John Bluck July 27, 2006
NASA Ames Research Center, Moffett Field, Calif.
Phone: 650-604-5026 or 604-9000
E-mail:

RELEASE: 06-57AR

NASA REPORTS THAT METHANE DRIZZLES ON SATURN'S MOON, TITAN

Liquid methane drizzles on the surface of Titan, a moon of Saturn,
according to a paper by NASA and university scientists that appears
in today's issue of the journal, Nature.

Data from the European Space Agency's Huygens probe indicates there
is a lower, barely visible, liquid methane-nitrogen cloud that drops
rain to the surface of Titan, reported a team of scientists from
universities, an observatory and NASA. The probe collected the data
on January 14, 2005, when it approached and landed on Titan.

"The rain on Titan is just a slight drizzle, but it rains all the
time, day in, day out. It makes the ground wet and muddy with liquid
methane. This is why the Huygens probe landed with a splat. It landed
in methane mud," said Christopher McKay, a scientist at NASA Ames
Research Center in California's Silicon Valley and second author of
the study. The principal author is Tetsuya Tokano from the University
of Cologne, Germany.

On Titan, the clouds and rain are formed of liquid methane. On Earth,
methane is a flammable gas, but Titan has no oxygen in its atmosphere
that could support combustion. Also, the temperatures on Titan are so
cold -- minus 300 degrees Fahrenheit (minus 149 degrees Celsius) --
that the methane can form liquid. Titan's landscape includes fluvial,
river-like features that may well be formed by methane rain,
scientists noted.

A gap separates the liquid methane cloud -- the source of the rain --
from a higher, upper methane ice cloud, according to the scientific
study. Scientists say the downward flow of methane due to the rain is
balanced by upward transport of methane gas by large-scale
atmospheric circulation.

According to scientists, the rain comes from thin clouds of methane.
The upper clouds are methane ice, and the lower clouds are liquid and
composed of a combination of methane and nitrogen. Computer models
indicate these thin liquid methane clouds cover about half of Titan,
even though methane abundance on the moon decreases with latitude,
the team reported.

"We determined that the rain on Titan is equal to about two inches
(about 5 centimeters) a year," McKay said. "This is about as much
rain as Death Valley (receives). The difference is (that) on Titan,
this rain is spread out evenly over the entire year."

The scientists reported that erosion potential from the very light
methane drizzle may be quite limited, but at least would be
sufficient to wet the surface material, and may explain its generally
wet character.

In addition to McKay the other co-authors of the scientific paper
include Fritz Neubauer, of the University of Cologne; Sushil Atreya,
University of Michigan, Ann Arbor; Francesca Ferri, University of
Padova, Italy; Marcello Fulchignoni, of both the Paris Observatory
and the University of Denis Diderot, Paris; and Hasso Niemann, NASA
Goddard Space Flight Center, Greenbelt, Md.

More information about the Huygens mission to Titan can be found at
on the Internet at:

http://saturn.jpl.nasa.gov/operation...ns-mission.cfm

More information about NASA can be found at:

http://www.nasa.gov

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