Using radar data from NASA's Cassini spacecraft, recently published research presents a new scenario to explain why some methane-filled lakes on Saturn's moon Titan are surrounded by steep rims reaching hundreds of feet high. The models suggest that explosions of nitrogen heating created pools in the lunar crust.
Titanium is the only planetary body in our solar system other than Earth, which is known to have stable fluid on the surface. But instead of water raining down from the clouds and filling lakes and oceans like on earth, on Titan it's methane and ethane – hydrocarbons that we think of as gases but that behave like liquids in Titan's frigid climate.
Most existing models that lay The origin of Titan's lakes shows liquid methane that dissolves the lunar bedrock of ice and solid organic compounds, carving reservoirs that are filled with the liquid. This may be the origin of a type of lake on Titan that has sharp boundaries. On earth, streams formed in similar ways, by dissolving surrounding limestone, are known as karstic lakes.
The new, alternative models for some of the smaller lakes (tens of miles across) turn that theory upside down: It proposes pockets of liquid nitrogen in the Titan's crust were heated and turned into explosive gas that blew out craters, which were then filled with liquid methane. The new theory explains why some of the smaller lakes near Titan's north pole, such as Winnipeg Lacus, appear in radar formations to have very steep rims that tower over the sea ̵
Radar data was collected by Cassini Saturn Orbiter – a mission handled by NASA's Jet Propulsion Laboratory in Pasadena, California – during the last near flight of the Titan, as the spaceship was preparing for its final fall in Saturn's atmosphere two years ago. An international team of researchers led by Giuseppe Mitri from Italy's G. d & # 39; Annunzio University became convinced that the karstic model did not sneak what they saw in these new images.
"The edge goes up and the karst process works in the opposite way, Mitri said." We did not find any explanation that suited a karstic lake basin. In reality, the morphology was more consistent with an explosion crater, where the edge is formed by the ejected material from the interior of the crater. It is a completely different process. " The work, published September 9 in Nature Geoscience meshes with other Titan climate models showing the moon can be warm compared to how it was in the earlier Titan Ice Age.  For the last half billion or billions of years on Titan, methane in its atmosphere has acted as a greenhouse gas and kept the moon relatively warm – even though it is still cold by Earth's standards. Scientists have long believed that the moon has gone through epochs of cooling and warming, as methane is drained of solar-driven chemistry and then reinvigorated.
During the colder periods, the nitrogen dominated, rained down and cycled through the ice-cold crust to collect in pools just below the surface, said Cassini researchers and study co-author Jonathan Lunine from Cornell University in Ithaca, New York.
"These lakes with steep edges, ridges and raised rims would be a sign of periods in Titan's history uneasy when there was liquid nitrogen on the surface and in the crust, "he noted. Even local heating would have been enough to turn the liquid nitrogen into steam, make it expand quickly and blow out a crater.
"This is a completely different explanation for the steep rims around the small lakes, which has been a huge puzzle," said Cassini project researcher Linda Spilker of JPL. "As researchers continue to mine the Treasury from Cassini data, we will continue to put together more and more pieces of the puzzle. Over the coming decades, we will understand the Saturn system better and better."
Cassini-Huygens mission is a collaborative project of NASA, ESA (European Space Agency) and the Italian Space Agency. JPL, a division of Caltech in Pasadena, manages the mission of NASA's Science Mission Directorate in Washington. JPL designed, developed and assembled Cassini orbits. The radar instrument was built by JPL and the Italian Space Agency and worked with team members from the US and several European countries.
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