17 December 2009

AGU 2009 – Day 2

Posted by Ryan Anderson

I started off day 2 of AGU at a couple of lunar talks showing off data from the Lunar Reconnaissance Orbiter. Unfortunately, I missed the early sessions about the high-res cameras, but the bright side was that I learned abount some instruments I was less familiar with. First was the Lunar Orbital Laser Altimeter – LOLA. A similar instrument on Mars Global Surveyor, MOLA, revolutionized our view of Mars. The MOLA map has become the standard to which all other mars maps are registered, and LOLA is going to do even better for the moon. LOLA works by sending five laser pulses in a pattern similar to the spots on the “five” side of a die. The spacecraft then recieves the reflected laser light and determines the distance to the surface, and therefore the topography. The advantage of having five spots is that it also gives astoundingly good measurements of the slopes.

Credit: NASA/LOLA team

After the LOLA talks, I heard about the results from the cosmic ray detector, CRaTER, on LRO. Apparently right now is a good time to observe cosmic rays because the sun is not very active. The current weak solar wind pressure allows more cosmic rays into the inner solar system! Understanding the radiation environment is important for sending hardware and people to the moon. One significant result that the CRaTER team reported was that even though the moon blocks cosmic rays as you get close to it, the total radiation increases because rays that hit the surface send up showers of secondary radiation. There is also no evidence that the amount of radiation on the moon decreases when Earth’s magnetosphere tail points toward the moon, as some people had suggested.

An animation of a cosmic ray hitting Earth's upper atmosphere. A similar shower of secondary particles is produced when cosmic rays hit the moon. Image creadit: U. Chicago

After that, I headed over to listen to Mars talks. Serina Diniega gave a nice presentation about her discovery of active gullies forming on dunes in the southern hemisphere. She showed evidence of several dune gullies for which there are “before and after” images showing noticeable changes. Serina suggested that frost accumulating in the upper alcoves of the gullies could trigger the changes, which would be consistent with the observation that most changes happened in southern winter. A related talk by Colin Dundas showed similar results, with HiRISE observations revealing fresh gullies on pole-facing slopes in the southern hemisphere.

An example of a fresh gully deposit in HiRISE image PSP_002200_1380.

After a few more Mars talks, I headed back to the moon to hear about LCROSS. I caught the tail end of a talk about the Lyman-alpha Mapping Project (LAMP) on LRO. This instrument uses the light emitted by hydrogen in stars to illuminate the dark craters on the moon, which is a really cool idea. Interestingly, the permanently shadowed craters look “dark”, implying that they contain something (ice) that absorbs UV light. LAMP also saw the plume kicked up by the LCROSS impact, and detected hydrogen emission, as well as, oddly enough, mercury (Hg) emission. Apparently, Mercury is volatile enough that over geologic time it also gets concentrated in shadowed craters. Future astronauts drinking the moon’s water will have to watch out for mercury poisoning!

Tony Calprete gave a nice overview of the LCROSS mission. He explained that the reason the plume wasn’t visible from earth was because they ended up selecting a crater that was known to have hydrogen, since LRO was going to be positioned to get good observations from orbit. He showed some of the spectra recorded by various instruments, which had evidence for all sorts of good stuff, including H2O, CO2, methane (CH4), SO2, ammonia (NH3), H2S, and even a couple of mystery lines that some people on the team think might be gold! (There’s gold in them thar hills?)

A second LCROSS talk by Peter Schulz focused on the cratering process. The most interesting aspect was the effect of a hollow projectile (such as the big empty centaur rocket used as the LCROSS impactor) on the plume behavior. It turns out a hollow projectile causes the crater ejecta to form a higher plume that spreads out less. He also pointed out that the reason the LCROSS impact did not look like the Deep Impact plume was because deep impact was a very high speed impact into a low-gravity object with a solid projectile, while LCROSS was a slow hollow impactor hitting a body with significant gravity.

Stay tuned for the Day 3 post, which will include some particularly interesting sessions about Venus and astrobiology and society!