Rivers on Titan, one of Saturn's moons, resemble those on Earth (Forwarded)
- From: Andrew Yee <ayee@xxxxxxxxxxxxxxxxxxxxxx>
- Date: Tue, 6 Dec 2005 00:30:05 -0500 (EST)
News Bureau
University of Illinois at Urbana-Champaign
Contact:
James E. Kloeppel, Physical Sciences Editor
217-244-1073; kloeppel@xxxxxxxx
12/5/05
Rivers on Titan, one of Saturn's moons, resemble those on Earth
CHAMPAIGN, Ill. -- Recent evidence from the Huygens Probe of the Cassini
Mission suggests that Titan, the largest moon orbiting Saturn, is a world
where rivers of liquid methane sculpt channels in continents of ice.
Surface images even show gravel-sized pieces of water ice that resemble
rounded stones lying in a dry riverbed on Earth.
But with a surface temperature of minus 179 degrees Celsius and an
atmospheric pressure 1 1/2 times that of Earth, could fluvial processes on
Titan be anything like those on Earth?
"The idea that rivers of methane moving chunks of ice on Titan ought to
obey the same rules as rivers on Earth is not what you would assume at
first," said Gary Parker, the W. H. Johnson Professor of Geology and a
professor of civil and environmental engineering at the University of
Illinois at Urbana-Champaign. "However, if river dynamics are truly
understood at a physical level, then relations that provide reasonable
results on Earth ought to provide similarly reasonable results on Titan."
Parker, who has collected data from rivers all over the world, has
calculated what should be key similarities and key differences between
river networks on Earth and Titan.
There are only three parameters that differ significantly between Earth
and Titan, Parker said. First is the acceleration due to gravity -- on
Titan it is about one-seventh the value on Earth. Second is the viscosity
of flowing fluid -- the viscosity of liquid methane on Titan is about
one-fifth that of water on Earth. Third is the submerged specific gravity
of sediment -- the value on Titan is about two-thirds of that on Earth.
"What this means is that for the same discharge of liquid methane as to
water, the channel characteristics on Titan should be remarkably similar
to those on Earth," Parker said. "However, because of the smaller
acceleration due to gravity, channel slopes on Titan should be wider,
deeper and less steep than those on Earth."
Wildcards that make Parker's predictions tentative include a freeze-thaw
process of methane that might not be analogous to the freeze-thaw process
of water on Earth, and the formation of hydrocarbons on Titan that might
add a kind of cohesion not encountered on Earth. "The interaction of
sunlight with a hydrocarbon rich atmosphere could possibly precipitate
very sticky compounds that could give streams on Titan a degree of
cohesion that makes them behave differently," Parker said.
If the underlying physics has been captured correctly, Parker's
correlations could be used to predict river features not just on Earth and
Titan, but elsewhere as well; revealing the internal consistency of
fluvial processes at work under vastly different conditions.
"We are now receiving images from Mars that show relic rivers. But these
analogues to what has happened on Earth are very, very old and the
processes may not have been very strong," Parker said. "What is happening
on Titan, however, may be every bit as active and exciting as what is
happening on Earth."
Parker will present his findings at the American Geophysical Union meeting
in San Francisco, Dec. 5-9. Funding was provided by the National Center
for Earth-surface Dynamics, a Science and Technology Center of the
National Science Foundation.
Editor's note:
To reach Gary Parker, call 217-721-2976.
.
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