You know what we don’t talk about enough? Martians.
No, not little green men—I mean real live organisms that we know currently exist on the red planet.
I’m referring to extremophile microbes–or microscopic organisms that have evolved to survive in extremely harsh conditions here on Earth. And how did these little dudes get to Mars? We sent them there, of course, and continue to do so every time we toss a spacecraft out to land on the red planet.
It’s practically unavoidable: Earth is simply swarming with invisible life, like a small sneezing child at the doctor’s office. Whatever comes from Earth is almost certainly contaminated. And once Mars is contaminated, we run the risk of false flags in the search of extraterrestrial life; we won’t know if any organisms we find actually had their origins on Earth. Not only that, but if there is indigenous life on Mars, our Earth organisms could potentially wipe it out or even alter the climate itself, as cyanobacteria once did on Earth. (You can thank them for the oxygen you’re breathing right now!)
The scientists who wanted to explore Mars knew about extremophile microbes, of course, even as early as 1958. The National Academy of Science passed a resolution that year that they would take “deep care” not to contaminate outer space with our filthy Earth germs at the risk of having them “make impossible forever after critical scientific experiments.” This was reaffirmed in the 1967 Outer Space Treaty, an agreement signed by 128 countries who promised not to send weapons into space to blow each other up, as well as “conduct exploration [of other planets] so as to avoid their harmful contamination and also adverse changes in the environment of the Earth resulting from the introduction of extraterrestrial matter.”
Contamination has already happened, though — probably the very first time Earth technology touched Mars in 1971, when the USSR landed (and promptly lost) the Mars 3 probe. The problem is that we can sterilize our spacecraft to the best of our abilities before we let them leave Earth, and we do, but we still end up with a few tough hitchhikers. In fact, with our harsh sterilization procedures, we may inadvertently be selecting for the hardiest, most-likely-to-survive-on-Mars microbes of all. And we know for a fact that some life on Earth can survive in environments mimicking the extremes of space. Indeed, in 2012, scientists simulating Martian conditions in the German Aerospace Center found that not only did some bacteria survive, some lichen did, too. That’s a big deal because the lichen was multicellular–and visible to the naked eye.
But how likely are these hitchhikers to be the kinds of extremophiles that can survive outer space? That’s a tougher question. Genetic tests of cloths used to wipe the outside of spacecraft have confirmed that some bacteria have definitely made it past the sterilization chamber, and a few have been identified, like the double-walled spores of fungus in the order Pleosporales. Those might be tough enough to survive the trip. And remember, as far as our knowledge of the microscopic life on Earth goes, we’ve only managed to identify and name an estimated 5 percent. If that. We have no idea of what most of the little guys are even capable of.
So: I hope I’ve convinced you at this point that life has pretty definitively made it to Mars. And if you don’t believe me, ask NASA! NASA scientist John Grunsfeld said at a press conference last year, “We know there’s life on Mars because we sent it there.”
But there’s another wrinkle to our tale: Microorganisms may be making the trip, but once they hit the Martian soil, what next?
Life might survive on Mars, but we’re not sure yet whether or not it can thrive there. Extremophiles may be able to withstand intense living conditions, but they may not be reproducing. Most organisms will hunker down and try to wait it out rather than waste energy making more of themselves in terrible conditions. Our experiments have yet to show that the thermophiles (organisms that can survive in high temperatures) who make it to Mars are of capable of, you know, making it there.
But it certainly isn’t impossible that thermophiles could reproduce on Mars, and if they do, we’re left with some interesting ramifications. I’m not just talking about a Mars rover finding microbes and calling them aliens when they’re really Earth imports. I’m talking more about what might happen if Earth life thrives and evolves in Martian conditions.
Will it rapidly evolve into those little green men we’re all familiar with, intelligent and intent on our destruction? Probably not. But since these microbes would be completely isolated from all other Earth life (barring whatever else we accidentally drop off there), they would no longer co-evolve as part of Earth’s ecosystem. And that’s kind of a big issue for us.
So far, I’ve been talking about a process called “forward contamination,” i.e., when we leave sticky little nuggets of Earth life in outer space. But there’s also a phenomenon tentatively called “back contamination,” where after a little jaunt through the solar system, that life comes back to Earth … and possibly wipes out the human species.
How is that a possibility? It’s not as though the microbes we accidentally send up there are super-dangerous to humans to start with. Why would living on Mars for a few hundred generations suddenly turn them deadly?
Essentially, we don’t know how a sample of Earth microbes, completely isolated from all other life, would evolve and change. All life that exists today has done so in the presence of other life. That includes pathogens and parasites, a.k.a. the things that make us sick. Paradoxically, most germs are actually evolving to become less deadly to their hosts over time, which makes sense if you think about it: An infectious disease that completely wipes out its food supply is not going to go far. Likewise, our immune systems have had time to adjust gradually to these evolving microbes. But what happens if we meet something we were never prepared for?
Naturally, this is only one possibility among many. Indeed, life evolving on Mars could go in the other direction and become completely incapable of living in Earth conditions. Or it could be harmless to humans, but disrupt Earth’s ecosystem in other terrible ways. We simply don’t know. What we do know, however, is that these Martian microbes would probably be pretty hard to get rid of if they ever come back to Earth. Remember, we already selected them to resist the very strongest of our decontamination protocols before we sent them up there.
Of course, spacefaring organizations like NASA are aware of all of this. In fact, Carl Sagan himself said in Cosmos (the book, not the show) that while it might be possible to return Martian samples safely to Earth, he would want to be very sure before attempting it. Likewise, the NASA planetary protection policy states that anything that touches Mars, stays on Mars. The only exception would be a sample inside a sealed, sterile container; upon reaching Earth, this container could only be opened inside a specialized facility designed to stop any microbes from escaping. Such a facility does not yet exist.
It looks like we won’t have a chance to meet the Martians, if any of them are reproducing, for a good while yet. But I don’t think we should fear them. After all, how incredible is it that there is life resilient enough to make it on Mars? Even if we never find life that truly originated outside Earth, it could very well be possible that as you read this sentence, new life is growing and evolving on extraterrestrial soil.