Instant Genius - Why the search for life on Mars is far from over

Episode Date: July 26, 2026

Way back in 1976, NASA’s Viking landers touched down on Mars to search for potential signs of microbial life that could currently exist on the planet’s surface. Despite the mission making a number of promising discoveries, so far, no further landers have returned to the surface of the Red Planet with the aim of repeating these fascinating experiments. As such, many questions still remain as to what organisms, if any, could potentially be living within the Martian soil. In this episode, we’re joined by astrobiochemist and author Steven A. Benner to talk about his latest book, Meet the Neighbours – Life on Mars and How to Find it. He talks us through some of the scientific debates surrounding the Viking data that continue to this day, tells us how our knowledge of the evolution of life on Earth informs our search for life elsewhere in the Solar System, and explains how recent innovations in the democratisation of spacecraft technology may reignite our search for life on Mars. Learn more about your ad choices. Visit podcastchoices.com/adchoices

Hello and welcome to Instant Genius, a bite-size masterclass in podcast form. Every Monday and Friday, you're here world-leading scientists and experts talking about the most fascinating ideas in science and technology today. I'm Jason Goodyear, commissioning editor, a BBC science focus. Way back in 1976, NASA's Viking landers touched down on Mars to search for potential signs of microbial life that could currently exist on the planet's surface. Despite the mission making a number of promising discoveries, so far, no further landers have returned to the surface of the red planet with the aim of repeating these fascinating

experiments. As such, many questions still remain as to what organisms, if any, could potentially be living within the Martian soil. In this episode, we're joined by astrobiochemist and author Stephen A. Benner to talk about his latest book, Meet the Neighbors, Life on Mars and How to Find It. He talks us through some of the scientific debates surrounding the Viking data that continue to this day, tells us how our knowledge of the evolution of life on Earth informs our search for life elsewhere in the solar system and explains how recent innovations in the democratization of spacecraft technology may reignite our search for life on Mars.

So welcome to the podcast. Thanks so much for joining us. It's my pleasure to be here. So today we're talking about your latest book, Meet the Neighbours, Life on Mars and How to Find It. So the kind of fulcrum around which the entire book pivots is the Viking mission to Mars, which this year marks the 50th anniversary of. I don't know there's an awful lot to say about this, but first off, so we'd get everybody up to speed, who may not know, you know, sort of briefly, what exactly was the Viking mission and what were its aims? Well, absolutely. So the Viking 1976 mission was the first and actually the last attempt by Homo sapiens, that is you and me, to see if we could find life living today on another planet. They landed two missions. They were essentially duplicates at two sites under

the theory that if one failed, they would have a second to back up. Actually both worked, none none failed, and both of them carried three life detection experiments. And you can, as your listeners can think themselves, how would they look for life if they were going to look for it? Well, the first thing they did was look for photosynthesis, because after all, carbon is presumed to be universal in life. If you go outdoors, right, there are green plants sitting there taking carbon dioxide out of the air and using sunlight to convert it into organic material. Mars has has an atmosphere almost completely of carbon dioxide. Now, the total atmosphere is maybe 1% of Earths, but the amount of carbon dioxide is roughly comparable to Earths. And so the first thing

they did was they put radioactive carbon dioxide. Carbon has an isotope, carbon 14, which decays with a half-life of about 5,000 years. This is how they use carbon radioisotope dating to figure out how old that skeleton was, so Henry, whatever it was, dug up from that parking lot. And they observed the observation of carbon dioxide, radioactive carbon dioxide, being fixed with light into the Martian soil. The amounts were small. About 1,000 cells per gram was what they fixed, if you assume that the cells on Mars have roughly the same amount of carbon in them as cells on Earth. There's not a lot of resources on Mars. It's roughly the same resources as we find in Antarctica and an ice where we also have about a thousand cells or the high desert of Chile,

the Atacama Desert where there's also about a thousand cells worth of carbon. So that was a positive life detection test and they thought they saw photosynthesis on Mars. The second experiment looked for sort of the opposite. If they took radioactively labeled food and they spooned it onto the surface of Mars, they looked for the release of radioactive carbon dioxide. This is respiration, so it's what you do. If I feed you radioactive food, you will exhale radioactive carbon dioxide. They saw it, again, about a thousand cells worth of radioactive respiration, assuming that the cells are sort of like the cells on Earth. And they also, in a third life detection experiment, saw the oxygen O2 stored in the soil sufficient to account for the respiration. So, three

life detection experiments were run, all were positive. Robert Jastrow, who was then head of the NASA Goddard Space Center, said, well, this is about as much a positive life as we can. Well, actually, what he said, I'm quoting as the case for life is as well determined as the Viking data could possibly make it. And science journalists at the time said, yep, it looks like, you know, scientists won't say so, is what they said, but it looks like Viking has discovered evidence for extent life, microbial life on the surface of Mars. Yeah, so we can get into some of those finer details there in a moment. But let's sort of backtrack a little bit.

So why was Mars chosen in the first place as a potential place to look for signs of life? Because, you know, say, I don't know, Venus is closer to the Earth than Mars. So why did we choose Mars? Right. So Venus does resemble Earth more than Mars does in terms of size and great. gravity. But Venus is closer to the sun. It has temperatures at the surface of about 800 degrees centigrade and the clouds above Venus, which give it its pale yellow color, which you can see in the evening or morning. Those are composed of maybe 98% concentrated sulfuric acid. So there might

be life in Venus. We have done a whole series of research projects on Venus as well, but sulfuric acid at 98% and 800 degrees centigrade on the surface was really an extreme case. Mars in contrast by ever since Mariner flew by in the 1970s. We've known that it has a thin atmosphere. It is colder. There's less gravity. But there was a time in ancient Mars where it was much like Earth with an atmosphere, very much like Earth's then nitrogen and carbon dioxide.

and there is evidence for flowing water on the surface of Mars. And as we now know, there are organic molecules on Mars and even signs of ancient life that can be detected by the curiosity and perseverance rovers, which your listeners may have heard of. Yes, you mentioned something that they're really important in this conversation. That's organic molecules. So I think we need to get it clear exactly what we're talking about there. you know, what exactly are organic compounds?

And why are they such an important consideration when we're searching for signs of life? No, an excellent question. And, you know, your listeners are fans of Star Trek. There have been cases where they've encountered silicon life. Carbon is very useful because unlike with silicon life, carbon-carbon bonds are very stable. So you can make molecules, fats in particular where you have 10, 12, 16, carbons strung together in a row, and that is what's essential for making membranes. Keep in mind that you are, in some sense, carbon-based, but only approximately.

Your proteins are carbon and nitrogen and oxygen and sulfur. DNA molecules have carbon, but also oxygen and nitrogen and phosphorus. And so you are really a composite of all of these elements, but carbon is the backbone because it's with a scaffold that holds together, unlike pretty much any other element. I can go find tellurium or silver or gold or xenon, but none of these are able to form carbon-carbon bonds in the same level. And even silicon does not do a very good job. Although it is true that just like your life and my life are mixtures of carbon with other atoms,

nitrogen, oxygen in particular, silicon life could also be partly silicon. with other atoms associated with it, oxygen, nitrogen atoms. In fact, maybe 20 years ago, we did some work in this particular area showing how you could perhaps get genetic molecules out of silicon combined with other atoms. But never mind. The bottom line is that if you're going to look for life at all, you've got to get carbon. Carbon comes from somewhere. Carbon dioxide is a very convenient place to look for carbon.

And they look for it in radioactive form in Sol, in salt, carbon, radioactively. fixed into the Martian soil. So that is a putative sign. It was certainly how the experiment was designed to be run. And that result was intended by the experiment designed to indicate active Martian microbial photosynthetic or, as we like to call it in biology, autotrophic life, that is life that makes its own carbon out of carbon dioxide. So you sort of touch on that. Carbon is, has this property of being able to make long change. of complicated molecules, some of which are in all of us and are essential for all of our, the reason that we're here. So how about things like this? So we've talked about carbon dioxide.

Did they find any more of these sort of more complex, longer chain carbon compounds? Yeah. Well, not at the time. At the time, all they observed was the fixation, as we like to call it, that is the movement of radioactive carbon dioxide, which is a gas into some sort of a solid. solid in the surface. Now, since 1976, NASA has put down four rovers and many stationary craft onto the surface. The Curiosity mission, which was a 2013 mission landed, in particular had devices looking for carbon in the soil. They found carbon all over the place. They have found long, straight chain, fatty acid-like molecules. They have found what are called aromatic molecules, which or six carbon atoms in a ring. And the challenge in finding them was that the soil of Mars also

contains an oxidant called perchlorate. It's chlorine with a bunch of oxygen attached to it. When you heat perchlorate up with organics, it sets them on fire. You actually make fireworks this way if you wanted to. The Curiosity rover was attempting to get a look at the organics in the soil by heating them up to 500 degrees centigrade. Of course, what they discovered was a lot of carbon dioxide, a little bit of chloromethane and other chlorine-containing compounds. And so they have worked very hard to dial back the temperature a little bit, be a little bit more delicate. They call it opportunistic derivatization to try to see these organics in the soil by heating them and getting them blown into some sort of a detection system without toasting them.

But yes, at this point, there's a rich inventory of organics. There was expected to be a rich organic inventory because meteorites fall to Mars all the time and bring organic materials. So you don't even need life on the surface of Mars to expect organics. They're falling to Mars all the time just like they fall to Earth. But, you know, of course, it could also be biological molecules. And there have been arguments, Alex Pavlov, for example, just published a paper, arguing that the amount of straight chain carbon, carbon, carbon, carbon, carbon, carbon molecules is so large that it really does require a biological source.

Yeah, so I was going to ask about this, something that you talk about in the book, and it's often discussed about meteorite strikes and the existence of organic compounds on them, you know, and obviously flying through space. So what do we know about those? And can we tell that it came from a meteorite? Yes.

So, well, we have actually now brought back samples from two near-earth asteroids that are very carbon-rich. One is called Benu and one is called Brugu. They have been analyzed for carbon in them, and they have been found. It's kind of interesting because there are clearly processes that use carbon and make organic molecules that are not biological. We have studied a lot of these because they're relevant to the origin of life.

If you want to get life started, you got almost, it's the sort of the logic, you have to start with something that's not life. And so these would include sugars like ribos. Ribos is the R in the molecule, RNA, which is a DNA-like molecule, but believed to have preceded life on Earth. You need organic molecules also associated with nucleobases, the N in RNA. These are the adenine-guanine that you learned in high school to contain the information in your nucleic acids. My buddy, Yoshi Furikawa in Sendai in Japan at Tohoku University just published a paper where they found ribos in Benu asteroid. So it's being made there presumably by non-biological processes, including processes that we have argued are important to form life on Earth or Mars originally.

Great news. is back. Eligible customers get up to $5,000 with the federal EVAP rebate on select 2027 Volt and 2026 Equinox EV models. Visit your local Chevrolet dealer today for more details. Let's stick with RNA there because I think this is fascinating. And you talk about something called the kind of RNA world theory of the evolution of life. You know, can you sort of give us a Cleft's notes on what that idea is? Sure, just getting you ready for the test. If you look at your biology, okay, we can go and you make DNA for transmitting information so that when you, you know, survive, get married, have children, you can transfer your dramatic material to your

kids. There is RNA, but there are also proteins, which is a big part of what you're drinking right now. I'm looking at your hair and all the rest of it. So, These are protein molecules. But the interesting part of it is that in your body, the way you make proteins is by an RNA molecule that catalyzes the synthesis of RNA using information from DNA. And the way you get the information from DNA to the ribosome, which is the machine that makes RNA, the RNA machine, is by using transfer RNA and messenger RNA. And so RNA is sitting there not only as the catalyst to make proteins, but also as the information

molecule that moves information from your DNA to your protein synthesis machinery. And then if you look at your vitamin pills, you have all sorts of what we call RNA cofactors. I don't know if your listeners study their labels on their vitamin pills, but they should. And there's niacin, for example, which is involved in oxidation reduction reactions attached to a piece of RNA in your body. it's one of the vitamins in your vitamin pills. Pantoithanic acid, if you look closely, that's associated with an RNA co-factor that makes fatty acids, actually, among other things. And that's something called co-enzyme. So about, oh my goodness, I guess it's been 50 years almost exactly as well.

Harold White put all this together and he said, well, wait a minute. These RNA molecules are vestiges of an RNA world where everything was done by, RNA molecules. The term RNA world was actually coined in 1986 by Wally Gilbert, but the idea was that before you had proteins and before you had DNA, RNA served as both the information molecule but also as the catalytic molecule. And that greatly simplifies the problem of the origin of life, right? Because if I have to originate you, I had to get DNA and RNA and proteins all to emerge out of a prebiotic soup at the same time, which is astronomically unlikely. However, if I assume that RNA could do both information and catalysis and structure, all I have to do is get out of the prebiotic soup,

some RNA that can do this. And so the RNA world, the idea that there was an episode of life on earth before protein synthesis was invented and before DNA synthesis was invented. By the way, Another twist there is that the building blocks for DNA all come from the building blocks for RNA. So RNA predates both DNA and RNA. And so a lot of the origins of life work has been focused on getting out of prebiotic soups, out of chemistry, operating on a rocky planet are the ribos and the nucleic acid. And the nucleobasis in A, which is, by the way, the phosphates that link them. So that's a key advance in our understanding that has emerged over the last 60 years as to how to get Darwinian evolution started with a single biopolymer, not with this three biopolymer mess, which is very hard to get put together spontaneously. Yeah, so let's stick with that thread a little bit then.

You also talk about Luca, which is the acronym for the last universal common ancestor. This, you know, often talked about. But what's the idea behind that? And how does it fit into this whole idea of looking for life elsewhere in the solar system? Right, right. So, yes, you are related to the plant growing on your desk as well as you are to biochemistry by common ancestry. And the evidence for that has to do with the fact that all of you, all of us, use the same RNA machine to make proteins. We all have the same vitamins, niacin.

And some of us, like bacteria, make their own vitamins. They don't have to eat the vitamins like we do. And so the fact that we have biochemistry everywhere in all the life that we find here on Earth, being the same, suggests that it all descended from a common ancestor, which had the same biochemistry. Now, Luca, last universal common ancestor, since we're discussing life and space, no one thinks that the word you, Luca, universal, applies here. It's not universal.

It's universal. But, you know, it makes a nice name like Luca Skywalker or the, you know, gospel according to Luca. And so the idea here is that we can. And in fact, this was a paper that we published in 1989. We can infer a lot of the details of that Luca by just looking at the common details of metabolism and chemistry and all the descendant organisms. And in Luca, RNA, the last universal common ancestor of life on Earth is also dominant. The ribosome has been invented.

Proteins are being made using RNA catalysts in the ribosome. So that Luca is a statement, well, it's a model. It's a model for ancient life that is the ancestor of us all. But it also points to an RNA world origins of life. That is the first way to get access to Darwinian evolution. that it came by RNA emerging from a non-biological process on a rocky planet like Earth, or the chemistry that we propose to create RNA on Earth is also adaptable to Mars. And by the way, also to Venus before it turned into a hellhole with the sulfuric acid clouds.

It also means that on all these rocky planets that we see circling other stars, the same kind of chemistry could operate. And so the bottom line conclusion from that is that life, at least microbial life, is universal or at least very abundant in the Milky Way galaxy and in the cosmos in general. So let's have a look at another sort of sign of potential, what people often call habitable planets. And that's the past or present existence of water. So first of, why is water considered to be so important? for the discovery of life. And what have we found on Mars? Right. Well, you have to dissolve things in water or some other solvent. Now, there are other

solvents. Titan, for example, which is the largest moon of Saturn, does have liquid methane, but it's at 95 Kelvin minus 200, no, 180 something Celsius, and nothing basically dissolves in liquid methane. It's a very hard solvent. But water is very useful because it is a solvent that has a very broad solvent range. It's very abundant in the cosmos. Mars, of course, has a large amount of it. A lot of it is frozen in the ice caps. But, you know, if you try to get life to work in the solid state or in the gas phase, Fred Hoyle had a science fiction book over the 1950s called the dark cloud, things don't really work. Gas is diffuse away from each other. Solids, you know, things don't move around in solids, so you don't get much reaction. So a solvent is useful. Water is a very useful solvent because it is

a solvent at temperatures where things react. And it is also a solvent over a very large temperature range. So from zero to 100 degrees centigrade is a very broad range. Methane, by contrast, is from 90 to 100 Kelvin, basically 10 degrees. And that depends on pressure. So water is very useful as a solvent. It is believed to be by far the best solvent. It is certainly the solvent that you and I use. But we can see on Mars mudstones that came from depositing rocks from water, just like we see in mudstones here on Earth.

We can see river deltas and we can see shorelines and we can see the precipitation of salts, much like you would see around the Great Salt Lake in the United States or in the Dead Sea in the Middle East. And so there was a lot of water on Mars at one point. Unfortunately, there was, of course, there was also a lot of atmosphere, but unfortunately the atmosphere went away. So the water has mostly either evaporated or frozen or retreated below the surface. Now, they're not far from the surface.

We can see Martian ice, water ice, within a meter or two of the surface. You can see that because when a meteorite hits Mars, you can see white ice there. The various rovers have found water in abundance. When cliffs collapse, you can see layers of ice that are there. So when human inhabitants go to Mars, they will most likely mine the near surface water ice to drink, to also make propellant for the voyage home. We hope to have our agnostic life finder standing astride that stream of water. If Elon Musk lets us do so on SpaceX and look for Martian life in that,

it's a very large astrobiological sample, which would be quite useful. So water is on Mars, water was on Mars, water was on Mars three and a half billion years ago when the planet was more hospitable to life. Jared Isaacman, who is the new NASA administrator, even went on television a couple days ago saying that there's a 90% chance that life existed on Mars in the past and certainly all the evidence science work that we do causes us to agree with them. So this is a question that might really answer itself, but I have to ask it because I think some people would want, you know, an expert to answer it. So what we've talked about so far, we're kind of comparing life as it evolved on

earth to how it may have evolved elsewhere. So is it possible that we're missing something there? and life could have evolved in ways that are different from how it did on Earth. No, absolutely. And there's a chapter in this book that addresses that issue. You have a natural history, right? Let's just say that life arose on Mars by similar chemistry as your ancestors used to create life on Earth, say, RNA basis. There's, you then involved DNA.

You evolved proteins. You then evolved your good looks and, you know, your excellent hair. So, right, there's no reason on Mars that the life there evolved the same way, especially since the challenges associated with the evolving planet, the loss of the atmosphere, the cooling and drawing of the surface lead to different challenges. So that creates a problem when we go to look for life on Mars. We're what we call synthetic biologists. We have tried to generate alternative strategies for doing Darwinian evolution. we've made dozens of them. And so this allows us to guess how life may have evolved with a natural history attuned to the Martian planet change, not the Earth planet change. And that helps us when we go

look for life on Mars. It helps to know that we're not going to look for something exactly like you, or even maybe exactly like you at the molecular level. But there are constraints we can tell you because we've tried to make alternative life form as we know things that work and things that don't. That helps us very much as we go looking for Martians. Yeah, so you sort of touched on this there, but let's finish up with looking forwards to the future, you know. So what would you like to see happen in our future exploration and search for life on Mars? Right. Well, as the book outlines, there's a whole story, a second story, I mean, as if the story life exists on Mars.

were not enough, but there's also a very interesting story as to why you don't know that already since it sort of has been known for 50 years. Now, we can't get into the story here, but it turned out to some data were misinterpreted early on. The misinterpretation led the scientists to conclude that there was no life on Mars. They accepted that conclusion very easily because none of them wanted to go out in front of TV cameras and say there was life on Mars, because if you did that, you know, and if you're proven wrong two weeks later, it's really very embarrassing. But the result has been that there's a consensus that life could not possibly exist on Mars. And that's why when the Astrobiology Institute was founded in 1999, we were told that NASA would never fly a mission to detect extant life on Mars.

And that, I think, is one of the biggest blunders in space exploration, at least a non-crued space exploration that we have had. had. So that's because, you know, textbooks began to be written. Data were shifted to match the consensus. What's happened lately is partly through reusable rockets, SpaceX, the Japanese, have now, the Chinese, reusable rockets now on the table, is that we can democratize the search for life on Mars. It is possible now for Elon Musk, not that he's so inclined, but maybe he will become so, to send a heavy lifter to Mars, which takes, say, three or four thousand probes, penetrators designed by high school kids or college kids to do their own life detection experiment. Maybe for $25,000 or $30,000.

This spreads the cost of the launch. It's a ride share system, so you don't have to have the $80 million for the launch born by one person. but you know, you could have a bake sale and put together $25,000 from the local merchants and then fly your own. And Jan Spachek, who is here in Florida, has come up with a international Mars penetrating ride share approach and architecture, and it just won a tech lead prize from NASA. So you could imagine now, and what I would very much like to see is the democratization of space exploration, especially life on Mars. Now, you had to worry about planetary protection.

You don't want people sending bacteria. You don't want Matt Damon cultivating potatoes in his poop, right? But at some level, to democratize, you know, 50 years ago, only major national efforts could afford the price tag of getting an experiment onto the surface of Mars. And now it's possible for us to think more broadly and get many more experiments, many that would be controversial, many that would never pass peer review. but at the end of the day might actually be more intelligent

than the experiments that Nobel Prize winners and National Academy members come up with. Thank you for listening to this episode of Instant Genius, brought you from the team behind BBC Science Focus. That was Stephen A. Benner. To discover more about the topics we've just discussed, check out this book, Meet the Neighbors, Life on Mars, and How to Find It.

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