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Posted on Apr 29, 2019
The largest moon of Saturn, the rain, the seas and an eroding surface of organic matter are found on Earth and Titan. However, on Titan, it is the methane, not the water, which fills the lakes with drops of melting rain. Searching for Titan's methane source, Caitlin Griffith, a researcher at the University of Arizona, a professor at the Lunar and Global Laboratory at the University of Arizona, and his team discovered something unexpected: a long ice pack surrounding Titan.
Titan, the giant moon of Saturn, contains no obvious source of methane, except evaporation of methane from polar lakes. But Titan's lakes contain only one-third of the methane in Titan's atmosphere and will soon be depleted by geological time scales. According to one theory, methane could be supplied by underground reservoirs that release methane into the atmosphere. Previous studies on Titan indicate the presence of a singular region called Sotra, which looks like a cryo-volcano, with iced flow characteristics.
On Titan, atmospheric methane molecules are continually broken by sunlight. The resulting atmospheric haze is deposited on the surface and accumulates as organic sediments, rapidly depleting atmospheric methane. This organic veneer is composed of the material of past atmospheres.
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Griffith's team set out to study the composition of Titan's surface, hoping to find subtle cryo-volcanic candidates. They analyzed half of Titan's surface and none was detected, but Sotra was exceptional in having the most powerful ice features.
Yet the main feature of ice found by the researchers was totally unexpected. It is a linear ice corridor that envelops about 40% of Titan's perimeter.
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"This frozen corridor is confusing because it does not match any surface features or measurements of the subsoil," Griffith said. "Given that our previous study and work indicates that Titan is not currently volcanically active, the Corridor Trail is probably a remnant of the past. We detect this feature on steep slopes, but not on all slopes. This suggests that the frozen corridor is eroding, potentially revealing the presence of ice and organic layers. "
The team's analysis also indicates a diversity of organic materials in some regions. These surface deposits are interesting because the laboratory simulations of Titan's atmosphere produce biologically interesting compounds such as amino acids.
Griffith analyzed tens of thousands of spectral images taken with the Cassini Visible and Infrared Mapping Spectrometer, using a method to detect weak surface features.
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This feat was accomplished by Griffith's application of Principal Component Analysis, or PCA. This allowed him to unravel the subtle traits caused by ice and organic sediments on Titan's surface from omnipresent haze and more obvious surface features. Instead of measuring the surface characteristics individually for each pixel in an image, the PCA uses all the pixels to recognize the main and more subtle signatures.
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The Griffith team compared its results with previous studies, including the Huygens probe, which landed on Titan in 2005. The comparison validated both the technique and the results. Plans are underway to use this technique to explore the poles where the methane seas are located.
"Titan and Earth have followed different evolutionary trajectories and have resulted in atmospheres and surfaces rich in unique organic substances," Griffth said. "But it's not clear if Titan and Earth are common patterns of body-rich organic matter or two among many worlds rich in organic matter."
The Daily Galaxy via the University of Arizona
Image credit: Titan methane lakes, Jurik Peter / Shutterstock
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