* Astronomy

and cover an area extending out to 30 kilometres.

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

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

from NPR.org

click here for interactive panorama

Huygens on the Ground	Image Credit: NASA/JPL

Huygens is going to descend during `daylight hours`. Sunlight filtering through the casts an orange glow across the landscape "like 1000 full moons, and bright enough to read a newspaper, but still about 1000 times dimmer than a sunlit day on Earth.
Just before Huygens lands it will turn on an intense flashlight to shine onto the terrain below. This is done to improve pictures of the landing site and help the probe's spectrometers get better readings of elements and minerals in the soil.
"The gods smiled on us." - ESA's space science director David Southwood,

On 17 December the orbiter was placed on a controlled collision course with Titan in order to release Huygens on the proper trajectory, and on 21 December all systems were set up for separation and the Huygens timers set to wake the probe a few hours before its arrival at Titan.

	Huygens discarding heat shield

The Huygens probe separated on the morning of 25 December at about 02:00 UTC (03:00 CET) . Since the Cassini orbiter will have to achieve precise pointing for the release, there will be no real-time telemetry available until it turns back its main antenna toward Earth and beams the recorded data of the release. This signal then took 1 hour and 8 minutes to cross the 1.2 billion kilometres separating the Cassini spacecraft and Earth. Separation was achieved by the firing of pyrotechnic devices. Under the action of push-off springs, ramps and rollers, the probe was released at a relative velocity of about 35 cm per second, and, to keep on track, will spin on its axis, making about 7 revolutions a minute.

Huygens drifted through space until it hits Titan's atmosphere on January 14 at about 1013 GMT moving at 10 miles a second. The dense air encountered by the probe rapidly slowed it down, allowing Huygens to drift downward under a deployed parachute for almost three hours.
During the descent onto Titan, the Huygens probe scanned the surrounding atmosphere to analyse its composition and take more than 1,000 images as it heads toward the surface.

Huygens entered Titans atmosphere at a relatively steep angle of 65° and a velocity of about 6 km/s. The target was over the southern hemisphere, on the day side. Protected by an ablative thermal shield, the probe decelerated to 400 m/s within 3 minutes before it deploys a 2.6 m pilot chute at about 160 km. After 2.5 seconds this chute pulled away the probes aft cover and the main parachute, 8.3 m in diameter, was deploy to stabilise the probe. The front shield was then released and the probe, whose main objective is to study Titans atmosphere, opened inlet ports and deploy booms to collect the scientific data. All instruments will have direct access to the atmosphere to conduct detailed in-situ measurements of its structure, dynamics and chemistry. Imagery of the surface along the track was also acquired. The Descent Imager/Spectral Radiometer took pictures as the probe slowly spins. These data was transmitted directly to the Cassini orbiter, which, at the same time, will be flying over Titan at 60 000 km at closest approach. Earth-based radio telescopes have detect the signals tone directly.

15 minutes into the descent, at about 120 km, Huygens released its main parachute and a smaller 3 m drogue chute which took over to allow a deeper plunge through the atmosphere within the lifetime of the probes batteries.

The descent lasted about 140 minutes before Huygens impacted the surface at about 6 m/s. The probe has survives all this, and its extended mission will start, consisting in direct characterisation of Titans surface for as long as the batteries can power the instruments and the Cassini orbiter is visible over the horizon at the landing site, i.e. not more than 130 minutes.

Titan Raindrops

At that time, the Cassini orbiter reoriented its main antenna dish toward Earth in order to play back the data collected by Huygens, which will be received by NASAs 70-m diameter antenna in Canberra, Australia, 67 minutes later. Three playbacks are planned, to ensure that all recorded data are safely transmitted to Earth. Then Cassini will continue its mission exploring Saturn and its moons, which includes multiple additional flybys of Titan in the coming months and years.

of descent.( 1.9Mb .Mov)

Huygens separates from Cassini

After release, Huygens did not communicate with Cassini for the whole period until after deployment of the main parachute following entry into Titans atmosphere. Titan's atmosphere, which is about 95% nitrogen and 5% methane, has a pressure near the surface that is one and a half times the Earth's sea level pressure.

On 28 December Cassini will then manoeuvre off collision course to resume its mission and prepare itself to receive Huygens data, which it will record, to later relay back to Earth.

Titan close-up

These images show the surface of Titan at two different infrared wavelengths. They were captured by the visual and infrared mapping spectrometer onboard Cassini as the spacecraft flew by at an altitude of 1200 kilometres - Cassini's closest approach yet to the hazy moon. The image on the left, taken at a wavelength of 2 microns, is the most detailed picture to date of the Titan's surface. It reveals complex landforms with sharp boundaries, which scientists are eager to further study. The image on the right was taken at a wavelength of 1 micron and shows approximately what a digital camera might see. It seems from the pictures received that this area is geologically alive, possibly with liquids moving on its surface.

	No evidence of oceans?

However, synthetic aperture radar images of the surface, captured on Oct. 26, when the Cassini spacecraft flew approximately 2,500 kilometres above the surface, show that the dark regions may represent areas that are smooth, made of radar-absorbing materials, or are sloped away from the direction of illumination. A striking bright feature stretches from upper left to lower right across this image, with connected 'arms' to the East. The fact that the lower (southern) edges of the features are brighter is consistent with the structure being raised above the relatively featureless darker background. Comparisons with other features and data from other instruments has determined that this is a cryovolcanic flow, where water-rich liquid has welled up from Titan's warm interior.
Previous Photometric profiles showed considerable variations across dark areas that were identified as possible lakes or seas. A liquid surface would have been more uniform.
"There is no evidence of oceans,"
But it turns out that there is hydrocarbon flows and lakes.
Most of the features seem to be volcanic in nature, produced by flowing ice rather than molten rock.

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.