July 26, 2006

Methane Rain Forecast for Saturn’s Giant Moon Titan

LONDON (Reuters) - The weather forecast for Saturn's giant moon Titan calls for methane rain, scientists said on Wednesday.

It ranges from a persistent drizzle that keeps the surface of Saturn's largest moon -- which has geological features similar to Earth -- damp to fierce storms that could produce huge droplets.

"We have found the first evidence of drizzly rain on a remote planet, in this case Titan, which consists of liquid methane and a little bit of nitrogen," said Tetsuya Tokano of Cologne University in Germany.

He and his team used data from the NASA/European Space Agency Cassini-Huygens mission to measure the atmospheric chemical composition, temperature and pressure on Titan.

The Cassini craft was launched in 1997 and reached Saturn in 2004 after cruising past Venus and Jupiter.

Information from the probe showed Titan, which is larger than the planet Mercury, is cold and windy with a dense atmosphere of methane and nitrogen.

According to team's the findings, reported in the journal Nature, much of the surface of Titan could experience a drizzle for the next few years.

In a separate report in the journal researchers from Spain did a modeling study of Titan's atmosphere which suggested clouds over the south pole would produce fierce storms that would pound the surface and could help explain the formation of its river valleys.

Ricardo Hueso and Agustin Sanchez-Lavega of the University of Pais Vasco in Bilbao said under the right conditions the storms could produce methane raindrops up to 5 millimetres (0.2 inches) across that would pound the surface similar to flash floods seen on Earth.

Tokano said although the Spanish researchers reached a different conclusion he believed both types of rainfall could occur on Titan depending on the conditions.

"We do not rule out the presence of such heavy rainstorms because such clouds have been observed near the south pole," he added.

The Cassini-Huygens mission to study Saturn's rings and moons is named after two 17th-century Europeans: Dutchman Christiaan Huygens, who discovered Saturn's rings and Titan, and Italian-French astronomer Jean-Dominique Cassini, who discovered the planet's other four major moons.