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Last Updated: Friday, 21 January, 2005, 10:08 GMT
Methane rain feeds Titan's rivers
Titan, Esa/Nasa/JPL/University of Arizona

Liquid methane rain feeds river channels, lakes, streams, and springs on the surface of Saturn's moon Titan, images from the Huygens probe show.

Scientists have also recovered much data from Huygens that had been thought lost due to a communications failure.

On 14 January, the spacecraft plunged through the moon's atmosphere, sending scientific data - including stunning images - back to ground controllers.

Teams outlined new results at a press conference in Paris, France, on Friday.

The liquid was within a few centimetres of the surface. Our feeling is that in the place we landed, it must have rained not that long ago
Marty Tomasko, mission scientist

"We have evidence of many Earth-like processes [on Titan] such as [rain], erosion and abrasion but with very exotic materials," said Marty Tomasko, who works on the probe's Descent Imager Spectral Radiometer (DISR).

Mission scientists confirmed that these processes were active today.

Fluid flowing on the surface of Titan is helping carve channels between hills of water-ice, seen in the pictures returned from the moon.

Fluid flow

They confirmed there was liquid methane (a carbon-based "organic" compound) on and just below the surface of Titan.

"The liquid was within a few centimetres of the surface. Our feeling is that in the place we landed, it must have rained not that long ago," Dr Tomasko said.

"The area we landed in is more typical of arid regions. The river beds are dry most of the time. Then after rains you have open flowing liquid. There are pools and then they dry out and the liquid methane sinks into the surface."

Marty Tomasko (left), Jean Pierre Lebreton (centre), David Southwood (right)
Scientists gave details of their findings at a conference in Paris
Professor John Zarnecki, principal investigator for Huygens' surface science package (SSP), said the probe detected methane evaporating as Huygens settled into the surface.

This suggests there was some liquid methane on the surface.

This methane must be constantly renewed from some unknown source within the moon.

The dark areas seen in the images are accumulations of smog particles that settle out of Titan's haze on to the surface. This dark organic matter is then washed into the drainage channels and basins where it gathers.

The pattern of rainfall on Titan may be seasonal.

Data recovery

The European Space Agency (Esa) launched an inquiry into the loss of one of two data channels used to relay information from Huygens to Earth via the US space agency's (Nasa) Cassini orbiter.

The channel was not operating on Cassini, and Esa has confirmed that the command to switch it on was not given. But the European agency has claimed full responsibility for the error.

Scientists now say that missing data can be recovered via a network of radio telescopes that listened for Huygens' signals as it plunged through Titan's atmosphere and settled on the surface on 14 January.

Scientists said they had been lucky to land in a prime spot, on a boundary between the light material and dark material.

Artist's impression of Huygens making its descent (Image: Esa)
The probe took two-and-a-half hours to reach the surface
"I didn't know how to express how scientists felt last week and I ended up quoting poetry. You have to understand, this is exploration, not just science," said David Southwood, Esa's director of science.

Huygens mission manager, Jean-Pierre Lebreton, said he would now like to send robotic explorers like Nasa's Mars rovers to Titan.

Huygens was released from its mothership, the Cassini orbiter, on 25 December. It coasted for three weeks towards Titan before hitting the atmosphere at about 0905 GMT on 14 January.

Huygens landed on Titan at 1138 GMT, at a leisurely speed of about 5m/s. Cassini received data from Huygens until 1250 GMT when the orbiter passed over the horizon and severed the communications link.

However, the Parkes radio telescope in Australia was still detecting a carrier signal from Huygens at 1555 GMT, scientists said.

The $3.2bn Cassini-Huygens mission is a joint venture between the US space agency (Nasa), the European Space Agency (Esa) and the Italian Space Agency (Asi).

See the latest pictures from Saturn's moon

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