to be here for this second of six christmas lectures on the general subject of planets in the last lecture we examined a strange and exotic planet the earth and only after some effort did we discover that it was inhabited that it had some living creatures on it now the life on earth is something we're concerned about that since we're a part of it we think it very important and yet that life covers an extraordinarily thin layer of the planet it is as sir james jeans once said a kind of rust on the planetary surface and one question which always arises every human culture has wondered about it is how did life come to be where did the rust come from and if we consider any organism even very simple ones it's astonishing what they're able to do take take some fairly humble organism let's say a rabbit think of what rabbits can do one thing they can do is hop now you may not be very impressed with a rabbit's hop but rabbits hop better than the best hopping machines which people have made so far rabbits do it better than we know how to make machines do it or consider the munching of lettuce rabbits eat lettuce but not only do they eat it they convert it into rabbit today's rabbit's brains are yesterday's lettuce [Music] now we can't do that we can take some lettuce and do something to it and the end product we have a rabbit brain but the rabbit is able to do that perfectly well probably the rabbit brain never thinks about where the rabbit brain came from many human brains never think about where human brains come from or think of the remarkable ability of rabbits to make more rabbits uh probably they don't know in great detail how that's how that comes about although the essentials i'm sure they've mastered that's a very complex business to make a rabbit from scratch and some lettuce animals and plants are able to do remarkable things they've been on the earth for a long time although human beings have not we are only a few million years on the planet and life has been here for some thousands of millions of years and what a remarkable diversity of life there is for example let's take a look at some kinds of life on the earth and just remind ourselves about how remarkable it is this is an orchid that goes to very great lengths to induce insects and in some cases bats to pollinate it to encourage it to make more orchids here is a great rain forest the largest trees on the earth go to hundreds of feet high think of the enormous lushness diversity and complexity of the organisms that inhabit this forest here is a mosquito able to fly what a remarkable thing to have things on your back which you flap and away you go humans have not figured out how to do that but we're a lot heavier than the insects or here's another organism that's managed to learn how to fly the only flying mammal of the bat and here is a cousin of ours a monkey that eats leaves and perhaps is uh not so far distant from us as some of us would like to think and here's lovely organism the zebra with a beautiful kind of pattern on its coat now these are all big animals that we're used to but most of the animals and plants on the earth are little animals things so small that we can't see them with a naked eye and i'd like to spend just a moment on those fellows so here for example are some bacteria very small much smaller than you and i can see unaided in the process of mating which they do occasionally not all the time to encourage genetic diversity here is an aphid which we're looking straight at and certainly an interesting beast that ants farm they use them as domestic animals here is one kind of pollen here is the surface of a leaf i think it's a geranium but i'm not sure these lovely three-dimensional pictures are taken with a machine called a scanning electron microscope and here is the surface of another kind of leaf look at the beauty the regularity of the geometry which exists in the microscopic world all produced by biological systems and here are some microbes which live in snow and it's quite interesting that there are organisms which are able to live in extremely exotic environments over here we have a bee's knee close up bees have knees six of them um spiders have eight knees humans have only two and you can see that the attention to detail which nature has made at the level of the bee's knee is pretty substantial and here is an astonishing creature called a tardigrade which when things are dry curls up into and becomes a kind of speck of dust and can last that way for very long periods of time probably thousands of years at least and then when things get wet you moisten a tardigrade and he uncoils and starts walking away looking a little bit like a bear with eight or ten legs however many he happens to have let's spend a moment on this lovely film here we see a boiling hot spring in yellowstone national park and you can see what the temperatures are almost 90 degrees organisms live there just fine here are people in the antarctic digging a core through the ice and it turns out in those extremely low temperatures there are organisms that survive simply fine here is a fish that swims in almost freezing water it has lovely fish it has a antifreeze like we use in automobiles so that it doesn't freeze over when the temperature drops below the normal freezing point of water that's a remarkable adaptation and antifreezes came into existence before automobiles here is um a kind of organism which happens to love uh sulfuric acid it doesn't doesn't like water at all they're organisms which can live in hot sulfuric acid but uh gasp and dye when you put them in in ordinary water here is one of the most remarkable organisms ever to come into existence on the earth the cellular slime mold you can see individual cells that have come together to make a kind of cellular collective which is big enough to see big enough to walk and is far more exotic than the strangest beasts ever imagined by the writers of science fiction and in my view life on earth has far outstripped what our science fiction writers have been able to imagine now this is just a small variety of organisms that i've shown you let me uh let me show a live organism just for a variety this little fellow oh goody stood up for the television camera um is a kangaroo rat uh so-called in part because he stands on his hind legs um remarkable among other things because uh the kangaroo rat at least some people think this is the case uh doesn't drink uh get all its water from metabolic water that is from eating food and breaking down the food and extracting water from the solids of the food uh obviously a good thing to do if you live in a desert environment there are many more strange organisms on the earth they there are organisms which have very strange sensory abilities there are insects which see in the ultraviolet many flowering plants have the flower pattern in the ultraviolet to attract the insects all sorts of garish signs arrows pointing to the pollen signs in b language saying free eats come this way which we can see because we only see visible light but the insects that know about ultraviolet light see those signs fine and pollinate the plants uh bees that recognize the polarization of sunlight pigeons that can detect magnetic fields of 10 to the minus fifth gauss 100 thousandth of a gauss such a tiny magnetic field that scientific instruments to measure such fields in space have only been developed in the last decade there are pit vipers that can observe the world in the infrared and strike the prey when it's dark there is a french grasshopper which has on its back a kind of thing that looks like a radio antenna it sends audio messages to female french grasshoppers which they enjoy receiving there is a an african fish called gymnarcus nyloticus which sets up an electric field in the water around it and discerns predators and prey by sensing a change in the electric field which it has set up a sense completely different for many that we have us humans now that's just a slight hint of the variety remarkable abilities of organisms on the earth where did they come from how long have they been around now if i could find some fossils i would be extremely happy thank you bro because the fossils give us some reminder that there has been life around for a while this is a single vertebra from the fossil of a single vertebra from the spinal column of an enormous ugly dinosaur called iguanodon which trunched around maybe even the british isles uh a few hundred million years ago and if we had one in this room uh he would just fit iguanodons and other dinosaurs do not exist anymore all sorts of kinds of life have disappeared many more varieties of life have become extinct than exist today on the earth here is a fossil of a crinoid which lived in the ancient ocean bottoms and waved around there there are no crinoids on the earth today and here is a lovely beautiful jewel of an organism called the trilobite trilobites lived as long ago as the cambrian period about five to six hundred million years ago they some people think hunted in herds on the ocean bottoms had beautiful compound eyes some of them much larger than this and there are no more trilobites on the earth today either now 600 million years is not very much in the lifetime of the earth which is almost 4.5 000 million years old i hope you'll forgive me if i use american billions henceforth an american billion is 1 000 million let us look at fossils that are microscopic if you take a rock and slice it thin and are lucky you might find something like this sphere with inclusions in it there is a detailed interior architecture which perhaps you can make out this is what you find from iraq 45 million years old here iraq 900 million years old here one 1100 million years old here 1800 or 1.8 billion years old and here 3.1 billion years old and in fact things like this have now been found in rocks about 3.5 billion years old these are bacteria and blue-green algae they are the simplest organisms on the earth but they are not all that simple they have a remarkable interior architecture they are very clever at turning one chemical into another chemical at making exact copies of themselves therefore these bacteria and algae could not be the earliest organisms they needed a long period of time before then for them to evolve the earth is only about 4.5 billion years old and in it in its earliest history was probably unsuited for life for example we believe the surface was molten and that makes it uncomfortable for living organisms if the rocks are melted all over the planet so life could not have come into being as early as four and a half billion and could not have come into being as late as three and a half billion there seems to be only a small period of time in which the origin of life happened at most a few hundred million years six days was once a popular hypothesis it is not excluded by this evidence but it could not have taken longer than a few hundred million years now if there's a process which happens in a period of time short compared to the time available we are tempted to say it is a likely process the origin of life happened on a time scale much shorter than the age of the earth and that at least suggests that the origin of life is in some sense easy it's not hard it happened fast something must encourage it must make it easy and we have to now ask what is that something how does life come into being now if we could understand the origin of life the origin of a system able to make identical copies of itself and if there are changes in its hereditary instructions those changes also are accurately repeated then we can understand at least in principle the entire future history of life because we understand from the epical work of charles darwin and alfred russell wallace in the united kingdom except it wasn't called the united kingdom then don't believe how evolution comes about mr darwin's portrait is sitting here i don't know if that's exactly a scowl but i like to think of him as delighted at having come upon such a splendid idea but he doesn't look extremely happy in this particular picture perhaps it was indigestion after breakfast but the basic idea of evolution is that there are occasional changes of variants different kinds of organisms which spontaneously arise most of those make the organism less suited to the environment more poorly adapted and that organism loses out in competition with other organisms but occasionally by accident an organism comes into being which is better able to deal with the environment it's in that particular millennium or era or epoch and it does better leaves more offspring and that variety tends to predominate there is nothing in this process which is so far as we know pre-ordained it is a process which is extremely wasteful because many natural experiments happen which result in organisms which are less suited to the environment only a tiny fraction are better suited and are the aperture the road to the future the secret of evolution is an enormous period of time and the deaths of many maladapted poorly adapted organisms now to understand the entire magnificent panorama of life the remarkable history over the last few billions of years we must understand what life is and in particular how the first system capable of making copies of itself could come into being to do that we have to understand how life today does it now we've just been looking at an astonishing diversity of life but that diversity is in a way misleading you for example look different from an oak tree i'm sure everybody would agree with that but down deep where it really counts you are not very different from an oak tree you are astonishingly like an oak tree the oak tree is astonishingly like you suppose we look closely at one of the cells in your body and you have something like 10 trillion cells so you could easily lose one without minding we find that it does an enormous amount of chemistry and that chemistry is controlled by molecules called enzymes all the enzymes are proteins it's a kind of molecule and these proteins control what chemical reactions occur in your body at what time and uh are really in charge of what the cell does now the instructions for the proteins to tell them when to be made and when to operate are controlled by a different molecule the other major molecule in your cells and those molecules are called nucleic acids nucleic acids are molecules able to reproduce themselves molecules able to instruct the cell as to what proteins should be made the proteins are the active elements that make the cell do its stuff if we could understand something of the proteins and nucleic acid origins we certainly would have understood something important about the origin of life now about you and the oak tree if we look at an oak trees cell we find again the same kinds of proteins the same kinds of nucleic acids and astonishingly enough the same code book which translates nucleic acid information into protein information the oak tree could read your genetic code which contains all the information there is about how to make a human being your cells could read the oak trees genetic code the oak tree is not motivated to make human beings human beings are not motivated to make oak trees but you could do it and this is true so far as we know of every organism on the earth they all use proteins to make the chemistry go or use nucleic acids to control the proteins and to reproduce and to pass hereditary information on from generation to generation there are no departures from this all the organisms down deep are the same this deep relationship suggests that we are all cousins us oak trees us beagles us begonias us baleen whales we're all related closely and that's one reason why it's so interesting to look for life elsewhere to see if life on other planets is built on the same chemical principles as on the earth or might be in some way very very different now i want to spend just a minute describing in a little more detail the proteins and the nucleic acids to do that we have to talk a little bit about chemistry before me on this table are models of lots of chemicals they look pretty complicated that's because the chemistry of life is pretty complicated we should not be intimidated by the complexity in fact i will start with a very simple molecule okay just sort of barbell not difficult to lift real atoms are about a hundred millionth of a centimeter across so if i held one up you would have difficulty seeing it even with the zoom lens on the television cameras so we make molecular models which make things about 100 million times larger and then we can get some sense of them each white sphere is a hydrogen atom the two together make a hydrogen molecule each red sphere is an oxygen atom the two together make an oxygen molecule each blue sphere is a nitrogen atom the two together make a nitrogen molecule here is a molecule made you can see it looks a little bit like mickey mouse of one oxygen atom that's the red and two hydrogen atoms that's the white that's h2o otherwise known as water now let's find one other nice one here is one carbon atom that's the black thaw and two red atoms that those are oxygens and the three together make co2 carbon dioxide now the earth's atmosphere is made mostly of nitrogen oxygen carbon dioxide and water so if we were to grab a handful of air and look closely at it we would find that it was made almost entirely of these particular molecules there are other kinds of molecules and i will come to them in a minute but it's interesting that most organic molecules the ones that life is made of the ones that contribute to uh proteins nucleic acids are made mostly of these four atoms carbon hydrogen nitrogen and oxygen now proteins are built out of building blocks called amino acids here is an amino acid with a nice little ticket on it it's aspartic acid they have very nice names and these amino acids link up into long chains called proteins and i think it would be nice if we were to do such a link and i will need volunteers from the audience who want to be molecules please all of you who wish to be molecules please come down and let's let's line up right here i have maybe 10 molecules okay now why don't you all face this way and let's make a kind of line and i'd like everybody okay that's i think enough that's good like a nice market i like everybody to do two things first of all stance come over here stand facing this way and i hope you all can read and when i give you the molecule say what it is asparatic acid aspartic acid very good and then would you please say what it is go ahead give it a try now i would like to have a link between two amino acids like that good the next one can you read this one glycine very good would you please hook up to lucine right here here is an alanine would you hook up to glycine very good here is glutamic acid terrific histidine you're a reasonably complex amino acid cysteine you are a sulfur-containing amino acid not many of them and asparagine comes from asparagus good i will do one more forgive me those amino acids in the back here is glutamine now would you hook up may i have one more amino acid for me i'll be valine and now we have a short chain of amino acids which is a kind of small protein now this protein controls some chemistry in the cell not all the amino acids work it might be only these four amino acids right here which do the work and the rest of us sit along for the ride and now we will have a little protein dance okay [Music] okay now back the other way [Music] good thank you very much [Music] good now would each person please put his amino acid back thank you i apologize to those amino acids who did not get to dance now that's not exactly how the amino acids link up but it gives you a kind of idea many proteins are so long that if every person in this room were an amino acid it would still we still could not make the protein of the appropriate length many more amino acids than the number of people in this room so that's about the proteins now let me say just a word about the nucleic acids they're made out of different sort of bits a bit that looks like this a bit that looks like this and these bits are arranged in pairs and i have the pairs the wrong way around as rungs in a ladder an enormous number of rungs in the ladder and what happens is the ladder is able to unzip and each half makes a copy of the other half and that is how the nucleic acids reproduce themselves and that is how we reproduce ourselves on the essential molecular level the nucleic acid molecule itself here is a very short piece of it looks like this and here the various atoms have been compressed closer than in these models so we don't have the little connections as we had in the previous model and this is only about two and a half loops or winds of this helical molecule imagine it going about 500 feet in the air and you'll have a sense of what nucleic acid molecules are really about now if i can surrender my nucleic acid extremely short molecule here let us return to the question of the origin of life how do we make such molecules well noting that air is made of essentially the same atoms as most amino acids maybe we would have the following idea let's take the molecules of air nitrogen oxygen carbon dioxide and water put them together in a kind of flask send some energy through the flask that will tear atoms apart and if we're very lucky maybe the atoms will recombine in a way to make some nice amino acid that would be very lucky so let's do that here behind me is an experiment in which that is being done this is an experiment first done by stanley miller in the early 1950s here we have a primitive ocean extremely small ocean it's boiling water is rising condenses in this flask which contains the other molecules of air and then circulates back through the ocean now we have to supply some energy maybe it would be ultraviolet light from the sun maybe it would be an electrical spark let's do an electrical spark maestro there so now before your eyes atoms of air are being torn apart and the pieces are reassembling themselves and if we let this go on for oh about a few hours we would have used up a lot of the air what would we have made would we have made molecules useful for life we would not have we would in fact have made smog we would have gone backwards from life instead of forwards well let's reconsider the experiment we started with air air contains oxygen oxygen is made by green plants could there be green plants before the origin of life unlikely right because plants are alive so we've made a silly mistake we put in a product of life before there could have been life let us throw the oxygen away do the experiment again with water nitrogen carbon dioxide we will do that in the second experiment here if we let this go for a few hours we do make some molecules we make formic acid and we make formaldehyde now because formaldehyde is used for preserving dead animals you might think it's not too useful for life either but that's not the case can i just get by bro thank you because if you have a lot of formaldehyde molecules and you let them sit together they will spontaneously combine to form sugars you can see that it's a repetition of this same formaldehyde unit which makes sugar molecules and sugars are very definitely part of what we're interested in sugars are part of the building blocks of the nucleic acids so we've done something right we just haven't done it enough now to do it enough we have to ask what is it we just did between the first and second experiment what we did is to have more hydrogen and less oxygen if we look at typical organic molecules we see lots of these little white spheres organic molecules have lots of hydrogen maybe we should do this experiment with lots of hydrogen but is that justified is there any reason to think that the early earth had more hydrogen than today well the early earth formed out of typical cosmic matter and we have to ask what is the universe made out of does it have a lot of hydrogen or only a very little now the way that scientists usually examine the stars gas between the stars planets to see what they're made out of is by spectroscopy and here what happens is light passes through a kind of slit then through a prism which breaks initially white light up into a kind of rainbow pattern and here we can have lights down we can see just such a thing happening in the apparatus that mr coates is handling this lovely rainbow is initially white light spread out into its constituent colors by a prism an experiment first done by isaac newton now if we take a particular kind of atom and send its light that it likes to shine through such a device called a spectrometer we will get not a full rainbow but a particular set of colors so here we have the mercury atom which is being induced by mr coats to give off light and that light comes in only three spectral lines that are strong here a yellow one a green one and a purple one if you saw such a spectrum coming from some object you would say my goodness that object is made out of mercury now in this way we can look anywhere in the universe that's giving off light and have some idea of what its chemistry might be so if we do that we find a remarkable result we find that almost anywhere we look we see that the universe is red this turns out to be a chemical not a political remark this is the horse head nebula you can see why it's called that the dark cloud there looks like a horse's head but the red gas that surrounds it is absolutely typical of what happens when you take long-time exposure photographs of virtually any place in the universe and the next slide is another example this is the rosette nebula and it also is mostly glowing red hydrogen likes to give off a spectral line in the red and that red line is seen almost everywhere the sun is mostly made of hydrogen the stars the galaxies the space between the stars the big planets like jupiter in our solar system in fact almost everything is made of hydrogen except the earth the earth is almost the only funny thing around in terms of chemistry why so first of all our assumption that the early earth should have been rich in hydrogen is is a perfectly good one and uh before i return to the original life experiment let me just ask this question why should the earth if it once had hydrogen not have it today and the answer is that hydrogen the simplest easiest molecule used to be here there it is can run away into space it is so light that if it's sitting around in the upper atmosphere of the earth it can be collided with by some other big heavy solid molecule and made to move very fast and if there are no other molecules in the way and if it's moving at escape velocity it will run away into space the earth's atmosphere the upper atmosphere is very hot and it is has very little gravity and so this is symbolic only hydrogen will run away from the earth on the other hand jupiter has such a low temperature in its upper atmosphere and such a high gravity that not a single hydrogen molecule could have escaped from it in the entire history of the solar system now let us return to our experiments suppose we now mix together not oxygen but water the kind of oxygen which has the most hydrogens on it not nitrogen but ammonia one nitrogen atom and three hydrogen atoms the kind of nitrogen which has the most hydrogen attached to it not carbon dioxide but methane one carbon atom and four hydrogen atoms if we mix those gases together as in the third experiment here supply some energy and let it go for a while we produce the most astonishing stuff and have made a major step towards the origin of life we're showing here an experiment done with a lightning or electrical discharges the energy source but in other experiments for example in this one in our laboratory at cornell university there is an ultraviolet light source you can see the transparent flask at the beginning of the experiment but at the end of the experiment we have a flask filled with brownish powdery stuff what is this brownish powdery stuff it is essentially all of the molecules on the table in front of me we have made a great variety of organic molecules the necktie that you saw there was for color comparison purposes only it we cannot do an experiment in which we start out with the gases and waters of the primitive earth and at the end of the experiment somebody crawls out of the test tube we haven't done that yet but what we can do is make all of the amino acids all of the building blocks of the nucleic acids and even hook them up to make short proteins and short nucleic acids now the rabbit that we talked about early in the lecture no one can make there isn't enough time to start such an experiment and wind up with let's say a rabbit as you might imagine i need a volunteer for this part of the experiment please um now it would be lovely if we could make any organism but remember how complex the organism was and how simple these molecules are there simply isn't enough time but maybe such a thing might someday be possible could you please examine this hat and show that it's empty oh it's not empty there is in it a molecule of cysteine see it's yellow it's a sulfur-containing amino acid could you now please see if it's if the hat is empty it's empty i'm i'm not good at this i see it's empty and i'm supposed to show you that it does that and now i have to open it up again there was a way i forgot there there it opens up now put the empty hat down could you please check that there's the table is okay there's nothing around there oh well okay yes that's certainly empty enough um could you not check that the the hat is still is still empty good thank you and how could we please pull off and here thank you in fact i'll give you this rabbit in just a minute to hold if you sit down for a minute i'll bring them over to you this is what we can't make but we've only just started these kinds of experiments have only been underway for something like 30 years once we have a few hundred million years to do such experiments as nature has perhaps we will be able to get as far as a microbe if not a rabbit thank you you get to keep them until the end of the talk [Applause] [Applause] i've always wanted to wear one of these we don't have them in america so we're going to wear this for a while now maybe you remember the looks kind of funny maybe you remember the kind of brownish powdery stuff which was inside that last experimental flask that material has a characteristic color it's always made in these experiments and therefore it's very interesting that there is a place in the solar system where such coloration is present extremely vividly and that's in the outer solar system in the vicinity of jupiter now here is an old i think 17th century picture of people looking up with an early telescope and there in the sky is duping and you can see even in this early picture there's a little bit of brownish coloration and you can see three or four of the four big or galilean satellites of jupiter if we look at a more modern picture this is a pioneer 11 photograph of jupiter we see the beautiful bands and belts the belts colored brown you can also see the great red spot so-called because it's orange you can see white clouds in fact everything we're looking at here is clouds and atmosphere there is no surface to be seen if there is a surface it's far below what is the source of the coloration in such a picture we can look more closely and here's another this is about the close the closest up picture of jupiter we have there's no question about the brown color in fact it's very similar in detail to the detailed spectroscopic signature to what we make in the laboratory what is this stuff well the atmosphere of jupiter is hydrogen-rich it has hydrogen water methane and ammonia ultraviolet light comes in from the sun there probably are electrical discharges lightning in the atmosphere jupiter is a place very much like this third experiment these same organic molecules ought to be made on jupiter and perhaps the brownish coloration is telling us that such organic molecules are indeed there here is a picture shot from beneath looking up towards the south pole of jupiter down at the bottom and if we look more closely at such a region we see astonishing bubbles cyclones storm systems the great red spot in fact is probably a storm system which has been in existence for a million years a hurricane that has lasted for a million years the weather on jupiter is astonishing and we can learn an enormous amount about climate weather circulation of atmospheres by looking at jupiter precisely because it's a different kind of place from here here is an artist's conception of the clouds of jupiter you can see high up in the atmosphere the white clouds which we believe are condensed ammonia frozen ammonia crystals just as the upper atmosphere of the earth has frozen water crystals and then below is the reddish or brownish stuff which maybe is organic molecules and you can also see that the artist has put a few lightning bolts in at lower right just to remind us that there is some energy there now the clouds of jupiter can be calculated to be something like this here we have up at the top the solid ammonia the next layer is a kind of mixture of ammonia and hydrogen sulfide below that is a cloud layer of ice and below that is a cloud layer of aqueous ammonia a little bit like the household ammonia solution that people use to disinfect now the temperature of the household ammonia on jupiter is about room temperature now i know room temperature is different in the united states and then in britain but the two are close enough uh jupiter has a place where there is lots of liquid water which is at room temperature and where organic matter is falling from the sky like manna from heaven now that is a place at least interesting in terms of biology we do not know if life has evolved on jupiter but it's clear that organic chemistry can proceed on jupiter at least for a period of time could there be living organisms on jupiter we do not know there have been speculations about it and here is one particularly ugly artist's conception of what life on jupiter might be like here we imagine enormous creatures like whales swimming floating through the clouds of jupiter gathering in the organic matter which may be there with eyes much too big to be reasonable and you can see they go like a ram jet um sucking in the atmosphere at the front and blowing it out the back and if i had that hydrogen balloon wait i have another one um i if i could only make a hole in there without bursting it the organisms on jupiter if any probably do better than that we do not know that there's life on jupiter i don't want you to think that it's something that is considered likely we do not on the other hand know that there isn't it is an interesting exciting possibility which we will have the opportunity to explore in future spacecraft exploration of jupiter by the way everything we've been talking about so far about jupiter is an extremely thin layer in the very top of the atmosphere of jupiter thank you it's this green layer right here in fact it's thinner than we were able to paint it is the atmosphere and clouds we've been talking about below that this pinkish region in this model is liquid hydrogen and below that is solid metallic hydrogen a sort of hydrogen you don't bump into every day on the earth hydrogen as a metal is not a common place on the earth and the reason is that the pressures here are simply not great enough to make hydrogen into a metal because jupiter is so massive it's the most massive planet in the solar system hydrogen does get made into a metal there possibly in the very heart of jupiter there is a core of rock and metal a planet something like the earth hiding in the inside of this enormous hydrogen-rich liquid and gaseous planet now let us examine briefly a few more things in the jupiter vicinity and further up here is simply a reminder that spacecraft are on their way to jupiter and beyond to take close-up looks much better than any which has been obtained so far here are four drawings made by visual observers on the earth of what they think they may have seen on the surfaces of the four big moons of jupiter and here are four maps of the four moons you can see here is eo the innermost moon europa the next one ganymede third one and callisto the fourth one and there are features on the surface but what do those features mean we haven't the foggiest idea we know that they're icy here is an astonishing picture of eo taken in the spectral line given off by sodium and it turns out that eo has left behind it a cloud of sodium gas swept away from its surface and what some people think is that eo once had oceans in which were sodium salts and potassium salts and other such salts the water escaped to space just as the hydrogen escapes from the earth leaving behind the salts which are now being blasted off by a high radiation environment which surrounds jupiter that is one of many indications that the moons in the outer solar system are not like our moon are very different sorts of places now beyond the jupiter system are many other objects interior to the jupiter system are many other objects also because between the orbits of mars and jupiter are an enormous array of asteroids little rocky objects but they're not all rocky this is an artist's conception of one but many of these objects now turn out to be rich in organic matter since they probably were formed in the earliest history of the solar system that suggested organic matter was very abundant early at the time that planets were being formed and the two moons of mars of which we'll talk about in a later lecture now seem to be made of organic molecules if we move outwards from the asteroids and jupiter we come to this object which may not look familiar to you this is in fact saturn but seen with the rings edge on so you can't see them and maybe you can see a little hint of color in the region just above and beneath the shadow of the ring if we look at saturn at another time we see much more color and whatever it is that colors jupiter is probably part of the coloration of saturn as well here is a lovely picture of saturn as seen from the surface of one of its moons notice the presence of some kind of ice maybe water but maybe ammonia maybe methane on the surface of the moon and notice the shadow of saturn on its rings and also note the break in the rings so-called cassini division which seems to be a place where ring particles aren't what are the rings of saturn well i'll mention it in just a moment here you can see the rings edge on from the surface of a moon about halfway out and you can see three interior moons in this artist's drawing in the ring flame were we to go very close to the rings we would see that they are a swarm of orbiting snowballs there are millions of snowballs in orbit around saturn be a great place for a snowball fight would also be a very interesting place to examine close up the rings are either a place where a moon was torn apart by the gravity of saturn or where a moon was prevented from being formed by the gravity of saturn in addition there is an amazing moon of titan of saturn called titan it is a moon with an atmosphere the atmosphere is made of methane and hydrogen it is hotter than its than it ought to be on the surface it seems to have a cloud layer which is brown and unbroken and possibly made of organic matter it is an astonishing place and it probably really looks more like this picture where we can see the brown clouds and the artist has drawn a kind of uh methane of volcano erupting the outer solar system is the object of many space vehicle missions now underway and i'd like to close by saying a few words about those space vehicle missions two of them have already been launched uh long ago pioneers 10 and 11. pioneer 10 has already passed by uh jupiter and leave the solar system pioneer 11 as passed by jupiter but in 1979 we'll enter the saturn system and if it still survives maybe we'll get some pictures and other data in a preliminary way of what saturn is about voyager which i talked about in the last lecture is a splendid magnificent kind of spacecraft you can see booms for magnetometers and atomic batteries an enormous antenna to send information back to earth and over here a set of instruments to examine very carefully jupiter and saturn and their 20 odd moons the rings of saturn uranus if we're lucky and the newly discovered rings of uranus this will be an astonishing set of results it will fly by the jupiter system in 1979 the saturn system in 1981 and therefore in just the next few years we will see coming through 50 000 photographs an enormous number of spectra telling us about composition and pressure and temperature we will really learn what these places are like and then beyond that there is one last approved mission by nasa in which a spacecraft called jupiter orbiter with probe will go into orbit around jupiter and then drop a probe into the atmosphere of jupiter so that for the first time we will examine close up the chemistry pressure and temperature of a jovian planet the jovian planets hydrogen-rich like the primitive atmosphere of the earth are very different from the terrestrial earth-like planets it may be that we can learn about the early chemistry of life best by examining the outer solar system perhaps even there is life out there what is guaranteed is that those worlds are entrancing fascinating and well worth a deep analysis in only a few years we will have made such a deep analysis [Music] [Applause] [Music] you

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Keywords: carl sagan, christmas lectures, cosmos, pale blue dot

Id: mXn2IU8c6kY

Length: 59min 33sec (3573 seconds)

Published: Thu Apr 07 2022