Titan's Weird Surface Dissolves Like Earth's Sinkholes

Saturn's moon Titan is a very alien place - the surface is covered in hydrocarbons and it rains liquid methane. However, planetary scientists are increasingly turning to the hazy little world to reveal clues as to the formation of our planet. And it seems the harder you look on Titan's surface, the more features and processes replicating terrestrial geology and atmospherics present themselves.

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Ever since the NASA/ESA Cassini-Huygens mission saw though the moon's thick, hazy atmosphere, scientists became fascinated with the huge bodies of liquid on Titan's surface. Titan's atmosphere is too cold for liquid water to persist, but liquid methane and ethane exists on the surface. Titan even has a methane cycle - similar to Earth's hydrological cycle - where liquid methane, not liquid water, rains onto the landscape, forming rivers and bodies of liquids like lakes and large 'seas.' However, some of these features have been hard to explain, including lakes of liquid ethane and methane that don't appear to be fed by rivers or streams. These are small lakes that appear to have smooth, rounded edges and steep sides that populate otherwise flat plains. Some of the lakes are filled with liquid, while others lie empty.

In new research published in the Journal of Geophysical Research, scientists have taken a long look at these lakes and realized that they are likely formed by similar processes that form 'karstic' landforms here on Earth. In other words, these Titan lakes are likely sinkholes.

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On Earth, sinkholes form when soluble rocks, such as limestone and gypsum, are eroded by rainwater and groundwater percolating through the rock. Over time, sub-surface caverns form, causing the surface to slump into a sinkhole. Often, sinkholes will naturally fill with water creating lakes.

As it is extremely cold on Titan and its seasons are much longer than Earth's, it would take far longer for these features to form. But new models suggest this is exactly what's happening on the moon's surface.

"We compared the erosion rates of organics in liquid hydrocarbons on Titan with those of carbonate and evaporite minerals in liquid water on Earth," said Thomas Cornet of the European Space Agency and lead author of the study.

"We found that the dissolution process occurs on Titan some 30 times slower than on Earth due to the longer length of Titan's year and the fact it only rains during Titan summer. Nevertheless, we believe that dissolution is a major cause of landscape evolution on Titan, and could be the origin of its lakes," he added.

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This means that it could take up to 50 million years to create a 100 meter-deep depression located at Titan's rainy high polar latitudes, Cornet's team found. Interestingly, they also found that it could take up to 375 million years to form these features in lower latitudes, where rainfall is predicted to be far less frequent. There is therefore a relative absence of lakes toward Titan's equator.

"By comparing Titan's surface features with examples on Earth and applying a few simple calculations, we have found similar land-shaping processes that could be operating under very different climate and chemical regimes," said Nicolas Altobelli, ESA's Cassini–Huygens project scientist.

"This is a great comparative study between our home planet and a dynamic world more than a billion kilometers away in the outer Solar System."

Source: ESA via Physorg.com