301 — Background levels of methane in Mars’ atmosphere show strong seasonal variations

The Curiosity rover has been collecting laser spectrometry from the Gale Crater area for around five years now. And from that rich dataset comes an amazing finding: The background levels of methane in these measurements varies pretty drastically, and in sync with the seasons. No one knows yet for sure what causes this variation.

On Earth, methane is usually a product of biological processes: Methanogenic archaea, for example, produce most of the methane on the planet as a product of the reduction of CO₂ to H₂. (The methane that comes out of the worse end of cows and sheep is a biological product of these bacteria, not of the animals themselves.)

Even though prior Earth-based research has shown variance in the level of methane on Mars, none of the measurements appeared to reflect the seasons. This probably means that the shifts are relatively local.

Some hypotheses for the seasonally dependent (greater in the end of northern summer) source of the methane include large underground stores that are released in waves that correspond to the condensation and submimation cycle of the polar caps; actual methanogenic bacteria as we see on Earth; or perhaps some other mechanism (such as UV light) for the degredation of organic compounds delivered via meteor.

No matter the source, it is clear that there are atmospheric processes taking place on Mars that we are only just now beginning to learn about.