* Astronomy

"Islands in the stream"... possible 'islands' on a dark plain

	These images from the Huygens DISR instrument show new features, such as evidence of flow around 'islands', deposits of water ice and channels which could have been created by methane springs.

Scientists have also recovered much data from Huygens that had been thought lost due to a communications failure, that missing data could be recovered via a network of radio telescopes that listened for Huygens' signals

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.

Mosaic of river channel and ridge area on Titan	Image Credit: ESA

" 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 "

The pattern of rainfall on Titan may be seasonal.

Surface	Image Credit: ESA

"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."

"We see a ridge system with a peak 100 metres tall."
There is a hint of how the hills are built:
"In another region we see a white streaky pattern, evidence of water ice being extruded by the surface."

8 kilometres above the surface ( Full Size Image)	Image Credit: ESA

DISR surface images show small rounded pebbles in a dry riverbed. Spectra measurements (colour) are consistent with a composition of dirty water ice rather than silicate rocks. However, these are rock-like solid at Titan's temperatures.

Titan's soil appears to consist at least in part of precipitated deposits of the organic haze that shrouds the planet. This dark material settles out of the atmosphere. When washed off high elevations by methane rain, it concentrates at the bottom of the drainage channels and riverbeds contributing to the dark areas seen in DISR images.

Huygens panorama of titan (Full Size Image)	Image Credit: ESA

Scientists speculate that the white streaks are a ground 'fog' of methane or ethane vapour

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Titan drainage channels

Titans orbit period of 15.95 days, and the moons position relative to Saturn would mean that the `tide` was rising.

"It looks like something has flowed at some time to make those channels. But is it something that has solidified?"

The drainage channels were either caused by falling rain or seepage of liquid hydrocarbons similar to lighter fuel or natural gas (CH₄) which had soaked into the ground.

A sound file generated from the communication between the Cassini spacecraft and the Huygens probe has been released by ESA. This was converted to an audio file to show the descent profile indicating how the Huygens probe moved through the atmosphere of Titan.
To Listen:

As the Huygens probe plunged through Titans atmosphere, it sent back scientific data. It landed on Titan at around 1138 and transmitted a signal until at least 1555 GMT.
Scientists will comb the data sent back for the chemical signature of life in a bid to identify the moon's source of methane.
Methane is constantly destroyed by UV light so there must be a source within Titan to replenish the atmosphere.
Life could be a possible source of this hydrocarbon along with geological processes.
Titan is too cold for surface biology, but microbes could survive deep within Titan.
Methane can also be released from a trapped form called clathrate and can be produced by a geological process called "serpentisation".
Neither of these involves biology.
Dominated by nitrogen, methane and other organic molecules, Titan resembles a deep-frozen version of Earth 4.6 billion years ago.
Liquid methane rains down on Titan into river channels carved between hills of water ice. Reservoirs of this hydrocarbon probably lie on or just below the surface.
But UV light would destroy all the methane on Titan within 10 million years if it were not being constantly renewed.

"We cannot say there is absolutely no chance for life. Models of Titan's interior show there should be an ocean about 100km deep at around 300km below the surface."

If the models are correct, this ocean would be composed mostly of liquid water with about 15% ammonia at a temperature of about -80°C.

"We have liquid water, organics not so far away; we have everything on Titan to make life.

If methane-producing microbes had colonised this habitable zone, scientists might detect its chemical signature by looking at the relationship of two forms (or isotopes) of the element carbon - C₁₂ and C₁₃.
Living cells preferentially incorporate C₁₂. So compounds produced by living things should be depleted of "heavier" isotopes such as C₁₃, and have a high C₁₂/C₁₃ ratio.
Scientists should be able to measure this ratio in data sent back by the Gas Chromatograph Mass Spectrometer (GCMS) instrument on Huygens.

"The GCMS can directly detect the C₁₂/C₁₃ carbon ratio. We haven't done that yet, but we're working on it".

"It's one factor we can take into account to figure out how methane is getting replenished."

However, scientists favour the geological process of serpentisation as a more likely source of the moon's methane.
In serpentisation, geothermal activity generates methane through the oxidation of metals such as iron, chromium and magnesium which could be contained in crustal rocks below Titan's surface.
Another possibility is that methane molecules are trapped in a water-ice matrix called clathrate (or methane hydrate).