Evidence of water found on one of Jupiter's moons

HOT ON the heels of last week's discovery of possible life on Mars comes news that there may be water, and even oceans, on one…

HOT ON the heels of last week's discovery of possible life on Mars comes news that there may be water, and even oceans, on one of Jupiter's moons, Europa. And there is already speculation that life might once have existed there and may still do so.

The discovery comes from the latest images taken by NASA's Galileo space probe. Other pictures include new detail of Jupiter's Great Red Spot, and an action-packed shot of a volcano erupting on the surface of the moon Io.

Scientists have been poring over pictures since they were taken in late June, as Galileo flew by the largest moon, Ganymede.

When they were published yesterday, NASA director, Daniel Goldin, said that the "fantastic new images of an icy moon, reminiscent of our own Arctic Ocean, raise the possibility of a liquid ocean on Europa, the only other place in our solar system where we suspect such an ocean might exist."

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Europa, the smallest of the four largest Jovian moons, is about the same size as our own Moon. Nothing was known about it until the Voyager missions 17 years ago, which revealed a relatively smooth, white, icy surface, covered in lines and striations, rather like a cracked billiard ball.

The Galileo pictures, though taken at a distance of 96,000 miles, show even more detail: features that resemble ice-floes seen at our own polar regions, and fractures in the icy surface that dwarf the San Andreas fault.

According to Dr Donald Greeley, a geologist working on the Galileo mission, "In some areas the ice broken into large pieces that have shifted away from one another... This shows the ice crust has been or is still lubricated from below by warm ice or maybe even liquid water."

Since the Voyager missions, scientists have thought that Europa, along with Mars and Saturn's moon, Titan, might once have harboured primitive life. They think the tidal forces exerted by the massive Jupiter could be enough to warm Europa's ice.

But for further details they will to wait until when Galileo will fly by Europa at a distance of just 370 miles.

Among the other images released yesterday is a spectacular shot of a geyser-like volcano erupting on Io. The fluorescent blue plume, which glows in the dark, extends some 60 miles into space from a surface feature called Ra Patera.

The colour is thought to come from tiny particles of sulphur dioxide `snow', which condense from the gas as the plume expands and cools.

Since the Voyager missions, it has been known that the bright yellow-orange coloured Io is volcanically active. It and Earth are the only bodies in the solar system known to be still active.

The latest images are helping, scientists to understand what powers this activity; whether it is heat from a radioactive core within, or tidal forces exerted by Jupiter.

On Jupiter itself, the Galileo images reveal new detail of the structure in the massive hurricane or Great Red Spot which has been raging in the planet's atmosphere for at least 300 years.

Winds in the storm, which is as wide as the Earth, reach 250 m.p.h.

The four biggest of Jupiter's moons (the other is Callisto) were named after favourites of the Greek god Zeus, and were first noted in 1610 by Galileo.

NASA's $1.4 billion Galileo mission, originally due to start in 1982, was delayed by the shuttle disaster until 1989. Its two-year mission, which began when it reached the Jovian system last December, will probe the detail of this massive planet, its climate, structure and atmosphere (including the aftermath of the 1994 collision with comet Shoemaker-Levy), and its complex system of satellites, dust rings and moons.

The latest images can be viewed at the Galileo homepage (http://www.jpl.nasa.gov/galileo), on the World Wide Web. Those without access will have to make do with the real world - Jupiter is currently the "evening star" and it can be seen from Ireland shining brightly in the southern sky in the late evening.