Published online 29 October 2004 | Nature | doi:10.1038/news041025-21

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Probe data reveal Titan's etched face

Cassini images suggest a surprisingly dynamic surface.

False colour image of Titan, showing its atmosphere (in blue).False colour image of Titan, showing its atmosphere (in blue).© NASA

Scientists analysing data captured by the Cassini-Huygens spacecraft as it swept past Saturn's moon Titan, have described a cold landscape carved by winds and perhaps puddled with organic lakes.

The spacecraft grazed Titan's atmosphere on 26 October, allowing its instruments a first opportunity to penetrate the opaque orange smog smothering the moon and glimpse the surface below.

At a briefing on Thursday, a team of scientists discussed some early analyses from Cassini's instruments, particularly those from a radar which scanned 1% of the moon's surface area. The black-and-white close-up images it produces reflect the pattern with which radar beams bounce back from the surface. This gives hints of the surface's texture, slope and chemical composition.

“It's an extremely dynamic and active place. It's a tremendous revelation.”

Planetary scientist Jonathan Lunine
University of Arizona, Tucson

The take-home message, although preliminary, is that Titan may be sculpted by fierce winds and cradle vast lakes of organic chemicals. "It's an extremely dynamic and active place," says planetary scientist Jonathan Lunine of the University of Arizona, Tucson. "It's a tremendous revelation."

Black cats and icy lava

The radar revealed a collection of dark splotches on Titan's surface, which the researchers suspect may be interconnected lakes of methane, perhaps gusted into waves. With a stretch of the imagination, they say that one looks like the head of black Hallowe'en cat.

Researchers are also puzzling over a series of long, linear streaks of material stretched across the moon's equatorial surface, glimpsed by radar and a near-infrared imaging camera. Like sand ridges shaped by the wind, these might, according to one idea, be particles of material pooled in sheltered areas.

Radar image of Titan’s surface. Brighter areas may correspond to rough terrain and dark areas are thought to be smoother. The Cassini team has nicknamed this feature “Si-Si the Cat”.Radar image of Titan’s surface. Brighter areas may correspond to rough terrain and dark areas are thought to be smoother. The Cassini team has nicknamed this feature “Si-Si the Cat”.© NASA

A third feature looks something like flows of molten lava from a volcano. But because the moon is thought to harbour a heart of water and ice, the flows may instead be frozen remnants of once-liquid water.

Data from Cassini are also strengthening the idea that Titan's surface is swathed in organic, or carbon-based, chemicals, rather than inorganic rock. These might include liquid ethane and propane or solid polymers of acetylene, all preserved at a chilly -179 ºC.

An early Earth?

Titan captivates space scientists because it is the second largest moon in the Solar System and the only one known to have an atmosphere. Its chemical make-up is thought to be similar to that on Earth long before life emerged.

Streaks of surface material near Titan’s equator. They may be caused by the movement of a fluid over the surface.Streaks of surface material near Titan’s equator. They may be caused by the movement of a fluid over the surface.© NASA

The team says it is too early in its analyses to say anything really definitive about Titan's surface. "You don't expect instantaneous satisfaction," says Charles Elachi, director of NASA's Jet Propulsion Laboratory in Pasadena, California.

Researchers hope to build up a fuller picture of the moon's surface from the space probe's 44 planned fly-bys and from the Huygen's probe, when it detaches and plunges down through Titan's cloak of gas early next year. "We can look forward to revealing all of Titan's nature over the next four years," Lunine says 

University of Arizona, Tucson