About science; About planetary atmospheres

This is about science produced by the California Institute of Technology in collaboration with station KPCC in Pasadena California. The programs are made available to the station by national educational radio. This program is about planetary atmosphere with host Dr. Peter Letterman and his guest Dr. Louis Caplan. Here now is Dr. lesson. We live on the bottom of an ocean of it. If you're 50 mile deep shell of gas good laying out and cool the atmosphere like the sea it has tides and currents which we feel as the winds and like the solid oceans of the world our atmosphere provides protection and life giving oxygen for air breathing creatures. We are as much a product of our airy environment as the fishers are of theirs and knowledge of the properties and composition of our atmosphere could give an intelligent Martian a great deal of information about the type of life which exists on the earth's surface in the same way. One aspect of

our interest in the atmospheres of the planets is because we believe that this knowledge can tell us a great deal about what goes on on the planet's surface. But there are many other compelling reasons for our interest and we have with us Dr. Louis Caplan a leading authority in this field to discuss some of these aspects in more depth. Dr. Kaplan did his undergraduate work at Brooklyn College and is a graduate of the University of Chicago. He has moved from the meteorology that is the atmosphere of the earth to the study of the atmosphere of the planets. Among the many institutes where he has conducted his research and taught other Clarendon laboratory at Oxford University and the Institute for Advanced sciences at Princeton he is presently doing and directing research in planetary atmospheres at the Jet Propulsion Lab in Pasadena where he is staff scientist to the Space Sciences Division.

Norris why are we really so interested in these planetary atmospheres. Well I think that part of our interest like in most scientific investigations is just curiosity that we'd like to know about the atmospheres we'd like to see what we can find out about them. We'd like to understand why they are the way they are why they are different from one another. Why in particular they're different from our own atmosphere. As a matter of fact one of the most compelling reasons I think for investigating planetary atmosphere is to obtain a better insight into our own atmosphere and how it got that way what its history and development is. They in a way this is looking for our own biography through trying to study a biography of the earth. I think as an Earth based meteorologist I may be more interested in this than most people but I think this is

probably a general interest. In other words the study of the atmosphere of the planets can give us much valuable information about things which go on. Yes particularly in the history of the Earth's atmosphere I think in the way it got the way it is. You say the way it got the way it is new US do suggest that this atmosphere is always changing and it wasn't always the way it is now. Yes I think one of the things that we do know about our atmosphere is that it has been very much different in the past and the way it is now. There is a strong body of evidence for this. We know that during the past few decades that there has been a change in the carbon dioxide content that people have thrown into the air due to combustion. This is a rather minor change actually much more major changes have taken place. Some of them probably the most drastic changes took place near the early development of the Earth's atmosphere although we

don't really know this for sure how long it took. I'll give one example and that is the presence of the rare and the amounts of the rare gases in the earth. Now the rare gases gases like Ayaan are gone and krypton and Xenon are not quite so rare. With regard to the abundance in the solar system or in the universe as a whole as they are in the Earth's atmosphere. We know that they have much lower that they are in a sun they are in the stars and it must be a reason for this and the most obvious reason is that at some point in the early development of the earth the earth lost these gases these gases do not combine with other gases they are very inert and therefore during some stage with your Earth's atmosphere and the earth system perhaps was very warm the red gases left the Earth's atmosphere whereas other gases such as

oxygen carbon and nitrogen carbon acting as a gas and carbon dioxide for example were probably kept in by combining with other compounds. As a matter of fact red relative to silicon which is usually used as a standard. Carbon and nitrogen and particularly oxygen is over abundant. When you say overabundant Could you elaborate on that. Lewis and in what terms do you mean. Well if there was more of these compounds relative to some of the more stable the more ordinary compounds the composite don't react. Then one would expect a one season the sun and the stars. But we in a way mean even more than this oxygen for example is present in our atmosphere. We know it is not cannot be an equilibrium it must sooner or later fall form sulfates and carbonates and dissolved in the ocean. So it is out of equilibrium with the atmosphere. In other words over a long period of time

one would expect the oxygen really to disappear and oxygen in a way has no business being there. So in a sense we have a quantity of oxygen which is waiting in a way to combine with things. How did we get this out of equilibrium situation with oxygen. Well partly the oxygen like these other gases carbon and the other atoms carbon and nitrogen and so on came out and out gassing from the earth as it came from the interior of the earth came out as gases and entered the atmosphere. The Carbon comes out as carbon dioxide that is combined with the oxygen the oxygen never really comes out as it by itself and as a matter of fact the main component of the outgassing which comes from volcanoes and hot springs and so on that continually throws large quantities of gas into the atmosphere comes out as a form of water.

The water however in general condenses and has formed the oceans over a long period of time. So I think we find then that some of the oxygen can be accounted for by our gashing from the interior of the earth. What about the vegetation of does that have any effect on the oxygen. Yes as a matter of fact most of the oxygen that we have present in our atmosphere almost certainly has come from the vegetation the plants supply through airport or synthesis our oxygen oxygen and their metabolic growing and chemical change process. They once thought of oxygen could be the coming from the disassociation of water that is the action of sunlight on water breaking it up into hydrogen and oxygen. However it is known that the oxygen itself would prevent the sunlight from getting down and associating the water after a certain amount of time so only a small fraction of the oxygen can be

accounted for in this way. The great bulk of the oxygen would have to have come out of a living process as you suggest. In other words just as a crowded smoky nightclub literally creates its own environment and the automobiles of Los Angeles themselves create changes in their atmosphere. So on a much larger global scale the vegetation of the Earth affects our atmosphere and subtly but steadily changes it. Yes and of course plant life also affects our atmosphere. And in a way this is ironic because we think of life adapting itself to the environment. But we say that in this case and probably in the history of any planet that has ever had life in it they the life itself will affect the environment and change the environment and it will be a sort of a feedback system. Feedback can now are there any other components which are notably out of

equilibrium and said yes there are other components out of equilibrium but none of them are present in large quantities at Oxygen the pressure is present to carbon dioxide. Some of them are quite startling for example that the methane that's present and let's present in our atmosphere it's present only in about one part per million which is a very very dilute solution in the atmosphere not very much of it. But methane is known to be very very unstable and particularly if it gets to the upper part of the atmosphere where it meets oxygen in Mana Tomic form that is oxygen is usually 0 to two oxygen atoms combined together form a molecule in the upper part of the atmosphere the sunlight breaks the oxygen into two atoms and atomic oxygen will very rapidly attack molecules like methane. And destroy them so that the methane cannot last for a long period and I

use fear for methane in particular we know the reason its present is being produced on the ground. It's bit being produced by organisms by bacteria that attack it. They were formed in cows and other domestic animals and it's being produced at about the same rate that is being destroyed up above by the oxygen. Other examples and I Trist oxide which is again formed by bacteria soil bacteria in this case and in both cases the bacteria Robeck that is they do not need oxygen to develop in both these cases its dependent upon life and its like thats producing these these molecules. Another molecule that is very much out of equilibrium is always on but ozone is not being produced by life although in large cities like Los Angeles it is being produced by other smog producing.

The process is combustion and so on. But the main part of the ozone in our atmosphere is produced by sunlight which again breaks up the oxygen. A man atomic oxygen combines with a diatomic oxygen that is with O2 to formal three which is ozone. So really we have a great deal of knowledge about the atmosphere. But I imagine that it's substantially different from the atmosphere we know of the atmosphere of the planets. Yes there are no two planets as far as we know it is in our solar system they have atmospheres that are very much alike. The closest the major planets are very large planets. But even they are very very much different. However as I take it that the planets do have atmospheres and I think it's fascinating that. In a sense that they should when did man's first suspect the planets did have a misuse which had certain similarities to atmosphere.

Well it's very hard to find out really when man first suspected that the planets had atmospheres. Because I think that almost in a very beginning. I think that Galileo for example probably felt from his writings that the planets did have atmospheres. I would suspect that Galileo had seen some sort of things that convinced him of that in the process but he was not surprised. And it wasn't until very recently that people I think began to raise the question Should planets have atmosphere as and to look for them. The first detection real detection of an atmosphere or the effect of an atmosphere probably occurred about I would say two centuries ago a little less than two centuries ago with the discovery of the variation of the polar caps on Mars which was suspected at that time. These are formed by ice and therefore indicated there must be an atmosphere in order to transport the water vapor and so on.

How about all the knowledge that we have live atmosphere as it is of course gained from observation of these planets from a flaw. What I want to some of the techniques which are used to to get detailed information about the constrains. Well I think the most obvious thing is to look at at the planet and see if there are any particular evidences from a visual inspection of the atmosphere to tell to see its effect. For example the dust clouds on on Mars that one can see through a telescope and the motion of the Red Spot on Jupiter which was also observed about two centuries ago by a hawk. But very recently I really shouldn't say very recently because it was almost a century ago people started looking at the Planet spectroscopic plate that is looking. It looking at the planets through a spectroscope attached to the end of a

telescope which the light from the planet either its own light or reflected sunlight came through the telescope into the spectroscope which breaks the light into its component parts in the same way as a prism does to form sort of a rainbow colored pattern and it is known that sunlight is like this if one looks in a visible light the light we see. Then you should see this rainbow pattern and you do accept that it was noticed that in even in the sunlight that there are places where there is no light getting through where it is it is dark and these. This was discovered again about a century ago a little more than a century ago and was correctly inferred to be due to some sort of absorption inside the sun's atmosphere itself. But now the sun's atmosphere is reflected from a planet gets to the earth and in the process of passing through the planetary atmosphere on its way to being reflected to the earth

whatever compounds are present in the planetary atmosphere could absorb some of these lights and give spectral lines option features which are characteristic of our of the molecule and is a sort of fingerprints of Teles molecules at present. So the. Script gives us an idea of the constituents of a gas through which the light passes. Hardly any great advances in this type of instrument. Recently or have we just evolved slowly and steadily with refinements of one sort or another. Well I think in general we can say as far as the whole history is concerned is that there have been periods of steady advances and then there have been large spurts ahead. The introduction of a grating instead of a prism has greatly facilitated the study of the breaking light into its parts and looking at it in more fine detail. Actually a very significant and

extremely important advance has been made recently by a French a French couple. Who had developed a new instrument called a an interferometer a Michelson interferometer in which they have been able to grip very very greatly by a factor of 100. Increase the spectral detail in which we can look at planets. I have been very fortunate to be able to work with them on their site and to be able do some of the work on the analysis of these atmospheres and so I am particularly excited about this and this. This increased resolution to us does this mean that one can detect elements which one might not have seen before or that one simply can detect a much more dilute traces of a particular element where one can detect both actually. One can do both things. The gases in most part that have been the fuel gases have been detected in planetary atmospheres and gases have been present in very very large

amounts like methane was detected the absorption of methane was found actually almost a century ago and was explained after quite a period of time on Jupiter and on the other major planets. Carbon dioxide but it's present in very very large amounts. Carbon dioxide is present in large amounts in Venus and it was found and vain as a matter of fact the first measurements of these carbon dioxide dance was made by looking at Venus because such a large amount has to be present that was not discovered in the laboratory and these are called Venus bands. However as one goes to this higher resolution be able to look at the fine structure. You can pick up much smaller much smaller quantities of gases that are present in the atmosphere. And you can find many more gases because there as you go to the smaller amounts of gases you begin to see many more of them.

Assuming one can get a rather good insight of the constituents of a planet's atmosphere what knowledge about the planet could still can we glean from that. Well hopefully we can tell from the planetary atmosphere as to what the constituents are. Why the why the gasses are present in the in the atmosphere and therefore some of its history we can understand by looking at the differences between the gases in different atmosphere as how the difference in size of the planets how the difference in their distance from the sun and so on affects the atmosphere. And as I said in the beginning this helps us to understand our own atmosphere and our own history. Anything any hypothesis that we have about our own atmosphere really in this way can be tested against other

atmospheres because it should be able to explain not only our own atmosphere but that the differences that occur and the planet. So we notice any striking things like the out of equilibrium oxygen that you remarked in our earth's atmosphere other than here. Analogously striking situations about some of the planet's atmosphere. Well for most of the planets we don't we haven't really seen things that we can say definitely out of equilibrium. The one case in which some of the gases seem to be out of equilibrium or seem that it may be out of equilibrium is a case of Mars and this is very recent and it is a matter of fact this is. Precisely the observations I was talking about was talking about before that the cons made and I have been very exciting very excitedly trying to interpret in looking at the Mars atmosphere we really didn't expect to find anything unusual. But to our surprise we found that there were many bands of molecules who

hitherto unsuspected and that have certain characteristics that we are now investigating. We have not come to any concrete definite conclusions about precisely what these compounds are. But we know enough about them to know that they may be actually out of equilibrium. They are present. They are interesting however in their own on their own merits. These compounds are in general classes which we call reduced compounds. That is compounds containing hydrogen and we know from they struck from the appearance of the spectra that there is hydrogen present in these compounds. What can we infer from this. Yes. Well the inference is really very interesting although there is very little that one can say specifically. One of the most interesting things is that until very very recently.

It was not known what the atmosphere of Mars was like. It was not known whether the Mars atmosphere could contain like compounds like molecules like hydrogen within the past few years. However there's been building up more and more evidence against it. For example in some of the in the measurements of the carbon dioxide amount the measurements of the water amount and these interesting enough are some of the include some measurements that I have been involved in. We discovered that the atmosphere was very thin and that it was certainly whatever out rocky as it had occurred whatever had come from the interior had mostly escaped or at least implied that it mostly escaped from the atmosphere. Since most of the gases had escaped one would expect the hydrogen being the lightest to

have escaped more easily. This sort of dealt a blow to the possibility of life on Mars or possibly of life having been developed because what we know about our own atmosphere we know about the life originating process or at least what we surmise about it indicates that hydrogen is a very key element in this that during the periods of the early development of life compounds like carbon and oxygen and nitrogen can have existed only in forms in which they combined with hydrogen. So you had just these reduced hydrogen present and some reduced compounds. It during a later stages we know it becomes more of a knocked oxygen atmosphere we have advanced life as we know it on on the earth but in your early stages there must have been life. There must have been hydrogen present in

order to have life since the indications were that there was no was probably no hydrogen present on Mars. It looked like life could not have developed therefore we were very excited when we found that we had direct evidence for hydrogen containing compounds. And another thing that is exciting about this although it is much more vague and we cannot say this proves anything is that compounds that are out I am like. As we discussed methane before which is a reduced compound and these reduced compounds may very well be out of equilibrium on Mars because again the carbon dioxide will break up under the action of sunlight into carbon monoxide and oxygen the oxygen will retract attack the reduced compounds. The fact that they are present may may hint to us that they are out of equilibrium they're being formed by some peculiar process and of course we

would like to think that the processes life but we can't prove it of life. Of course there is a fascinating topic of fascinating to the public as to the scientists. What about the planet Venus. What knowledge do we have about the possibility of life there. Well I'm afraid that on Venus we have to be much more pessimistic. We know from measurements we have been made and is again a spectroscopic measurements although they are made at much longer wavelengths in the visible wavelengths the wavelengths I was talking about Mars before are longer than the visible wavelengths in the infrared that is beyond the red part of the spectrum where you cannot see the colors. One can say of the light. But these are the measurements of Venus that were made in microwave. Wavelengths that has a wavelength of about a length of about 1 centimeter. Show that the surface of Venus is very hot. This

has been measured from again from the earth from a very large radio telescopes. It has also been verified from measurements a map of Venus magnet. So in a sense the atmosphere shields freeness and is one of the reasons that it remains so hot all the time. What about Jupiter and US what do we know about that. Yes well Jupiter also I would say is that I am very pessimistic about the possibility of life on on Jupiter because Jupiter almost certainly doesn't have a solid surface. And you need some sort of a surface for life to develop. Or if it does have as a surface the surface is so cold that that metabolic processes the activity that has to take place in life processes really could not occur. I'm afraid that outside of the earth the only planet likely to contain life is Maus in the hope that we have it there.

Well that that is a most fascinating conclusion I think it's very remarkable that we should be able to learn so much from the planets. By sitting here it's such a great distance and making these optical measurements. What are the techniques. Mike we possibly used to get more information about the planetary atmospheres. LOUIS Well I'm afraid that if you sit on the earth about the only thing you can use to determine anything about the planets is a light that comes from the planet sees that its own intrinsic light its own heat. That is our light that's reflected from the sun. If you want. And this of course limits us there are certain questions we can't ask there are certain things we cannot find out if we want to to find out more beyond this point. And probably if we want to find out such interesting questions as is there really life on Mars as a.

As a question and which we would like to know yes or no answer almost certainly we have we will have to go to that. Planets now not very many years ago of course with this with a thing like a fantastic thing in science fiction. But as we know we are preparing to go to the planets were planning planning to send instruments and even people perhaps they had to make measurements and to find out more from them directly as we're studying the earth. And so we see a little bit about the atmosphere of the planets from knowledge of the planetary atmospheres. We can gain knowledge about our own Earth about its origins and about its biography and in other ways more fascinating. We can find out about the planets about the possibilities of life there and some of the fascinating insights which are being opened by new space probes. Thank you Louis.

This was about science with host Dr. Peter less a man and his guest Dr. Louis Caplan join us again for our next program when Dr. Leslie Mann will lead a discussion about the mechanics of chemical reactions about science is produced by the California Institute of Technology in cooperation with station KPP C. Pasadena California. The programs are made available to the station by national educational radio. This is the national educational radio network.