June 29, 2012
Liquid Water Revealed By Cassini On Titan
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Lee Rannals for redOrbit.com - Your Universe Online
Researchers using data from NASA's Cassini spacecraft have revealed that Titan has a layer of liquid water under its ice shell.
During their study, they saw a large amount of squeezing and stretching as the moon orbited Saturn. They determined that if Titan were composed entirely of stiff rock, the gravitational attraction of Saturn would cause bulges, or solid "tides," 3 feet of height.
Cassini reveled that Saturn creates solid tides at about 30 feet in height, which suggests that the moon is not made entirely of solid rocky material.
"Cassini's detection of large tides on Titan leads to the almost inescapable conclusion that there is a hidden ocean at depth," Luciano Iess, lead author and a Cassini team member, said in a press release. "The search for water is an important goal in solar system exploration, and now we've spotted another place where it is abundant."
Titan takes 16 days to orbit Saturn, giving scientists plenty of opportunity to see the moon's shape at different parts of its orbit.
The Saturn moon is not spherical, but slightly elongated like a football. The moon's long axis grew when it was closer to Saturn, and as it was further away, it became less elongated and more spherical.
By studying six close flybys of Titan from February 27, 2006 to February 18, 2011, researchers were able to determine the moon's internal structure by measuring variations in the gravitational pull of Titan by using data returned to NASA's Deep Space Network (DSN).
"We were making ultrasensitive measurements, and thankfully Cassini and the DSN were able to maintain a very stable link," Sami Asmar, a Cassini team member at NASA's Jet Propulsion Laboratory in Pasadena, California, said in a press release. "The tides on Titan pulled up by Saturn aren't huge compared to the pull the biggest planet, Jupiter, has on some of its moons. But, short of being able to drill on Titan's surface, the gravity measurements provide the best data we have of Titan's internal structure."
A layer of water does not have to be deep in order to create these tides, according to NASA. The space agency said a liquid layer between the external deformable shell and a solid mantle would enable the moon to bulge and compress as it orbits Saturn.
Although the presence of liquid water on Titan could spark some interest in the idea of finding alien life on the moon, scientists believe life needs liquid water that is in contact with rock. Scientists are unable to tell whether the ocean bottom is made up of rock or ice.
NASA said that rather than finding extraterrestrial life, the results have a bigger implication for the mystery of methane replenishment on Titan.
"The presence of a liquid water layer in Titan is important because we want to understand how methane is stored in Titan's interior and how it may outgas to the surface," Jonathan Lunine, a Cassini team member at Cornell University, Ithaca, N.Y., said in a press release "This is important because everything that is unique about Titan derives from the presence of abundant methane, yet the methane in the atmosphere is unstable and will be destroyed on geologically short timescales."
A liquid water ocean could produce ammonia-water liquids that bubble up through the crust, and liberate methane from the ice, thus providing a deep reservoir for storing methane, according to NASA.
The research appears in the latest edition of the journal Science.
Image 2 (below): This artist's concept shows a possible scenario for the internal structure of Titan, as suggested by data from NASA's Cassini spacecraft. Scientists have been trying to determine what is under Titan's organic-rich atmosphere and icy crust. Image credit: A. Tavani