20 December 2009

AGU 2009 – Day 3: Venus and the Moon

Posted by Ryan Anderson

I’m splitting day 3 into two posts because there were so many interesting sessions. Stay tuned for the second post about astrobiology and society. But for now, Venus and the moon!

Image credit: Nick Anthony Fiorenza/NASA

I started the day off at the Venus session. One of the first talks I heard was by Cedric Gillman about the history of water on Venus. He suggested a very thick primordial H2O atmosphere with a surface pressure of 300 bars, eventually escaping until just 15 bars of O2 were left. That oxygen then was absorbed as it reacted with the rocks. Gillman cautioned that Venus’ evolution shows that you can have a very hostile environments but still have water and oxygen in the atmosphere; something that we should keep in mind when looking for “habitable” exoplanets.

The next two Venus talks described using two complementary laser-based techniques on a lander mission. Shiv Sharma showed that Raman spectroscopy, which uses laser pulses to characterize the molecules in a target, would work under Venus-like conditions for a variety of rock types. In the following talk, Sam Clegg showed that Laser-Induced Breakdown Spectroscopy (LIBS), which analyzes the elements in a sample by zapping it with a laser and collecting the spectrum emitted by the resulting plasma, would also work under Venus conditions. Sam is my main contact on the ChemCam team and allows me to use his laser lab for some of my work, so it was cool to see some of the other LIBS work that he does.

A sample being zapped by a LIBS laser.

Both Raman and LIBS are great for Venus because they are fast, capable of remotely analyzing a sample in seconds. When your probe is only going to live for an hour in the crushing pressure and deadly heat of Venus, every second counts, and these techniques could be extremely useful.

The final Venus talk that I heard was a status report on the Japanese Venus climate orbiter. They unveiled its new name: Akatsuki, which means “dawn” in Japanese, specifically the time of the morning when Venus is just visible as the morning star. Akatsuki is going through final thermal vacuum tests in January and will launch some time in 2010.

Artist's rendition of Akatsuki at Venus. Image credit: JAXA/Akihiro Ikeshita

Later that day, I stopped by the lunar dust session to hear a talk by Bonnie Cooper about the toxicity of lunar dust and implications for astronauts. Chronic exposure to dust on earth can cause serious problems, especially to the lungs, but I was surprised to hears some of the other effects. My lack of biology knowledge is probably getting this partly wrong, but Cooper said that very small dust particles can actually enter the tissue around small blood vessels and prevent them from expanding when the body needs them to do so! Not good!

Crushed quartz is quite nasty stuff on earth and Cooper said that there was reason to believe that moon dust might be even more reactive because of its jagged surface, the many fresh fractures in the grains caused by micro-meteorites, and because of solar wind protons. All of these things result in unbonded ions known as free-radicals, which are very reactive and cause damage to the body. Dust loses its danger somewhat when it is exposed to air and all the free radicals are neutralized, but Cooper said that their experiments show this takes several hours. They are working on doing experiments with actual lunar samples and lunar soil simulant to find the exact effects of dust inhalation, but it sounds like this is a significant problem that human explorers will have to face.

A particle of moon dust. Image credit: David S. McKay, NASA/JSC

Finally, at the end of the day there were a couple of talks about the detection of water on the moon with the Moon Mineralogy Mapper on Chandrayaan. The most interesting one, given by Roger Clark, showed that the initial water detection actually underestimated the depth of the water absorption feature because it didn’t correct for an overall slope in the background of the spectrum. With that correction, the mapped water extends to all latitudes. There is still a stronger signature near the poles, but that is superimposed on much more complex variation with geology. There are craters that appear to be digging up material with a stronger water band, but other fresh craters dig up less water-rich debris. He also said that he was cautiously optimistic that they had detected some hematite, an iron oxide responsible for Mars’ rusty color, but said that scattered light in the instrument made it difficult to tell for sure. Clark concluded, saying that he didn’t think that the variation of the band strength observed during the lunar day represented a change in the actual amount of water, but rather was due to the viewing geometry.

The press-released M3 map of water on the moon (blue). With recent corrections (not shown here), the mapped water extends all the way down to the equator.