MainlyMartian

The Elysium Sea?

Rather than go on about Carol and Larry -- since I think most of what needs to be said is there in the links from the previous post -- let us turn our minds to thoughts of the sea. In an abstract for the Lunar and Planetary Science Conference, which will be held in March, a team using the high resolution camera (HRSC) on Mars Express, makes the case that there was a sea the Elysium region of Mars in the very recent past -- ie the last 5 million years.

The abstract was picked up by New Scientist who seem to me to have done a very good job of it. The gist of the story is this: a flood pours out of the ground in the Cerberus Fossae region and drains into a local basin, about 800km by 900km, where its surface freezes and gets covered with ash. While fresh water and volcanic heat keep getting added the system stays in flux, with plates of floating ice being formed and broken up in the flow. When the volcanism ceases, the whole thing freezes; the plates of dirty pack ice are set into a matrix of fresher ice, which unlike the pack ice is not covered with ash.

The dirty pack ice is fairly stable, because of its cover of insulating ash. The cleaner ice in which the pack ice is set, though, starts to sublime -- to turn straight into water vapour. As this ice starts to sublime, its surface gets dirtier, because sediments that were in the water when it froze are left sitting there on the surface after the ice sublimes. As this "lag deposit" of sediment builds up the sublimation slows down.

This seems a pretty good job of explaining what the cameras (HRSC and MOC) see. This sort of "platy" landscape has been seen and discussed before, with lava and mud flows also suggested as explanations. But to act in this watery a way, the lava would have to have incredibly low viscosity. Water really does, at least on first inspection, seem a much better option. If water is the explanation here, then it probably fits for other platy landscapes, too. If this is a fossil sea, then there are more of them.

The open question is whether any of the ice remains. It might all have slowly sublimated away, leaving the lag deposits on its surface draped over what was previously the seabed. Or some of it might still be there. The case for it still being there is that craters in the area seem to be filled in by something, and that the surface is very very flat. Good arguments, but not entirely compelling.

At 800km by 900km, and about 50 metres deep, the putative sea is about the size of Europe's North Sea. Crater counts on the surface put it at about 5 million years old -- with the plates a touch older than the stuff in between (I imagine there are decent sized error bars on that). That's a really respectable body of water to have gush out of the subsurface -- and if there's life in that subsurface, all that water should have carried some of that life up with it. The silty lag deposits on the surface should have little microbial corpses in them -- even if there's no ice left under them; they'd effectively be seabed sediments laid out on the surface. How well the corpses are preserved is of course an open question.

Needless to say, the response to this paper will be fascinating to watch. If the morphological arguments carry the day and it is accepted as evidence for a real sea, then Mars has a new "most interesting place".

After all this excitement, a note on propriety. When New Scientist reported this story, it did so on the basis of the abstract, freely available at the LPSC site, which it followed up with insights from a scientist who was not on the team (the lead author, btw, is John Murray at the Open University). After the New Scientist story hit the web, the abstract had a big red headline added to it to the effect that the material within was under embargo by Nature until mid-March. The inference I draw from this (I've not talked to the principals) is that the work has been accepted by Nature, and Nature sees the abstract as a form of prior publication, which it doesn't want. I can see their point -- but in this case trying to embargo something freely available for all the wired world to see, and which has been reported on entirely legitimately by a good magazine, just seems silly. And refusing to publish the paper now would look pretty silly, too. I'm sure the editors at Nature wish the researchers hadn't published the abstract -- but the paper wouldn't have been accepted by LPSC, where it needs to be presented and discussed, without an abstract. Anyway, this is the way things have turned out, and it seemed to me it would be rather silly not to comment, seeing as the story’s out there anyway.

Formaldehyde again

As Rick Sterling has kindly pointed out in the comments, there's been movement on the Formisano front. Jenny Hogan at New Scientist reports that he is now claiming very large amounts of formaldehyde have been picked up by the Planetary Fourier Spectrometer that he runs on Mars Express. He thinks the formaldehyde is being made as methane is oxidised, and that the formaldehyde level he sees is equivalent to an annual production of 2.5m tonnes of methane. It's near impossible to see how that much methane could be made by any process other than life. This is presumably the stuff he was keeping quiet about on Ischia. He's going to be talking about these results at an ESA meeting this coming week.

I've posted on the formaldehyde story before. And, even more now than then, I think Formisano is making a mistake. As Jenny points out, so do a number (quite possibly, from what I hear, all) of his colleagues on the PFS, including those who have more experience modelling atmospheric chemistry and interpreting spectrometer data than Formisano has. I don’t want to rehash everything in the earlier post on the subject, but the gist is that a) formaldehyde is expected to have a very short lifetime in the atmosphere, and thus it is very hard to explain how there could be so much of it and b) earth-based telescopes have looked for the stuff and found no evidence for it even at levels far lower than those that Formisano appears to see.

In addition, I’ve spoken to someone who’s seen the data and has a quite good theory as to what might be up. While no one else thinks there’s any formaldehyde in the atmosphere, everyone agrees that there’s carbon dioxide -- the atmosphere is almost entirely composed of the stuff. And carbon dioxide has some complexities. Since there are two stable isotopes of carbon (12 and 13) and two stable isotopes of oxygen (16 and 18) there are in fact six different possible types of carbon dioxide molecule, all with very slightly different spectral features and present in the atmosphere at very different levels. In the area of the spectrum that Formisano is looking at, around 3.7 microns, you’d expect some little features due to minority isotopes, and it seems plausible that this explains what Formisano is seeing. I believe this has been pointed out by reviewers of a paper Formisano has written on the subject, which may be why it hasn't appeared anywhere yet.

Another relevant point here is that there are two different regions where formaldehyde signals might be looked for in the PFS data. The 3.7 micron region is where one would expect a weak signal; the 5.1 micron region is where one would expect a stronger one. But Formisano seems to have said nothing about a signal in the 5.7 micron region, even though, at the sort of formaldehyde levels he’s talking about, you’d expect something quite visible there.

I think Formisano has put together a very good instrument, and that he’s also a nice guy. But on the issue of formaldehyde, he seems mistaken.

I’ll try and post on the Carol Stoker and Larry Lemke story (mentioned in comments here) a bit later, but for the time being it seems to me that that comment thread sorts out the story pretty well. Take note of this, a comment on the matter by Carol, relayed to us by Penny Boston and Phil Plait, and provided in the comments here yesterday by Bruce.

Steve Squyres rocks

That title was originally going to have a possessive apostrope in it, but I decided to leave it off. Yesterday Steve gave a simply wonderful hourlong overview of the rover mission at a packed plenary session of the AAAS meeting here in DC. It was a straightforward narrative of the two transits to date, taking in the highlights -- nothing new, and no hyped up drama. But it was just so nicely and winningly put together, and it brought home the essential wonder of the undertaking so well, that I felt it needed salute.

A few things that stood out. One is the remarkable ground track of Opportunity's landing -- the way that it took a right angle turn, as far as I could see, on the first bounce so as to trickle down into Eagle crater (I also hadn't fully taken on board the pun in Eagle's name -- Apollo 11 hommage and hole-in-one on a three-par). Another was the clear evidence in the lower levels of Endurance crater that wind-blown dunes underlie the water-borne sediments, very strongly arguing for a marginal environment not a sea: "This is a place that was only wet occasionally". Then there was interesting fact, doubtless fully appreciated by those keeping up with things, that the horizontal boundary between the highly-chemically-altered sediments and the less altered ones originally seen in Eagle crater -- the Whatanga contact -- is not quite parallel to the physical layering in the rock, another indicator that a lot of the water actvity was later on and subsurface, as the chemistry suggests.

Another neat thing was that after seeing a meteorite by the heat shield, they saw what looked like another, complete with a disturbed bit of regolith where it might have landed -- but this rock turned out to be a martian native, which is presumed to have been thrown through the air by an impact.

Also highlighted was the abrupt nature of the geological change at the foot of the Columbia hills. One moment Spirit was surrounded by lava rocks of the sort at the landing site; and then it never saw another of them again. Now it's among rocks that seem ever higher in salt content, in what's either a pyroclastic or impact-generated suite of rocks subsequently thoroughly doused in water.

And with any luck there's more to come. There are bold objectives and a chance to actually get to them. The death of an electronics component is probably now what will finally kill the rovers, and we can't know when that will be -- so the missions have taken on an intriguing mixture of long-term planning and living every day as if it were their last.

But the real wonder was just a year of this remarkable team doing their thing on Mars with the magnificent tools that they worked so hard to build and to get there.