Martian Methane May Come From Comets

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.

Dirk Schulze-Makuch | | READ MORE

Dirk Schulze-Makuch is a Professor at the Technical University Berlin, Germany, and an Adjunct Professor at Arizona State University and Washington State University. He has published eight books and nearly 200 scientific papers related to astrobiology and planetary habitability. His latest books are The Cosmic Zoo: Complex Life on Many Worlds and the 3rd edition of Life in the Universe: Expectations and Constraints.

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