The Mars rover Curiosity has been making some startling discoveries. First, evidence that water once flowed on the Martian surface and now, evidence of organic compounds. It’s too early to say that these are life—you would have heard by now if that were the case—but they’ve definitely got scientists talking. Astrobiologists, who study whether life could exist elsewhere in the universe, are particularly excited. Adam Smith meets them.
Adam Smith: The Mars rover Curiosity, a souped-up remote controlled car stumbling over the Martian surface in search of signs of life—right now—has some news. John Grotzinger, NASA’s chief scientist on the Curiosity team, said recently that the news is one for the history books. He’s had astrobiologists on the edges of their seats. Here’s one of them: Lewis Dartnell, from University College London.
Lewis Dartnell You can’t blame a scientist, I don’t think, for being excited, for being enthusiastic about this what will undeniably groundbreaking mission. Curiosity will tell us things we’ve never discovered before, and it will be a very important mission for astrobiology and working out whether Mars ever did have life.
AS I’m Adam Smith. Welcome to Pod Academy… The full news from Curiosity finally came on the 3rd of December . Curiosity has found evidence of chlorine, sulfur and water, and of organic compounds (these are chemicals containing carbon). But Grotzinger and his colleagues at NASA cannot be sure whether the compounds really come from Mars or whether they hitched a ride onboard Curiosity all the way from Earth.
I’ve been finding out about astrobiology. It’s a field made up of astronomers, cosmologists, geologists, microbiologists and chemists, who all come together to study life in the universe by extrapolating what we know about life on Earth. I started by asking Lewis Dartnell just how big finding organic molecules would be.
LD Finding organic molecules on Mars does not mean we’ve found evidence of life. It means we’ve found the kinds of chemistry you need to make life. So scientifically that is incredibly exciting, but I don’t think it’s the sort of announcement that the general public has been led to believe to expect. And that’s why I think, particularly in astrobiology when you’re dealing with such potentially revolutionary discoveries, I think you’ve got to be that extra little bit more careful, about not allowing speculation to become rife, about not hinting at stuff before you’re prepared to announce what you’ve actually found.
AS: If Curiosity has found organic molecules on Mars, that’s big news. But it’s not little green men or women. It’s not even microscopic green people. Describing a molecule as ‘organic’ is another way of saying it’s made up of carbon atoms, as life on Earth is. But it doesn’t mean that Mars’ organic molecules – if they exist – are created by life. Checking that would be the next step. I asked Lewis whether Curiosity could do that.
LD: Well, if we’re lucky, Curiosity will be able to detect another biosignature, another sign of life and organics. And this is slightly more complicated to explain but there’s different types of carbon atoms, different isotopes. Some are heavier, some are lighter. And again through a quirk of the biochemical reactions that life uses to power itself and feed itself, we preferentially pick out the light carbon and leave the heavy carbon behind. So if you find an organic molecule that may have been created by some kind of Martian cyanobacteria, some kind of Martian cell that’s been growing by sunlight, you’d expect it to be enriched in light carbon, not heavy carbon. So if you see a bias in the carbon isotopes in the organics, that again is another smoking gun.
AS: For now, these maybe-discoveries should not overshadow what Curiosity has actually found. And that, scientists are sure, is evidence that water once flowed on Mars, an announcement that came in September, not long after Curiosity touched down. But why are scientists so obsessed with finding water beyond Earth?
CS: Water has helped sculpt the Earth and we think, or we had thought, hoped, speculated that it had helped sculpt Mars. And that is very interesting because of water’s critical role in life: life on Earth is utterly reliant on water, water molecules are incredibly solvent, an incredibly versatile piece of Earth’s biochemistry. And so we think you need water, you need it in a liquid form, if you’re ever going to have living organisms.
AS This is Caleb Sharf, director of astrobiology at Columbia University in New York.
CS: So the fact that water really did once flow on the surface of Mars tells you a number of things. It tells you there was plenty of water around, there’s a lot of water we know frozen in Mars, beneath the surface, but it means that at some point it was on the surface, even if only temporarily. And that tells us something about the atmospheric conditions. Right now, Mars is a pretty hostile place, the atmospheric pressure on MArs is less than one thousandth of what it is on Earth, so you can’t breathe on Mars, it’s like a vacuum, it’s bad news. With a thin atmosphere like that, water quickly turns into a gas on the surface, it doesn’t sit around as a liquid, so the discovery of flowing liquid water on the surface of Mars suggests that some time in Mars’s past the atmosphere could have been different, the temperature could have been different, the environment could have been very different—warmer, much more like that on Earth.
AS: Unlike Lewis Dartnell,
is not a biologist. He’s an astrophysicist -.putting the ‘astro’ in ‘astrobiology’. It’s a relatively new field and is interdisciplinary by nature. As Caleb explains, astrobiology arrived when NASA made a strategic shift a few years ago
CS: Back in the early 1990s, NASA had this sort of sudden revelation that the search for life in the universe was a big and important thing. They’d always had that in their science programme but really the administrator at the time, Dan Golden, decided this is what we should be doing. I think at first people were a bit taken aback because this was a radically different approach—it took away some of the emphasis on human exploration, which wasn’t really going anywhere at the time, and put it on something different, which included biology, but big in that picture was the idea of planetary exploration. So out of that came the modern Mars exploration programme. So in that sense NASA has poured billions of dollars really into astrobiology. Astrobiology has become the motivating science if you will behind most of NASA’s robotic exploration of the solar system and planets. If funding holds up there will be further missions to Mars and to other places. There is discussion of trying to go back to Saturn, to try to possibly land on Titan. Titan is a radically different environment than any we’ve seen but there’s a possibility that there could be some sort of life there, but it would be extreme, it would be truly alien.
AS: So astrobiology is enjoying a boom, for two reasons—an explosion of understanding around the extreme conditions life can survive under and the increasingly frequent discoveries of planets orbiting other stars in the galaxy, as Lewis explains.
LD The massive growth industry at the moment, the big increase in the field at the moment, is with exoplanet, or extra solar planets. These are the worlds we’re now discovering orbiting other stars, other suns in the galaxy. And there are all sorts of different techniques you can use to infer or indirectly detect and essentially invisible planet orbiting a sun. this is right down to the nitty gritty of astrophysics, high resolution spectrometers attached to telescopes that detect the ever so subtle nuances of the starlight that get modified by the planet.
AS: is it just me or do we seem to be finding new Earth-like planets every day?
LD : We haven’t really found a true Earth-like planet yet. And that still is what we’re really striving for. That will be the big announcement, hopefully in the next couple o f years. Mostly what we’ve been discovering are the big fat planets orbiting close to the stars. Those are the easiest ones to spot.
AS: But of course Lewis’ expertise is in biology, not stars. So what I want to know is, what happens when an astrophysicist like Caleb comes to a biologist like Lewis with a new planet and asks, what are the chances for life here? This, of course, brings us back to water.
LD: The major parameter that you care about for any planet is whether it’s got the right temperature regime on the surface for liquid water. So you want to have a planet that orbits not too closely to its star, not too hot, but it’s also not too far away and cold. So you want it to orbit in the habitable zone or the Goldilocks zone around the star. That’s the first and foremost characteristic you look for. What we haven’t discovered yet is an Earth-like planet orbiting a star in the habitable zone,and that key combination of planet type and orbit around a star that we’re hopeful for.
AS: Can you give us some specific examples of locations on Earth?
LD: There’s a whole field of study in terrestrial analogue sites. Particular locations on Earth that for some reasons are very similar to regions on other planets. And a lot of places that are similar to Mars are the kinds of terrestrial locations I’m interested in for finding biology you can get there. Some of the most Mars like places on Earth are regions like the dry valleys in Antarctica, which is one of the driest, coldest deserts on the planet. Or places like the Atacama Desert in Chile and Argentina, which is also exceedingly dry in that respect. Some of the main focus of my research is on radiation resistance, how biology on Earth survives high levels of radiation. That’s a prime hazard on Mars, is the cosmic radiation, because life on Earth is shielded from this radiation from outer space by a lovely thick atmosphere and a magnetic field that cocoons and shields our planet. but Mars doesn’t get either of those. So if you are a Maritan bacterium, a Martian organism, just in the surface soils, you’re constantly being irradiated by the hazards from outer space. And trying to survive that is going to be a constant battle.
AS: And are there any models on Earth that you can look to for that?
LD: There’s microorganisms that can survive radiation doses thousands of times higher than what would kill you or I. The best example is called deinococcus radiodurans. I’ve got some of that growing on my lab bench at the moment, it’s this beautiful bright pink colony of bacteria.
AS: And you’ve got some growing your lab bench right now?
LD: Yeah. And I’ll quite often be cack-handed when I’m doing my experiments and stick my thumb into the colonies and touch another agar plate and come back in a few days when it’s essentially contaminated, and it’ll have my fingerprint laid out, the ridges of my fingerprint laid out in these pink colonies. So this is a really interesting organism to study because it can soak up the punishment of the radiation. It’s DNA will be shattered in hundreds of pieces, and it’ll patiently put together the jigsaw puzzle of its DNA and then get on with surviving. It’s that kind of survival skill that life on Mars would need to tolerate today’s conditions.
AS: When it’s not living on your lab bench, where does it normally live?
LD: It was first discovered back in the 50s in cans of canned food that we still irradiate food to sterilise and make the cans last longer, and yet these cans kept on going off and they could not work out what was going on because the radiation dose being given to that can should have killed anything known on Earth. And they isolated this deinococcus from it. But since then it turns up in high radiation environments, artificial environments, like the cooling waters of nuclear power stations. But curiously also in very dry environments like the Atacama or the dry valleys that I study. And it turns out that this organisms isn’t strictly radiation resistant because it had never been exposed to radiation in a natural environment that high. It’s actually desiccation resistant, it’s a desert liing organism and it just so happens that being dried out gives you the same skills you need being irradiated.
AS: All this complex biology research is going on while the search for exoplanets is scanning deeper into the universe than ever before, and scientists from all angles are becoming more and more specific in their areas of study. I’d imagine it must be pretty hard for researchers from such different fields to be able to work together. As director of an astrobiology institute at Columbia, incorporating fields as diverse as planet formation and groundwater microbiology, Caleb’s job depends on matchmaking.
CS: Yeah, so it’s very interesting. There are number of things. At the simplest level it turns out that scientists like to talk to each other
CS: Yes, and particularly scientists in different fields. Because you find out stuff you didn’t know, you’re not afraid of asking stupid questions because if someone’s a biologist and I’m an astronomer, if I ask something really stupid, it doesn’t go on my permanent record. So that’s a lot of fun. I think everyone has the same sense of intrigue and wonder about are we alone. That applies to biologists, it applies to astronomers, physicists, chemists, you name it. And so part of my job is to get people to talk to each other, to get people together, but also to look for scientific areas of research where it’s useful to have an astronomer and a biologist talk to each other, so for example as we’re looking for planets that could support life but aren’t a sort of earth type environment. It’s important to understand the limits of biology as we understand it, that’s a starting place. And it’s important for the biologists to understand the possible environments out there, and so an astronomer of planetary scientist can talk to a biologist and exchange these ideas. And you come up very quickly with a strategy and you say, ok, this is the sort of thing we should look for first, because the biology says this and the planetary science says this, and so on. So it’s that sort of co-joined research that I really try to look for.
AS: I’m thinking of the microbiologist who’s spending her days looking down a microscope, studying an organism that she found in some kind of extreme, acidic environment here on Earth, and then on the other hand her astronomer friend who’s saying, ‘ah, I’ve spotted a planet’. How does this go into actual academic research?
CS: We have microbiologists looking at what lives inside ice cores taken from Antarctica. Some of this is from deep down, it’s been isolated from the surface for a long time and the chemistry is very different down there—there’s very little oxygen so things change.
AS: So an ice core is when you drill down really deep into the ice and you pull out a big tube of ice that the further you go down it, the older the ice is and therefore the older the stuff that’s trapped in there, right?
CS: Exactly, that’s exactly right. And these cores can be lifted up very carefully so you don’t contaminate them, so you’re not allowed to sneeze on them when they go up. And they go into protective sleeves and they’re frozen or re-frozen and so on. Now what’s interesting about that is by studying what lives in those ice cores, or what tries to live in these ice cores, and how those organisms survive, we learn something that you can then take to an astronomer and, say, we’re interested in icy moons, for example. In our own solar system there are many moons around giant planets that are coated in water ice and Europa around Jupiter is a great example and Enceladus around Saturn is another great example. And there’s been a long suspicion, because there’s lots of water and because you go deep enough, if may get a bit warmer, those are potential habitats for life. But what’s going to live there? Well, it might be the sorts of things that live in the ice of Antarctica. They might not be identical organisms but the speculation is that organisms on Earth have found certain chemical tricks to survive. The same sort of tricks might apply somewhere else in our solar system. Those chemical tricks leave behind traces, so there you have a situation where the microbiologist and the astronomer or planetary scientist can sit down and have a conversation and say, what should I be looking for. And the question goes back and forth.
AS: So then do they produce a research paper looking at the microbiology of the organism, which is a thing they can look at, that is tangible, and then producing lots of speculation from the astronomer’s part about various moons and planets where that could exist? Is that the form the research paper might take?
CS: That’s the hope. it doesn’t always end up as a research paper but I think increasingly it’s possible to publish these sorts of papers that are a combination of scientific disciplines and there are now a number of respectable astrobiology journals.
AS: So astrobiologists—whether they’re more from the astro or the bio end of the spectrum—have been content if their collaborations end up in a scientific journal. But of course now, thanks to the frequent discovery of new planets and the ever-so cautious hints of something very special indeed from the Curiosity rover on Mars, astrobiologists might have something else that would make them very happy. Just imagine it: critters from another world. We’re closing in on them.
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This podcast was produced by Adam Smith