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Controversy is Rife on Mars


At Carl Sagan's invitation I covered the Viking I landing for CQ. (The last time I stayed up all night was my last [deleted] meeting years ago.) It was a psychedlic occasion once again as Mars gradually came through all that press equipment and muddle and took over. The first photo of the Martian surface, which came immediately after landing, was electrifying. You felt you could reach out and touch those rocks - how far away?

These two phone interviews were done the weekend of Sept 3-6, 1976, just after Viking II landed successfully. The first complete set of life-detection experiments by Viking I was over and was busily being interpreted. Lynn Margulis had just returned to Boston from the Viking scene at the Jet Propulsion Laboratories (JPL) in Pasadena, California. She'd been at JPL for several days as a member of the Exobiology Subcommittee of the National Academy of Science Space Science Board, observing the quality and content of the biology going on with Viking.

Lynn has a special interest in Mars because she and her co-author of The Gaia Hypothesis, James Lovelock, have formally predicted that no life would be found on Mars. Their reasoning is that the Martian atmosphere is consistent with strictly chemical processes, in contrast with the Earth's atmosphere which shows chemical anomalies explainable only by the presence of gas-producing organisms. According to the Gaia Hypothesis, the Earth's life effectively modulates the atmosphere, buffering it against major perturbances (Summer '75 CQ). By now, late 1977, it is the increasing consensus that the Viking biological experiments give no evidence for Martian life - an apparent victory for Margulis, Lovelock, and the Gaia Hypothesis. But in some ways, as Carl Sagan has pointed out, the discovery of the exotic, active, "pro-life" Martian soil behavior is even more instructive than finding familiar bugs.

We're extremely grateful for Carl's invitation to the Viking landing, and we support his campaign for a Martian rover next time.


Stewart Brand: Hello Lynn. How are you?

Lynn Margulis: I broke my rib in California.

SB: What?

Margulis: This guy had just got a motorcycle and was rifling it, so I thought I could do it too - consummate self confidence based on nothing. So I pushed the handlebars in the wrong direction, and accelerated instead of stopped, and the whole goddamned bike landed right on my rib.

SB: Well, how's the Gaia Hypothesis, in view of Viking?

Margulis: It's flying. We may be right. It looks like there's no life on Mars.

SB: You'd better get specific. First of all, how does Viking overall look to you?

Margulis: It's an unbelievable success. Everything is working beyond their wildest dreams.

SB: How do the biology experiments look to you at this point?

Margulis: The thing is that if there's any problem, it's a problem in interpretation, rather than in technical problems, because the engineering's worked unbelievably well. They're getting good data, as good as conditions permit. Do you want me to tell you about it from the beginning?

SB: Sure.

Margulis: There are three experiments that are called the biology package, and there's a fourth experiment, more important than any of those for biology, and that is the GCMS, the Gas Chromatograph Mass Spectrometer. It is an instrument that was tuned up to look for organic carbon and organic nitrogen compounds, going up to molecular weights of 400 or so. There's not a piece of soil in the world you can pick up that it wouldn't detect organics in. In fact, you can just run your fingers across a piece of glass, and there's plenty of organic matter in your fingerprint to show up in that machine, because the sensitivity goes from parts per million to parts per billion of organic stuff. This is Klaus Biemann's instrument.

The chromatograph is very sensitive, and it's hooked up to a mass-spectrometer which allows you to immediately look at the mass numbers, the number of atoms in whatever you see on the gas chromatograph. It's a double control on it - an excellent instrument. The point is that it's detected zero. That's No organic compounds, no organic nitrogen or carbon compounds. Therefore all the biology experiments have to be looked at in that light, the fact that there's no organics in the samples at all.

SB: How many tests has the gas chromatograph made?

Margulis: As far as I know it's made two. One is a low temperature run with stuff pyrolyzed - that is it's heated up without oxygen - and that gets almost all of the not very-tightly-bound organics. That would give off all your amino acids and all kinds of small organic acids, if you ran it on an arbitrary soil sample on the Earth. And then they did a high temperature run, I think at 600 degrees C, which will break up organic goop, tars and things they call kerogen and humic acids. High molecular weight incomprehensible materials get broken down into component parts, and you never know what the high molecular weight stuff is but you know what it yields. Both those runs were done with internal controls on them to be sure the instrument is working, and the instrument is definitely working. For example the instrument is seeing background atmospheric gases the same as the entry probes did, so it's definitely seeing things that are there.

It's essentially seen no carbon except oxidized carbon, CO2 and CO, so any biology results have to be interpreted in the light of the fact that there's no evidence of organic compounds. Now, such organic compounds may be there, they could be under the surface or they could be hiding somewhere, but they're not in the samples.

SB: If they were in the atmosphere, would they be picked up?

Margulis: Oh yeah. They're not in the air by other criteria. Everything is in a very oxidized state. You know what happens to organic matter, it just burns, so the carbon is in CO and CO2, and that's very bad for organic material, those conditions.

Most people feel that some organics ought to be on Mars because of meteorites. There's organic matter being brought in by meteorites, and we're not even detecting that. So that means that it's either been destroyed, or it's been preserved deeper down than the samples have gone.

SB: So the finding is even lower than expected?

Margulis: It's incredible. To me, it makes the biology much more easy to interpret, because it's a much more clear cut negative result than I would have anticipated. I was anticipating a very low organic finding, which would be ambiguous, because you don't know whether that's from meteorites, or whether it's from pre-biotic processes, or what else. But in fact it's a moot point now, because the reading is zero.

SB: Why is everyone interpreting the other three experiments as being still possible for life?

Margulis: I wouldn't say everyone. There's no doubt some fancy chemistry going on on that surface, because you've got the results of the three other experiments - all mutually contradictory, so there's almost no way of getting a single result to satisfy all three of them. There's been a lot of criticism of those particular experiments. They were designed under a much more favorable impression of the Martian surface. They were designed in '68 or something, and that's part of the problem. They were fixed very early.

SB: I remember you said in Florida at the Viking launch that they were probably too hot and too wet.

Margulis: Both, yeah, with the exception of Horowitz's, which is only too warm. You've got three of them. The first is the gas exchange experiment. That's Vance Oyama's experiment. The whole concept of monitoring gases is I think basically an excellent one, but the problem with that particular experiment is that it's only been run by moistening the soil with one of the most complex media I've ever seen. It has I don't know how many components, all kinds of organic compounds and vitamins-dozens of different things in that medium. That's the "chicken soup." They moistened the soil, and then they monitored the gases above it. Now, if you do that on the Earth you get a whole profile of gases being removed for respiration, and being produced, and metabolism - you get a whole lot of gas exchange going on. What they found is that as soon as the moisture hit that Martian regolith (I say regolith instead of soil because to me soil is a very organic thing that's the word they use for the moon covering) . . . as soon as it hit that, you got this production of oxygen, relatively large, about 15 times what would have been expected, and most people feel that you've got some sort of peroxide, or some kind of oxygen-holding material in the sample that released the oxygen on wetting. In fact Phil Ponnamperuma (he's an incredible guy) may have already been able to simulate this result with very very dry peroxide-containing material. You add water and you heat it up and oxygen is eliminated. The exact Martian simulation isn't known, but most people feel that it's a chemical response to the adding of the water. Also it may or may not have anything to do with the complex medium.

SB: They don't have the ability to do a control with just water?

Margulis: Don't ask questions like that.

SB: Come on.

Margulis: They make me laugh, and laughing is very bad for a broken rib. They do have certain controls, but one of them is not water alone as far as I know. They have a "sterile" soil control, and you get less response after you heat the soil up first. But whether you're sterilizing, or whether you re inactivating a chemically active surface or what the hell you're doing by heating it up is ambiguous. There's all kinds of things that respond to heat that aren't biology, right? Anyway, I think most people feel that the release of oxygen is very interesting, and you're going to learn something about the Martian surface, but it has probably nothing to do with any kind of living response. You see, it stayed constant. It gave off the oxygen and then it stayed constant over quite a long period of time. Which is what happens when you add chemicals and mix.

OK. The second experiment is Gilbert Levin's labeled release experiment in which he has carbon-14 - radioactive carbon-labeled materials - in his so-called medium. Again, hot and moist. Too hot, and too moist. Much hotter and much more moisture than one would expect on the Martian surface. Parenthetically, the gas chromatograph, the GCMS that I spoke about first, measures water, and some water came out at low temperatures, but what was very impressive was that a lot of water came out at relatively high temperatures, implying that the water is tightly bound. It's water of hydration in the minerals themselves.

So it's really dry stuff. Basically we're talking about a slight amount of water vapor, measured in preciptable microns, where on the Earth it's centimeters. Now, the labeled release experiment shows some incorporation. What they're looking for is release of the radioactivity as radioactive 14CO2. In other words, they're adding radioactive food and looking for radioactive waste products. And indeed they got radioactivity in the form of 14CO2 coming off, and I think they got more released than with the "sterilized" sample. But, again, you don't know whether you're releasing natural radioactive C-14 in the soil, or what kind of chemistry is going on in the components of the medium. This labeled release experiment is another one that can be essentially imitated in the laboratory in a non-living way. You can just add chemicals until you release radioactivity. So both of those experiments are too hot and too wet, and have alternative interpretations, and neither of them are giving you the kind of complex response you get if you tried to monitor even a desert soil on earth.

The third one, the pyrolytic release experiment, had a very interesting result, and no one knows how to interpret it. It's got to be interpreted. This is Norman Horowitz's experiment which looks at the incorporation of radioactivity introduced as 14CO and 14CO2 - tagged carbon atoms. Now, this is tricky, because if you were on the Earth you'd be convinced by the finding, but the Martian conditions are weird, and you're not sure. What you do is, in the light you add a sample of radioactive 14CO and 14CO2. (That carbon monoxide is in much higher percentage, unfortunately, than in the Martian atmosphere.) Now, on the Earth you'd get photosynthesis. You'd get the incorporation of these carbon14 gases into organic matter in the light. You'd also get non-photosynthetic carbon dioxide and carbon monoxide fixation, which means that these things react and get incorporated into living material even in the dark, although the light reaction is a much stronger reaction on the Earth. Now again, the experiment was run at ambient conditions for the spacecraft, which means higher temperatures than have ever been seen on Mars, at least at the latitude of Viking.

SB: What temperatures are those?

Margulis: I think it's 12 or 15 degrees Centigrade (50 to 60 degrees Fahrenheit). All temperatures around Viking so far have measured below 0 degrees C, below freezing, and this experiment is definitely above freezing. They had to run it at the same conditions as the spacecraft, because the machinery won't run at ambient temperatures. But it's not wetter than ambient. There's no liquid water at all in this experiment - only what vapor there would be anyway. Of all the experiments it's closest to Martian ambient. (one could argue in the other two experiments that you essentially drowned everything, because you've added more water than probably has been seen on that planet in a billion years.) On this one even the temperature's not that unreasonable, because in equatorial regions in Martian summer temperatures do get that high.

So in the pyrolytic release experiment after you've added the tagged 14CO and 14CO2 you heat the sample and measure the radioactivity of what cooks off. The 14CO and 14CO2 that was not reacted goes off first. You get rid of that. And then you get only the material that is retained by the column, called the organic vapor trap, which under Earth conditions would mean that it's organic matter. And they did see that there was enhanced radioactivity in this second peak, which implied that the carbon-14 was incorporated into something organic. The results superficially imitate quite handsomely results from pretty barren Antarctic soil. There was something like 96 counts per minute in that second peak, and the "sterilized" control had something like 15 counts, close to the ambient background. So there was an enhanced signal. But we haven't done the same experiment in the dark yet. That's coming.

In some people's minds you've got some sort of positive signal here. In my mind you've got a positive signal that has nothing to do with life at all. That's my particular prejudice, and only time will tell. I know that I'm ready right now to start working on a piece with Jim Lovelock about what this says about the Gaia Hypothesis. We have two controls - Mars and Venus - and Earth is the experiment. Earth has life on it and has all this atmospheric modulation going on which Mars and Venus don't have. I think we're going to get a consensus before the end of the year that there's no life on Mars.

Something else terribly interesting that I realized when I was out at JPL is: the camera's been sitting there surveying the landscape for 40 days, and not one thing has moved in 40 days. Nothing. Not even a dust particle. I just can't imagine sitting anywhere on the Earth for that long and having nothing move except shadows. Even some wind, some weather or something. I'm just asking for some geology, and you're not even seeing that. It's very possible that the surface you're looking at was formed 2-1/2 billion years ago and there's been very little change since then. An occasional meteor impact and an occasional dust storm of very very fine dust.

SB: Do you mean those little trails of sand behind the rocks could have been there for some good while?

Margulis: For thousands if not millions of years. That's something that people want to do is date these things. You do see those river-like channels - everyone agrees that some of those were made by water. There's now no disagreement on that. When you get water-formed channels that have meteorite craters in them it's possible that they're recent craters, but it's much more likely that the channels occurred at very very early stages, when the meteorite rate was higher, and that pushes back the problem to: did life ever arise on Mars? It's certainly possible. Did it arise and die out?

SB: If life were introduced now to Mars, would it find a foothold?

Margulis: If you just set something out, it would die very quickly. It might pop open from the low atmospheric pressure. The cold temperature per se you can survive in, but you can't metabolize in it, and there's only so long you can sit around waiting.

SB: How big a deal would it be to make the planet habitable, do you suppose?

Margulis: A big deal. A very big deal.

SB: If you carted in the stuff for the atmosphere . . .

Margulis: You're not going to increase the gravity, so you'd have trouble keeping it there. You'd have to have closed containers for atmosphere.

SB: In terms of Gaia, you made some predictions a while back that there'd be no life on Mars because of what you knew about the Martian atmosphere. Does the Martian atmosphere still pretty much have what you thought was in it?

Margulis: It has very much what we thought. It's got all those exhaust gases, all those highly oxidized states of carbon. I'm glad they found the nitrogen, cause now we have a number on it, but there's no reduced nitrogen in there, which you need. You see, there are no reduced compounds in the presence of the oxidized ones. Which is our clue. Everything's essentially oxidized.

SB: If there were life you'd look for what gases?

Margulis: You'd look for ammonia, methane, hydrogen, or hydrogen sulfide or any of these things that are flagrant contradictions in the presence of oxygen and CO2. What you have on the Earth is this sort of flagrant contradiction which would, if left alone, go to a Martian type of state. The fact that you have these reduced gases on Earth wiyh its oxygen-rich atmosphere means that they're constantly being produced by organisms. You don't have any of those kind of contradictions on Mars at all. And that's why Jim and I are going to try to capitalize on the interest in this.

SB: What was your impression of the scene at JPL when you were there?

Margulis: People were pretty much ecstatic. There was the possibility of a crash landing, or of everything not working, but everything worked. They're really getting data, a lot of data. Everyone is up to their ears. I know that the biology team has been having 6 a.m. meetings. Everyone's exhausted, but elated. It's a regular high around there.

SB: You sound pretty excited yourself.

Margulis: Well, Mars is interesting to me because it's kind of like a naked Earth. As soon as you get a consensus there's no life on Mars, that's where the ball game begins as far as I'm concerned. Because that's when we'll be able to define the ways in which we know life has modulated the Earth. But as long as someone's holding out that there's life on Mars that's modulating the planet, then we don't know how to subtract it, because it would be a totally different kind of life, and its effects would be unknown, and so on. I can't begin on the exercise. So I'm one of the few people, I guess Jim Lovelock too, who are really excited about a good negative result. What I would call this, if I were writing your article, is "The Three Billion Dollar Negative." I don't know if that's the right price, but it's some huge number like that.

SB: So Earth is alone.

Margulis: As far as the eye can see in the Solar system, we're here by ourselves. When you start talking about life eisewhere, that's highly probable, but it's terribly distant, far outside the solar system.

SB: What does this say about the delicacy of the position of Earth in relation to the Sun? Venus is just a bit closer and Mars is just a bit father, and if they're both dead, that puts us in a very narrow cambium.

Margulis: That's true, but on the other hand, it's known by anyone who's cared to think about it that for life to persist you've got to have open bodies of liquid water. I don't mean steam, and I don't mean ice, which excludes constant temperatures above boiling and below freezing. Life is essentially a variation on the theme of water.

SB: Do you know anybody else besides yourself and Lovelock who've formally predicted no life on Mars?

Margulis: That's a good question. You find someone else* and I'd be very interested. I never ran across it, but you know I don't really read Martian literature very much except what's sent to me that I have to read. I think that there's a general sentiment amongst astronomers that there probably isn't any Martian life, but I don't know if they've said that in any kind of intellectual framework or in a formal way.

*In '67 Hitchcock & Lovelock made this prediction based on what eve knew then of the atmosphere of Mars. -LM


Stewart Brand: How's it look for Viking II right now?

Carl Sagan: Well, we had a hairraising time during entry because we lost communication with the orbiter, so it was sort of wild, but everything seems to be in fine shape there now. As far as I know, there are no malfunctions at all. We landed in a place with the promising name of Utopia. The landing site some people thought would be filled with small sand dunes, but there's nothing but rocks as far as the eye can see. Many of the rocks are quite strangely shaped, they may be aeolian ventifacts, rocks which are sculpted by sandblasting by windblown dust. Some of them certainly seem volcanic in origin.

SB: It looks enough different from the Viking I site to be interesting?

Sagan: It's different, but both Viking I and Viking II landing sites were chosen fundamentally for their blandness, so we should not be surprised if we find that close up they're reasonably bland We know the planet as a whose is remarkably exuberant and challenging. The reason for the Viking II landing site is that it's warmer and particularly more humid, and since two of the microbiology experiments are oriented towards liquid water it was reasonable to take some additional risks to in some way increase our chances of finding the sorts of microbiology that the experiments are geared to detect. We won that gamble. The landing was successful.

SB: What's your current feeling about the life experiments on Viking I?

Sagan: Well, the results are tantalizing. All three microbiology experiments have given positive results, and what's more each one different from its control experiment in a manner that if we had seen it on Earth, we would not have hesitated to ascribe it to microbiology. But there certainly is a possibility that there's an extremely active and unfamiliar sort of surface chemistry going on on Mars, perhaps due to the fact that ultraviolet light gets to the surface of Mars more than gets to the Earth, and that there's a lot of water bound up in the rocks of Mars, as there is not in the rocks of the Moon. If that's the answer, it's still a remarkably important conclusion because it means that there is a kind of nonbiological surface chemistry which duplicates in some substantial detail the biological chemistry of living systems on the Earth. That's both oxidation and reduction reactions. If that's the answer, we have learned something quite important about the origin of life.

SB: Say more about that.

Sagan: Well, if it turns out that (and I stress this is the least interesting possible result) that the surface chemistry is able to simulate biological chemistry, is able to reduce carbon dioxide to organic molecules, well, that's what photosynthesis does; that's what green plants are about. And if the surface materials are able to oxidize organics to collect oxygen and make water, well, that's what respiration is about. If processes which, to some extent, simulate respiration and photosynthesis can occur before there's life on a planet, that means that all biology has to do is simply use the pre-existing surface chemistry. Some aspects of biological chemistry would then be not as major an invention as people usually thought before. So in that sense, these results make the origin of life easier and clarify an important question on the origin of life.

SB: The idea being that such might have been the conditions here before life got going?

Sagan: We would have had ultraviolet light reaching the Earth's surface before there was oxygen in our atmosphere and it was still a reducing atmosphere. And we would have had abundant water on the surface. So in that respect we duplicated that sort of chemistry.

SB: Is it the case that if abundant liquid water were made available on Mars, then something might get going?

Sagan: No, I think both for the Earth and for Mars, the reducing atmosphere necessary for very large scale synthesis of organic molecules is absent. I think if all life were wiped off the Earth in some unimaginable catastrophe, life would not arise again, because of the escape of hydrogen and the absence of reducing conditions. You might have a sort of low level and faint rhythm in the bass, so to say - surface chemistry of both oxidation and reduction reactions which would to a small extent resemble biology. But the theme would be gone.

Of course the other possibility is that all of this peculiar chemistry is indeed due to microbes, and that we have uncovered a Martian biology. I think this is a more interesting conclusion, but either way we will have learned something extremely important.

SB: What do you make of the gas chromatograph experiment which is not showing much of anything?

Sagan: Well, that certainly is interesting, but you have to bear in mind that the large amount, almost 1% of bound water in the Martian soil, poisoned the ability of the gas chromatograph mass spectrometer to detect simple organics up to about two or three carbons. So these results were only for much more complex organics, and the results are quite negative down typically for a given molecule to something like 10 parts per billion. That's not very abundant; that's a very very sensitive test. Some people say that there are places on the Earth which have an indigenous microbiology but exceptionally low levels of organic matter, and other people see that as an open question. But suppose it's true that in the one or two places that we've looked there is microbiology but there is no organic chemistry. What's the conclusion? The most likely conclusion is that life on Mars exists in what Lederberg and I 15 years ago called microenvironments. That is, in certain specialized zones of the planet, maybe wet places for example, microbiology thrives; but it's dispersed, possibly by wind. So you can find the bugs lots of places, but they reproduce and are concentrated only in a few. That's at least one possible explanation.

SB: I understand that the GCMS in this experiment was showing even less organic carbon than would be expected from meteorites and such things.

Sagan: That depends very much on the rate of infall and the rate of destruction of the organics, so I don't think that conclusion can be too clear. There are certainly some models of the meteorite infall and ultraviolet photo destruction which would be consistent with the upper limits of organic matter detected by the GCMS.

SB: Let me be real clear in my understanding of what that is not finding. What would have to be there for it to get a positive?

Sagan: Let's take a molecule, napthalene. You'd have to have more than ten parts per billion of naphthalene for it to be detected. on the other hand you could have huge quantities of propanol or formic acid, say, and you wouldn't detect it, because those are low carbon number organics, which would be totally obscured by the bound water. That will be avoided by a clever maneuver in the second lander, and so we have information on the simple organics in the next few weeks.

SB: What other matters look interesting at this point besides the biology?

Sagan: There are a whole bunch of other questions. Why do various landscapes look the way they do? How did they get that way and what does it say about the origins of the planet? How sure are we now that there really was a dense early atmosphere during which water flowed - which looks a lot more likely now than it did a few months ago.

SR: Are they getting a better idea on when that might have been that the waters flowed?

Sagan: Not yet. That'll involve very careful crater counting in the channels the only available quantitative method of determining the ages of geological features on Mars, and the method certainly has uncertainties attached to it.

SB: What's your activity now?

Sagan: Now that we're done with landing site certification I have a little more time to devote to scientific questions. I'm interested in the physics of wind-blown dust on Mars, the possible influence of ultraviolet light on the microbiology and organic chemistry results, sand ripples on Mars, and a number of other questions. You understand, the Viking mission is a team effort. The results we have were obtained by a large group of very competent scientists and engineers.

One other issue I'm quite interested in is an apparent paradox. There are remarkably well preserved rocks at the two landing sites - sharp angular faces and so on. Yet it seems that the rate of wind erosion in the great sand storms should be phenomenally high. How can we reconcile those two? One possibility is that both landing sites have been only recently exhumed. They might have been covered over with dust for quite long periods of time, and of course there are other places which are in the opposite condition. There may be something wrong with our calculations of abrasion rate and so on, but right now I'm quite excited about this question.

SB: Would it bode well for the biology experiments if those were recently uncovered areas?

Sagan: Interesting question. Maybe. I can only see one model in which that would be the case, which is if there were biology early, and it was covered so the bugs were dormant and protected under a heavy blanket of dust. If the overlying dust has recently been removed perhaps the bugs are now accessible.

SB: Obviously what you'd like to be able to do is drill and make some kind of a core.

Sagan: That's absolutely right, and go to many places investigate in all three dimensions. I'd like to have a rover with deep-boring core capability. That would be heaven.

SB: Is there hope for such a vehicle?

Sagan: Well, it's interesting. As a precaution against various system failures of the two Viking orbiter lander combinations, essentially all the pieces of a third orbiter-lander combination were constructed and assembled. So all that's necessary is to put it together, mount it on wheels or tractor treads, make some adjustments in the experiments and launch it off to Mars.

SB: What adjustments?

Sagan: That's still to be debated. At the very least you would want a more elaborate pharmacy.

SB: Namely?

Sagan: I'd like to see more molecules, I'd like to see them added one at a time, and I'd like to have somewhat more control over sequencing, so that if the experiment goes one way you do this, and if it goes another way you do that.

SB: A branching regime.

Sagan: Exactly, a branched contingency tree. Now, that might involve certain additional items of artificial intelligence - which are well within our reach. You know, it's so frustrating, because you see from orbit this fabulous geology exciting terrain, and then you consciously go and land in the least exciting place. And you're stuck. You can't hop an inch. In the Viking I stereo pictures you see these gently rolling hills with hints of a valley between the hills, and you have this extremely human urge to go take a walk. And you can't do it. But the technology for mounting the whole thing on tractor treads and going off is at hand. You could wander to your own horizon every day quite easily. You'd look around, see the most interesting thing that's far away, go to it, look at it close up, and look around again. And in the likely lifetime of such a space craft you could travel at least many hundreds and perhaps even thousands of kilometers. That's a very big turf.

SB: You're on terrain that treads can handle?

Sagan: Yes. It's a lot easier to wander over rough terrain than it is to land on it. You could have in the vehicle the sorts of feedback loops that you see on toys. When they come to the edge of the table or an obstacle, they know to stop and turn around. It would be able to pick its way among the boulders. if such a device ran into trouble, it could stop and ask for instructions.

SB: Since Viking I landed a month and a half ago have there been any changes in the terrain or the weather?

Sagan: The atmospheric pressure is steadily declining every day. In less than two years it'll go to zero, at this rate. . . that's not likely to happen. What's happening, we think, is that it is winter and one of the polar caps is rapidly growing at the expense of atmospheric CO2. So the atmospheric pressure is going down. When the season changes the trend in the atmospheric pressure will reverse.

SB: What's the expected lifetime of the landers?

Sagan: It's hard to tell. it might be extremely long, many years. They're not going to run out of power, because they're powered by the decay of radioactive isotopes, so it's just a question of parts failing.

SB: Years being two years, ten years, twenty years?

Sagan: Well, twenty sounds long. Two sounds perfectly possible. The nominal lifetime it's been geared for is 60 to 90 days.

SB: How about Earthside? Is the program up for staying with Viking as long as it's alive?

Sagan: There are plans for an extended mission now.

SB: What's an extended mission?

Sagan: That begins after solar conjunction in late December There are a number of marvelous things that can be done. One is we can move an orbiter so that it can proceed sufficiently close to Phobos - 50 kilometers - to take pictures of one meter resolution, which should be quite an eye opened In less than three years operation we could photograph the planet pole to pole at better than 80 meters resolution. But the money for such an extended mission is not yet allocated.

SB: I was looking at an image of Phobos and wondering about its size. Is it large enough that if you stood on it would it hold you to the surface?

Sagan: Yeah, you would be held to the surface, although you could probably do a standing high jump of one kilometer. And you could, if you were at all good, pitch a baseball to escape velocity.

SB: And run yourself into some kind of an orbit? If you could get the footing?

Sagan: Well, let's see, at about 20 miles an hour you could launch yourself into orbit.

SB: Considering the kind of jumps you could take, that might be possible.

Sagan: The whole prospect of inter-planetary Olympics arises - different records for different worlds.

SB: One thing I've wondered about looking at the eery familiarity of the Martian domain, how much more habitable is it in terms of humans than say the Moon?

Sagan: An unprotected human being would be in trouble in both places of course, but Mars has so much more in the way of available resources than the Moon does, it's just no comparison. Mars is loaded with water. Not in a liquid state but it is available, and all those puffs of oxygen in the gas exchange experiment show it's loaded with oxygen. Not exactly so that you could stick your head into the ground and take a deep breath, but with a little technology you could collect that oxygen. So I would say if people had a serious reason to do it - and I don't know of any yet - I think it would be possible to make some colonies on Mars.

SB: The atmospheric pressure is the equivalent of what altitude above the Earth?

Sagan: 100,000 feet.

SB: Is the Martian atmosphere pretty much as expected from the early data?

Sagan: Yes, the important findings are a few percent of both nitrogen and argon. The importance we give to the nitrogen is that if you want to imagine a microbiology in any way similar to the terrestrial sort, you have to have nitrogen in the atmosphere. But the main thing is the abundance of isotopes of argon and nitrogen - argon 36 and argon 40, and nitrogen 14 and nitrogen 15, which by two separate arguments give evidence for an early dense atmosphere on Mars.

SB: It is less dense now because why?

Sagan: A variety of reasons. The ones that I lean towards are the freezing out of the atmosphere in the polar caps. I think it very likely that the dense early atmosphere is still there, but it's buried.

SB: What's the sunlight at high noon at the site of Vikings I and II versus sunlight at high noon in Pasadena?

Sagan: Half. It's like what you have here on an overcast day.

SB: How does Mars compare with Venus?

Sagan: Well, despite the good operation of the Soviet spacecraft on Venus it got fried in an hour.

SB: So if you have a choice between fire and ice, take ice.

Sagan: Yes. Although it's not always that icy on Mars. But both planets are exotic by terrestrial standards.

SB: It's assumed at this point that Venus has no life?

Sagan: Well, it would have to be a remarkably hardy form of life to survive that 900 degrees Fahrenheit on the surface. A completely airborne sort of biology may not be totally out of the question.

SB: What's the next planetary number for us now?

Sagan: There are two more approved missions, both approved many years ago. One is called Mariner Jupiter-Saturn, which will be launched next year and go by Jupiter in '79, Saturn in '81. That means 30,000 photographs for those two planets. That's a fly-by mission, preliminary reconnaissance, it's not at all a detailed study. And then there will be launched one year later Pioneer Venus, a small rather modest set of entry probes. And that's it. We have no approved Viking follow - on for Mars. Nothing like a lander on Titan, a probe into Jupiter, an orbiter around Venus, a rendezvous with a comet, all sorts of meaty kinds of missions that we're fully capable of and our scientific knowledge cries out for. There are no such missions, and there's a serious question that the remarkable set of talents put together for this sort of exploration is going to just simply dissipate, go into other things. As yet there is no government approval for continuing the systematic exploration of the solar system.

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