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For many years, astronomers
have wondered about Europa. It's surface is scarred by a myriad of
cracks, and Cassini has determined the unmistakable signature of liquid
water. Because water is known to be the essential ingredient for
"life as we know it (Jim)" the obvious connection is that if
we are to find life anywhere else in the solar system than here on
Earth, it is more likely to be on bodies where water exists. Even
though temperatures on this icy moon of Jupiter are extremely low, if
liquid water can show to exist, then conditions suitable for the
formation of some form of life could well exist.
Well, scientists have now found the
best evidence yet for water just beneath the surface of Europa. Analysis of the
moon's surface suggests plumes of warmer water well up beneath its icy
shell, melting and fracturing the outer layers - hence the scarred and
cracked surface which we see. The results, published
in the journal Nature, predict that small lakes exist only 3km below
the crust. Any liquid water could represent a potential habitat
for life. From models of magnetic forces, and images of its
surface, scientists have long suspected that a giant ocean, roughly
160km (100 miles) deep, lies somewhere between 10-30km beneath the ice
crust.
Many astro-biologists have
dreamed of following in the footsteps of Arthur C Clarke's fictional
character David Bowman who, in the novel Odyssey Two, discovers aquatic
life-forms in the deep Europan sea, but punching holes through the
moon's thick, icy outer layers has always seemed untenable.
The discovery of shallow
liquid water by an American team makes a space mission to recover water
from the moon much more plausible. The shallow lakes also means
that surface waters are probably vigorously mixing with deeper
water. The icy eddies could transfer nutrients between the surface
water and the ocean's depths, which could make Europa and its ocean more
habitable. Glaciologists have been studying the surface of Europa
for many years, trying to work out what formed its scarred, fractured
surface. By looking at Antarctica, where we see similar features
- glaciers and ice shelves - we can infer something about the processes
that are happening on Europa. Upwelling of warmer water causes melting of surface ice, forming
cracks.
Freezing of water between the cracks occurs so you end up with
the existing ice cemented in with new ice. The underside then
freezes again, which causes the uplifting.
The US and
Europe
are working on missions to Europa, and Jupiter's other moons, which they
hope to launch either late this decade or early in the 2020s.
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