There’s life on Mars! Maybe. Again. What’s going on?
Nasa has announced that the Curiosity rover has detected spikes in methane concentration in the atmosphere within the Gale Crater. Over the last 20 months Curiosity has sampled the chemical makeup of the air around it a dozen times, finding that normally there are seven methane molecules per ten billion other air molecules (which on Mars is about 96 per cent carbon dioxide) – except on two occasions, where it jumped to ten times that. That’s a big deal because methane doesn’t just linger around; it’s produced by some chemical process and then dissipates relatively quickly, so whatever’s producing it must be doing it recurrently and frequently.
We all have experience with methane production (particularly around the Christmas season, with brussel sprouts on the table), but it’s important to stress this isn’t a definitive proxy for Martian life. Sure, it could be microbes, but it could also come from the reaction of the mineral olivine with water, as this Nasa infographic shows, and that’s been the suspicion ever since methane was first detected in the atmosphere by astronomers in 2009. But we’ve always known that Mars’ methane is unevenly distributed, and possibly seasonal, and that there are a number of alternative sources for it than bacteria “burping”.
The announcement also included the news that the rock sample that Curiosity drilled into in May 2013 yielded further organic molecules when analysed, and also revealed important data about the history of the planet’s water – and when it was lost. What we can really say here is that we have even more evidence to support the conclusion that Mars was habitable and Earth-like (or at least from the perspective of microbial life) billions of years in the past, but also that we don’t know yet if it still is today.
Something we have to think about when we find life somewhere else – and we will find aliens, eventually, in centuries if necessary – is what the means for us, humanity, in the big picture. Statistically. Those of us who gamble might well consider it a bad omen.
There’s this idea that there’s a “Great Filter” which none, or very little, life gets through, on the cosmological scale. It was first outlined by economist Robin Hanson in 1996, and others have since refined it or challenged it, but basic premise is this: we haven’t met aliens yet because all intelligent life capable of star travel is killed off before it spreads beyond its home star.
We know now that the number of planets far outnumbers the number of stars in the universe, and that it’s therefore probable that there are billions upon billions of planets capable of hosting life. And, if life is like us, and works out how to colonise other planets and stars, we know that the amount of time it should take to colonise a large part of, say, a galaxy, should be short compared to galactic timescales – that is, if there’s a lifeform that can colonise another star, it’s reasonable to assume that it’ll colonise almost all the stars it can in pretty short order, at a rate of a few centuries perhaps. So, if there are lots of Earth-like planets with (presumably) Earth-like intelligence on them, where the hell is everybody? (This is the famous Fermi paradox.)
The explanation Hanson and others have suggested is that somewhere, between the emergence of single-cellular life and interstellar travel, there’s the Great Filter – many planets reach it, but few get through, because of asteroid strikes or runaway climate change or resource depletion or… anything we have yet to experience as a species. We can’t see anybody else, and the universe feels like an empty place, because the cumulative probability of making it through every step – a safe planet where RNA appears and then single-celled life and then multi-celled and then the evolution of a tool-using lifeform that then develops interstellar travel – is so low as to be zero.
What makes the possibility that life evolved independently on Mars (especially multi-cellular life) so worrying from this perspective, then, is that it means the first few stages of that process are even easier than we thought – and that means getting beyond the stage we’re at now must be much, much harder than we thought. The probability works out to tell us that we’re at the stage of biological and cultural and technological development where we’re wiped out before we take the next step.
There are, though, a dozen or more retorts to this: maybe intelligent life is intelligent enough not to have to colonise everywhere, or maybe it’s intelligent to the extent that it’s able to choose to remain invisible to us. But it’s still a sobering thought that the thrilling discovery of alien life could be one of the last great moments in our species before a statistically-likely mishap hits us from left field.