January 15, 2005

Titan: Up Close and Orange

The European Space Agency has released the first of several hundred images captured by the Huygens probe during its descent through the atmosphere of Saturn's giant moon Titan. They reveal a world of diverse landforms, shaped at least in part by fluid erosion. Some the images are reminiscent of early photographs of Mars.

Astrobiology Magazine -- The European Space Agency has released the first of several hundred images captured by the Huygens probe during its descent through the atmosphere of Saturn's giant moon Titan.

Although most of the images have not yet been cleaned up - they were released in their raw form - they reveal a world of diverse landforms, shaped at least in part by fluid erosion. Some of the images are reminiscent of early photographs of Mars.

The left half of the first image, taken from a height of 16 kilometers (10 miles) above Titan's surface, shows a pattern of branching channels that look like canyons on Earth cut by water. It's unlikely that water was responsible in Titan's case, though; Titan is far too cold for liquid water to flow on its surface. Scientists say it's too early to speculate about what the fluid might be.

On the right side of the image is a large flat dark area that is being interpreted initially as a large body of liquid with a visible shoreline. This is the first image of Titan that seems to confirm scientists' speculation that Huygens would find large pools of liquid hydrocarbons, methane or ethane, on the moon's surface.

The second image, taken from 8 kilometers (5 miles) above the surface, shows a hodge-podge of light and dark areas that are more difficult to interpret. The darker areas may be bodies of liquid as well. More work is needed to be certain.

In the coming hours and days, image-processing teams will enhance the contrast of this and other images and clean up artifacts in attempt to extract more detail. This will then be combined with spectroscopic data that will tell scientists how reflective various areas of the image are. Combining imaging and reflectance data will help scientists figure out what they are looking at.

The third image is perhaps the most stunning of all. It was taken from the surface of Titan, and shows a plain of what appear to be boulders stretching to the horizon. At first glance, it resembles a martian landscape.

"The amazing thing to me is how familiar this kind of scene seems. All of us on Earth see scenes not so different from this all the time. We see boulders strewn around. We've seen things that kind of look like this on Mars. We've seen things that look like this everywhere," said Marty Tomasko, the principal investigator for Huygens' camera, the Descent Imager/Spectral Radiometer (DISR).

"These probably are not really rocks of silicate. These are probably blocks of ice, perhaps water ice frozen solid. The temperatures on Titan are so cold that water would be as stiff and as hard as a boulder would be on the Earth," he said.

"But there are questions that come to mind, too. How did this scene get produced? What physical processes happened on the surface to produce this? What kinds of motion, and the uplift, and the breaking of the rocks and the migration of the rocks - there are lots of questions that people will be debating."

That debate has already begun, as the Huygens image-processing team and data-processing teams from Huygen's other instruments hunker down to work through the night in an effort to turn the billions of bits of raw data returned by Huygens into meaningful information.

There is one sour note to the day's events. Only one of Huygens' two communications channels functioned properly, resulting in a significant loss of data. One set of missing data was designed to help scientists learn about wind speeds in Titan's atmosphere.

Fortunately, scientists will be able partially to reconstruct the wind-speed information by studying variations in the frequency of the Huygens carrier signal detected on Earth by a global network of large radio telescopes.

Also lost, however, were half of the images captured by Huygens. This may make it difficult to construct the panoramic mosaic images that Tomasko's team was hoping to produce.

New Photos Show Titan Has Orange Surface

New, refined pictures from Saturn's moon Titan released Saturday show a pale orange surface covered by a thin haze of methane and what appears to be a methane sea complete with islands and a mist-shrouded coastline.

Space officials worked through the night to sharpen the new photos taken by the space probe Huygens, which snapped the images Friday as it plunged through Titan's atmosphere before landing by parachute on the surface.

Many scientists at the European Space Agency center in Darmstadt, Germany, looked tired from their overnight work but were still clearly elated about the successful arrival of data from Huygens the day before - a major triumph for the European space program.

"The instruments performed brilliantly," said John Zarnecki, in charge of the surface instruments. "We can't find a single missing data frame. The link and the quality of the data was absolutely superb."

Officials played back sound gathered from Huygens' microphone at the surface - a whooshing noise they did not identify. But the center of attention was the pictures.

One shot taken from an altitude of 10 miles showed dark lines that suggested stream beds carved by liquid flowing into a dark area suspected to be a sea of liquid methane - with light areas in the dark that could be islands.

"It is almost impossible to resist speculating that the flat dark material is some kind of drainage channel, that we are seeing some kind of a shoreline," said scientist Marty Tomasko from the University of Arizona, head of the camera team. "We still don't know if it has liquid in it."

Titan's notorious haze - which has kept astronomers from getting a better picture through telescopes - is obvious in the two refined images shown Saturday.

An image taken on the surface shows chunks of what scientists say looks like water ice scattered over an orange surface overcast by methane haze. On Friday, the chunks were described as boulder-sized, but overnight examination showed they are much smaller and simply look big because they are close to Huygens' camera.

Deep shadows and depressions around the chunks suggest they could have been surrounded by liquid at one time, scientists said.

Titan is the only moon in the solar system known to have a significant atmosphere. Rich in nitrogen and containing about 6 percent methane, its atmosphere is believed to be 1 1/2 times thicker than Earth's.

Shushiel Atreya, part of the group studying the atmosphere, said the instruments revealed "a dense cloud or thick haze approximately 11-12 miles from the surface."

"Presumably there is a reservoir of methane on the surface," Atreya said.

The surface itself appears to be "material which might have a thin crust followed by a region of relative uniform consistency," Zarnecki said. "The closest analogues are wet sand or clay."

The $3.3 billion Cassini-Huygens mission to explore Saturn and its moons was launched in 1997 from Cape Canaveral, Fla., in a joint effort by NASA, the ESA and the Italian space agency. Huygens was spun off from the Cassini mother ship Dec. 24.

Titan is the first moon other than the Earth's to be explored. Scientists believe its atmosphere is similar to that of early Earth's and studying it could provide clues to how life arose on our planet.

The heart of Huygens' mission was its 2 1/2-hour parachute descent, during which it also sampled the atmosphere and deployed a microphone to gather sounds.

Scientists want to know whether Titan has lightning and if it has the seas of liquid methane and ethane that have been theorized. Both ethane and methane are gases on Earth, but are believed to exist in liquid form on Titan because of high pressure and extreme temperatures of minus 292.

After entry into Titan's atmosphere, Huygens shed its wok-shaped heat shield and deployed a series of parachutes. The data were transmitted back to Cassini, which relayed them to Earth.

Titan's images came streaking across the cosmos Friday, and scientists grew increasingly ecstatic with the scenes from the probe, named after Titan's discoverer, the 17th-century Dutch astronomer Christiaan Huygens.

"I think all of us continue to be amazed as we watch our solar system unveil," NASA science administrator Alphonso Diaz said Friday as the extraordinary images were displayed on screens at mission control in Darmstadt. "It challenges all our preconceptions that all these planets are static places."


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Where is Cassini Now?