Telescopes take close-up on Titan

[Mike]

Astronomers at the Paranal Observatory in Chile have obtained the best images yet of Titan - Saturn's major moon.

They show what may be clouds in its thick and hazy atmosphere of nitrogen, methane and oily hydrocarbons.

The Chandra X-ray telescope in orbit also studied Titan's atmosphere as the moon passed in front of the glowing wreckage of an exploded star.

In January 2005, we may find out more when the Huygens probe attempts a splashdown onto Titan's oily oceans.

Although it was imaged in some detail by the Voyager missions of the 1970s there is much about Titan we do not know. Astronomers are aware that it is one of the most significant objects in the Solar System - the second largest moon and the only one with a thick atmosphere.

It has a hazy atmosphere of nitrogen, methane and hydrocarbons, testimony to a world in which complex chemistry is taking place. It may even have oceans of methane or ethane beneath its clouds.

Ground-based observations are essential to ensure the success of the Huygens entry probe that will plunge into Titan's atmosphere in January 2005.

Using an adaptive optics package on the 8.2-metre 'Yepun' telescope at the Paranal Observatory astronomers have obtained the most detailed images yet of its clouds.

The adaptive optics package uses a flexible mirror to adjust the optics of the telescope to compensate for the distortions in the image caused by the Earth's turbulent atmosphere, thereby obtaining sharper images.

The extraordinary images show a formation near the moon's south pole, apparently a cloud feature of some sort.

Further observations are planned later this month.

At about the same time, Nasa's Chandra X-ray telescope in Earth-orbit, observed Titan pass in front of the X-ray glowing wreckage of an exploded star.

The glowing gas comes from the Crab Nebula - the hot debris of a star that destroyed itself in a supernova explosion seen in 1054.

Titan appears dark against the X-ray glow
Titan's silhouette against the glowing gas enables the extent of its atmosphere to be probed.

Curiously, its atmosphere seems slightly larger than previous estimates of it.

"Saturn was about 5% closer to the Sun in 2003, so increased solar heating of Titan may account for some of the atmospheric expansion," says Hiroshi Tsunemi of Osaka University, one of the observers.

The expanison of the atmosphere may have implications for the Huygens probe.

"If Titan's atmosphere has really expanded, the trajectory (of Huygens) may have to be changed," says Tsenemi.


By Dr David Whitehouse
BBC News Online science editor