Study reveals new evidence of saltwater ocean on Europa

Europa

By Richard Stenger
CNN.com Writer

(CNN) -- A spacecraft orbiting Jupiter has provided the strongest evidence yet that a liquid ocean lies beneath the icy surface of the jovian moon Europa. The discovery enhances the chances that life could be present there, according to a new report.

Using observations from NASA's Galileo probe, scientists determined that a body of salty water inside the Jupiter's fourth-largest moon most likely caused unusual magnetic readings.

The ocean, at least 4.5 miles (7 km) deep, would lie beneath an icy layer with a thickness anywhere from .5 miles (.8 km) to 6 miles (10 km), said Margaret Kivelson of the University of California, Los Angeles, lead author of the report published Friday in the journal Science.

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After Galileo detected a magnetic pole on the moon, NASA sent the probe back for another check in January. The craft's magnetometer revealed that the pole changed direction every 5.5 hours. That's consistent with fluctuations that would occur if Europa contained a shell of electrically conductive material, such as a salty ocean.

"The evidence that Europa's field varies temporarily, strengthens the argument that a liquid ocean exists beneath the present-day surface," Kivelson and her colleagues wrote in Science.

The eccentric magnetic pattern is associated with tidal flexing, the powerful pull of Jupiter and neighboring moons that regularly expand Europa.

Earlier observations indicated that water ice covers Europa, a relatively smooth satellite covered in long grooves and ridges and riddled with what seem to be icebergs. Europa is nearly twice as large as the Earth's moon.

A false color image of cracks and ridges in the Minos Linea region of Europa

Scientists had theorized that the icy surface hid a liquid interior, but the new study offers convincing evidence that it exists.

"The most likely explanation is that Europa has a salty, global water ocean beneath its ice shell," said California Institute of Technology planetary researcher David Stevenson in a Science editorial.

The question could be settled by the Europa orbiter, which NASA plans to launch in 2003. The sophisticated satellite would use radar to measure the depth of the icy surface and any liquid body underneath.

Given that microbial life thrives in water in even the most extreme conditions on this planet, biologists searching for life beyond Earth have expressed particular interest in Europa, where tidal heating could allow liquid water near the surface.

"After Mars, (Europa is) the most attractive extraterrestrial environment within our solar system in which to seek evidence of past or present life," Stevenson wrote.

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