Last week, Curiosity made its strongest detection of methane on Mars yet. Its laser spectrometer instrument registered a methane spike of 21 parts per billion by volume (ppbv) in the Gale Crater, a region the rover has been exploring since it landed in 2012.
Generally, methane presence on Mars has a global average of 10 ppbv, so NASA is conducting follow-up observations to see if it can find where the unusually high concentration has come from.
What makes this so interesting is our knowledge of methane sources: it can be produced by living creatures. Hence, tracking down the source of methane on Mars could be a way to find out if there are microbes living in the extreme conditions of the Red Planet.
But it’s way too early to get excited, as microbes are certainly not the only potential source.
“With our current measurements, we have no way of telling if the methane source is biology or geology, or even ancient or modern,” said Mars scientist Paul Mahaffy of NASA’s Goddard Spaceflight Center.
Curiosity and other instruments have made a few methane detections over the years, but levels seem to rise and fall, and methane seems to appear and disappear again like a mischievous ghost.
It wasn’t until earlier this year that scientists realised two independent instruments had detected the same puff of methane in 2013. Tracking down where it’s coming from, and what’s creating it, is proving quite tricky.
And there are reasons to be cautious about jumping to any major conclusions. Here on Earth, we have a fair amount of methane – about 1,800 ppbv in the atmosphere as of 2011, of which 90 to 95 percent is generated by living or deceased creatures.
But when we look elsewhere in the Solar System, there are also plenty of geological processes that can generate methane abiotically, without the presence of life. On gas and ice giants such as Jupiter, Saturn, Uranus and Neptune, plenty of methane has emerged via chemical reactions.
Pluto has methane ice. Saturn’s moon Titan has lakes of liquid methane. The compound isn’t exactly rare in the Solar System, yet as far as we know, only Earth’s is a product of biological processes.
There’s another spanner in the works. The European Space Agency’s ExoMars Trace Gas Orbiter, with the ability to detect 50 parts of methane per trillion by volume in the Martian atmosphere, has been collecting data for a little over a year, and has so far come up completely empty handed.
So whatever methane there is on Mars could only exist very briefly on the surface before dissipating into the atmosphere.
The observations currently underway will help figure out more about this detection. Whatever they find – whether Curiosity does or does not detect the methane again – scientists at NASA will have more context to determine if the gas was transient, or local to the Gale Crater.
They’ve also been in contact with the Trace Gas Orbiter team at the ESA to see if an atmospheric detection was made at the same time. This could help locate the source of the gas, and calculate how long it lasts in the atmosphere.
Whether the source of the methane is biological or not, figuring out where it comes from will teach us something new about Mars. Keep watching this space.