Cassini's Radar Shows Titan's Young Active Surface
The first radar images of Saturn's moon Titan show a very complex
geological surface that may be relatively young. Previously,
Titan's surface was hidden behind a veil of thick haze.
Image above: In this radar image, brighter areas may correspond to rougher terrains and darker areas are thought to be smoother. This image highlights some of the darker terrain, which the Cassini team has nicknamed "Si-Si the Cat" after a team member's daughter, who pointed out its cat-like appearance
Image credit: NASA/JPL.
+ Click for full caption
"Unveiling Titan is like reading a mystery novel," said Dr.
Charles Elachi, director of NASA's Jet Propulsion Laboratory,
Pasadena, Calif., and team leader for the radar instrument on
Cassini. "Each time you flip the page you learn something new,
but you don't know the whole story until you've read the whole
book. The story of Titan is unfolding right before our eyes, and
what we are seeing is intriguing."
The Oct. 26 flyby marked the first time Cassini's imaging radar
was used to observe Titan. The radar instrument works by
bouncing radio signals off Titan's surface and timing their
return. This is similar to timing the returning echo of your
voice across a canyon to tell how wide the canyon is. Radio waves
can penetrate the thick veil of haze surrounding Titan.
Approximately 1 percent of Titan's surface was mapped during the
Oct. 26 flyby. Radar images from Titan's northern hemisphere, a
region that has not yet been imaged optically, show great detail
and features down to 300 meters (984 feet) across. A wide
variety of geologic terrain types can be seen. There are bright
areas that correspond to rougher terrains and darker areas that
are thought to be smoother.
"In the two days since this flyby, our understanding of Titan has
grown tremendously," said Dr. Jonathan Lunine, Cassini
interdisciplinary scientist, University of Arizona, Tucson.
"Titan is a dynamic place with complex geologic processes that
may be shaping its surface. Its surface may well be covered with
organic materials, but we still don't know how much of the
surface is liquid or solid. The fact that we have seen few
craters tells us that Titan’s surface is young."
The radar images show a world brimming with features that are
dark and white, indicating sharp contrast. One area dubbed "Si-
Si" or the "Halloween cat" because it is shaped like a cat's head
is very dark and relatively smooth. That leads scientists to
speculate that it might be a lake of some sort, but they caution
that it is too soon to know for sure.
"With the radar in its active mode, it is like shouting at Titan
and listening for the echoes," said Dr. Ralph Lorenz, Cassini
radar team member, University of Arizona, Tucson. "But we can
also just listen with the sensitive radar receiver, the
radiometry. The radiometry data shows early indications of the
composition of the surface materials. One interpretation of what
it is telling us is that Titan is a place covered with organics."
The optical imaging cameras on Cassini show streaks on the
surface. The streaking may be caused by movement of a material
over the surface by wind, flowing hydrocarbon liquids, or a
moving ice sheet like a glacier. Imaging scientists are also
seeing multiple haze layers in Titan's atmosphere that extend
some 500 kilometers (310 miles) above the surface. At the
surface Titan's atmosphere is about four times denser than
With a remarkable flyby and complicated set of spacecraft
gymnastics, Cassini will try its luck with Titan again on Dec.
13, 2004. The European Space Agency's Huygens probe will detach
from Cassini on Christmas Eve and descend through Titan's dense
atmosphere on Jan. 14, 2005.
"It's as if we were building a puzzle without the top of the
box," said Lunine. "It will be necessary to piece together the
clues provided by Cassini and Huygens over the next few years.
Sometimes we'll be wrong and we'll need to take the pieces apart
and reassemble them again until finally, a complete picture of
the nature and evolution of Titan pops into view," said Lunine.
More information on the Cassini-Huygens mission is available at
The Cassini-Huygens mission is a cooperative project of NASA, the
European Space Agency and the Italian Space Agency. The Jet
Propulsion Laboratory, a division of the California Institute of
Technology in Pasadena, manages the Cassini-Huygens mission for
NASA's Science Mission Directorate, Washington, D.C.
Carolina Martinez (818) 354-9382
NASA's Jet Propulsion Laboratory
Don Savage (202) 358-1727
NASA Headquarters, Washington, D.C.