Another misty morning in Xanadu. At -179 °Celsius, this bright continent on Saturn's largest satellite, Titan, is much too cold for liquid water. Instead, the morning mist consists of tiny droplets of methane. The daily drizzle may be the result of prevailing easterly winds that are driven upwards by the mountainous region, causing cooling and condensation, a new study suggests.
The early-morning methane drizzle neatly explains a daily increase in the opacity of the lowest portion of Titan's atmosphere, detected in spectroscopic observations with the Keck telescope in Hawaii, US, and the Very Large Telescope in Chile.
According to a team from the University of California in Berkeley led by Máté Ádámkovics, the drizzle may even be responsible for why Xanadu is so bright. It could be "rinsing the bright surface" of dark hydrocarbons, the researchers say.
Meanwhile, the Cassini spacecraft has started to explore Titan's south polar region with its radar and has found the first lakes there (see image above right). It had already mapped about 60% of the moon's north polar region and turned up about 400 lakes and seas there (see image below right and watch a video of the radar mapping).
"Titan is indeed the land of lakes and seas," says Rosaly Lopes, a member of Cassini's radar team at NASA's Jet Propulsion Laboratory in Pasadena, California, US. "It will be interesting to see the differences between the north and south polar regions."
Cassini scientists believe the lakes fill depressions originally formed by volcanism or by the dissolution of rock. Methane and ethane rain is thought to fill the lakes and seas in a process similar to what occurs on Earth.
"The lakes we are observing on Titan appear to be in varying states of fullness, suggesting their involvement in a complex hydrologic system akin to Earth's water cycle," says Alex Hayes, a graduate student at Caltech who is studying Cassini's radar data. "This makes Titan unique among the extraterrestrial bodies in our solar system."
Both Ádámkovics and Lopes presented their results today at a meeting of the American Astronomical Society's Division for Planetary Sciences in Orlando, Florida, US.
Journal reference: Sciencexpress (doi: 10.1126/science.1146244)
Cassini: Mission to Saturn - Learn more in our continually updated special report.
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18:53 05 September 2008
