NASA'S Cassini Finds Probable Subsurface Ocean on Saturn Moon

June 28, 2012

Dwayne Brown
Headquarters, Washington
202-358-1726
dwayne.c.brown@nasa.gov

Jia-Rui C. Cook
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-0850
jccook@jpl.nasa.gov

RELEASE: 12-218

NASA'S CASSINI FINDS PROBABLE SUBSURFACE OCEAN ON SATURN MOON

WASHINGTON -- 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
(JPL) 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. "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.

For more information about the mission, visit:

http://www.nasa.gov/cassini


-end-



To subscribe to the list, send a message to:
hqnews-subscribe@mediaservices.nasa.gov
To remove your address from the list, send a message to:
hqnews-unsubscribe@mediaservices.nasa.gov