This afternoon Gerhard Neukum (among many others) talked to us in the EGU press room, running through the results from the Mars Express High Resolution Stereo Camera with a beaming paternal pride. He stressed that strictly speaking the science phase of the Mars Express mission has not yet started -- the spacecraft is still being commissioned, which means that uninterrupted camera time has not been as available as he might have wished. Still, the HRSC team (42 researchers from 32 institutes in 16 countries, I think he said) has produced pictures of about 10 million square kilometres of the martian surface -- 8% of the total, and an area roughly the size of the USA.
Probably the most striking image he showed (I'll link when it's put on the web somewhere, but I don't think it is, as yet) was of an alp-sized mountain in the eroded eastern rim of Hellas with what looks like a rock glacier streaming off it, and a strange bright patch on top that Neukum suggested might conceivably be ice. But most of the talk was about volcanoes, and a map of the places that HRSC has taken pictures of so far sugests that this is because volcanoes have been the main topic of their research to date. Neukum says they are seeing evidence of volcanism 100 million years ago or less -- and sometimes much less -- in various volcanic calderas, and on the flanks of Hecates Tholus. They are also seeing evidence of what looks like melt water and glacial flow on some volcanic flanks that seems similar in age. That makes sense, especially in light of what people are now thinking about cyclical climate changes driven by changes in obliquity. If the climate was such that there were snowpacks on a volcano at the beginning of a period of activity, then the increase in surface heat flow due to active volcanism might melt it from underneath; water would stream down the flanks and then refreeze at the foot of the mountain. This might fit quite nicely with the ideas about glaciers on the western flanks of the Tharsis mountains that Jim Head, among others, has been getting into over the past few years.
Neukum also teased us, saying that the really hot results (I'm guessing this is a figure of speech, since HRSC doesn't have an infrared channel) weren't going to be discussed at this meeting, since he's trying to get them rushed into publication at a journal (I'd guess Nature). The gist of these results seems to be that some of the surfaces they have studied, in and around the Athabasca Vallis region in Elysium/Amazonis, are really, really young. The idea that parts of that region are very young has been around for some time. Ray Arvidson, who was also in the press room, pointed out that radar reflections from that area show a brighter, rougher surface than any other that's been studied from earth on any planet in the solar system, and that presumably means it's young. Existing images from MOC make it look pretty young, too, but there's been debate about quite how young. It sounds as though Neukum thinks he can now settle it in quite a dramatic way.
His advantage here is that HRSC produces high-resolution pictures of quite large areas, making it a much better tool for assigning ages to surfaces than MOC is. This is not a coincidence -- Neukum has worked on dating the surface of Mars for three decades, so it's entirely natural that the instrument he masterminded is well adapted to such a use. But as he admits, there's a nice irony to the results. For years, questions about how old any given surface on Mars was had two different answers. If you followed the Neukum (or Neukum and Wise) system, everything was really, really old. If you followed Bill Hartmann's system, some things were not quite as old as all that. Now Neukum, originally the champion of the oldest ages, the man to whom more or less nothing on the surface was less than a billion years old, is delightedly producing evidence of activity in the geologically very recent past. The inference I drew from his coyness was that when the analysis of the youngest region they've seen so far is published in the next month or so we'll be looking at an age of no more than ten million years, maybe less.
There was a fairly clear subtext to all this. Space missions, like the proverbial pudding, work better when they have a theme, a simple take-home message. It feels as though the emerging theme for Mars Express is that Mars is still an active planet -- not very active, but certainly not completely dormant either. The work on volcanoes obviously fits into this. Tomorrow there will be a press conference on methane where I imagine the same point will be made again.