Artist's concept of Titan surface beneath its foggy atmosphere. Courtesy NASA. Click to embiggenate.
Astronomer Mike Brown of CalTech (who tweets under the name PlutoKiller) has a fascinating discussion on his blog about fog banks hovering over Titan’s south pole. Titan, if you haven’t been following outer solar system news, is the largest moon of Saturn. It has this thick atmosphere hanging over a frigid surface which itself boasts pools of hydrocarbons in the form of liquid and ice. The hydrocarbons are in the form of ethane (on the surface) and now it appears that the methane forms fog banks in the atmosphere. Methane breaks down in the presence of sunlight to make ethane, so this whole thing seems to point to some sort of cycle between atmosphere and surface on Titan.
I say “seems” because, as Mike discusses, there’s a lot of atmospheric science work to be done to completely understand what’s happening on this shrouded world to make methane clouds form. Want to know more and see a cool pic? Run over to Mike’s blog and read what he has to say. He also has a link to his science paper outlining the fogbank on Titan and a nice, insightful discussion on peer review of his paper — and he invites folks knowledgeable in the Titan atmosphere to review his paper before it goes to publication. How cool is that!
Nili Fossae: one area where methane outgassing has been detected on Mars. (Mars Reconnaissance Orbiter image)
Within the past hour or so, planetary scientists reported the first definitive detection of the gas methane (often referred to as CH4) on Mars. However, contrary to some of the breathless headlines that are already floating around out there, this does NOT mean that there’s definitely life on Mars.
We need to be careful to understand what this means because methane IS one indicator of life on a planet, but it’s not proof that there’s life. The finding is proof that there’s methane. There’s a distinct difference.
Nonetheless, this is a very cool finding because it means that methane is definitely on Mars. It also means that scientists have detected WHERE it’s coming from on Mars and that it seems to be most evident during the summer season. In that sense, Mars is a living, breathing planet because it’s sending out gases from beneath the surface and that implies “action” of some kind.
Syrtis Major: another area where methane emissions have been found on Mars. (Mars Global Surveyor image)
The places where they found the methane emissions are called Terra Sabae (where there is also evidence of subsurface hydrogen), Nili Fossae (where there are hydrated minerals — meaning minerals that have been formed when water was added to another mineral to form a hydrate), and Syrtis Major (where planetary scientists have been studying evidence of a volatile-rich substrate (i.e. gas-rich areas under the surface)).
The big questions are: where is the methane coming from? What’s causing it to be released? Is methane being produced constantly on Mars? The answers are in the details and we don’t know all the details, yet.
Terra Sabae region on Mars: another spot where methane emissions have been detected. (Mars Mars Odyssey mission)
Where the methane is coming from is relatively easy to answer: it’s coming from under the surface through cracks or breaks in scarps in at least three regions.
What’s causing its release? Well, that’s an interesting question. It could be that water is seeping down through the surface and coming into contact with warm rocks (anything from body-temperature-warm rocks to hot, volcanic ones), which could heat the water to its boiling point. When the water does warm up and interact with the hot rocks, methane is produced and it escapes to the surface.
That’s one scenario. Of course, you have to ask; where did the water come from, and there could be a number of courses. One that comes to mind readily is cometary material — which is often methane-rich. But, comets and asteroids with methane would be the source of only a small amount of this methane. So, questions about the water need to be answered. And, what we may be looking at is the methane release from interactions of long-stored water ice with methane in it (what planetary scientists call a clathrate) that melted and reacted with warmer underground rocks.
Another source for the methane requires some kind of life form that produces methane as part of its metabolic process (the same way, for example that everything from certain microbes to cows, cats, dogs, humans produce gases here on Earth). If those microbes (and that’s probably what would be doing the production) exist on Mars — or (and this is important) existed in the past and produced methane, they would be sending their little methane signals out seasonally. If they produced it in the past, then what we may be looking at is the slow release of stored-up methane from old, long-gone biologic sources.
There’s still a lot of work to be done to understand the sources and mechanisms of these methane releases on Mars. And, as much as I’d personally LOVE to find out that these are proof of life–I’ll have to wait, along with everybody else, for more data to prove it one way or another. I don’t know about you, but I think it’s exciting news no matter what the ultimate source turns out to be. It shows us that Mars has a lot of surprises in store for us yet.
