 This
false color image of Europa taken by the Galileo Spacecraft highlights
color differences in the moon's predominantly water-ice crust.
Fluctuations
in Europa's magnetic field signal salty waters below.
Magnetic
readings by NASA's Galileo Spacecraft have provided the strongest
evidence yet that Jupiter's fourth-largest moon, Europa, hides
an ocean of water beneath its icy coat. Because life as we know
it requires water, this makes the moon a prime target in the search
for exobiology, or life beyond Earth.
"The
direction that a magnetic compass on Europa would point to, flips
around in a way that is best explained by the presence of an electrically
conducting liquid, such as saltwater beneath the ice," says
Margaret Kivelson of the University of California, Los Angeles.
She and four colleagues performed an analysis of the moon's magnetic
fields that appears in the Aug. 25 issue of the international
journal Science.
"We
have good reason to believe that the surface layers of Europa
are made up of water that is either frozen or liquid," she
says. Earlier gravity measurements showed a low density, such
as water's, for the moon's outer layers. "But ice is not
a good conductor, and therefore we infer that the conductor may
be a liquid ocean."
Galileo has
flown near Europa frequently since the spacecraft began orbiting
Jupiter in December 1995. Pictures from those flybys show patterns
that scientists see as evidence of a hidden ocean. In some, rafts
of ice appear to have shifted position by floating on fluid below.
In others, fluid appears to have risen to the surface and frozen
there.
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