Tuesday, February 22, 2011

Ed Cloutis' PSERF: Feb 4, 2011

Plumes of methane on Mars as detected by Mike Mumma's group using the IRTF facility. Top concentrations are 45 ppb or so and are centered on the Nilli Fossae region of Mars.

Ed's talk was all about Methane on Mars, the discovery of which in the Martian atmosphere has, in his words, reinvigorated our exploration plans for the planet. Where in the past Martian Exploration was all about "Follow the Water" Ed contends that it is now "Follow the Methane." Certainly that makes sense from a Canadian Analogue Mission perspective with two separate groups (the other being led by Mike Daley of York University) running analogue missions to examine the problem of how rovers can help ferret out the sources of methane.

The talk wasn't a long one, but there were two major components. First, we got a primer on the current state of methane on Mars. Noted in the talk was the IRTF detection by Mike Mumma's group of methane plumes in 2003 (published in Science in 2009) and the detection of methane by Mars Express in 2004 (also published in Science). This was an exciting result, since Methane is not a stable gas in the martian atmosphere. Thus, the concentration alone suggests ongoing production. Furthermore, as Ed noted, the Martian atmosphere will mix entirely on a timescale of less than 10 years, so to find plumes of the stuff again argues for ongoing modern production.

What could that ongoing production entail? Well basically there are three known options. First, the region in question could have primitive rocks such as olivines which are undergoing a chemical process called serpentization as they react with water under warm conditions (perhaps as high as 300-400°C). Second Nilli Fossae might be the site of a recent comet strike and the frozen methane continues to be released (this seems rather unlikely). Or most excitingly, there could be life down there within the surface happily going about its business and metabolizing energy sources to produce this waste gas.

If I was a betting man, I think I would side with the geological story. There seems to be a lot of good context for water in that region and if the source is deep enough, you could have heat even though there is little evidence for volcanics in the area. Furthermore, OMEGA spectroscopy is directly comparable to regions on Earth where we known this sepentization is taking place.

What Ed is trying to do through his analogue mission is to simulate the kinds of tools that a rover might have at its disposal if it were expressly looking for methane, but he has hedged his bets and strapped on some astrobiology detection equipment as well. Over the next few summers, the rover will be poking around an Asbestos ("Serpentenite") mine in Quebec to see how the release of methane gas relates to what we see on the surface and the geological structure of the site (i.e. faulting).

I should note that there are still issues with the measurement and some teams have come out arguing that neither the IRTF nor the Mars Express group have a discovery above the noise. The two teams also disagree on the location of the plumes with the Mars Express team seeing large outgassings of methane from the northern polar cap in spring (released from a clathrate perhaps?) which Mumma's group doesn't see. But either way, there is certainly a great interest in the topic and much work going on as evidenced by the special issue in P&SS that was just released (v59, issues 2-3, feb 2011).

Hopefully, MSL will begin the work of unravelling this issue starting in 2012 and it can finally be put to bed in 2016 with the ambitious Trace Gas Orbiter mission. Notably, this mission has a significant Canadian Component in the form of Co-PI Vicky Hipkin and the participation of several Canadian Scientists, like York University's Jack McConnell. The real smoking gun is thought to be the carbon-13 to carbon-12 ratio. On the Earth, excesses of C-12 are associated with Life whose biological processes prefer the lighter isotope. What about on Mars? The answer to that question will have to wait.

For now, I leave you with this illustration of the Martian Missions on offer which are going after Methane. Note the originating article from Nature Magazine. The image itself was prepared by N. Spencer:

Author's note: this was the first presentation that I have been able to watch using UWO's new system for recording PSERF talks. By and large it was quite good, though the focus could do with improvement. I should point out one thing, however: there was a questioner afterwards who pointed out that the mixing time in the martian atmosphere should be much shorter than 10 years because of the large fraction of the atmosphere which condenses out on the winter pole. However, this would not be expected to create an incredible wind for one simple reason: the pressure difference is relatively low because Mars's overall atmospheric pressure is low. Winds on Earth are driven by pressure differences of a few thousand Pa (typically) or at most about 15,000 Pa in the case of strong hurricanes. However, on Mars, the entire atmospheric pressure is only about 600-1000 Pa. Thus, even a 25% or even a 50% difference doesn't create much wind.

No comments:

Post a Comment