We’re fitting in one more episode this week, before Fraser heads off to Costa Rica for a week. Our next episode will record on Dec. 23, 2016.
Enceladus and Europa are all the rage these days, but classic Mars is still a great place to search for life. In fact, ESA’s ExoMars is scanning the planet’s atmosphere for methane, evidence that there might be life there right now. Let’s talk about the search for life on the Red Planet.
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Show notes here
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Fraser Cain: Astronomy Cast Episode 431: Searching for Life on Mars
Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos, where we help you understand not only what we know but how we know what we know.
My name is Fraser Cain. I’m the publisher of Universe Today and with me is Dr. Pamela Gay, the director of CosmoQuest.
Hey, Pamela. How are you doin’?
Dr. Pamela Gay: I’m doin’ well. How are you doin’, Fraser?
Fraser Cain: Doin’ great. This is sort of the last episode and then we’re going to be – for a couple of weeks – because we’re going to be, both, on various trips. I’m going to be down in Costa Rica, tromping through the jungle, looking for insects with my wife.
Dr. Pamela Gay: And I’m going to be in San Francisco at the American Geophysical Union meeting. So, yeah – I’ve got all the science and you’ve got all the bugs.
Fraser Cain: All the bugs, yeah. And pit vipers and all kinds of – There may be monkeys, though, so that’s going to be alright. And sloths, if you’ve been watching Planet Earth II.
Dr. Pamela Gay: And they have the kind of iguanas that live on the beach. And there’s a fabulous video floating around of this one amazing iguana, like, totally runnin’ for its life down the beach of snake death.
Fraser Cain: Yeah, yeah, yeah. You’re talking not about Costa Rica but about the Planet Earth II, yeah.
Dr. Pamela Gay: Yeah.
Fraser Cain: That is the greatest piece of nature photography – nature video – I think I’ve ever seen. What an amazing shot. The internet went crazy for that.
But that’s not what we’re talking about today. We are talking about searching for life on Mars.
So, sure, Enceladus and Europa are all the rage these days, but classic Mars is still a great place to search for life. In fact, ESA’s ExoMars is scanning the planet’s atmosphere for methane right now, searching for evidence that there might be life there. Let’s talk about the search for life on the Red Planet.
Alright. Well, this is a big long story. So let’s kind of go back to the beginning of the – When did people really kind of think, “Hey, there might actually be life on Mars”?
Dr. Pamela Gay: Like, when they realized it was a planet.
Fraser Cain: Right.
Dr. Pamela Gay: It’s once they had telescopes and were able to resolve that Mars was a disc and Venus was a disc. It started to become the stuff of science fiction that Mars had life, Venus had life; that these worlds that appeared to be not to different from our own were definitely places that we should, like, go and meet the others. And early science fiction is rife with amazing stories of tumbleweeds on Mars.
And, of course, we’ve all read about Percival Lowell’s canals that he imagined seeing through his telescopes. So, as he peered at Mars – you can make out with any perfectly good telescope that has a sufficient eyepiece – that Mars has different colors on his surface. And he was able to – using his imagination, as well as his intellect – envision all of these different colorations as man-made linear canals, or Martian-made linear canals, all across the surface of the Red Planet.
Fraser Cain: Right. But really, it was just an optical illusion and none of these things – I mean, I love the imagination; that he imagined this dying Martian society where they were trying to use up the last of the water on the planet. They had these big, long canals that went from the poles to feed the – you know, irrigation canals – to feed the cities and feed the final crops and the planet was dying.
And, of course, that led to some of the other – you know, the science fiction of the time. We think of John Carter, Warlord of Mars or, you know, The Invasion from Mars.
Dr. Pamela Gay: Martian Chronicles.
Fraser Cain: No, no, no. Oh, God – you know, the one where – The War of the Worlds. War of the Worlds, where you’ve got, you know –
Dr. Pamela Gay: Oh, yes – War of the Worlds.
Fraser Cain: The Martians give up Mars or they, you know – they come to Earth, looking to kind of expand their territory and deal with their ecological collapse, so – And it turns out that it wasn’t Mars that was destroying the environment, it was Earth all along. That’s too much science, I guess; too much reality.
So – Okay, so that was sort of the imagination, but when did we sort of start to really look for life on Mars? Like, actually, practically try to see if there’s anything there?
Dr. Pamela Gay: So, it actually took being able to get there before we could start rationally looking for life. The early fly-by missions were able to go, “Oh, clearly no big cities”, “Oh, clearly no big canals.” So it was in the 1960s that we ruled out civilizations on the Red Planet.
But hope lives eternal and so, when we sent the Viking missions in the late ‘70s, the Viking missions had a whole series of experiments on board that allowed them to land on the surface, scoop up samples of the soil and look, experimentally, for life as we knew it. And that may be the key is, at that point, we were looking for life that behaved in ways that we knew how to test for.
Fraser Cain: But, so far, all of that searching – nothing. Just desert, right?
Dr. Pamela Gay: Well –
Fraser Cain: So there was no large life forms, right? There was no trees, there was no cities, there was no canals – irrigation canals – Martian farms, right? There was just rocks –
Dr. Pamela Gay: No tumbleweeds.
Fraser Cain: No tumbleweeds – just rocks and dirt and more rocks.
Dr. Pamela Gay: Ice.
Fraser Cain: Some ice.
So, I guess the search needed to get more detailed, right? They had to take that exploration to the next level and actually examine really close up.
Dr. Pamela Gay: And so, just like in parts of Death Valley, in parts of Antarctica and Arctica, a quick glance around the blasted landscape seems to reveal no signs of life. We thought, hoped that on Mars, that, while the landscape appeared to be lifeless, that if you looked a little bit further – just like is true in the poles and the deepest deserts – there would be life there between the grains of dirt.
Fraser Cain: So, any luck?
Dr. Pamela Gay: No. Well, sort of. We don’t know.
Fraser Cain: We don’t know, yeah.
Dr. Pamela Gay: This is one of the things where, the reason I said those answers in the order I said them was, our initial analysis of – and by “our”, I mean the scientists who came before me because, like, I was 4.
Fraser Cain: But we were alive.
Dr. Pamela Gay: We were alive for this.
Fraser Cain: Yeah, we were like 6? I’m trying to think. It landed in, what – ’79? ’78, ’79?
Dr. Pamela Gay: Yeah –
Fraser Cain: Yeah.
Dr. Pamela Gay: ‘78ish. And so, while they were doing these experiments, we were alive.
Fraser Cain: Yeah, we existed.
Dr. Pamela Gay: We were not the ones analyzing it. And early analysis was, for the most part, conclusive of no life. But the reason I say, “for the most part, conclusive of no life” is, there were three different experiments that they ran on the Viking missions. And one of them, Labeled Release – in which they looked for specific gasses to be released in a way that would indicate respiration was taking place – that one experiment of the three had a null result; it neither said “no life” nor “life”, it was simply inconclusive.
Fraser Cain: Right. So – but the others were – Weren’t the others inconclu – or they thought they had a positive result but the – but non-biological processes would also provide the same result, right?
Dr. Pamela Gay: It depends on which of them when you’re looking at.
So, with the gas exchange, the gas exchange was negative; there was just no gas exchange taking place.
But then, with the gas chromatograph, mass spectrometry experiment, they were looking to separate all of the vapors and try and measure organic molecules. And this is one of those cases where the Viking landers heated the compounds and we now understand that this process might have destroyed any organics that were present. So it appears that, what was initially a null result – a negative result in this case; an initial false, no life result – can now get budged into the “inconclusive” result category.
Fraser Cain: Right.
Dr. Pamela Gay: So, this is where it’s like, “No”, “Yes”, “I don’t know.”
We don’t know. And what’s amazing, as journalists, is we get to see, on a regular basis, scientists continuing to analyze and reanalyze this data and find ways to argue both directions, which really says, “We just need to keep sending robots to Mars until we settle this problem.”
Fraser Cain: Those poor robots.
Dr. Pamela Gay: Poor robots.
Fraser Cain: But the – So, I mean, this was actually – I mean, the crazy thing about this is that we still write stories about this on Universe Today, where somebody reanalyzes the results and then takes a stand either way. And so, we will have a story on Universe Today that will be something like, you know, “The discovery of life has been confirmed” and then, the – and then, you know, “No evidence found in Viking data.”
Oh! And sorry, the landing date was in 1976. So I was 5.
But, right? So, the powerful life lesson that NASA learned from this is that if you’re going to say – or going to search for life – and you’re going to spend the hundreds of millions, even billions of dollars to send this experiment to the surface of Mars and answer this question, you better get it right.
Dr. Pamela Gay: Yes.
Fraser Cain: Right? That you had better answer this question to a level that no scientist is going to question the validity of your discover.
Dr. Pamela Gay: Well – and this gets us to the “extraordinary claims require extraordinary evidence” argument that we’ve heard articulated by folks like Carl Sagan when it comes to talking about life on other worlds.
And, in fact, one of the scholarships I got my senior year of high school was, there was a Carl Sagan essay contest to write essays on how you should search Mars for life. And my essay got honorable mention and it paid for all of my books my first year of college.
And so, folks have been trying to figure this out and have been challenging new generations to try and figure this out, because we do have to figure out that extraordinary evidence.
Fraser Cain: Yeah, exactly.
So, this was the powerful life lesson that NASA learned and so they – the next time that they really started to, not search for life but they sent Spirit and Opportunity, and this was to search for the conditions – I mean, not even like, “Was there water on Mars?”, really. And we’ve done a whole episode on this, so – You know, this is the new tact that NASA went down, which is, like, it’s not about the search for life, it’s the search for the conditions for life first.
Dr. Pamela Gay: And what they’re doing is interesting because, just like with the Viking program, Viking had two landers, two different locations. Ideally, any evidence you find, you want to find it in multiple places. We had two rovers, Spirit and Opportunity – and Curiosity just goes wherever the heck it feels like, very slowly; it does it very slowly. So we’re searching those multiple locations.
Mars 2020 is, again, going to be a rover capable of searching multiple locations. We are increasing the number of experiments carried per robot, so that hopefully, we can – just like we’ve proved cosmic expansion using multiple lines of evidence for multiple experiments – hopefully, when we find life – just like Viking tried to identify it via three different routes – hopefully, when we do find it, we’ll be able to identify it via multiple routes, in multiple places.
Fraser Cain: Right. And so the other, sort of complete separate way that researchers are looking for this is, of course, the detection of methane in the atmosphere of Mars. And this is something that was turned up probably a decade ago but still, we’re only finally getting the right toolset to be able to do some kind of conclusive analysis and try to get to the bottom of it.
So, what does it mean that they found methane in the atmosphere of Mars?
Dr. Pamela Gay: So methane, which is a carbon-hydrogen molecule, is a molecule that breaks down in sunlight. So you take methane – put a cow in a field; leave it alone, methane will be produced. That methane, left alone in sunlight, is going to cease to be methane. And so, whenever you detect methane, that means that it’s something that has been recently produced that isn’t a bi-product of formation. And the only two things we know that should be producing methane are geologic forces – so, volcanoes, things like that – and life processes.
So, the fact that we see methane on Mars and Titan and other worlds in our solar system, indicates that one of two things is possible: These worlds are geologically active or – and this is an and/or; you can actually have both. Earth has both – or there is life. One or both of these – One of these has to be possible; both of these is possible.
Fraser Cain: And that’s the funny thing is, literally, it answers two really – or at least, it gives us two intriguing mysteries that we’re trying to solve about Mars: Is there life on Mars? But also, is there volcanic activity on Mars? Both of these are very important questions that we really need to have answered for us.
And so, the fact that this methane has been discovered in the atmosphere, it may, sadly, tell us that, you know – it may not be evidence that there – for life – but it may very well be evidence for active volcanism that’s still going on to this day, which is kind of amazing it answers all these really important geological questions.
So don’t feel totally sad if they – if it turns out that there’s, you know – there’s sulfur in your methane, as opposed to the – whatever you need for life.
Dr. Pamela Gay: And I feel like I should point out, you can get involved in actually helping with this over at cosmoquest.org, because we have two sets of Mars images.
The set you’re going to look at right now is of the potential Mars 2020 landing site, where we’re trying to find areas that have the fewest craters because that means they are the ones that are getting the most weathering, the most disturbed by environmental factors. Which means, hopefully, anything – any fossilized – haven’t yet been broken down by ionizing radiation and the sun; any of those organics will be fresh on the surface.
And the other set of images that we have are of the youngest volcanoes on Mars, where we’re looking to find areas, again, with the fewest craters because that indicates where the youngest volcanoes are, so that, hopefully, we can figure out how recently was their volcanism on Mars.
Fraser Cain: So, when – If all goes well, when will we get an answer from the ExoMars mission? Like, are we going to be able to find this out in the next months, years? I mean, we’re around the corner from it –
Dr. Pamela Gay: So –
Fraser Cain: I mean, it’s sensitive enough to answer this question, right?
Dr. Pamela Gay: So, ExoMars is sensitive enough to start getting at hints of: What kind of volcanism or life is it? So, for instance, if it was one set of origins, we might expect it to be related to the seasons, where perhaps ancient, locked-up-in-the-ice methane was getting released during seasonal melts. Or, more likely, if it’s seasonal – but again, inconclusive – more likely, if it’s seasonal, it indicates life that comes awake when it’s warmer and then goes back into hibernation when it’s colder.
What we’re currently actually finding is the Mars methane appears to not be seasonal. And “not seasonal” means either – again, inconclusive – that you have life that is perfectly happy to be frozen or you have some sort of outgassing that happens year-round and isn’t tied to melt. And geologic processes usually – “usually”, this isn’t conclusive again – aren’t tied to seasons. We do find that volcanoes are more likely to be unhappy during major seasonal changes in the amount of snow on them. Iceland experiences this on a regular basis – different situation.
Fraser Cain: So – Okay, so we’re still gathering the data. And I guess it’s not going to be one those just slam-dunk things. Like, unless someone sees a fossil – big fossilized dinosaur or big fossilized salmon on the side of, you know, a crater on Mars – like, we’re just not going to have that conclusive evidence. Instead, really, at this point, what kind of life are we talking about? You know, if we were to sort of look at it in the lab, what would we imagine this is?
Dr. Pamela Gay: So, what is most likely on Mars is some sort of an extremophile. So, to give you a for-instance: On Earth, we have this creature that is named in Latin and I’m going to mispronounce it. It’s Deinococcus radiodurans – I think. I last took Latin in eighth grade.
But this particular critter is perfectly happy to live through blasts of radiation that make the surface of Mars look friendly. And it’s happy to live through complete vacuum and icy cold. This is the critter that does not want to die.
So these kinds of – not in this case, it’s not single-celled – but these little, tiny, walled bacterium. This is perhaps the most advanced that we could hope for, is a bacteria with a few cells that you need a microscope to find.
It would be fabulous if we happened to find trilobites fossilized on the side of one of these dried out river basins but I’m not holding my breath.
We have had – again, in the land of inconclusive with lots of argument – nanobacteria, potentially, but probably not – stress on the “probably not” – found in Mars meteorites. When you hit Mars hard enough with an asteroid, it throws chunks of Mars, at escape velocities, off the surface of Mars and occasionally, they make it all the way to the planet, Earth, where we pick them up and scientists then look at them under microscopes.
And, back when I was in grad school, there was a researcher by the name of Helk, who looked at a coated meteorite slice underneath a scanning microscope and saw what he thought, might be nanobacteria similar to what are seen and debated about at places like Yellowstone. But there are those who claim that it was simply a bad coating. There are those saying that it’s just weird mineralogy. And no one has been able to find similar samples in other rocks.
Fraser Cain: Is this the Allan Hills meteorite? The one, like, –
Dr. Pamela Gay: Yeah.
Fraser Cain: – back in, like – I’m trying to remember. It was like 1998 or something like that, where Clinton announced –
Dr. Pamela Gay: Yep – when I was in grad school.
Fraser Cain: Yeah. Clinton announced the discovery of life on Mars and – But, I mean, the amazing science on that is that they – You know, they have this meteorite and they’re able to cut it open and sample the gasses inside the cracks of the rock of meteorite and they are identical to the atmosphere on Mars. And no one disputes that science. Like, this rock –
Dr. Pamela Gay: Right. We know it’s a Mars rock.
Fraser Cain: – definitely came from Mars, which – I think that alone is an amazing piece of science to know that. And then the question, I guess, is, you know, did the life remnants that was found – or, you know, fossilized life or, you know – did that get in from Earth? Did it contaminate?
So, this is the problem, right? If we ever find these meteorites on Earth, there’s always going to be this question of contamination. You know – and we just don’t know where it came from.
Dr. Pamela Gay: Well, and like I said, with this one, we don’t even know if it’s actually nanobacteria because they did have to coat this slice so that they could use it in the microscope. Certain samples, you coat them with films with – it’s usually a single atom layer thick coating of gold – and if you sputter that on wrong, it looks like nanobacteria. So we don’t even know if they actually saw something or if they screwed up in the prep of the sample.
Fraser Cain: Right, right. And if the sample was contaminated by sneaky Earth life, so –
Dr. Pamela Gay: Yeah.
Fraser Cain: So, where we stand right now – you know, the next big mission that’s on its way to Mars is the Mars 2020 rover. This is going to be the follow up of the Curiosity rover. It’s going to look identical – to all intents and purposes – to Curiosity but it’s going to have a very different payload. It is going to be a mobile, life-searching laboratory. It’s going to have all those instruments that we were all, like, “Why can’t Curiosity just use its microscope to find life?” “Why can’t Spirit and Opportunity look for fossils?”
That this is the machine that’s going to fulfill almost all our dreams. I love the idea that it’s going to have scoopers and it’s going to find, you know, scoops of samples. It’s going to drop them into this, like, oven on it. It’s going to perform very similar experiments to the kinds of things that the old Viking landers did and then poop these, you know, out on the surface of Mars as it moves along. And it’s got some number of experiment bags that it can do.
So, this is it, right? We are going to finally, hopefully have our best crack at finding life right there on the surface of Mars.
Dr. Pamela Gay: So, the way NASA frames it is: The science instruments are state-of-the-art tools for acquiring information about geology, – easy and safe – atmosphere, – easy and safe – environmental conditions, – we know how to do that – and then, the last one is “potential biosignatures”.
And, like I said, we’re looking to send it to the places on Mars where you have the freshest soil. So this is sort of like going to the beach and sweeping away the top layer of dirt and getting to the wet soil underneath and being able to occasionally find critters there. Well, we’re probably not going to find clams staring up at us but we might find those extremophiles. And, if not, we might at least find the organic molecules that haven’t yet been – and this far more likely, folks – there is the potential at a better chance than anywhere else we’ve gone so far to find organics that haven’t yet been broken apart through ionizing radiation and ultraviolet light from the sun.
Fraser Cain: Yeah. And then, if that goes well or if it’s inconclusive, the next step is some kind of sample return. And so that is something that Europe has been working on. That’s something that NASA’s considering and that will be, probably, within another few years after that is to, you know – that one of the jobs that the 2020 rover is going to do is gather up samples that then some future mission may retrieve back to Earth.
Dr. Pamela Gay: And this is the cool idea, is this thing is basically going to be carrying rocks around in hopes – according to some talks I’ve seen – in hopes of some future mission landing and there’s basically a handoff of samples.
And this is really that ground truth that scientists talk about so much. It’s one thing to have a rock that got hurled at us by Mars but we don’t know where on Mars that rock came from. It’s the same issue with lunar meteorites but when we went to the moon and we said, “And this rock is from the Sea of Tranquility” and “This rock is by over near Hadley Rille” and “This rock is – ”, we could say exactly what part of the surface the rocks came from. We could use various forms of radio dating to be able to get at the histories of these surfaces.
And suddenly, we could take our laboratory science and use it to calibrate the crater counts we’d been doing; the spectral returns that we’d been getting from reflected sunlight. We want to do that with Mars. We really want to do that with Mars and we just need something to send the rocks back to us.
Fraser Cain: Yeah. Yeah, absolutely.
So, where we stand right now, in conclusion – the search for life on Mars – Do we know if there’s life on Mars?
Dr. Pamela Gay: Nope.
Fraser Cain: No. We know that – But, oh, we’re so close. We know that Mars was wet for long periods of time in the past. We can see, with multiple lines of evidence, that there’s, like, these great little blueberries; there’s different kinds of olivine and other compounds. There are –
Dr. Pamela Gay: Olivine forms in water. Other molecules formed in water.
Fraser Cain: One of the most compelling discoveries that were made by Curiosity, I think, was this – what looks like a bacterial mat on the surface of Mars. I don’t know if you saw this research. It saw, on the side of a crater, like, what looks like a deposit – like a sediment deposit – but it’s of life, over some long period of time. And we have these on Earth, so it could very well be that that’s the case.
We have this evidence from the atmosphere of methane. We’re still not sure of the source. So –
Dr. Pamela Gay: And the problem that we have is everything we’ve seen so far has more than one explanation.
Fraser Cain: Yes.
Dr. Pamela Gay: And “not life” is the more – it’s Occam’s razor – is the “no life” answer. But there is nothing conclusively ruling out life and there is not extraordinary evidence that there is life.
So there’s room for hope, there’s room for doubt and people will be arguing over their beers for, unfortunately, a long time to come.
Fraser Cain: Yeah, absolutely. So stay tuned. As soon as life is discovered, I promise we will let you know.
Thanks a lot, Pamela.
Dr. Pamela Gay: Thank you, Fraser.
Male Speaker: Thank you for listening to Astronomy Cast, a non-profit resource provided by Astrosphere New Media Association, Fraser Cain and Dr. Pamela Gay. You can find show notes and transcripts for every episode at astronomycast.com. You can email us at firstname.lastname@example.org. Tweet us @astronomycast. Like us on Facebook or circle us on Google Plus.
We record the show live on YouTube every Friday at 1:30 p.m. Pacific, 4:30 p.m. Eastern or 2030 GMT. If you missed the live event, you can always catch up over at cosmoquest.org or our YouTube page. To subscribe to the show, point your podcatching software at astronomycast.com/podcast.xml, or subscribe directly from iTunes. Our music is provided by Travis Serl and the show was edited by Chad Weber.
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Duration: 31 minutes