European joy as Huygens probe lands on Titan

The European-built Huygens probe has successfully landed on Titan, penetrating the thick, orange-coloured clouds that have until now prevented scientists observing details of the moon's surface.

The first scientific data to reach Earth arrived at the European Space Operations Centre (ESOC) in Germany at around 16:30 GMT today.

Descending by parachute over a period of two-and-a-half hours, Huygens has gathered invaluable atmospheric readings and taken some 750 images of Saturn's largest and most mysterious moon along the way.

“Titan was always the target in the Saturn system where the need for ‘ground truth’ from a probe was critical. It is a fascinating world and we are now eagerly awaiting the scientific results,” said Professor David Southwood, Director of ESA’s scientific programme.

Huygens is mankind’s first successful attempt to deliver a probe onto to a target so far out in the solar system, and is being hailed a great achievement for Europe and its US partners in this ambitious international endeavour.

The probe started its descent through Titan’s hazy cloud layers from an altitude of about 1270 kilometres at around 10:15 GMT, and during the next three minutes Huygens had to decelerate from 18,000 to 1400 kilometres per hour.

A sequence of parachutes then slowed down the probe to less than 300kph. At a height of about 160 kilometres the probe’s scientific instruments were exposed to Titan’s atmosphere, and at about 120 kilometres the main parachute was replaced by a smaller one to complete the descent, with touchdown at around 12:34 GMT.

The earliest indication that the mission was a success came this morning when the Robert C. Byrd Green Bank Telescope (GBT) of the National Radio-astronomy Observatory in West Virginia, a part of the global network of radio telescopes involved in tracking the probe, detected a 'carrier' signal to NASA's Cassini spacecraft, currently in orbit above Saturn. The presence of the carrier signal indicated that Huygens had survived the trip intact and had begun to transmit.

Cassini then began to relay the signal back to Earth at around 15:30 GMT.

Scientists are as yet uncertain what kind of surface the probe encountered when it 'landed', but speculate a richly diverse topography. A splash down in an ocean would probably mean better data from Huygens, as even if the probe lasted only a few minutes before sinking it would have at least stayed in an upright position, essential for sending the data back to Cassini and to the scientists on Earth. Moreover, some of Huygens's instruments are better prepared to analyse liquids.

One of the main reasons of sending Huygens to Titan is that its methane-rich nitrogen atmosphere and its surface may contain many chemicals of the kind that existed on a young Earth.

Huygen's journey began on Christmas Day 2004 when Cassini, which spent seven years travelling to the ringed planet, deployed the European Space Agency's 2.7m-wide, 319kg probe, sending the craft on its 22-day trip to Titan.

(GB)