Methane Rain and River Beds Found on Saturn Moon
January 21, 2005
By THE ASSOCIATED PRESS
Filed at 11:07 a.m. ET
PARIS (AP) -- A probe to Titan has found that liquid
methane rains lash Saturn's largest moon, a freezing,
primitive but active world of ridges, peaks, river beds and
deserts scoured by the same forces of erosion as Earth,
scientists said Friday.
Methane is a highly flammable gas on Earth, but on Titan,
it is liquid because of the intense pressure and cold.
"There is liquid that is flowing on the surface of Titan.
It is not water -- it is much too cold -- it's liquid
methane, and this methane really plays the same big role on
Titan as water does on Earth," said mission manager
Jean-Pierre Lebreton at a news conference.
Titan's rains appear to be liquid methane, not water, and
black-and-white photos from the probe showed a rugged
terrain of ridges, peaks and dark vein-like channels,
suggesting the moon 744 million miles away is scoured by
the same erosion forces that shape Earth.
Titan's appearance has long intrigued scientists -- and
Europe's Huygens probe landed Jan. 14, making it the first
moon other than the Earth's to be explored.
Scientists believe methane gas breaks up in Titan's
atmosphere, forming smog clouds that then rain methane down
to the surface.
"We've got a flammable world, and it's quite
extraordinary," said Toby Owen, a scientist from
Honolulu's Institute for Astronomy.
But unlike Earth, where water constantly circulates back
into the atmosphere, Titan's methane never evaporates back
into airborne smog.
"There must be some source of methane inside Titan which
is releasing the gas into the atmosphere. It has to be
continually renewed, otherwise it would have all
disappeared," said Owen.
Titan has river systems and deltas, protrusions of frozen
water ice cut through by channels, apparent dried out pools
where liquid has perhaps drained away, and stones --
probably ice pebbles -- that appear to have been rounded by
erosion, the scientists said.
The bottoms of the dried-out river channels are coated with
what seem to be particles of smog that fall out of Titan's
atmosphere, coating the whole terrain. The dirt apparently
gets washed off the ridges to collect in the river beds.
It did not appear to be raining when Hyugens descended
through Titan's haze on parachutes, "but it has been
raining not long ago," said Lebreton.
"Does it rain only once a year? Is there a wet season once
a year? Does it rain more frequently? We don't know," said
another team member Martin Tomasko of the University of Arizona.
The area where the probe landed is "more like Arizona, or
someplace like that, where the river beds are dry most if
the time," he said. "Right after the rain you might have
open flowing liquids, then there are pools, the pools
gradually dry out."
Huygens was spun off from the Cassini mother ship on Dec.
24. The $3.3 billion Cassini-Huygens mission to explore
Saturn and its moons was launched in 1997 from Cape
Canaveral, Fla. -- a joint effort between NASA, the
European Space Agency, and the Italian space agency.
Scientists think Titan's atmosphere is similar to that of
the early Earth and studying it could provide clues to how
life arose here.