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Thursday, December 3, 1998 Published at 14:59 GMT


Scars on an icy moon

Ice ridges travese vast distances over the surface

By BBC News Online Science Editor Dr David Whitehouse

New images of the surface of Europa have prompted scientists to speculate about the possibility of life somewhere on the world.

Speculation that Europa, one of Jupiter's large moons, may have liquid water beneath its frozen surface received a boost with the arrival of the Galileo spaceprobe in the Jupiter system in December 1995.

We may not know for certain about Europa's under-ice oceans until a probe lands on it. But recent images sent back to Earth from Galileo are suggestive.

The newly released picture is a mosaic of images from Europa's the southern hemisphere.

[ image: No one knows what the brown stuff is]
No one knows what the brown stuff is
The brown, linear ridges extending across the scene are thought to be frozen remnants of cryo-volcanic activity.

"Cryo-volcanoes" (cold volcanoes) occur when liquid, partially frozen water erupts onto the Europan surface, freezing almost instantly in the extremely low temperatures so far from the Sun.

North is to the lower left of the main picture on this page, and the Sun illuminates the surface from the upper left.

The image covers an area approximately 800 by 350 kilometres (500 by 220 miles). The resolution is 230 meters (250 yards) per picture element.

Europa is the smoothest world in the solar system. Nowhere on its icy surface is any feature larger than 1000 metres high.

Dark spots, several kilometres in diameter, are distributed all over the surface. A geologically older, smoother surface, bluish in tone, underlies the ridge system.

[ image: Blue regions may be the youngest]
Blue regions may be the youngest
Scientists believe that the blue surface is composed of almost pure water ice, whereas the composition of the dark, brownish spots and ridges is unknown.

One possibility is that they contain evaporates such as mineral salts in a matrix of high water content.

Water is an important ingredient of life as we know it on Earth. If liquid water does exist beneath the icy crust of Europa, as many scientists believe, then it is possible that some form of life may exist there as well.

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