NASA scientists have found compelling evidence for lake-level changes on Saturn's largest moon, Titan—the only other place in the solar system other than Earth observed to have a hydrological cycle with standing liquid on the surface.On Earth, lake levels rise and fall with the seasons and with longer-term climate changes, as precipitation, evaporation, and runoff add and remove liquid.
Using data gathered by NASA's Cassini spacecraft over a span of four years, the researchers—led by graduate student Alexander G. Hayes of the California Institute of Technology (Caltech) and Oded Aharonson, associate professor of planetary science at Caltech—have obtained two separate lines of evidence showing roughly a 1 meter per year drop in the levels of lakes in Titan's southern hemisphere. The decrease is the result of the seasonal evaporation of liquid methane from the lakes—which, because of Titan's frigid temperatures (roughly minus 300 degrees Fahrenheit at the poles), are composed largely of liquid methane, ethane, and propane.
"It's really exciting because, on this distant object, we're able to see this meter-scale drop in lake depth," says Hayes. "We didn't know Cassini would even be able to see these things."
One of the lakes—Ontario Lacus (named after Earth's Lake Ontario, which is of comparable size) —is the southern hemisphere's largest lake, and was the first lake to be observed on the moon. In a paper submitted to the journal Icarus, Hayes, Aharonson, and their colleagues report that the shoreline of Ontario Lacus receded by about 10 kilometers (6 miles) from June 2005 to July 2009, a period of time that represents mid-summer to fall in Titan's southern hemisphere. (One Titan year lasts 29.5 Earth years.)
http://www.dailygalaxy.com/my_weblog/2010/07/the-great-lakes-of-saturns-titan.htmlalso more with video:
http://www.nasa.gov/mission_pages/cassini/whycassini/cassini20100715.html
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