16 March 2011

LPSC 2011 – Day 1: Cryospheres and Making Moons

Posted by Ryan Anderson

Greetings from Texas, loyal readers! As you may have noticed, this year’s Lunar and Planetary Science Conference came and went with barely a peep here on the blog. This is because, unlike some members of the planetary science community, I do need to sleep occasionally, and I spent almost all of my time at LPSC either in sessions or working on my never-ending paper. Yeah, remember the one that I had grand plans of submitting before the conference? Still not submitted. Instead on Wednesday I had a good chat with my co-authors, and got a to-do list of things to add and change, which took up all my spare time for the rest of the conference and the weekend after.

But now the latest draft is back in their court, I am installed at NASA’s Johnson Space Center for a month of lab work, and I have a little bit of time to breathe and blog. So! Before it gets too stale, let’s get cracking on the LPSC summary! I’m going to start a new thing that I really should have been doing all along, and will be linking to the LPSC abstract for each talk that I mention.

Monday started off with a session on the Martian cryosphere. Jim Head gave an interesting talk suggesting that the current climate on Mars is actually pretty strange. He pointed to (among other things) the discovery of shallow ice at the Phoenix landing site, an ice-bearing latitude-dependent mantle that mutes topography and may be a source of gully-forming water, and evidence for CO2¬†glaciers¬†formed during low obliquity periods to argue that Mars’ climate is intimately tied to how much it is tilted. Right now, Mars is moderately tilted, so it doesn’t have the CO2 glaciers formed when it has almost no tilt, nor does it have the extensive water ice that gets deposited when it is highly tilted.

Another interesting talk was by one of Jim Head’s students, Ethan Schaefer. Ethan talked about his studies of Vaduz crater which is an example of an “excess ejecta crater”. Basically, that means that the apparent volume of the ejecta is larger than the volume of the hole in the ground. This happens when a crater forms in icy material and then the climate changes and the ice starts to sublimate away. The ejecta protects the ice underneath it, so the surrounding plains sink but the ejecta and the ice beneath it remain. Based on the volume of ejecta remaining and the drop of the surrounding terrain, Schaefer interprets the ice as being due to precipitation rather than just ice trapped between the pores in the soil.

Colin Souness gave a cool talk investigating whether the “glacier like forms” on Mars act like glaciers on Earth. Terrestrial glaciers act like icy conveyor belts, with ice added at high elevations and removed at low elevations. The alternative is the flow of a pre-existing mass of ice due to local topography. Souness found that the “glacier-like forms” on Mars were correlated more with local topographic relief than elevation, so they are likely not behaving like glaciers on Earth.

After the Cryospheres session I went to the Masursky Prize lecture, given by Robin Canup. Dr. Canup is famous for her simulations of the giant impact that formed the moon (although apparently not famous enough for Bill O’Reilly to know about her work…) and she gave a great lecture about how various moons in the solar system formed.

She showed that for rocky planets like ours, the trick is getting the debris from a giant impact into orbit. It turns out that based on the way the planet and the giant impactor interact, most of the material that ends up in orbit (and therefore clumping together to form the moon) comes from the leading edge of the impactor.

A frame from one of Robin Canup's simulations of the formation of the moon. Color corresponds to temperature (red is hot, blue is cold).

For giant planets things are more complicated because the planet formed from the accretion of gas from the solar nebula into a big disk. While this is happening, there is so much energy being dumped into the forming planet that it is puffed up to 100s of times its final size. The planet’s moons form from the accretion disk, and multiple generations of moons probably formed and then spiraled too close to the planet and were consumed. The familiar moons that we see around Jupiter and Saturn are just the last survivors. This model has the bonus advantage of supplying material to form rings around the planet as the final moons drift too close and are torn apart.

There were probably many more fascinating talks on Monday, but I spent most of the afternoon working, so I’m afraid that’s all i have for you! Stay tuned for more from the rest of the week!