Martian Methane May Come From Comets

A new explanation for one of planetary science’s big mysteries.

Methane plumes as discovered by Michael Mumma in the northern summer of Mars in 2003. Higher methane concentrations are shown in yellow and red.

At last week’s Mars Polar Science Meeting held in Reykjavik, Iceland, Marc Fries from the NASA Johnson Space Center and colleagues presented yet another solution to the long-lasting puzzle of methane detections on Mars: They could be due to meteor showers.

The authors noticed that all detections of methane plumes on Mars, either by Mars Express or the Curiosity Rover, have been preceded by close interactions of comets with Mars, which had previously been identified as likely sources of meteor showers on the Red Planet. Fries and his colleagues claim that an especially good case can be made for the large methane plume observed by Michael Mumma of NASA’s Goddard Space Flight Center in the northern Martian summer of 2003, which, according to the authors, is consistent with the break-up of the comet C/2007 H2 Skiff. The idea that Martian methane comes from cometary debris rather than the planet’s own chemistry might also explain why the methane vanishes much more rapidly than expected—by a factor of about 100—if it were due to other processes.

This new hypothesis, which the authors spell out in more detail in the journal Geochemical Perspectives Letters, joins three other proposed explanations for methane on Mars. One idea is that the soil in Gale Crater adsorbs methane when dry, and releases it to the atmosphere when the relative humidity in the Martian soil is high enough for perchlorate salts to attract water vapor from the atmosphere and dissolve in that water. Another possible explanation, known as the biological solution, is that microbial life on Mars is converting organic matter in the soil to methane when the microbes are in liquid solutions. Still other scientists have suggested that deep subsurface aquifers might be responsible for the outbursts of methane.

One advantage of the new hypothesis by Fries and colleagues is that it can be tested. Will future methane “spikes” correlate to meteor showers on Mars, or were past correlations noticed by Fries and his colleagues just a coincidence? It’s a good question for the ExoMars Trace Gas Orbiter, due to arrive at the planet next month, to tackle.

Get the latest stories in your inbox every weekday.