After Cassini-Huygens what next for Titan?
6 June 2001With only four years to go before the Huygens probe arrives at Titan, plans are already being drawn up for possible follow-up missions to Saturn's largest moon.
Space scientists must be a patient lot. Between the time it takes to plan a mission and then to accomplish its goals, decades can pass by. This is particularly the case for those involved in planetary exploration. Despite this, studying the planets and small bodies of our Solar System is a passion for many.
One such target of affection is Titan, Saturn's largest moon, and the destination of the Huygens probe carried by the Cassini spacecraft. Our current knowledge of Titan comes from 'remote-sensing' - observations with ground-based telescopes and space-based observatories. Huygens will revolutionize our vision of Titan with its unique measurements.
In just four years time the spacecraft will arrive at Titan and the Huygens probe will be released. As it descends Huygens will make detailed in situ measurements of Titan's atmosphere. Images and other remote-sensing measurements of the surface of Titan will also be made during the descent. If the probe survives the impact with the surface of Titan it will also make direct measurements of the state and composition of the landing site surface.
These results are eagerly anticipated by all. Our first close-up view of this far-flung moon will no doubt be a cause for admiration and wonder.
Yet despite the fact that Cassini-Huygens has not yet reached its destination, scientists are already considering possible follow-up missions. Opportunities for interplanetary travel depend on favourable alignments of the planets which allow the spacecraft to reach their destination sooner by taking advantage of the gravity boost of the planets.
A trip to Titan requires a favourable alignment between Jupiter and Saturn, an occurrence which arises only once (for a three year period) every 20 years. So planetary explorers must be ready when these relatively rare opportunities arise.
One of the more imaginative suggestions for such a follow-up mission, put forward by Ralph Lorenz, a space scientist at the Lunar and Planetary Laboratory at the University of Arizona, was discussed at the recent exo/astrobiology workshop held in Frascati, Italy.
Ralph's idea is to use a helicopter, which would be capable of repeated takeoff and landing, flying a few hours every day. Titan's dense atmosphere and low gravity could favour such a solution.
"For detailed investigations of Titan's landscape we really need higher resolution images than will be obtained with the instruments on the Cassini orbiter," according to Ralph Lorenz. "Moreover, a detailed surface chemical analysis is required in order to identify the key chemical processes that generate prebiotic molecules."
The Huygens probe will land at a random location on the surface of Titan, and will provide detailed measurements of the surface at that spot. It may well be the case that the Cassini orbiter identifies more interesting locations for a follow-up mission to explore.
"Scientifically speaking," says Lorenz, "if a single lander were available, exploring a different place might be more useful, but the advantage of a helicopter or an airship is that it could visit many sites, including the Huygens landing site."
The arrival of Huygens at Titan in 2004 will mark the first milestone in the exploration of Saturn's enigmatic moon. What we learn from Cassini-Huygens will influence the missions which follow in its footsteps.
"Our understanding of Titan is still very uncertain," says Jean-Pierre Lebreton, Huygens project scientist. "With Cassini-Huygens we will really see Titan at close quarters. What we find there will strongly influence our requirements for future explorations of this moon."
For more information please contact:
Jean-Pierre Lebreton, Huygens project scientist
Tel: +31 71 565 3600