GALILEO - Scientific - http://maxpages.com/stargate/Galileo

GALILEO FINDINGS BOOST IDEA OF OTHER-WORLDLY OCEAN

When NASA's Galileo spacecraft swooped past Jupiter's moon
Europa a week ago, it picked up powerful new evidence that a
liquid ocean lies beneath Europa's icy crust.

As the spacecraft flew 351 kilometers (218 miles) above the
icy moon on January 3, its magnetometer instrument studied
changes in the direction of Europa's magnetic field. Galileo's
magnetometer observed directional changes consistent with the
type that would occur if Europa contained a shell of electrically
conducting material, such as a salty, liquid ocean.

"I think these findings tell us that there is indeed a layer
of liquid water beneath Europa's surface," said Dr. Margaret
Kivelson, principal investigator for the magnetometer. "I'm
cautious by nature, but this new evidence certainly makes the
argument for the presence of an ocean far more persuasive."

It appears that the ocean lies beneath the surface somewhere
in the outer 100 kilometers (60 miles), the approximate thickness
of the ice/water layer, according to Kivelson, a researcher at
the University of California, Los Angeles (UCLA).

"Jupiter's magnetic field at Europa's position changes
direction every 5-1/2 hours," Kivelson explained. "This changing
magnetic field can drive electrical currents in a conductor, such
as an ocean. Those currents produce a field similar to Earth's
magnetic field, but with its magnetic north pole -- the location
toward which a compass on Europa would point -- near Europa's
equator and constantly moving. In fact, it is actually reversing
direction entirely every 5-1/2 hours."

On previous Europa flybys, Galileo identified a magnetic
north pole, but did not determine whether its position changes
with time. "We wondered, 'Was it possible that the north pole
did not move?' " Kivelson said.

The new evidence was gathered during a flyby specially
planned so that the observed position of Europa's north pole
would make it clear whether or not it moves. In fact, Monday's
data showed that its position had moved, thus providing key
evidence for the existence of an ocean.

It is not likely that the electric currents on Europa flow
through solid surface ice, Kivelson explained, because ice is not
a good carrier of currents. "But melted ice containing salts,
like the sea water found on Earth, is a fairly good conductor,"
she said.

There is no other likely current-carrying material near
Europa's surface, Kivelson added. "Currents could flow in
partially melted ice beneath Europa's surface, but that makes
little sense, since Europa is hotter toward its interior, so it's
more likely the ice would melt completely. In addition, as you
get deeper toward the interior, the strength of the current-
generated magnetic field at the surface would decrease."

These latest findings are consistent with previous Galileo
images and data showing a tortured surface seemingly formed when
Europa's surface ice broke and rearranged itself while floating
on a sea below. Further theoretical work is under way to analyze
the fluid layer and its properties.

"It will be interesting to see whether this same type of
phenomenon occurs at Jupiter's moon Ganymede," Kivelson said.
Galileo is tentatively scheduled to fly by Ganymede twice this
year.
-JPL

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