Understanding planets is harder than it seems like it should be. Us astronomers are off modeling the evolution of the universe from first principles as homework sets, while planetary researchers are struggling to make sense of basic chemistry happening right now, where we can see its effects.

To be fair, organic chemistry is a subject I dreaded so much, I convinced my advisor to let me take graduate-level stellar nucleosynthesis as a replacement for basic undergraduate organic chemistry.

One of the biggest organic chemistry mysteries of our solar system is the methane on Mars. Methane is an unstable molecule that breaks down in sunlight. When we see it, we know it has to have recently come from some source — typically a biological process or a volcanic-related process. On Mars, we see seasonal methane production using the Mars Curiosity rover, but we don’t detect it in the overall atmosphere using the Trace Gas Orbiter. 

In a review of recent papers, Germán Martinez, Anni Määttänen, and David Baratoux find the data is consistent with a small methane source existing on the northwestern rim of Gale Crater — a result that seems to indicate we were either very lucky in putting Curiosity where we did and finding Mars’ one lone methane source or that Mars is particularly good at destroying methane in its atmosphere and there are other sources of methane.

Scientists don’t like the “we got lucky” solution to any problem, and the idea that Mars has one and only one methane source is weird. At the same time, everything else we know about chemistry on Mars fits our understanding of chemistry, and it is also uncomfortable to think methane alone behaves super weirdly.

Bottom line: in looking through the research, they find the Curiosity measurements look solid and the lack of methane seen from orbit looks solid. And Mars is now more confusing than ever before.

More Information

The Mystery of Methane on Mars Thickens (Eos)

“Mars Methane Sources in Northwestern Gale Crater Inferred From Back Trajectory Modeling,” Y. Luo et al., 2021 November 4, Earth and Space Science

“Constraints on Emission Source Locations of Methane Detected by Mars Science Laboratory,” D. Viúdez-Moreiras, M. I. Richardson, and C. E. Newman, 2021 December 7, JGR Planets