Monday was my first day at the 2009 Division of Planetary Sciences meeting in Puerto Rico. Unfortunately, I was off to a late start because of one of the worst migraines of my life. But I did get to the afternoon science sessions.
Editor's note: Liz is posting updates regularly from DPS09 to Twitter.com/AstronomyMag.
I spent the early afternoon at the Titan science session. Nine scientists talked about the saturnian satellite’s atmosphere and geological features. William Smythe of the Jet Propulsion Laboratory discussed his team’s deduction that transient features seen on Titan are likely patches of pure ammonia frost. These features are too close to the ground to be clouds, so they’re either ground fog or surface coating. When scientists look at the features’ spectral signatures, they most closely match ammonia.
Ralph Lorenz of the Johns Hopkins University Applied Physics Laboratory discussed his team’s (and other groups’) observations of Titan’s brightness and how it changes over time. Lorenz summed up almost 40 years of observations (starting in the early 1970s). Various astronomers started observing Titan in 1972 and saw that it was brightening … but then it started darkening.
Since then, astronomers have determined that the northern hemisphere is some 20 percent darker than the southern. Seasonal changes could explain the observed brightness changes, but this doesn’t explain the full amplitude of brightness changes. Plus, the cycle isn’t perfectly symmetric, and right now Titan is darker than previously recorded. Why could this be? The Lorenz group thinks there is something going on with Titan’s haze layers, which could be affecting the observed brightness.
In the late afternoon I sat in on a session about rocky extrasolar planets. After quite a few technical problems, the program started. This session was filled with what to look for when trying to detect earthlike planets and life on those planets. A few talks focused on what our Earth looks like from a distance (this is data that the EPOXI mission was able to collect), and therefore what we should look for in similar planets.
Editor’s note: EPOXI is a combination of the names for two extended mission components: a search for extrasolar planets during the cruise to Hartley 2, called Extrasolar Planet Observations and Characterization (EPOCh), and the flyby of comet Hartley 2, called the Deep Impact eXtended Investigation (DIXI).
Carolyn Crow of the University of Maryland talked about EPOXI observations of Earth and the Moon using seven spectral filters. Crow and colleagues compared those Earth observations with spectra of the other planets, and found that in low resolutions Earth is brighter than the others with certain filters.
Eliza Miller-Ricci of Harvard University discussed a possible way to directly image terrestrial planets. Back in November 2008, astronomers announced that they had directly imaged gas giant planets orbiting their stars in two systems. However, gas giant planets hold onto their initial heat (from formation) for longer than rocky planets, so astronomers have a better chance of finding a young gas giant planet than a rocky one. Miller-Ricci (and colleagues) recommended that, instead, astronomers might want to search for the afterglow of a young super-Earth collision. (As we know from the formation of Earth, a Mars-sized object initially slammed into the forming Earth. Such collisions are likely typical in young solar systems.)
The surfaces of these super-Earths will be hot initially (1,500 to 4,000 K) and cool in free space within about 100,000 years. However, if the object has a thick atmosphere, it takes 1 to 10 million years to cool. So maybe 10 percent of young stars have hot super-Earth afterglows at any given time.
There was a lot of information that came out of Monday’s sessions. Tuesday should be similar, with the addition of three major talks in the morning, given by three scientists awarded DPS prizes for their research.