One of the more unusual targets for the search for extraterrestrial life is the frozen moon of Jupiter, Europa. At about the same size as our moon, Europa lies more than 500 million miles from the sun under an icy surface where the temperatures never rise above a bone-chilling minus 280 degrees Celsius. Europa is dark and cold and has almost no atmosphere. So why search for signs of life in a place that makes an antarctic winter seem positively balmy?

Planetary scientists are almost certain that under the icy surface of Europa lies an ocean of liquid water, the only other known ocean in our solar system besides those on earth. Europa's surface is covered with hundreds of miles-long cracks and rafts of ice.

"These rafts appear to be floating and may, in fact, be comparable to icebergs here on earth," says Michael Carr, a geologist with the U.S. Geological Survey.

Europa might be like a gigantic Arctic Ocean, except with much thicker ice.

The renewed speculation of living organisms on Europa is being encouraged by new and intriguing close-up pictures of the surface of the Jovian satellite taken by the Galileo spacecraft, as well as by the recent discovery, here on earth, of teeming animal life miles under the ocean in places once thought to be utterly barren. These shrimps, worms, fish and other creatures thrive around deep-sea volcanic vents, where they survive completely without energy from the sun and under pressures equivalent to a person supporting the entire weight of a bus.

Noting the active volcanism on its sister moon Io, scientists think that Europa might have volcanic features on its ocean beds that create niches similar to those here on earth and that, just maybe, living creatures, perhaps only bacteria, might cling to life there.

But, before we get ahead of ourselves, let's remember that the existence of liquid water on Europa has not yet been observed-let alone subsurface oceans, volcanic vents or little creatures that might call them home. GN