Methane rain feeds Titan's rivers
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, Descent Imager Spectral Radiometer (DISR).
Mission scientists confirmed that these processes are 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 is liquid methane (a carbon-based "organic" compound) 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."
Professor John Zarnecki, principal investigator for Huygens' surface science package (SSP), said his instrument had detected indications of methane evaporating as Huygens settled into the surface.
But Titan's 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 Nasa's 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.
"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 around 0905 GMT on 14 January.
Huygens landed on Titan at around 1138 GMT at a leisurely speed of around 5m/s. Cassini received data from Huygens until 1250 GMT when the orbiter passed over the horizon and severed the communications link.
But the Parkes radio telescope was still receiving a signal from Huygens at 1555 GMT, scientists said.
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Published: 2005/01/21 10:08:33 GMT
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