Nasa’s announcement on Tuesday that its Curiosity rover had detected wafts of methane in the Martian air was met with immediate speculation that life might be the source. It might. Communities of microbes could be living under the Martian surface and churning out the gas. Perhaps the corpses of long-extinct bugs are being heated in the Martian interior and vaporised into methane. But any number of other processes that involve nothing as spectacular as life can and do make methane too. The problem is that detecting methane alone is never enough to answer the question of whether or not we are alone.
“You need to know a lot more about what’s going on right at the source,” said Michael New, an astrobiologist at Nasa’s headquarters in Washington DC. “You need to know the context. It’s very hard to look at methane alone and say it came from life.”
It’s good to see that bit of caution, that bit of skepticism in the quote from Michael New. That’s how science is supposed to work.
The hints of methane are tantalizing, though. It’s been decades since yr. obdt. trained as a biologist and only a few years less than that since I worked in the field, that last stint being a few months in a microbiology lab in 1990-1991. But an abiding interest in the topic and a lifelong penchant for reading everything I can lay hands on has kept me reasonably current on the topic, and it’s easy to see how the wisps of methane on Mars could be a sign of biological activity under the surface. But, as NASA points out, there are plenty of possible non-biological sources as well.
Discovering life on Mars – or anywhere other than Earth – would be one of the greatest discoveries in the history of mankind. It would be a discovery with vast implications, implications affected subjects ranging from biology to physics to religion.
The linked article concludes: Good evidence for a biological origin for methane on Mars could come from measurements of the isotopes of carbon and hydrogen that make up the methane molecules. On Earth, at least, life tends to use lighter isotopes, so more carbon-12 than carbon-13.
Seeking those isotope ratios would be a good next step.