Now that April is nearly here, it is time for the planetary science community to shake off its winter torpor, head south (mostly) and converge on the South Shore Harbour area of Houston like a vast mutation of thrushes, singing their songs twice over, recapturing their careless rapture and generally bigging it up. Yes, it's the 35th Lunar and Planetary Science Conference, the annual shindig that started with the first big symposium on moon rocks in 1970. The big talking points this year will undoubtedly be the papers giving results from MER and Mars Express, but the program (an interactive pdf download here lets you browse through the all sessions and abstracts, downloading as you go) contains all sorts of other goodies, too.
Particularly interesting is a special session dealing with climate change on Mars. There's a lot about evidence of surface activity that might fit in to some sort of ice age hypothesis (I blogged on this here). Mark Richardson and his colleagues have a number of abstracts looking at various aspects of this through their computer simulations of the martian climate. Their climate model is getting better as they work on it, and now manages to produce realistic looking dust storms in a pleasingly convincing way, which is probably a big step forward. As Bob Haberle points out, no Martian climate models yet deal with clouds well, which is one of the reasons why they still have to be taken, like the waters of Meridiani, with more than a pinch of salt. But then, earthly climate models aren't too good on clouds, either... (For more than you are remotely likely to want on matters cloudy, I have a monograph sort of thing here.)
Imperfect as they are, these models have a lot of insights into past and present climate on Mars. One of the Richardson et al abstracts seems to offer a way of getting some ice at low latitudes in more or less the same places that the gamma ray spectrometer on Mars Odyssey shows hints of such ice. And another of their abstracts throws up a peculiarly interesting and counterintuitive possibility. If you thicken the atmosphere, thus producing more of a greenhouse effect, you end up decreasing the number of places where there is any chance of liquid water. The greenhousing traps warmth and additional atmospheric pressure increases the boiling point, both of which will encourage liquid water; but the thicker atmosphere is much better at transporting heat away from warm places and towards cold ones, and that trumps the other benefits. So a colder Mars, in this case, is also a wetter one, if only in parts.
If you accept the "long diminuendo" view of the Martian climate, in which there was a thick atmosphere and a significantly warmer climate early on which slowly cooled and thinned out until you get to today, this finding would mean you that surface habitability (by which I just mean wetness) didn't simply drop steadily in line with atmospheric pressure. Instead, having started off high, the habitability would have crashed into what the authors call a "dead zone" when the pressures got down to about a tenth of a bar (10 percent of what it is on earth, 10 times what it is on Mars today). Then it would have picked back up under today's conditions. The idea that Mars is more habitable now than it was a billion years ago is a new and exciting one.
Another interesting area in the climate discussions is the asymmetry between the north pole and the south pole. The gamma ray spectrometer team argues that the ground ice in the north comes all the way to the surface, while that in the south has a dry insulating layer above it. They take this as suggesting that the Northern ice is more recent, and possibly actively growing. Bob Haberle and some colleagues find various things going on in a climate model that argue for water currently being trapped in the north, which would seem to fit. They also explore the idea that as recently as 25,000 years ago, when the planet was closest to the sun at the end of the northern spring, rather than in the southern summer as it is today, things would have been different. Water vapour might then have been given up by the north polar cap and its surrounding ground ice, rather than sequestered there. The idea that changes in the timing of the seasons with respect to the closest approach to the sun, rather than longer term changes in the tilt of the planet's axis, could be climate-change drivers is a fun one, because it makes everything more contemporary. I was first introduced to it by Mike Hecht at JPL, whose abstract on it from a meeting a couple of years ago is here, with some possible consequent implications for recent liquid water here.
Various presentations deal with aspects of the rover landing sites as seen from above, or theorised about. Phil Christensen looks at orbiter data and concludes that the evidence strongly favours a body of standing water in Meridiani. One of the arguments is that the haematite-bearing material seems to be confined to a vertically thin layer that's horizontally very broad; if the haematite was being made in a hydrothermal system, it's hard to see why it would sit at exactly the same elevation hundreds of kilometres apart (if its being made on a shallow sea bed, the constant elevation is much more likely). There would definitely have been a hydrothermal system in Gusev, though, if there was any water around at all just after the impact that formed it; Abramov and Kring have an abstract that says the rocks would have stayed hot enough for a hydrothermal system to last as long as a million years, and that there could be some distinctive mineralogical signs of it left over. The minerals involved -- vesuvianite, sepiolite, richterite and biotite -- are probably underground now, but may have been excavated by later, smaller impacts. Another intriguing abstract of conceivable relevance to the MER missions makes the case for looking for meteorites on the Martian surface as a way of tracking the climate. At LPSC a few years ago Phil Bland and a colleague estimated that there might be 10,000 meteorites per square kilometer on the surface of Mars; the number is surprisingly high because a lot of them fall and nothing gets rid of them. Because we know in great detail what fresh meteorites look like mineralogically, the ways in which these meteorites have weathered on the Martian surface could offer neat insights into past climates.
Elsewhere, Alfred McEwen argues that the crater-counting techniques used to date features on Mars aren't necessarily to be relied on for very young surfaces, and thus that some "recent" features may be a bit older than they have been taken to be. I'm not sure this changes things that much but the argument looks elegant to me, and in passing he makes a strong case that Zunil, a crater on the Cerebus plains, is the source of some of the Martian meteorites found on the earth.
Dirk Schulze-Makuch and some members of Vic Baker's "Tucson mafia" have a poster that goes over some of the ground we've been discussing in the comments to "We're going to be here a while...", specifically the question of what life does on a planet where the surface water disappears. Dirk was one of the people who got me interested in life in the clouds of Venus. Meanwhile Eors Szathmáry and various Hungarian colleagues develop further their idea that there may be bacterial mats on dunes near the south pole that lie dormant in the summer and winter, but become active briefly in the spring, when the frost above them acts as a physical greenhouse and allows the ice around them to mel, providing water. This sounds pretty unlikely to me, especially since the late David Wynn Williams was very sceptical about it, but ESA has shown interest in the idea, so maybe we'll get some more data next south-polar spring. If this unlikely idea is shown to have some promise, it will be hard to believe that Szathmáry and his colleagues didn't have some sort of inside knowledge, and a long held belief about Hungarians will look more plausible than ever.
NB, haematite is also known as hematite