Titan as seen by Voyager in 1979

Over 1,200 million kilometres (800 million miles) away, Titan is larger than the planet Mercury and has a thick, chemically-rich atmosphere.

It will be visited by the Huygens spaceprobe in 2004.

The new images were unveiled by Dr Athena Coustenis of the Paris-Meudon Observatory, at the General Assembly of the International Astronomical Union being held in Manchester, UK.

They were obtained with the 3.6-metre Canada-France-Hawaii Telescope in Hawaii.

Frozen methane

The images confirm earlier observations that there is a highly reflecting area in the equatorial zone spread over about 50 degrees of longitude. There are at least three individual bright features within this area.

Dr Coustenis and her colleagues say that a continent of frozen methane could account for the observed bright region. One possibility is an ice-covered mountainous plateau.

The Huygens probe will reach Titan in 2004

The astronomers are investigating whether methane ice could exist at high altitudes in Titan's equatorial regions, or at higher latitudes, where the temperature is lower than near the equator.

Titan is of special interest to astronomers because it is the only moon in the Solar System with a thick atmosphere. A little larger than the planet Mercury, Titan is the second largest moon in the Solar System.

The atmosphere is almost entirely nitrogen and about half as thick again as Earth's atmosphere. Astronomers also suspect that Titan's surface may have lakes or oceans of liquid hydrocarbons.

Titan is the target of the Huygens probe due to arrive in 2004 as part of the Nasa/Esa Cassini-Huygens mission to Saturn and its moons.