Cassini Finds Likely Subsurface Ocean on Saturn Moon

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News release: 2012-190 June 28, 2012

Cassini Finds Likely Subsurface Ocean on Saturn Moon

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2012-190&cid=release_2012-190

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/cassini and
http://saturn.jpl.nasa.gov .

-end-


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