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WASHINGTON -- Magnetic readings of Europa, a moon of Jupiter, strongly suggest that it has an ocean of liquid water covered by ice, a finding that strengthens the possibility for the presence of life, experts say.
Margaret G. Kivelson, a space physics scientist, said the evidence from a magnetic field detection device on the Galileo spacecraft gives the strongest evidence yet that Europa is awash with liquid water below a thick outer layer of ice.
``This is not absolute proof that there is a salty ocean there,'' said Kivelson, a researcher at the University of California, Los Angeles. ``The evidence is indirect. But nobody has been able to come up with another sensible explanation.''
Kivelson is first author of a study published in the journal Science.
Proof of liquid water on Europa ``is a good first step'' toward finding life on the Jovian moon, she said.
``It is a long way from finding water to finding life,'' said Kivelson, ``but it certainly makes it a more intriguing possibility.''
If Europa was dry or frozen solid, she said, ``it would certainly reduce the possibility'' of life being there.
Many experts consider Europa and Mars as the most likely places to find life in the solar system beyond the Earth. Photos of Mars have been interpreted as evidence that liquid water has flowed recently on Mars.
Earlier studies of Europa showed that it was covered with a thick layer of ice. Planetary experts had suggested that there might be liquid water beneath the ice but until now there was little evidence to support that idea.
Kivelson and her colleagues used a magnetometer to take readings while the Galileo spacecraft passed close to Europa last January. She said the pattern of the moon's internal magnetic field was consistent with the presence of an ocean on the Jovian satellite.
She said the pattern suggested a body with liquid water at least 4.5 miles deep, covered with ice that could be a half a mile to six miles thick.
David Stevenson of the California Institute of Technology said in Science that ``the most likely explanation'' for the findings of Kivelson and her team ``is that Europa has a salty, global water ocean beneath its ice shell.''
Kivelson said that stronger evidence for liquid water may come from planned NASA spacecraft that will be sent to orbit around Europa. She said a magnetometer aboard that craft could provide more detailed evidence for water.
Jupiter has 17 named moons with four, called the Galilean satellites, large enough to be seen by telescopes on Earth. Europa is the brightest of the large Jovian moons.
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