3 March 2010
Well, I made it to Houston about a day later than expected so I missed all of the monday talks and sessions, but I took notes yesterday and I’ll share some highlights here.
The day started off with a series of talks about terrestial planet cryospheres. In other words, ice on Mars and the earth. Robert Grimm gave the first talk, describing his latest model results for groundwater and ice on Mars. His model showed that it doesn’t take very much water to reproduce ice distributions like those seen on Mars today.
But in the following talk, Steve Clifford had some criticism for Grimm’s model. In particular he pointed out that it is incorrect to say that once the water ends up in the atmosphere it is lost: it spends some time in the atmosphere before being lost, and in that time it can precipitate out at the poles as frost or snow. And if the polar caps grow thick enough they act as an insulating blanket, trapping the planet’s heat and causing their base to melt and recycle water into the subsurface.
Next up Jeff Plaut gave a cool talk about thick lobes of ice that have been discovered using SHARAD radar in the Deuteronilus Mensae region. The ice is surprisingly pure, and it preserved by a layer of rocky debris on the surface. He said that the amount of water trapped as ice in Deuteronilus Mensae (6,325 cubic kilometers) is comparable to the volume of Lake Michigan: a small amount compared to the total amount of ice on Mars, but still not insignificant.
A later talk also focused on Deuteronilus, and showed some of the really bizarre shapes formed by the ice and the debris on top of it. I could describe it, but I’ll let this HiRISE image do the work for me:
Later in the afternoon, after having a nice lunch with some of the ChemCam team, I headed over to check out the Dunes session. It began with a talk by Jani Radebaugh about dunes on Titan and the Earth. It turns out that Cassini radar observations of Titan reveal huge expanses of linear dunes near the equator. The dunes are probably made of grains of ice and organic molecules, and they tell a puzzling story. The shape of dunes can be used to infer the wind direction, and that’s just what Radebaugh has done, but the confusing thing is that her inferred wind directions are completely opposite what is expected from atmospheric models!
Another talk in the dunes session, by my friend Lauren Edgar, took a close look at the crossbeds preserved in the walls of Victoria crater, where the Opportunity rover spent quite a lot of time. She suggested that the patterns of beds seen in the walls might be explained by a “draa” which is essentially a giant dune with smaller dunes on top of it. This would be evidence of a big, well-developed sand sea in Meridiani in the distant past.
Matt Chojnacki, a fellow pancam PDL, gave another interesting talk where he showed some observations of sand dunes in Endeavor crater that disappeared. This is a big deal because despite all the wind and sand on Mars, there is only one other case where sand dunes have actually been observed to move from orbit.
Finally, Matt Golombeck gave an interesting talk, using evidence from the fresh craters that Opportunity has visited in Meridiani to constrain how old the ripples are. He found that the ripples that are ubiquitous in Meridiani probably last moved sometime between 100-300 thousand years ago. He also made the interesting observation that the fresh craters have no hematite blueberries exposed in their ejecta. Essentially the explosion from the impact blows away the blueberries on the surface, and until the ejecta rocks erode to expose new blueberries, they are much rarer near the crater.
That pretty much sums up Tueasday. I wish I could report from the poster session, but I had a lot of visitors at my own poster and didn’t get the chance to look around at any of the other posters!