Magazine article USA TODAY

Searching for Life on Jupiter's Moon

Magazine article USA TODAY

Searching for Life on Jupiter's Moon

Article excerpt

If the icy surface of Europa conceals a liquid ocean, which seems increasingly likely, then the moon orbiting Jupiter will become one of the hottest spots in the solar system to look for alien life. Europa Orbiter, a NASA mission in the early planning stages that is scheduled for launch in 2003, is being designed specifically to look for evidence of a Europan ocean. If one is found, Europa and Earth would be the only two worlds in the solar system where liquid water--thought to be essential for the development of life--is known to exist, explains Christopher Chyba, the Carl Sagan Chair for the Study of Life in the Universe at the SETI Institute and a consulting professor of geological and environmental sciences at Stanford (Calif.) University.

Europa looks something like a cracked cue ball. The possibility that a liquid water ocean may lurk beneath its ice crust was first raised at the time of the Voyager missions in the late 1970s, and reinforced in 1996 when images of Europa's surface were beamed to Earth by the Galileo spacecraft. The images showed areas where the surface ice has been broken up and shifted around like pieces of a jigsaw puzzle, leading astronomer Ronald Greeley of Arizona State University, Tempe, to propose that the Europan icebergs must be lubricated from below by soft ice or liquid water. Since then, "there has been a convergence of evidence that supports the existence of a liquid ocean on Europa," Chyba notes.

* In addition to the iceberg-like areas, Galileo imagery has revealed an impact crater that appears to have been filled in at the bottom, areas that seem to show localized melting near the surface, and other features consistent with a liquid layer below the ice.

* Galileo's onboard magnetometer, which measures the magnetic fields, has detected fluctuations that are consistent with the magnetic effects of currents flowing in a salty ocean.

* Lack of cratering on Europa's surface indicates that it is very young--less than 10,000,000 years old--which suggests that it is being continually resurfaced, possibly by frost falling from liquid water geysers encountering Europa's frigid surface temperatures, which hover at minus-170 [degrees] C.

* Theoretical estimates of the amount of heat produced by the gravitational push and pull exerted on Europa by other Jovian moons indicate that it should be adequate to warm the moon's interior enough to sustain a liquid ocean. …

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