5 March 2010
Wednesday started off with a summary of results from the Opportunity rover, given by Steve Squyres. He started off talking about the several iron meteorites discovered in the past year. I thought it was particularly interesting that there are hematite blueberries on top of some of the meteorites: the blueberries are way too big to be lifted by the wind, so that means the meteorite must have been buried and then exhumed! Another find out on Meridiani Planum was Marquette Island: a strange rock that is unlike any other seen on Mars, or any of the Mars meteorites. It is probably a chunk of ejecta from a distant impact crater, but it isn’t clear exactly what kind of rock it is. Squyres suggested that it was a crystalline igneous rock, but in a later talk Duck Mittlefehldt seemed to favor a “clastic” origin, meaning that the rock is made of small fragments stuck together.
Finally, Squyres talked a bit about Opportunity’s current location, Concepcion crater, which is the youngest crater ever encountered by either rover. The coolest thing that he showed was a block of ejecta which had one side coated with a plate of blueberries, probably the result of hematite precipitating out of solution along a fracture.
[Update: Emily has an excellent and more detailed summary of Steve’s rover update and the debate over what the heck Marquette actually is.]
A later talk by Hap McSween took a look at the composition results derived from the TES and GRS instruments in orbit and the APXS on the ground. TES is an infrared spectrometer so it only sees the upper few microns of Mars, while the Gamma Ray Spectrometer samples tens of centimeters into the surface. The two datasets give different predictions for the surface composition. Oddly enough, even though surface APXS measurements only detect the upper few microns, they match more closely with the GRS results. McSween suggested that perhaps thin, ubiquitous layers of dust were tainting the infrared signals, but not the GRS or the brushed surfaces of rocks analyzed by APXS. Another possibility suggested by Steve Ruff was that sulfates can actually look quite similar to silica in TES spectra! If that’s the case, sulfur might be messing up the calculated compositions from TES and Mini TES.
The rest of the morning was filled with quite a few other talks about iron and magnesium-bearing minerals on Mars, but some of the most interesting talks of the day were in the afternoon planetary atmospheres section.
The first atmospheres talk was given by James Lyons for Kevin Zahnle, who wasn’t able to make it. Zahle called the recent methane detections into question by pointing out that the observed methane band might be due to methane in the Earth’s atmosphere that wasn’t properly removed from the spectrum. Unfortunately the authors of the Mars Methane paper that was being questioned weren’t there to respond, so I don’t know whether they took this into account in their atmospheric corrections.
Another talk by Malynda Chyzek focused on modeling methane on Mars. She found that, with some assumptions about the rate of methane destruction, the rate of methane production predicted in previous papers might be about 30 times too low! To put the revised production rate into perspective, she calculated that it would require about 5 million cows to produce the same amount of methane, placing the population density of cows on Mars at about 2 millicattle per acre.
Another really interesting atmospheres talk by Spiga (I missed his first name) showed the effect of Katabatic winds on surface temperature. Katabatic winds are winds that blow downhill due to gravity, and they occur on broad high slopes like those on the polar caps or Olympus Mons. The thing is, as the wind heads down in elevation it gets compressed and compressing gas heats it up. The warmer gas then warms the surface, which can have a big effect on orbital measurements of thermal inertia, and that means that we have to be careful about using thermal inertia to infer what type of material the surface is made of in locations with strong downward winds.
There were several talks about modeling the water cycle and rainfall on early Mars. Soto (again I missed his first name) made an interesting comparison between areas of predicted rainfall and areas where valley networks are visible. He found that with just wt soil, there isn’t much precipitation, but with a northern ocean, the rainfall patterns match pretty well with the location of valley networks. The lack of valley networks toward the south pole makes sense in a model like this because all the water is in the northern hemisphere, and it would rain out on the slope up to the southern highlands, leaving a desert in the center of the highlands (the south pole).
Some of the other atomospheres talks considered the early atmospheres of rocky planets. Jenny Suckale gave an interesting presentation about the possibility that early atmospheres formed by “catastrophic degassing” of the magma ocean rather than gradual release of the gases. The idea is that as the magma ocean is cooling, it solidifies from below. That pushes the volatiles in the magma up into the upper layers until it becomes saturated and bubbles begin to form. Once the bubbles start to form, they can cause parts of the magma to become more buoyant, and as the magma rises more bubbles form. This might cause sudden a sudden violent release of gas from the magma (similar to the sudden catastrophic release of gas from a shaken can of pop).