How windy is Jupiter? And other planetary questions

Scientific American's Observations blog reports back from the American Astronomical Society's Division for Planetary Sciences meeting, held at the Arecibo Observatory in Puerto Rico.

One scientist explored just how windy it gets on Jupiter, in order to create those whorls we see. Another looked at recent news from the space probe orbiting Mercury, and wondered at the planet bearing the marks of having been impacted by significant projectiles (six miles in diameter) not just once, but twice. And thinking outside the solar system, another considered the possibility that earth-like planets might be based on carbon, rather than silicon, like ours.

But the real sexy star -- erm, focus -- of the meeting was Titan, one of Saturn's 61 moons.

Much of Tuesday afternoon was turned over to the wonders of Saturn's moon Titan, a land of lakes, rivers and rain, where hydrocarbons such as methane and ethane play the role that water does on Earth. The Cassini probe has been studying Titan for five years now, long enough that it has re-imaged many areas several times to look for any changes. In the lake district near the south pole, Alex Hayes of Caltech, Jonathan Lunine of the University of Arizona and their colleagues discovered that one lake has receded and two others have dried up altogether. It's summer now in Titan's southern hemisphere, and every year about a meter's worth of liquid evaporates off the lakes.

One interesting thing about lakes on Titan is that the lake district around the north pole has a lot more lakes than its southern counterpart. This isn't just because the north is in the throes of winter, Oded Aharonson and Sonja Graves of Caltech argued yesterday. Because Saturn's orbit is elliptical -- its distance from the sun varies by about one astronomical unit over the course of its 30-year orbit -- the summer shorter is hotter than the northern one, which favors lake formation in the north. But over tens of thousands of years, the ellipse itself shifts around, so the northern summer becomes the more intense one. Then the north lake district should recede and the south one should grow. Thus the lake asymmetry appears to be a direct product of long climate cycles -- meta-seasons -- on Titan.

While an observatory in Puerto Rico is a better conference destination than your basic convention center, chances are these meeting planners can't wait to book rooms some place more... out of this world.

-- Carolyn Kellogg

Photo: Jupiter at its equinox, September 2009. Credit: NASA