NASA's intrepid Mars rover, Curiosity, has detected methane on Mars—an indication that life may be present on the parched planet. Is it premature to get our hopes up, since the odds seem impossibly stacked against life?

Well, Occam's razor says that the simplest answer is probably the correct one. Instead of life surviving against the odds on the desolate planet, it's more likely that the methane we're seeing is actually from Curiosity itself.

"I am convinced that they really are seeing methane," said Kevin Zahnle, a scientist at NASA's Ames Researcher Center, who was not involved with the methane discovery. "But I'm thinking that it has to be coming from the rover."

It must be very embarrassing to try and sneak out a cheeky Martian fart and then have scientists gawk over the evidence for the next few years. 

The Mars rover didn't find any traces of methane when it sampled the atmosphere between October 2012 and June 2013. Then, a few months later, it mysteriously detected a wealth of methane gas. The positive result for methane continued for four months.

According to Zahnle, it wouldn't take much for Curiosity to fool scientists that Mars has methane pockets. The rover has its own tiny reserve of methane onboard. The amount isn't enough to contaminate Mars, but it might be disrupting the detector. While the evidence isn't entirely compelling that the methane is from the rover, it unfortunately can't be ruled out either.

"And while it's true that the concentration of methane in that chamber is 1,000 times higher than in Mars' atmosphere, the comparison is actually misleading. You have to look at the amount of methane, not the concentration," says Chris Webster, a research scientist at NASA's Jet Propulsion Laboratory. "The concentration of methane on the rover may seem high, but the actual amount is very small because the chamber is very small. To produce the amount we detected in Mars' atmosphere, you'd need a gas bottle of pure methane leaking from the rover. And we simply don't have it."

There are a few alternative theories about the presence of methane on Mars: It's possible that microbes living underground could produce it as a byproduct of making energy and then release the methane through vents in the ground. Alternatively, energetic light from the sun could give organic compounds on the surface of Mars enough energy to form methane. Differences in the soil could explain why the methane isn't detected everywhere.

However, another unverifiable theory is that the rover was contaminated with microbes before it left Earth. These microbes could be happily surviving on Mars and churning out their own methane that Curiosity is detecting. We already know that the rover was contaminated with Earth air before being launched into space. While it was eagerly sitting on the launch pad, some terrestrial air seeped into the laser spectrometer used to detect methane. 

Unfortunately, we can't ascertain whether the methane is coming from Curiosity or not since the only way to test for methane is by using the rover itself. 

Illustration of possible sources of methane on Mars via NASA

[Via Astrobiology Magazine]