I got to Naples about nine o'clock Tuesday night, took the train to Pozzuoli, and first thing in the morning made my way to the quay, admiring the catches of the octopus fishermen as I waited for the ferry over to Ischia. This was probably a fairly daft trip to make, but what the hell -- there are worse places to see the day in than the deck of a ship cutting across the Bay of Naples, Vesuvius behind you, Capri to port, and the smell of wood smoke on the air.
I caught up with Vittorio Formisano at lunchtime, and asked him what was going on. Here's the gist. His presentation was basically what is now up on the ESA website: the data from the Mars Express Planetary Fourier Spectrometer (PFS) seem to show three patches of enhanced methane and enhanced water vapour in the martian atmosphere, one of which is over Arabia. Formisano puts some weight on the idea that these three areas are also the areas where the Mars Odyssey sees hydrogen in the shallow subsurface; if the hydrogen is a layer of ice, he suggests, water vapour and methane from could be pent up beneath it and leaking out, or something along those lines. Having talked to Bill Boynton -- who’s the principal investigator on the Odyssey gamma ray spectrometer -- a bit in the afternoon, I found him not terribly supportive of that interpretation. For one thing, the regions Formisano is talking about aren’t a terribly good match to the regions that Boynton and his colleagues have mapped out. For another, Boynton tends to think that the hydrogen they’re seeing in those low-latitude regions is more likely to take the form of hydrated minerals than ice. One piece of evidence for this view is that the same regions have high chlorine levels, suggesting the rocks there have been weathered, which would be a way of getting hydrated minerals to form.
Formisano’s notion that methane, like NASA, follows the water is, as I understand it, a new analysis, one that probably goes beyond what's said in the paper on martian methane that he and various PFS colleagues have submitted to Science. That paper, various people have now told me, has already been through one round of revisions at the behest of the journal's referees, and the revised and resubmitted version has still not satisfied all of those referees. It has not yet been accepted.
The talk Formisano gave was quite different from the talk one might have expected from his abstract, which the Enterprise Mission has posted on its website. That abstract, he told me, is "all wrong" and "a mess". That's not to say it's not the abstract that's in the abstract book for the meeting -- it is -- but he says it at no point reflected what he really wanted to say. I suspect the big issue here is that the abstract talks about formaldehyde, and that Formisano at the moment doesn't want to talk about formaldehyde, because he has a paper on the subject under review at Nature. Another factor could be that the abstract talks about a weirdly high level of formaldehyde (much higher than the level of methane) and Formisano may no longer think that that level is real. (The general assumption is that formaldehyde is made from methane and much shorter lived, so you’d expect it to be present at lower levels; and observations form earth tend to bear out those expectations.) Given the way in which he’s not talking about it I’d be very surprised if Formisano doesn’t think he has a formaldehyde measurement of some sort or other, but he's adamantly saying nothing to the press or, apparently, to his colleagues on the subject for the time being. As always, it’s worth noting that the referees at Nature may not think the data strong enough for publication, and even if it is published other scientists may not buy the story. We’ll see.
For what it's worth, Formisano gave absolutely no indication, nor any impression, that he was under any sort of duress or pressure to change his presentation.
One other thing about the abstract is that it talks about hydrogen fluoride. Formisano didn't mention it in his presentation, but when we chatted it seemed to me he was saying that he thought he had indeed spotted some. If so, it appears that that would be pretty good evidence of current igneous activity. He wouldn't talk about levels, but he did say that there had been a misprint in the abstract, and we’re talking parts per billion not parts per million.
I asked Formisano about the ammonia story, and here's his version. He says they were asked by the Beagle team to look for ammonia, since it was the gas used to inflate Beagle's airbags. Ammonia seen in the atmosphere over Isidis very shortly after the Beagle loss would have been likely to have come from the airbags, and that would have been interesting to know. I remember Colin talking about the possibility of such a search in the days right after the loss. However, Formisano says they didn't do it. He also says that the relevant markings on the spectrum that was posted on the ESA website were there as indicators of where one might look for particular compounds, not as tentative identifications. That seems plausible to me. I don’t know if it’s the whole story, but it covers a fair bit of the ground.
After lunch (a very nice lunch indeed, shared with Friend Of This Blog Leo Enright) the highlight of the day's talks was another methane presentation, this one by Formisano's collaborator Sushil Atreya of the University of Michigan. The talk wasn't about the evidence for methane; it was about how a methane level of 10 parts per billion in the martian atmosphere could be explained. (Just to recap; ten parts per billion is the average level that the two earth-based teams which have reported observations of methane say they see, as well as the average level the PFS people are talking about. Much more here.)
The gist of the talk was that a steady state level of 10ppb requires a flux of 126 tonnes of methane a year (in the units used back here, that's about a thousand cows. I think Atreya uses a longer lifetime for methane than I did, and thus needs a smaller supply). That said, there's no requirement that Mars be in a steady state. Specifically, the insertion of a large amount of methane at some time in the past by a comet impact could explain a much lower level now -- we'd be seeing the 10ppb tail of something that had once been much higher and would eventually settle down to zero again. If my notes are right, Atreya suggested that a 200-metre-radius comet that hit 500 years ago would do it, assuming a 600 year lifetime for methane. Years of kibitzing on debates over the hazards posed by near-earth objects make me think that that sounds pretty unlikely. Most of the hazard on earth comes from asteroids, not comets, and a hit by a comet that size would be expected to be a pretty rare event. (There is a minority opinion in the NEO community which would say that comet chunks of this size are actually more common than the rest of us think -- Hi Duncan -- but let's let that slide for the time being).
A comet impact is the least interesting of the mechanisms for providing martian methane, but it's also nicely testable. If this is what happened then a) the methane levels are going to be homogeneous the whole planet round and b) they'll be dropping over time.
The other possible exogenous source -- meteoritic dust -- doesn't deliver remotely enough methane to make a difference, according to Atreya's calculations.
Since there's no way to make methane in the atmosphere, that leaves us with the subsurface. Atreya pointed out that both high temperature and low temperature reactions between water and basic rocks in the presence of carbon dioxide could produce methane. He cited work by others which suggested that a warm wet early Mars could conceivably have produced 10^15 tonnes of methane through aqueous alteration of basalt. If a small fraction of that had been squirreled away as methane clathrates, it could be enough to give the flux needed today. On the other hand, if there's subsurface igneous activity in the presence of water today, the stuff could be being generated fresh. On the gripping hand, it could be being made by methanogens, using either carbon monoxide and water or hydrogen and carbon dioxide.
What about the spatial variation in the methane? At first blush it looks almost impossible. Methane given off at a particular point on the martian surface would be spread through the whole atmosphere in weeks or at most months, after which it would stick around for centuries. This implies that almost all the methane in the martian atmosphere will be well mixed at any given time. But both Atreya and Formisano point out that it's possible methane has a much shorter lifetime than has previously been thought (something they were already hinting at back in Nice). The calculations that give lifetimes of a few centuries assume that the methane is destroyed only by chemicals in the atmosphere. If chemicals on the surface play a role too, then a) the life time could be a lot shorter and b) you could get more regionality if the chemicals to blame were concentrated in particular regions. It’s also worth bearing in mind, Atreya pointed out, that atmospheric chemicals are not in fact evenly spread out: he showed a recently made map of hydrogen peroxide in the martian atmosphere in which the concentrations varied quite a lot from place to place.
One particularly interesting thing Atreya said came almost as an aside. Without going into detail, because it's other people's ongoing research, he seemed to hint that there was a possibility that some abiogenic ways of making methane could also make formaldehyde. I'll try and find out a little more about this; if it’s true it may be important in the months to come. I suspect significant HF, some formaldehyde and a plausible story about an abiogenic source for that formaldehyde might strengthen a purely igneous story.
As I mentioned in the previous post, this all makes the prospect of seeing under the surface with Marsis amazingly tantalizing. But there's still no definitive word on the safety of the deployment. Apparently some simulations of the deployment have the long thin radar antennae springing out then springing back and hitting the dish of the high gain antenna -- the antenna through which data get sent back. That's really not something you want to happen. However other simulations show the antennae just springing out and staying put with grace and decorum. It seems no-one yet knows which models to trust. There's going to be a big meeting about this at JPL on October 5th, apparently. If deployment goes ahead, the likely date would be November 15th.
The politics seem to be rather as I'd imagined. The Marsis people are keen to be up and running as soon as possible, and very keen indeed to be up and running by next March, when their radar will be in a position to probe the foundations of the north polar ice cap. People working on other instruments are less gung-ho, and don't see why they should risk the whole mission this way. Why not wait a bit first, and deploy Marsis when the spacecraft has already taken a Mars-year’s worth of data. Among other things, that would make the case for an extended mission over a second Mars year a sure thing (though things would have to get pretty damn dire for ESA to close down a functioning spacecraft round Mars just because its primary mission had ended). But every day in orbit is another day that things might go wrong regardless of whether Marsis is deployed, and if the mission is lost to something else first we won’t see the deep subsurface until 2012 or so. Which option would you choose?
There were various other interesting things -- including the fact that MRO is a real spacecraft these days, with some of the instruments integrated to the bus and all. (And the interesting insight that although the O stands for Orbiter, in one crucial sense it’s a lander. In order to get the best data back -- a staggering 34 terabytes of the best data, according to current plans -- MRO is in a low orbit, so low that at some point after the mission is over it will fall to the surface. Because of this, in planetary protection terms it’s being treated as a lander and sterilised appropriately.) But having now hydrofoiled back over the bay (hydrofoils are neat, but they’re also fundamentally disappointing, because though the idea of flying over the water is cool, the sheer amount of work the engines do to make it possible kind of rips the poetry apart – flying’s meant to be easy); flown back over half of Europe; and struggled home from Gatwick, and what with it being unpleasantly late, I’m going to post and sleep.