Friday, January 30, 2009

Methane on Mars. Does this mean Life?

So, the science and popular press was all in a huff in the last week or two about the possibility of life on Mars because of the confirmation (first reported in 2004 in many popular press reports) that there is methane (natural gas to you earthlings; CH4 to us nerds) being generated on Mars.

Now, part of the problem is that NASA's PR people think nobody cares if it's not instantly life-changing for everybody. And in part, they're right.

But, come on! Is this really appropriate?

NASA: Martian Methane Reveals the Red Planet is not a Dead Planet

Who besides a geologist is going to interpret that as anything other than meaning there's life on Mars?

So, here's the deal.

In 2004, Krasnopolsky et al. reported that they had discovered methane in the martian atmosphere. In 2009, Mumma et al. reported that they had seen methane appear, disappear, and reappear over several martian seasons. The methane appeared in the summer time. The amount of methane detected is in the parts per billion (ppb).

Methane has, at most a ~350 year half-life in the martian atmosphere. The amount detected should have disappeared long ago unless it is currently (as-in right this minute, not "currently" as-in geologically) being generated.

So, there are two ways to make methane: geologically and biologically.

  1. Hydrothermal systems generate methane. We see no evidence for elevated temperatures or other features signifying a hydrothermal system.
  2. Methane Clathrates can generate methane when heated.
  3. Various volcanoes release methane.
  4. Methane hydrates (clathrates are a form of hydrate).
  5. I'm sure there are others that I don't know about
  1. Most (90%) of methane production on Earth is biogenic.
  2. That's really all I know. I'm not a biologist... ;)

So, we know that on Earth there's life, and most of the methane we find comes from that life. So, obviously this means there's life on Mars, right? Of course not.

Each of the geologic origins of methane has problems on Mars, but extraordinary claims require extraordinary evidence, and I think a claim that methane on Mars proves the existence of life on Mars is extraordinary.

Would I be excited? Of course! But, there's no reason yet for President Obama to open a new cabinet position dedicated to intrasystem relations.

Here's another thing. That 350 year life of methane I quoted above is for photodisassociation due to photons (from the sun) striking methane and imparting enough energy to break the molecular bonds that hold the carbon atoms to the hydrogen atom...


So, why is the methane disappearing so much more quickly than 350 years? That's the geologic question of interest to me. It's certainly not life destroying the methane. I don't know what it is. Perhaps there's a regular/periodic absorption and release of methane from clathrates or other hydrates? I'm not sure. I would love to know. Someone with more geochemistry background than I will answer this in the next few years. Whatever it is, Mars is becoming more interesting the more we study it... :)

In the meantime, rest assured that as soon as I hear anything about better evidence for life on Mars, I'll post it here.


Jennifer said...

The answer is so simple. Invisible Martian cows. Duh!

deborah said...

I think there's life.....not sure about the little green men part and of course this scientist I happen to know very well is the one who is going to download the first picture.....=)!