Assistant Professor Robert Pappalardo and doctoral student Amy Barr previously believed the mysterious domes may be formed by blobs of ice from the interior of the frozen shell that were being pushed upward by thermal upwelling from warmer ice underneath. Europa is believed to harbor an ocean beneath its icy surface.

But the scientists now think the dome creation also requires small amounts of impurities, such as sodium chloride or sulfuric acid. Basically the equivalent of table salt or battery acid, these compounds melt ice at low temperatures, allowing warmer, more pristine blobs of ice to force the icy surface up in places, creating the domes.

"We have been trying for some time to understand how these ice blobs can push up through the frozen shell of Europa, which is likely about 13 miles thick," said Pappalardo of the astrophysical and planetary sciences department. "Our models now show that a combination of upwelling warm ice in the frozen shell's interior, combined with small amounts of impurities such as sodium chloride or sulfuric acid, would provide enough of a force to form these domes."

A paper on the subject co-authored by Pappalardo and Barr was presented at the annual Division of Planetary Sciences Meeting held Sept. 2 through Sept. 6 in Monterey, Calif. DPS is an arm of the American Astronomical Society. The meeting schedule is available at http://dps03.arc.nasa.gov/administrative/schedule/index.html.

Europa appears to have strong tidal action as it elliptically orbits Jupiter strong enough "to squeeze the moon" and heat its interior, said Pappalardo. "Warm ice blobs rise upward through the ice shell toward the colder surface, melting out saltier regions in their path. The less de
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Contact: Robert Pappalardo
Robert.Pappalardo@colorado.edu
303-492-6423
University of Colorado at Boulder
2-Sep-2003