July 19, 2006
Dwayne Brown/Erica Hupp
Jet Propulsion Laboratory, Pasadena, Calif.
CASSINI REVEALS TITAN’S XANADU REGION TO BE AN EARTH-LIKE LAND
New radar images from NASA’s Cassini spacecraft revealed geological
features similar to Earth on Xanadu, an Australia-sized, bright
region on Saturn’s moon Titan.
These radar images, from a strip more than 2,796 miles long, show
Xanadu is surrounded by darker terrain, reminiscent of a
free-standing landmass. At the region’s western edge, dark sand dunes
give way to land cut by river networks, hills and valleys. These
narrow river networks flow onto darker areas, which may be lakes. A
crater formed by the impact of an asteroid or by water volcanism is
also visible. More channels snake through the eastern part of Xanadu,
ending on a dark plain where dunes, abundant elsewhere, seem absent.
Appalachian-sized mountains crisscross the region.
“We could only speculate about the nature of this mysterious bright
country, too far from us for details to be revealed by Earth-based
and space-based telescopes. Now, under Cassini’s powerful radar eyes,
facts are replacing speculation,” said Jonathan Lunine, Cassini
interdisciplinary scientist at the University of Arizona, Tucson.
“Surprisingly, this cold, faraway region has geological features
remarkably like Earth.”
Titan is a place of twilight, dimmed by a haze of hydrocarbons
surrounding it. Cassini’s radar instrument can see through the haze
by bouncing radio signals off the surface and timing their return. In
the radar images bright regions indicate rough or scattering
material, while a dark region might be smoother or more absorbing
material, possibly liquid.
Xanadu was first discovered by NASA’s Hubble Space Telescope in 1994
as a striking bright spot seen in infrared imaging. When Cassini’s
radar system viewed Xanadu on April 30, 2006, it found a surface
modified by winds, rain, and the flow of liquids. At Titan’s frigid
temperatures, the liquid cannot be water; it is almost certainly
methane or ethane.
“Although Titan gets far less sunlight and is much smaller and colder
than Earth, Xanadu is no longer just a mere bright spot, but a land
where rivers flow down to a sunless sea,” Lunine said.
Observations by the European Space Agency’s Huygens probe, that
Cassini carried to Titan, and by NASA’s Voyager spacecraft strongly
hint that both methane rain and dark orange hydrocarbon solids fall
like soot from the moon’s dark skies.
On Xanadu, liquid methane might fall as rain or trickle from springs.
Rivers of methane might carve the channels and carry off grains of
material to accumulate as sand dunes elsewhere on Titan.
“This land is heavily tortured, convoluted and filled with hills and
mountains,” said Steve Wall, the Cassini radar team’s deputy leader
at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. "There appear
to be faults, deeply cut channels and valleys. Also, it appears to be
the only vast area not covered by organic dirt. Xanadu has been
washed clean. What is left underneath looks like very porous water
ice, maybe filled with caverns.
“In the 1980s, it took the shuttle imaging radar to discover
subsurface rivers in the Sahara. Similarly, if it hadn’t been for the
Cassini radar, we would have missed all of this. We have a newly
discovered continent to explore,” Wall said.
Cassini will view Titan again on Saturday, July 22, exploring the high
northern latitudes. In the next two years the orbiter will fly by
Titan 29 times, nearly twice as many encounters as in the first half
of Cassini’s four-year prime mission. Twelve of the planned flybys
will use radar.
For Cassini images and information, visit:
The Cassini-Huygens mission is a cooperative project between NASA, the
European Space Agency and the Italian Space Agency. The Jet
Propulsion Laboratory manages the Cassini-Huygens mission for NASA’s
Science Mission Directorate, Washington.