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Last Updated: Monday, 27 December, 2004, 10:48 GMT
Cassini's goodbye Huygens picture
Huygens pictured by Cassini (Nasa)
Huygens appears as a white blob just a few pixels across
Cassini has snapped an image of the Huygens probe it has just despatched to study Titan, Saturn's largest moon.

The image, taken some 12 hours after release, shows the 2.7m-wide robot lab moving away from its mothership.

Although Huygens appears in the image only as a few pixels, the information will help mission engineers better understand its trajectory.

This will allow them to narrow down the likely area on the surface of Titan where Huygens will land.

Ground controllers received confirmation at 0324GMT on Saturday that the 319kg robot lab had ejected from Cassini.

The probe was released at a gentle, relative speed of 30cm/s and at a spin rate of seven revolutions per minute, which will help stabilise the craft when it enters Titan's atmosphere.

HUYGENS' INSTRUMENTS
Huygens diagram (Nasa/Esa)
1. HASI - measures physical and electrical properties of Titan's atmosphere
2. GCMS - identifies and measures chemical species abundant in moon's 'air'
3. ACP - draws in and analyses atmospheric aerosol particles
4. DISR - images descent and investigates light levels
5. DWE - studies direction and strength of Titan's winds
6. SSP - determines physical properties of moon's surface
That entry is scheduled to begin at just after 0900GMT on 14 January - although it will be some hours later before scientists on Earth learn if the mission has been a success or a failure.

The Saturnian system is so far from Earth that it takes over an hour for signals to be sent back, even at light-speed.

Titan is the only known planetary satellite with an appreciable atmosphere.

Dominated by nitrogen, methane and other organic (carbon-based) molecules, conditions on Titan are thought to resemble those on Earth about 4.5 billion years ago.

As such, scientists hope to see many of the chemical processes that led to the conditions in which life developed on our planet (but with temperatures down to -179C, Titan itself is considered too cold to host biology).

It is possible, also, that Titan retains great expanses of liquid ethane and methane on its surface.

Launched on 15 October, 1997, Cassini-Huygens went into orbit around Saturn on 1 July this year after a voyage of 3.5 billion km (2.2 billion miles).

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

The adventure has already produced some extraordinary pictures of the ringed planet and its moons - the images surpass anything previously obtained.

The two spacecraft components of the mission are named after 17th-Century astronomers who made the first clear observations of Saturn and its moons, Italian Jean-Dominique Cassini and Dutchman Christiaan Huygens.

Although the short life of Huygens' batteries means nothing will be heard from the probe after 14 January, the mothership Cassini's mission around the Saturnian system will continue for at least another three-and-a-half years.




BBC NEWS: VIDEO AND AUDIO
How Huygens detached from its mothership



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