U.S. News & World Report - August 13, 2009
On Titan, Saturn's largest moon, methane clouds drift through a dense, nitrogen-rich atmosphere, clustering mainly in the polar regions. Methane lakes dot Titan's surface, also at high latitudes. Closer to the moon's equator, by contrast, clouds appear rarely if at all, and the surface seems arid. But in January 2005, the Huygens probe, after detaching from the Cassini spacecraft and descending through Titan's atmosphere, gave planetary scientists their first close-up view of the moon's surface. Huygens imaged small channels and river beds at low latitudes, in regions that scientists had assumed to be devoid of flowing liquids that could carve such features. Now, astronomers working at Earth-based telescopes have for the first time observed, near Titan's equator, large and persistent clouds that might be capable of raining liquid methane onto the surface.
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At visible wavelengths, Titan's hazy atmosphere—whose surface pressure is about one and half times that of Earth's—gives it a fuzzy, opaque appearance. At certain infrared wavelengths, however, the atmosphere is transparent while methane clouds are highly reflective. Schaller and her colleagues used NASA's Infrared Telescope Facility (IRTF), situated on Hawaii's Mauna Kea, to check Titan's infrared brightness as many nights as they could. IRTF measures the brightness of Titan as a whole, so when it revealed an increase in infrared reflectivity, the team turned to another telescope, Gemini North, to see where on Titan that infrared light was coming from. Gemini North, also on Mauna Kea, is one of a pair of 8-meter infrared telescopes funded in part by the National Science Foundation; its twin is Gemini South in the Chilean Andes. The Gemini telescopes achieve high resolution through the use of adaptive optics, meaning that the shape of their mirrors can be rapidly tweaked to overcome the blurring of images that results from light passing through the Earth's turbulent atmosphere.
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