15 December 2010

AGU 2010: Day 1 – Astrobiology, Volcanoes, and More!

Posted by Ryan Anderson

It never ceases to amaze me how ridiculously huge the AGU fall meeting is. This year there are something like 16000 abstracts and 19000 attendees. Somehow it’s also very small though, because most people stick to their own discipline. It’s more like a few dozen parallel conferences in the same place. As you’ll see, I mostly just hang out in the planetary sessions unless something really catches my eye elsewhere.

I started off the week on Monday with a good dose of astrobiology. The first talk I saw was all about autonomous submersibles and how they are used in deep sea exploration to search for life. I didn’t catch the presenter’s name, but he described how these submersibles have been used to explore hydrothermal vents, hydrocarbon seeps, and even the BP Deepwater Horizon spill site. The Nereus submersible can dive up to 11 km deep, and carries good stuff like mass spectrometers, and sonar. For now the astrobiology connection is a bit tenuous, but if we ever can access the oceans on icy bodies like Europa, it is going to be really important to have rugged and autonomous submersibles.

Today: Earth's oceans, tomorrow: europa?

There was a lot of discussion of methane in the astrobiology session, since it has been detected on mars and the big question is whether the martian methane is just from the alteration of volcanic rocks (a.k.a. serpentinization) or if it could be due to microbes. Penny Morril studied the Tablelands Ophiolite, which is a mountain of rock that was uplifted from deep in the earth, and is a pretty good analog for the rocks on Mars. Alas, Morrill found that the methane at the Tablelands Ophiolite was just from serpentinization and not from microbes, but she did find microbes in the high pH water percolating through the ophiolites.

Nadia Mykytczuk, who wins for the most consecutive consonants in a last name, gave a presentation about her studies of very cold ecosystems. She pointed out that more than 80% of earth’s biosphere is cold, and obviously martian microbes will probably have to be adapted to some chilly temperatures. She said that cold-tolerant bugs don’t do well in pure ice, but dirty ice or the “active layer” of soil above the permafrost were good habitats. Mykytczuk said that they had even found a type of bacteria that can survive and even grow at -15 degrees Celsius!

Brad Bebout took a look at whether the presence of methane is actually a good biomarker. He showed that even though isotopes are usually used to tell whether the source of methane is biological, there are cases in hypersaline environments when the carbon and hydrogen isotopes in methane are outside the typical biogenic range, but the methane is definitely from microbes. This means that when MSL makes measurements of the methane in the martian atmosphere, it might be hard to tell what the source really was.

Next, Valeria Sonza talked about the interesting stromatolite colonies in a lake in Cuatro Cienegas basin in the middle of the Chihuauan desert. The lake has really low phosphorus and high arsenic (sound familiar?) so there are some really interesting adaptations in response to such a harsh environment. For example, the bacteria use sulfur in their cell membranes rather than phosphorus, and have lost the genes for metabolizing nitrogen. Sonza admitted that these microbe mats are probably nto a great Mars analog, but they might be very informative about the precambrian earth.

The stromatolites at Cuatro Cienegas are analogs for precambrian life.

After lunch I headed over to hear John Holdren, Obama’s top science adviser, give a talk about science policy. Unfortunately is was mostly a list of obscure government agencies, buzzwords and org charts. I’ll spare you the details. The key message was that the Obama administration thinks science is important, and there was a major emphasis on interdisciplinary and the interconnectedness of issues.

After lunch it was time for explosive volcanism! Lori Glazer presented a study of how eruption plumes behave from circular versus linear vents on Earth, Venus and Mars. She found that on Venus plumes from linear vents go higher, but they have to have just the right conditions to be stable. On Mars the traditional models predict that the plumes go up to 100 km, but the atmosphere is so thin that that’s not really realistic. More accurate models lead to plumes about 15 km high. In general, Glazer found that only Earth forms stable convective plumes for a wide range of conditions.

Next up, Josh Bandfield gave a great talk about the possibility that Mars’ history was dominated by explosive volcanism. I liked this talk a lot because it used very basic observations but led to a pretty profound result. Bandfield pointed out that even though the surface of Mars is traditionally thought of as being made of flood basalts or regolith, the morphology of the layers around valles marineris (the best cross section of the crust that we have) erode into slopes that are shallower than you would expect if they were due to flood basalts, and the fact that they form layers at all is not consistent with megaregolith. Hi also pointed out that the thermal inertia of the valles marineris layers is low and that any boulders donlt survive more than a few hundred meters downslope. Likewise, most crater walls don’t show blocky material. Bandfield argues that all of this points to poorly consolidated rcoks like you might get from the deposition of ash from explosive volcanism. He suggested that the presence of younger lava flows might mean that the martian mantle has dried out over time, so that more recent eruptions were less likely to be explosive. He also pointed out that our impression of the martian surface as being covered in rocks might be biased because hard basalt rocks can survive as ejecta from impacts while soft ash deposits would just be pulverized. The flat plains of Meridiani may be more representative than the rocks at other landing sites.

Rocky, basaltic surfaces may not reflect the true character of the martian crust, which might be made of crumbly ash deposits from early explosive volcanism.

From volcanism, we moved on to water on small solar system bodies and atmospheric evolution. Roger Clark gave an interesting talk about explaining the diverse spectra of the icy satellites and showed that extremely small iron grains in the ice can actually give a good fit to spectral features that were previously attributed to organic molecules. He was careful to emphasize that this doesn’t mean the heavy organics aren’t there, they just aren’t spectrally dominant.

Another talk took a look at the history of water on Venus and suggested that it might have been habitable as a “dune-like” all-land planet before it lost all of its water. The idea is that if you start off with lots of water, Venus would be an ocean planet, but that water would end up in the atmosphere causing a brief “moist greenhouse” effect in which most of the water is lost to space in about 10 million years.

Later on in the atmospheric evolution session, Chris McKay brought the day full circle and talked about methane, this time on Titan rather than the earth and mars. The problem with the methane on Titan is that it’s hard to tell where all the methane comes from. To get lakes and storms at the equator sufficient to erode the branching valleys seen by Huygens, you need lots more methane than present-day levels. He suggested two models for Titan’s evolution. The first is that Titan has always been wet like it is today, but that requires you to start off with about 40 times as much as the current levels. As McKay said, “We like to think that the solar system has never changed. That’s a comforting thought”. The alternative model suggests that Titan is only recently wet, but both models are less-than-satisfying because they imply that we are seeing Titan just as we are running out of methane . Invoking special timing makes a lot of scientists uncomfortable, so the issue is really up in the air.

To get hydrocarbon rainfall near the equator necessary to form the branching channels seen by Huygens, Titan must have had lots more methane than it does now.

So, there you have it! Those were the highlights of my first day at this year’s AGU. Well, those and the huge quantities of Dungeness crab and alcohol that my research group consumed during and after dinner last night. Stay tuned for my post about day two!