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Cassini
Spacecraft Images Seas on Saturn's Moon Titan
03.13.07
Instruments on NASA's Cassini spacecraft have found
evidence for seas, likely filled with liquid methane or ethane,
in the high northern latitudes of Saturn's moon Titan. One such
feature is larger than any of the Great Lakes of North America
and is about the same size as several seas on Earth.
Cassini's
radar instrument imaged several very dark features near Titan's
north pole. Much larger than similar features seen before on
Titan, the largest dark feature measures at least 100,000 square
kilometers (39,000 square miles). Since the radar has caught only
a portion of each of these features, only their minimum size is
known. Titan is the second largest moon in the solar system and
is about 50 percent larger than Earth's moon.
A
comparison view of a lake on Titan and Lake Superior.
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"We've long
hypothesized about oceans on Titan and now with multiple
instruments we have a first indication of seas that dwarf the
lakes seen previously," said Dr. Jonathan Lunine, Cassini
interdisciplinary scientist at the University of Arizona, Tucson.
While there is no definitive proof yet that these seas
contain liquid, their shape, their dark appearance in radar that
indicates smoothness, and their other properties point to the
presence of liquids. The liquids are probably a combination of
methane and ethane, given the conditions on Titan and the
abundance of methane and ethane gases and clouds in Titan's
atmosphere.
Cassini's visual and infrared mapping
spectrometer also captured a view of the region, and the team is
working to determine the composition of the material contained
within these features to test the hypothesis that they are
liquid-filled.
The imaging cameras, which provide a
global view of Titan, have imaged a much larger, irregular dark
feature. The northern end of their image corresponds to one of
the radar-imaged seas. The dark area stretches for more than
1,000 kilometers (620 miles) in the image, down to 55 degrees
north latitude. If the entire dark area is liquid-filled, it
would be only slightly smaller than Earth's Caspian Sea. The
radar data show details at the northern end of the dark feature
similar to those seen in earlier radar observations of much
smaller, liquid-filled lakes. However, to determine if the entire
dark feature is a liquid-filled basin will require investigation
through additional radar flyovers later in the mission.
This
image is a portion of a larger view of Titan that features
some of the largest bodies of liquid ever seen. The lake on
the far right is larger than any lake on Earth and could be
legitimately called a sea.
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credit: NASA/JPL
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The presence of these seas
reinforces current thinking that Titan's surface must be
re-supplying methane to its atmosphere, the original motivation
almost a quarter century ago for the theoretical speculation of a
global ocean on Titan.
Cassini's instruments are peeling
back the haze that shrouds Titan, showing high northern latitudes
dotted with seas hundreds of miles across, and hundreds of
smaller lakes that vary from several to tens of miles.
Due
to the new discoveries, team members are re-pointing Cassini's
radar instrument during a May flyby so it can pass directly over
the dark areas imaged by the cameras.
The
Cassini-Huygens mission is a cooperative project of NASA, the
European Space Agency and the Italian Space Agency. JPL, a
division of the California Institute of Technology in Pasadena,
manages the Cassini-Huygens mission for NASA’s Science
Mission Directorate, Washington. The Cassini orbiter was
designed, developed and assembled at JPL.
Source
/ credit: NASA / JPL
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