What if there’s Life on Mars?

by Tim Sommers

Perseverance, the fifth NASA/JPL rover to land successfully on Mars, is currently looking for life there. What if it finds it?

The discovery of life on Mars would provide evidence that life is ubiquitous and likely to arise spontaneously under moderately favorable circumstances. It would be evidence that life everywhere is very similar – or, alternatively, very different – and give us more reason to suspect that there is life elsewhere in our own solar system. It could even suggest that we – you and I – are Martians. What evidence of life on Mars will not do, despite what some have argued, is make it more probable that human beings will go extinct. That last suggestion, proffered by Nick Bostrom and echoed by others, is (to use a technical, philosophical term) bonkers. So, I will leave it for last.

Perseverance is not just looking for life. It’s exploring the potential habitability of Mars for future missions, collecting samples that may be returned to Earth later, collecting instrument data, and taking spectacular photographs. I am excited about it as I have been excited about every mission since Viking 1 in 1976. (Excited, that is, once I recovered from my initial disappointment that there didn’t seem to be any dinosaurs on Mars. Don’t judge me. I was eleven years old.) But occasionally when I share my excitement with others, usually in the form of photographs, I get a dispiriting response. “It’s just a bunch of rocks,” more than one person has said to be. Either way, it’s still fascinating to me. But, well, maybe, it’s not just rocks. Maybe there is life on Mars.

For the purposes of this discussion, I am not going to distinguish between definitive evidence of past life and current, you know, actual life. Of course, it’s more exciting if there is actual respirating and metabolizing going on there right now. Fossils of extinct life are, well, still just rocks. But we are much more likely to find evidence of past life than anything living. To see why consider the question, why can’t we just see that there is or isn’t life on Mars? It looks pretty dead. Whereas a probe to Earth would detect life from orbit.

But imagine the Earth losing its magnetic field because the spinning, molten core becomes solid. Then the solar wind strips away the ozone layer and the planet is exposed to all manner of radiation. Meanwhile, Earth slowly leaks most of its atmosphere into space and, then loses 99.99% of its water, probably the same way (but partly, maybe, it’s absorbed into the crust). Then the planet sits for a billion years bombarded by radiation and debris from space. Life might well be wiped out and most evidence that there was life would be greatly obscured.

So, it is with Mars. Mars once had the right conditions to support life as we know it – in fact, it was likely habitable before the Earth – but all those conditions changed for the worse over time. So, I am interested in what it would mean for us if there either is or was life and I am going to stop distinguishing between the two scenarios.

The most exotic scenario for life on Mars might actually be the least interesting. What if it’s just us? Or, more accurately, what if we are Martians? Since Mars was habitable before the Earth, life might have evolved there first. Meteorites come here from Mars quite regularly. (Some scientists still believe that at least one such meteorite contains evidence of fossilized life.) Microbes may well be hardy enough to survive the journey from Mars to Earth – scientists recently revived microbes from ocean sediment that had been dormant for 100 million years. So, it could be that life started on Mars and came to Earth, then was wiped out on Mars but flourished here. If there is Martian DNA, and we can get our hands on it, it’s possible that we could even prove it.

Why think such a mind-blowing possibility is the least interesting one? One thing that made the Apollo mission less interesting than one might have hoped was the discovery that the Moon was the Earth – or, rather, a piece of the Earth knocked off by a Mars-sized object early on. The idea that Earth life comes from Mars is an exciting headline, but evidence that life evolved independently in more than one place is a story that has legs.

What then if there is life on Mars that is very similar to life on Earth? For example, what if Martian life has DNA or something very much like, but not identical to, DNA. That would mean that at least two of the three small, rocky planets in our solar system independently evolved familiar forms of life. The Kepler mission to identify exoplanets (planets not in our solar system) estimated that there are 11 billion Earth-like planets orbiting Sun-like stars in the habitable zone and another 29 billion orbiting Red Dwarfs in the habitable zone. If there is life on Mars it suggests, at least, that life like ours is not a fluke and there is likely a lot more like it out there. It also bolsters the hope that there might be life in the warm salty seas under the frozen crusts of several of the ice moons in our solar system – seas warmed by the massive gravitational pull of the gas giant planets they orbit.

What if life on Mars is very different, but recognizable as life? In that case, it would almost certainly teach new us things about chemistry, biochemistry, and biology, while still suggesting that life, in all its variety, is present in many other places. It would also make it more likely that there are more exotic forms of life in more surprising places, for example, on Titian, a moon of Saturn. Titan is the only moon with weather and liquid lakes and rivers. The thing is it’s 290 degrees below zero on Titan and the lakes are filled with Methane in its liquid state. But if an exotic alternative biology is possible on Mars, why not on Titan as well?

Whether life is very different, or very similar, on Mars, its discovery suggests in a breath-taking way that we were probably right to assume that life arises naturally under the right conditions and is ubiquitous throughout the universe. So, why does Nick Bostrom say that the discovery of life on Mars should worry us? Really worry us. Here’s what he says.

“I hope that our probes will discover nothing. It would be great news to find that Mars is a completely sterile planet. Dead rocks and lifeless sands would lift my spirit. On the other hand, if we discovered traces of some simple extinct life form: a bacterium, some algae, it would be bad news. If we found fossils of something even more advanced – like a trilobite or even the skeleton of a small mammal, it would be horrible news. The more complex the life we found, the more depressing the news. Scientifically interesting yes, but dire news for the future of the human race.”

If you have heard of Bostrom before it’s probably because of another wildly counterintuitive argument of his, the “Simulation Argument”. To oversimplify, he argues that it is overwhelming likely that we live in a computer simulation and not in what he calls “base-line reality”. Such skeptical scenarios are familiar enough. How you know you are not a butterfly dreaming it’s a person (Zhuangzi (2500 years ago)) or just dreaming (Descartes (400 years ago)), being fooled by an evil demon (Descartes, again), a brain in a vat (Hillary Putman (60 years ago), or in The Matrix (1999). What’s different with Bostrom’s argument is that he says not that its possible that such a skeptical scenario obtains, but that it is very likely. Why?

He thinks that we have every reason to believe that right now or in the future our ancestors and other intelligent beings will run lots and lots of simulations indistinguishable from base-line reality. So, given that there is only one base-line reality we could be in, but there are lots and lots of simulations we could be in, pure probability favors us being in a simulation. (If we are being simulated and discovered the technology to run a simulation, I suppose we could be in a simulation of a simulation of a simulation of… I am just going to stop now.) Whatever you think of this argument (I am not a fan), it’s gotten a lot of press for a philosopher’s argument.

So, what about this argument that life on Mars is bad news? It’s based on the Fermi paradox. The Fermi paradox, basically, asks, “If life and therefore intelligent life is so ubiquitous, where is it? How come we have no evidence of the existence of intelligent life elsewhere if there’s so much of it?” The lack of radio signals, or really anything, from somewhere else is sometimes called, poetically, “The Great Silence”. The Drake equation is an attempt to formalize our reasons for thinking there should be a lot of intelligent life out there. It says N (the number of civilizations in our galaxy that we might communicate with) is equal to the average rate of star formation times the fraction of stars that have planets times a bunch of other stuff including the fraction of planets that could develop life times the fraction of those that do times some other stuff. I am not going to lay out the whole thing, and its not clear that we know enough (including any of the values we are supposed to multiply by) for this to be at all helpful. But the one thing that might be relevant to us is “the fraction of planets that could develop life times the fraction of those that do”. Evidence of life on Mars would give us some reason to raise these values which would make N greater such that the discovery of life on Mars should be evidence that there are more, and not fewer, intelligent neighbors out there. So, why is life on Mars supposed to be bad news?

Bostrom says as N gets higher and higher that should make us worry more and more that we don’t have evidence of a very high number of Ns. It makes the Fermi paradox more puzzling. Bostrom then assumes one particular solution to the Fermi Paradox, “the Great Filter”. The Great Filter says we don’t see evidence of more civilizations, because intelligent beings tend to wipe themselves out long before colonizing the galaxy. Evidence of life on Mars, then, is evidence for the Great Filter.

But, of course, it’s not. Evidence of more life is evidence of more life, at best. It’s maybe not even that. After all, the sample size even after the discovery of life on Mars will still be infinitesimal given the size of the galaxy. Furthermore, Bostrom is assuming there’s only one solution to the Fermi Paradox. There are many more. I really like Stephen Webbs’ book which offers 50 solutions. I haven’t read Alexander Popoff. He claims to have 100. Here are a few. Maybe, the vast Galactic Federation only communicates with civilizations capable of FTL travel. (See, Star Trek: First Contact). Maybe, by sheer chance we are in a relatively deserted part of the galaxy. We are pretty far out on a spiral arm, after all. Maybe, for a variety of reasons other intelligences tend to not to leave signs. Maybe intelligent beings tend to move into simulations (a la Bostrom) when they can and then hide their servers from nosy corporeal beings. Lately, I’ve been favoring this answer. Maybe, we are just projecting our own growth oriented, expansionist outlook onto the rest of the universe. There’s plenty to do on your own home planet or your own solar system.

In any case, evidence that there is more life out there is evidence that there is more life out there. It’s not evidence that intelligent beings tend to destroy themselves. Cheer up, Nick, and get ready for the good news that there is life on Mars. I hope.