Star-gazers track storms that scar Saturn

TOM WILKIE

Science Editor

Storms on the planet Saturn, whipping up winds of nearly 600 miles an hour, have been seen by an international team of astronomers.

Previously, observers of the ringed planet had thought that such storms were rare. Only five large-scale disturbances have been seen over the past century - with those in 1933 and 1990 resulting in Great White Spots near the planet's equator.

But in an impressive display of international scientific cooperation, five Earth-bound telescopes in four countries - together with the Hubble Space Telescope - have been trained on Saturn over the past couple of years. In today's issue of Science magazine, the astronomers report that Saturn may be a much stormier place than had been believed.

Fly-bys of the planet by the Pioneer and Voyager satellites more than 15 years ago had revealed some activity but the general presumption was of a quiescent system. The research published today shows that Saturn's atmosphere is more turbulent than first thought, and, that sources of heat internal to the planet may be more active than astronomers had believed. Most of the observations were taken with a French telescope specifically dedicated to studying the planets, at the Pic-du-Midi Observatory in the Pyrenees. But the project also involved optical telescopes in Florida, Japan, Spain, a Nasa infra-red telescope, and the orbiting Hubble Space Telescope.

Between July and December 1994, the astronomers tracked a large storm consisting of a cloud pattern of small and large white spots. The succession of white spots - one measuring 27,000km by 12,000km - raced across the planet's northern hemisphere at about 274 metres per second. A small white spot, was followed closely by the main storm but had in its train "an elongated dark feature" which was in its turn followed by a smaller white spot.

"According to our images, the 1994 event does not fit into the classical Great White Spot cloud pattern. The spot was still visible, albeit much smaller, 11 months later in May 1995. The persistence of the white spot against wind shear (which will destroy cloud patterns in a few days) was unique," the astronomers write, "suggesting the white spot was a coherent, dynamically stable structure."