This morning Vladimir Krasnopolsky presented his paper, and he and Toby Owen then gave a press conference. There's not a huge amount to add to the discussion here. A few points do come up, though. One is that these people, particularly Krasnopolsky, are experts on atmospheres, and it shows. They aren't geochemists, and their belief that abiogenic sources can't produce enough methane should be understood in that light. They haven't, for instance, addressed the question of serpentinization. Similar caveats should probably be applied to the figures they offer on the amount of biomass. What they have is a careful and thoroughly worked through piece of spectroscopy and some other calculations of various worth intended to establish a context of interpretation that favours life over other sources.
One surprise, for me, had to do with the hydrogen that the methanogens might be assumed to be using (methanogens can make do without hydrogen, I think, using water and carbon monoxide, but I believe they get a lot more bang for their buck by using hydrogen and carbon dioxide). Krasnopolsky thinks of his hypothetical methanogens as things that make use of hydrogen from the atmosphere. As he pointed out, there's hydrogen in the atmosphere at a level of about 15 parts per million. I don't know if that's enough for a methanogen to go to town on, but Krasnopolsky thinks so, and points out that its a thousand times greater than the amount of methane. This hydrogen wouldn't diffuse very deep into the subsurface, but it would get some of the way in, and that, he imagines, might be enough; he talks of the methanogens being confined to the top 100 metres of the subsurface.
This is an interesting argument that fits with Krasnopolsky's predilections and scientific background. For a start he was the one who discovered the molecular hydrogen in the atmosphere, so it makes sense that when he thinks of methanogens using hydrogen, that's the hydrogen he thinks of. Secondly, using atmospheric hydrogen (produced by sunlight from water vapour) allows the methanogens to be independent of goings on in the planet's deep interior. Since Krasnopolsky et al argue that the planet is volcanically dormant, or even extinct, and thus can't be producing methane abiogenically, it would be a little inconvenient for them to have to invoke deep activity to provide hydrogen for the methanogens to feed on. An atmospheric source makes things easier for them.
If the methanogens use atmospheric methane, though, why are there so few of them? Some of Krasnopolsky's calculations suggest a total biomass of just a few tonnes, and he's adamant that we are talking about a few isolated oases, rather than a planetary biosphere. (In some ways, it feels that Krasnopolsky goes out of his way to minimise the amount of methane being produced. It struck me while listening to him that if you have strained for years to make such a subtle and delicate detection, you might be predisposed to thinking that the phenomenon detected is as marginal as you can imagine.) But shallow oases sound a little unlikely to me. It's much easier to imagine oases in the deep subsurface, making use of local heat and hydrogen in some sort of hydrothermal setting a bit like a deep ocean vent, but without the ocean. (That said, it may be easier to imagine just because I have more practise in imagining it -- it's a sort of conventional wisdom).
If the methanogens are in the shallow subsurface using atmospheric hydrogen, why aren't they doing so all over the place, or at least in quite a lot of settings? The obvious answer would be that although atmospheric hydrogen (=food) is available all round the planet, liquid water is available in only a few special places. But is that really plausible? What would be so special about them? It's not that I discount the possibility of near surface water; but I don't see how it could be at the same time possible and very, very rare. The best argument for subsurface water is that shallow aquifers might feed some of the gullies. But if that was so, and the methanogens live near the surface, why wouldn't all those aquifers be inhabited?
The disappointment of the press conference was that Vittorio Formisano didn't show. It's not entirely clear why not -- he was asked, but seems to have declined. He was in Krasnopolsky's talk, though, and asked a few questions that hinted that he thinks there may be more methane produced and more sinks to use it up. His team will be presenting their data tomorrow, presumably within their own context of interpretation. It's worth noting here that Krasnopolsky is keen to maintain his priority in this subject; he stressed to us that his team's abstract for this conference was the first published detection of methane, since Michael Mumma's presentation at the DPS last year was published only in abstract form, and the abstract says only that detection was attempted and details would be presented. Formisano's data, too, has still to be published -- but it will be on display tomorrow. Kransopolsky and Owen are eager to see the shape of his spectra.