ESA Science & Technology - 4th anniversary celebration for Huygens team

"The Huygens mission would not have been possible without the hard work and dedication of everyone on the team," said Jean-Pierre Lebreton, ESA project scientist for the Huygens probe.

"Cassini-Huygens is now well over half way to Saturn," he added, "and a great deal has been achieved since the spacecraft set off from Florida."

"We still have a long way to go, but the Huygens probe is in good shape and I am looking forward to a flood of exciting new information when it enters Titan's atmosphere in January 2005."

As is commonly the case on such long duration missions, a number of assumptions made by scientists and engineers prior to the 1997 launch have now had to be re-evaluated. One of the most fascinating questions still unresolved concerns the nature of Titan's smog-shrouded atmosphere and surface.

When Huygens' odyssey began, many scientists believed that much of Titan's surface could be covered by liquid methane or ethane a substance similar to the more familiar paraffin and kerosene. It was thought that lakes or even a global ocean of methane/ethane covered the surface. However, recent ground-based and Hubble Space Telescope observations have shown that such global oceans are unlikely to exist.

Instead, the new studies suggest that a layer of water-ice, possibly overlain by a coating of organic 'sludge', must be present over the entire surface. However, the presence of methane in large quantities in the atmosphere remains a big mystery.

"Somewhere on or under the surface, there seems to be a big methane reservoir that continuously replenishes the atmosphere," said Lebreton.

No-one knows whether Huygens will splash down into a sea of liquid methane, or touch down on a frozen, solid surface that may have some resemblance to the ice sheets of Antarctica and Greenland.

"Fortunately, both of these scenarios were considered in the design of the measurement sequence that will be carried out at landing, as we had to be sure that it could survive either type of landing," said Lebreton.

Another unexpected change since the launch has been the revision of the operational timetable for Huygens' intrepid plunge into Titan. After engineers last year identified a design flaw in the probe's communications system, the flight plans of the Cassini-Huygens spacecraft had to be changed so that none of the unique Huygens data would be lost during its descent to Titan's surface.

In the new plans, the Cassini spacecraft will release Huygens towards Titan around Christmas Day 2004. After a 21-day cruise, the probe will plunge into the thick atmosphere of Titan and parachute onto its icy surface on 14 January 2005, seven weeks later than originally planned.

"On such an ambitious, seven-year-long mission, we always have to be prepared for the unexpected," said Lebreton. "However, thanks to the excellent work done by a joint ESA/NASA team earlier this year, we are now confident that, in just over three years' time, Huygens will successfully penetrate Titan's orange clouds and allow us to see for the first time the alien landscape of this mysterious moon."

The Cassini-Huygens spacecraft is currently more than 900 million kilometers from Earth and moving away from us at a relative speed of around 20 kilometres per second.

For further information please contact:
Dr Jean-Pierre Lebreton Huygens project scientist
ESTEC, The Netherlands
Tel: +31 71 5653600
Email:Jean-Pierre.Lebretonesa.int