Cassini Finds Likely Subsurface Ocean on Saturn Moon
Data from NASA's Cassini spacecraft have revealed Saturn's moon Titan  likely harbors a layer of liquid water under its ice shell.
PASADENA,  Calif. -- Data from NASA's Cassini spacecraft have revealed Saturn's moon Titan  likely harbors a layer of liquid water under its ice shell.Researchers  saw a large amount of squeezing and stretching as the moon orbited Saturn. They  deduced that if Titan were composed entirely of stiff rock, the gravitational  attraction of Saturn would cause bulges, or solid "tides," on the  moon only 3 feet (1 meter) in height. Spacecraft data show Saturn creates solid  tides approximately 30 feet (10 meters) in height, which suggests Titan is not  made entirely of solid rocky material. The finding appears in today's edition  of the journal Science."Cassini's  detection of large tides on Titan leads to the almost inescapable conclusion  that there is a hidden ocean at depth," said Luciano Iess, the paper's  lead author and a Cassini team member at the Sapienza University of Rome,  Italy. "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 only 16 days to orbit Saturn, and scientists were able to study the  moon's shape at different parts of its orbit. Because Titan is not spherical,  but slightly elongated like a football, its long axis grew when it was closer  to Saturn. Eight days later, when Titan was farther from Saturn, it became less  elongated and more nearly round. Cassini measured the gravitational effect of  that squeeze and pull.Scientists  were not sure Cassini would be able to detect the bulges caused by Saturn's  pull on Titan. By studying six close flybys of Titan from Feb. 27, 2006, to Feb.  18, 2011, researchers were able to determine the moon's internal structure by  measuring variations in the gravitational pull of Titan 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," said Sami Asmar, a Cassini team  member at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "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."An  ocean layer does not have to be huge or deep to create these tides. A liquid  layer between the external, deformable shell and a solid mantle would enable  Titan to bulge and compress as it orbits Saturn. Because Titan's surface is  mostly made of water ice, which is abundant in moons of the outer solar system,  scientists infer Titan's ocean is likely mostly liquid water.On  Earth, tides result from the gravitational attraction of the moon and sun  pulling on our surface oceans. In the open oceans, those can be as high as two  feet (60 centimeters). While water is easier to move, the gravitational pulling  by the sun and moon also causes Earth's crust to bulge in solid tides of about  20 inches (50 centimeters).The  presence of a subsurface layer of liquid water at Titan is not itself an  indicator for life. Scientists think life is more likely to arise when liquid  water is in contact with rock, and these measurements cannot tell whether the  ocean bottom is made up of rock or ice. 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," said Jonathan Lunine, a Cassini team member at Cornell  University, Ithaca, N.Y. "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, "salted" with ammonia, could produce buoyant ammonia-water  liquids that bubble up through the crust and liberate methane from the ice.  Such an ocean could serve also as a deep reservoir for storing methane.The  Cassini-Huygens mission is a cooperative project of NASA, the European Space  Agency and the Italian Space Agency. The mission is managed by JPL for NASA's  Science Mission Directorate in Washington. DSN, also managed by JPL, is an  international network of antennas that supports interplanetary spacecraft  missions and radio and radar astronomy observations for the exploration of the  solar system and the universe. The network also supports selected  Earth-orbiting missions. Cassini's radio science team is based at Wellesley  College in Massachusetts. JPL is a division of the California Institute of Technology  in Pasadena.For  more information about the mission, visit:http://www.nasa.gov/cassiniandhttp://saturn.jpl.nasa.gov.