NASA's Curiosity rover has been sniffing out Mars' atmosphere in search of methane. Methane is a precursor chemical for life. It's also thought that 95% of the methane in Earth's atmosphere is organismal in origin. Methane on the Red Planet would therefore be suggestive of past or present life.
But in a press conference held earlier today, NASA announced that their intrepid rover had yet to find any signs of methane bouncing about the Martian firmament. Curiosity's equipment is incredibly sensitive. Capable of detecting methane in quantities of just a few parts methane per billion parts of Martian atmosphere, it's possible there are some undetectable traces of the gas, but still "enough uncertainty," says NASA "that the amount could be zero."
So what does all this mean, exactly, in the search for life (or the potential for life) on Mars? Does the absence of some tetrahedrally bound carbon and hydrogen atoms preclude the possibility of life? Is Mars a barren, lifeless wasteland? Has it always been this way? Is Curiosity rover (as its rollicking twittergänger, @SarcasticRover, implied earlier today) really "ALL ALONE " UP THERE? ARE WE ALONE IN THE UNIVERSE?!
Hardly. I mean, maybe. Look, basically, we don't know. A methane-containing atmosphere isn't exactly a linchpin piece of evidence in the search for Martian life, or life-sustaining conditions; even if Curiosity HAD found traces of methane in Mars' atmosphere, that still wouldn't have been nearly enough evidence to say: "yes, there is/was life on Mars." Nondetection comes with the same caveat. Planetary scientist Sarah Horst summed up the situation nicely in a tweet:
"Important to remember: no CH4 [methane] does not equal no life. just like if they saw methane that wouldn't have been definitive evidence of life."
Nondetection also doesn't imply a total absence of methane. Given the detection of seasonal methane emissions from the Red Planet in 2009, one possibility is that the effects of methane sinks may currently be winning out over those of methane sources - some examples of which are depicted in the image below.
For now, it's important to remember that Curiosity's mission on Mars is still very much in its infancy. Methane or no, excitement surely awaits the rover in the months and years to come.
"Methane is clearly not an abundant gas at the Gale Crater site, if it is there at all. At this point in the mission we're just excited to be searching for it," said Curiosity scientist Chris Webster of NASA's Jet Propulsion Laboratory in a statement. "While we determine upper limits on low values, atmospheric variability in the Martian atmosphere could yet hold surprises for us."
Those surprises could even include traces of methane - just remember that this gas is not the end-all-be-all of evidence for (or against) life on Mars.