The case of the disappearing-reappearing Martian methane

Acme Disappearing-Reappearing Ink, from "Who Framed Roger Rabbit?"

Acme Disappearing-Reappearing Ink, from “Who Framed Roger Rabbit?”

Methane on Mars is a huge deal, so much so that every announcement finding evidence for it in probe or telescope data gets a big media hoopla. That’s because methane is a common byproduct of life as we know it, though some non-biological processes make it too. (We’re pretty certain, for example, that the methane on Neptune isn’t made by ice bacteria burps.) Whatever the possible source, though, the Mars Curiosity rover is the latest in a long line of missions to turn up tantalizing signs of methane.

The problem is that it isn’t so easy to just say “here is methane, and it comes from process X” (where X could be microbes, Martian cows, or some geological chemical reaction). And the situation is complicated by the way the methane behaves: rather than a steady supply, the amount in the Martian atmosphere increases relatively quickly, then decreases again as abruptly. That’s weird, and could mean we aren’t measuring quite what we think we are, as I explained for The Daily Beast:

All of this depends on Martian methane being a real thing, and that’s where it could get sticky. Kevin Zahnle, Richard S. Freedman, and David C. Catling argued persuasively in 2010 that there’s no realistic way for Mars’ atmosphere to get rid of that much methane that quickly, even if it can be produced on a short timescale. Instead, they argue that the methane analysis from other probes is based on assumptions of how the data is processed, and could be entirely an artificial result.

That doesn’t necessarily mean the methane isn’t real, but it does mean researchers have more work to do to figure out exactly what could cause rapid chemical fluctuations in Mars’ atmosphere. [Read more….]

I want to make it clear, in case it wasn’t in my Daily Beast piece: this is a tricky measurement, largely because the amounts of methane gas are so tiny. I asked Kevin Zahnle, one of the authors of the earlier critique of methane measurements, about this issue, since he has a soon-to-be-published response to the latest Curiosity paper. While I’m not sure if I should quote his specific comments yet (you can’t get them from the Science website, and they aren’t even embargoed), suffice to say he thinks there isn’t a definitive detection of methane yet.

While we all may want to see methane on Mars (with or without life involved), it’s important to be that much more careful in understanding what we’re seeing, and knowing what makes the measurements behave as they do.

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