Cassini Spacecraft
Finds Ocean May Exist Beneath Titan's Crust
(20 March 2008) 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 will 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 in Laurel, Md., "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 (JPL) in,
Pasadena, Calif. Stiles also is 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," Lorenz said. "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 south-east quadrant.
The
Cassini-Huygens mission is a co-operative 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 in Pasadena. The Cassini orbiter also
was designed, developed and assembled at JPL.
(source: NASA)
|
||||||||||||
