Jupiter's moon Callisto may hide underground sea

October 22, 1998
Web posted at: 1:00 PM EDT

The textured surface of Callisto (click to see a global view of Callisto)

(CNN) -- Callisto could be Jupiter's second moon to harbor a liquid ocean tucked under its icy, cratered crust, NASA said Thursday. The report, based on data gathered by NASA's Galileo space probe, bolsters hopes of finding life in seemingly inhospitable places in the solar system

The Galileo findings, to be published in the October 22 issue of the journal Nature, reveal similarities between Callisto and another of Jupiter's moons, Europa, which has already displayed strong evidence of a subsurface ocean.

"One could expect life in such oceans," said Krishan Khurana, a geophysicist at the University of California at Los Angeles and lead author of the research published Thursday in the journal Nature.

Heat and water in liquid form, as opposed to ice, are considered fundamental requirements for life. The latest findings were put together by a team from UCLA, the California Institute of Technology and NASA's Jet Propulsion Laboratory.

Ice-encrusted moons like Europa and Callisto, and other frozen moons even farther from the sun, were long thought to be too cold for life to form.

"If we find out 4 1/2 billion years after the formation of the solar system that there's still enough heat that ice will melt on the interior of these bodies, we have to do a little bit of rethinking," said one of the researchers, UCLA physicist Margaret G. Kivelson.

"The new data certainly suggest that something is hidden below Callisto's surface, and that something may very well be a salty ocean," Kivelson said.

Europa

Earth is 93 million miles from the sun; Jupiter, 483 million.

The scientists hypothesized the existence of underground seas from data collected by the Galileo spacecraft. Galileo measured strong disturbances to Jupiter's magnetic field as the spacecraft zipped past Europa and Callisto.

However, the moons lack strong magnetic fields of their own that could exert such a force. The scientists concluded that Jupiter's magnetism must be giving rise to secondary fields within some powerful electrical conductor on each moon -- a phenomenon known as electromagnetic induction, which is at work on Earth in generators and electromagnets.

The researchers could imagine only one sufficiently strong conductor that is plausible on those moons: huge bodies of salt water. They would be within about 60 miles of the frozen surface, kept from icing over by heat within the interior of the moons.

Assuming they are as salty as Earth's oceans, they would be about 6 miles deep.

"It's making all of us go back to our models and think about our understanding of these icy bodies," said Ronald Greeley, an Arizona State University geologist who studies moons.

Europa was already viewed as a leading candidate in the search for life, because its jigsaw crust resembles broken icebergs and thus points to the possibility of oceans at least in the past.

However, Callisto's pockmarked surface contains few visible trace of liquid movement below.

The Associated Press contributed to this report.