New Study Of Jupiter's Moon Europa May Explain Mysterious Ice Domes, Places To Search For Evidence Of Life

http://www.colorado.edu/news/releases/2003/340.html

New Study Of Jupiter's Moon Europa May Explain
Mysterious Ice Domes, Places To Search For Evidence
Of Life

University of Colorado at Boulder News Release
September 2, 2003

A new University of Colorado at Boulder study of Jupiter's
moon Europa may help explain the origin of the giant ice
domes peppering its surface and the implications for
discovering evidence of past or present life forms there.

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/administra...ule/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 dense blobs
can continue rising all the way to the surface to create the
observed domes."

The domes are huge - some more than four miles in diameter
and 300 feet high - and are found in clusters on Europa's
surface, said Barr, who did much of the modeling. "We are
excited about our research, because we think it now is
possible that any present or past life or even just the
chemistry of the ocean may be lifted to the surface, forming
these domes. It essentially would be like an elevator ride for
microbes."

Barr likened the upwelling of warmer ice from the inner ice
shell to its surface to a pot of boiling spaghetti sauce. "The
burner under the pan sends the hottest sauce to the top,
creating the bubbles at the surface," she said. "The trouble is
Europa's icy skin is as cold and as hard as a rock."

The idea that either small amounts of salt or sulfuric acid
might help to create Europa's domes was Pappalardo's, who
knew about similar domes on Earth that form in clumps in
arid regions. On Earth, it is salt that is buoyant enough to
move up through cracks and fissures in rock formations to
form dome clusters at the surface.

"In addition, infrared and color images taken of Europa by
NASA's Galileo spacecraft seem to indicate some of the ice
on the surface of these domes is contaminated. Impurities
seen at the surface are clues to the internal composition of
the Jovian moon, telling of a salty ice shell," he said.

"The surface of Europa is constantly being blasted by
radiation from Jupiter, which likely precludes any life on the
moon's surface," said Barr. "But a spacecraft might be able to
detect signs of microbes just under the surface."

Both Pappalardo and Barr also are affiliated with
CU-Boulder's Laboratory for Atmospheric and Space
Physics. The project was funded by NASA's Exobiology
Program and Graduate Student Research Program.

Pappalardo recently served on a National Research Council
panel that reaffirmed a spacecraft should be launched in the
coming decade with the goal of orbiting Europa. He currently
is part of a NASA team developing goals for the Jupiter Icy
Moons Orbiter mission.

The scientific objectives of the mission probably will include
confirming the presence of an ocean at Europa, remotely
measuring the composition of the surface and scouting out
potential landing sites for a follow-on lander mission.