From Stig Agermose

Source: Discovery (Channel) Online News,

Europa Ocean Theory Gets New Twist


By analyzing the amount of salt in rings surrounding an impact crater on
Jupiter's moon Europa, researchers have calculated that a salty ocean may lie
just below its icy surface, one potentially capable of supporting life.

For over a year, images from the Galileo spacecraft have hinted at water just
under Europa's surface, bolstering scientific speculation that an ocean does
exist. But unlike past studies, the new findings, announced last week during the
Lunar and Planetary Science Conference in Houston, relied on chemical signatures
recorded in the ice.

Using Galileo's Near Infrared Mapping Spectrometer (NIMS), a team led by Steve
Kadel of Arizona State University measured salts frozen in the ice around
Europa's largest crater, Tyre Macula. It was formed when a mountain-sized object
slammed into the moon, Kadel says. After the impact, long cracks developed on
the surface, allowing more salty liquid to escape from 2 to 3 kilometers below
the surface.

These features were shown in a multicolor map of Tyre Macula produced by the
Galileo-NIMS team, not yet publicly available. Like the color-coded rock layers
in a geologic map of Earth, the chemical signatures revealed the landscape's
history, according to Kadel.

In a separate study of Europan craters that conflicts with the findings of
Kadel's team, Elizabeth Turtle of the University of Arizona concludes the ice
shell must be at least 6 kilometers deep. Turtle's study, also presented last
week, was based on image s of Europa's 22 largest craters.

"At a minimum, there had to have been several kilometers of ice at these sites.
Anything less wouldn't support the craters that we see," says Turtle.

Other researchers have concluded that an ocean lies even further below than
that, with a thick layer of flowing, "warm" ice wedged between the cold, brittle
surface and liquid water.

NASA may answer the ocean question within the decade, using a sort of orbital
dowsing rod. The proposed probe, described by NASA planetary specialist Chris
Chyba, would use ice-penetrating radar to map the suspected ocean from space and
determine the exact thickness of the ice -- and the depth of any water below it.

By Michael Ray Taylor in Houston, Discovery Online News

March 1999
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