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January 25,
2005
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Frigid Titan Harbors Exotic Chemistry
Saturn's moon has a thick atmosphere of nitrogen and methane |
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ELIZABETH K. WILSON
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| UPWELLINGS An image taken by the Huygens probe's imager and spectral radiometer shows a bright linear feature suggesting an area where water ice may have been extruded onto the surface. Also visible are short, stubby dark channels that may have been formed by “springs” of liquid methane. |
The first detailed glimpse of Saturn’s moon Titan comes a week after the European Space Agency’s Huygens probe plunged through Titan’s thick nitrogen-and-methane atmosphere. Scientists are now plowing through the chemical data collected by Huygens’ six instruments.
The Huygens team has deduced that the probe arrived on Titan just after a methane rainstorm. The warm probe settled into the moon’s gooey, icy organic “topsoil,” releasing a burst of gaseous methane from liquid just below the surface.
Methane on Titan—which is –180 °C—appears to play the role of water on Earth.
As the Huygens probe fell, its mass spectrometer found nitrogen dominant in the upper atmosphere, which gave way to methane. Once the probe was on the ground, the instrument recorded a 30% jump in methane levels. “That means there’s liquid methane very near the surface,” says Tobias C. Owen, an astronomer at the University of Hawaii. “This is a planet where liquids are right there.”
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| ISLAND CHAIN Huygens captures a dark plain area on Titan that indicates flow around bright “islands.” The areas below and above the bright islands may be at different elevations. |
The predominance of liquid methane surprised scientists who expected to see perhaps higher concentrations of liquid ethane. Previous models had suggested that photochemical processes would convert atmospheric methane to other molecules like ethene and acetylene, which would then collect on the surface in large pools.
There’s still evidence for a photochemical smog rain in the form of dark material that has collected into channels and drained into lake beds. These lake beds are mostly dry right now, but Martin G. Tomasko, a professor of planetary science at the University of Arizona, says: “The pools gradually dry out and liquid sinks into the surface. Liquid is just underneath the surface as if it rained not long ago.”
Numerous mysteries remain about the chemistry of methane and other organics on Titan. For example, how does the methane replenish itself after making photochemical smog? Owen asks. “There must be some source of methane inside Titan.”
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CHANNEL NETWORK A mosaic of three images taken by the Huygens probe shows details of a high ri dge area, and a major river channel fed by smaller channels.
ESA/NASA/JPL/UNIVERSITY OF ARIZONA PHOTOS |
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Chemical & Engineering News
ISSN 0009-2347
Copyright © 2005 |
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