WASHINGTON, May 4 (Reuters) Saturn's moon Titan has huge regions covered with dunes, possibly made out of ice crystals, sand or some other unknown material, international space scientists reported today.
Images of Titan beamed back to earth from the joint U.S.-European Cassini mission look very much like sand dunes in the Sahara desert, Namibia, Saudi Arabia and Australia, the researchers said.
''It's bizarre,'' said Ralph Lorenz of the University of Arizona, who worked on the study.
''These images from a moon of Saturn look just like radar images of Namibia or Arabia. Titan's atmosphere is thicker than Earth's, its gravity is lower, its sand is certainly different -- everything is different except for the physical process that forms the dunes and resulting landscape.'' The Cassini craft was launched in 1997 and reached Saturn in 2004 after an interplanetary cruise that took it past Venus and Jupiter.
The latest radar images show the dunes are up to 150 metres high and hundreds kilometers long.
Dark patches on Titan, the largest of Saturn's 47 moons, were at first thought to be seas -- but now they appear to be largely made up of these dunes.
Titan's flat surface is very cold, with a temperature of minus 180 degrees Celsius and scientists believe its thick atmosphere may occasionally rain methane.
The existence of pristine dunes, piled over other geological features, shows that wind recently blew fine grains of some material around, the researchers wrote in their report, published in the journal Science. It could be sand, ice or something else, they added.
But they called the presence of the dunes ''comforting'', because at least the processes that lead to their formation can be studied on Earth.
Also today, the European Space Agency released new movies of the descent of its Huygens probe to Titan's surface.
The probe is piggybacked onto the Cassini spacecraft.
The four-hour movie shows what the probe actually ''saw'' within the few hours of the descent and the eventual landing.
''At first the Huygens camera just saw haze over the distant surface,'' said Erich Karkoschka of the University of Arizona, who created the movies.
Then the moon's sandy surface comes into view.
The films can be seen on the Internet at http://saturn.esa.int or http://www.lpl.arizona.edu/DISR/.
Reuters VD VP0245