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Streams, rivers, springs and rain

New images from Saturn’s moon Titan show familiar Earth-like features including springs, rivers, streams and rainfall – but with exotic ingredients, scientists say.

The researchers held a press conference Friday in Paris to present their first analysis of results from Huygens, a European-built probe that landed on the smog-shrouded world a week ago.

“There are truly remarkable processes on Titan’s surface which are very similar to those occurring on Earth today,” said Jean-Pierre Lebreton, Huygens project scientist and mission manager for the European Space Agency.

Although researchers didn’t find any living things, they did report plenty of evidence of chemistry and processes that could be conducive to life. Titan’s chemistry is thought to be similar to the chemistry on Earth at life’s dawn.

Part of their analysis was based on images created by Huygens with stereo views. These are images consisting of combinations of two pictures from slightly different vantage points, which reveals three-dimensionality better than normal images. The stereo images have not yet been made public.

In one photograph, “We see a ridge system with a peak; the ridge is about 100 meters [109 yards] tall,” Said Martin G. Tomasko, principal investigator for the Descent Imager and Spectral Radiometer, the camera aboard Huygens. Tomasko is with the University of Arizona in Tucson, United States.

Branching off the ridges are dark lines, which are probably evidence of rain, he said. The dark lines are riverbeds or river channels created by rain washing off the hilltops, he explained.

“It might have rained yesterday,” said Toby Owen, Cassini Interdisciplinary Scientist for the atmospheres of Titan and Saturn, from the Institute for Astronomy, Honolulu, United States. “This is really a very active situation.”

Another feature of the landscape, Tomasko said, is short, stubby dark lines—in contrast to the long ones. The short ones “I think are what you would see if you had springs, or water flowing out of the side of a hill,” he added.

The rain and the liquid in the channels, however, consists of not water but methane, a substance which on Earth is a colorless, flammable gas. Methane is also produced by the decomposition of living things. And like many other chemicals found on Titan, it is a hydrocarbon. Hydrocarbons are chemicals composed of hydrogen and carbon, a family of substances crucial to forming living things on Earth.

The dark material in the images is “a concentration of dirt, organic material, that lands on everything and gets washed into low regions,” Tomasko said.

“The methane rain washes the dark material off the high points and concentrates it on the bottom of these channels. They eventually flow out to these broad plains,” Tomasko said. There, the liquid settles into the ground.

“The riverbeds are dry most of the time,” however, Tomasko said. “You have pools [of liquid] that sink into the surface” shortly after it rains.

“We don’t see indications of open pools of liquid,” he added. “The liquid is just underneath the surface, as if it rained not very long ago.” However, “even in dark regions there’s plenty of evidence of fluid flow,” said Tomasko.

“We were extraordinarily lucky to come down on the boundary between this bright and dark material,” he added.

Many of the speculations that astronomers had made about Titan before the mission have turned out to be correct, according to the researchers.

They said they found proof of the previously hypothesized presence of methane and hydrocarbons, using the mass spectrometer aboard Huygens. A mass spectrometer is an instrument that identifies the chemical components of a substance by separating them according to their differing mass and electric charge.

Bigger than the planets Mercury and Pluto, Titan is one of the few moons in our solar system with its own atmosphere. It is cloaked in a thick, smog-like haze. Further study of this moon promises to reveal much about planetary formation and, perhaps, about the early days of Earth as well, scientists believe.

The probe’s landing last week was the last phase in a seven-year journey strapped to the Cassini Orbiter, a spacecraft built as a collaboration among 17 nations. Cassini, the first craft to orbit the Saturn system of rings and moons, began its orbit on June 30. Huygens was released from Cassini on Dec. 25 and later dropped through Titan’s atmosphere, collecting data as parachutes slowed it from super sonic speeds.

The probe carried six instruments designed to study the content and movements of Titan’s atmosphere and collect data and images on the surface. It sent data and images to the Cassini mothership, which relayed them to Earth.

The probe began transmitting data to Cassini during its descent and after landing at least as long as Cassini was above Titan’s horizon. Radio telescopes on Earth continued to receive this signal well past the expected lifetime of Huygens. It was expected to last only about half an hour in the moon’s harsh climate, researchers said, but it went on working for as long as three hours.

Lebreton said future missions to Titan might include rovers and airborne devices, such as balloons.

World Science. Jan. 21, 2005.

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