July 28, 2006

Space probe spots foggy lakes on Saturn’s moon

WASHINGTON (Reuters) - It has methane rain and white
crystalline sand dunes, and now scientists say Saturn's moon
Titan also has many lakes.

The lakes are probably made up of methane, with a little
ethane mixed in, and they are probably the source of the
obscuring smog in the frigid moon's atmosphere, researchers
reported on Friday.

"This is a big deal," said Steve Wall, deputy radar team
leader at NASA's Jet Propulsion Laboratory in Pasadena,
California. "We've now seen a place other than Earth where
lakes are present."

The numerous, well-defined dark patches were seen in radar
images of Titan's high latitudes taken during a flyby Saturday
by the Cassini-Huygens spacecraft, a cooperative project among
NASA, the European Space Agency and the Italian Space Agency.

Titan's flat surface is very cold, with a temperature of
minus 180 C, and scientists believe its thick atmosphere may
occasionally rain methane.

Another team reported on Wednesday that the rain includes a
persistent drizzle that keeps the surface of Saturn's largest
moon damp. Fierce storms could produce huge droplets of

Saturn has at least 47 moons. Titan, the largest, has
geological features similar to those on Earth.

During the flyby, Cassini's radar spotted several dozen
lakes, including one about 60 miles long.

"It was almost as though someone laid a bull's-eye around
the whole north pole of Titan, and Cassini sees these regions
of lakes just like those we see on Earth," said Larry Soderblom
of the U.S. Geological Survey in Flagstaff, Arizona.

Titan's dense, smoggy atmosphere makes it very difficult to
get good visible images, so Cassini uses radar.

Dark regions in radar images generally mean smooth terrain,
while bright regions suggest a rougher surface. Some of the new
radar images show channels leading in or out of a variety of
dark patches. The shape of the channels also strongly implies
they were carved by liquid.

"We've always believed Titan's methane had to be maintained
by liquid lakes or extensive underground 'methanofers,' the
methane equivalent of aquifers. We can't see methanofers, but
we can now say we've seen lakes," said Jonathan Lunine of the
University of Arizona, Tucson.

The Cassini spacecraft was launched in 1997 and reached
Saturn in 2004 after passing Venus and Jupiter. In May,
Cassini's instruments spotted regions covered with dunes,
possibly made out of methane ice crystals, and last year it saw
what appeared to be a big lake on Titan's south pole.