A 300-mile-wide patch that outshines everything else on Titan atlong infrared wavelengths appears not to be a mountain, a cloud or ageologically active hot spot, University of Arizona scientists andCassini team members say.
"We must be looking at a difference in surface composition," saidJason W. Barnes, a postdoctoral researcher at UA's Lunar and PlanetaryLab. "That's exciting because this is the first evidence that says notall of the bright areas on Titan are the same. Now we have to figureout what those differences are, what might have caused them."
When NASA's Cassini spacecraft flew by Titan on March 31 and againon April 16, its visual and infrared mapping spectrometer saw a featurethat was spectacularly bright at 5-micron wavelengths just southeast ofthe continent-sized region called Xanadu.
The bright spot occurs where Cassini's visible-wavelength imagingcameras photographed a bright arc-shaped feature approximately the samesize in December 2004 and February 2005.
Cassini's radar instrument, operating in the "passive" mode that issensitive to microwaves emitted from a planetary surface, saw notemperature difference between the bright spot and surrounding region.That rules out the possibility that the 5-micron bright spot is a hotspot, such as a geologically active ice volcano, Barnes said.
Cassini microwave radiometry also failed to detect a temperaturedrop that would show up if some two-mile high mountain rose fromTitan's surface, he said.
And if the 5-micron bright spot is a cloud, it's a cloud that hasn'tmoved or changed shape for three years, according to ground-basedobservations made at the Keck Telescope and with Cassini's visual andinfrared mapping spectrometer during five different flybys. "If this isa cloud," Barnes said, "it would have to be a persistent ground fog,like San Francisco on steroids, always foggy, all the time."
"The bright spot must be a patch of surface with a compositiondifferent from anything we've seen yet. Titan's surface is primarilycomposed of ice. It could be that something is contaminating the icehere, but what this might be is not clear," Barnes said.
"There's a lot left to explore about Titan. It's a very complex,exciting place. It's not obvious how it works. It's going to be a lotof fun over the next couple of years figuring out how Titan works," hesaid.
Barnes and 34 other scientists report the research in the Oct. 7issue of Science. Authors include UA Lunar and Planetary Laboratoryscientists and Cassini team members Robert H. Brown, head of Cassini'svisual and infrared mapping spectrometer team; Elizabeth P. Turtle andAlfred S. McEwen of the Cassini imaging team; Ralph D. Lorenz of theCassini radar team; Caitlin Griffith of the Cassini visual and infraredmapping team; and Jason Perry and Stephanie Fussner, who work withMcEwen and Turtle on Cassini imaging.
The Cassini-Huygens mission is a cooperative project of NASA, theEuropean Space Agency and the Italian Space Agency. The Jet PropulsionLaboratory, a division of the California Institute of Technology inPasadena, Calif., manages the mission for NASA's Science MissionDirectorate, Washington, D.C. The Cassini orbiter and its two onboardcameras were designed, developed and assembled at JPL. The imaging teamis based at the Space Science Institute in Boulder, Colo. The Visualand Infrared Mapping Spectrometer team is based at The University ofArizona in Tucson .
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