NASA's Cassini spacecraft has discovered evidence that
points to the existence of an
underground ocean of water and ammonia on Saturn's moon
Titan. The findings made using radar
measurements of Titan's rotation appear in the March 21
issue of the journal Science.
"With its organic dunes, lakes, channels and
mountains, Titan has one of the most varied, active
and Earth-like surfaces in the solar system," said Ralph
Lorenz, lead author of the paper and Cassini
radar scientist at the
Johns Hopkins Applied Physics Laboratory. "Now we see
changes in the way
Titan rotates, giving us a window into Titan's interior
beneath the surface."
Members of the mission's science team used Cassini's
Synthetic Aperture Radar to collect
imaging data during 19 separate passes over Titan between
October 2005 and May 2007. The radar
can see through Titan's dense, methane-rich atmospheric
haze, detailing never-before-seen surface
features and establishing their locations on the moon's
surface.
Using data from the radar's early observations, the
scientists and radar engineers established
the locations of 50 unique landmarks on Titan's surface.
They then searched for these same lakes,
canyons and mountains in the reams of data returned by
Cassini in its later flybys of Titan. They found
prominent surface features had shifted from their expected
positions by up to 19 miles. A systematic
displacement of surface features would be difficult to
explain unless the moon's icy crust was
decoupled from its core by an internal ocean, making it
easier for the crust to move.
"We believe that about 62 miles beneath the ice and
organic-rich surface is an internal ocean of
liquid water mixed with ammonia," said Bryan Stiles of
NASA's Jet Propulsion Laboratory and a
contributing author to the paper.
The study of Titan is a major goal of the
Cassini-Huygens mission because it may preserve, in
deep-freeze, many of the chemical compounds that preceded
life on Earth. Titan is the only moon in
the solar system that possesses a dense atmosphere. The
moon's atmosphere is 1.5 times denser than
Earth's. Titan is the largest of Saturn's moons, bigger
than the planet Mercury.
"The combination of an organic-rich environment and
liquid water is very appealing to
astrobiologists," said APL's Lorenz. "Further study of
Titan's rotation will let us understand the
watery interior better, and because the spin of the crust
and the winds in the atmosphere are linked,
we might see seasonal variation in the spin in the next few
years."
Cassini scientists will not have long to wait before
another go at Titan. On March 25, just prior
to its closest approach at an altitude of 620 miles,
Cassini will employ its Ion and Neutral Mass
Spectrometer to examine Titan's upper atmosphere.
Immediately after closest approach, the
spacecraft's Visual and Infrared Mapping Spectrometer will
capture high-resolution images of Titan's
southeast quadrant.
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, a
division of the California Institute of
Technology. The Cassini orbiter also was designed,
developed and assembled at JPL.
For more information about Cassini, go to
www.nasa.gov/cassini.
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