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- SAN FRANCISCO (Reuters)
- Scientists looking for possible alien life are focusing on Jupiter`s
moon Europa, where huge cracks in the surface indicate that a massive
liquid ocean may be sloshing under an icy crust.
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- ``I don`t know if there are organisms (on Europa), but
it`s a great environment to live in,`` Richard Greenberg of the Lunar
and Planetary Laboratory at the University of Arizona-Tucson said on Thursday.
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- Scientists have posited the possibility of life on Europa
before. But Greenberg told reporters at a meeting of the American Geophysical
Union here on Thursday that new evidence from the moon, including photographs
returned only last week from the Galileo spacecraft, show a ``clement
and comfortable`` world where microorganisms may well have taken hold.
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- ``It really is an environment very conducive to life,``
he said.
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- Key to the evolving theory of possible life on Europa
is the notion that the moon is not only covered by ocean, but that it
also experiences tides which -- interacting with the icy surface crust
-- could generate friction and heat enough to sustain life.
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- Scientists are fairly certain that Europa, which is
about the size of our moon, has a 100-mile thick layer of water which,
at least on the surface where temperatures hover around minus 170 degrees
Celsius (minus 274 Fahrenheit), is ice.
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- But if liquid exists beneath the surface then Jupiter,
which is 300 times as massive as the Earth, would exert an enormous tidal
pull.
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- Greenberg said that this theory was gaining strength
as new photographs show Europa to be covered by a network of mysterious
surface cracks, known as ``cycloids``, which may have been caused by tidal
forces in the partially frozen ocean.
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- Stressed by the ebb and flow of the tides, the cracks
open and close, pushing water and partially-frozen slush to the surface,
the scientists believe.
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- ``As a result of tides, liquid water regularly bathed
crustal cracks and surfaces with heat and whatever nutrients are included
in the oceanic chemistry, creating a variety of potentially habitable
crustal environments,`` Greenberg said in his report.
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- ``Moreover, these various processes in the crust make
life possible in the ocean as well, because if the ocean were not regularly
exposed to oxidants in the surface, oceanic life would suffocate,`` he
added.
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- Other parts of Europa`s surface show evidence of huge
``melt-throughs`` as the ocean reached the surface through thin ice, leaving
terrain which appears to include huge icebergs that have been refrozen
into the surface.
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- And Greenberg said that scientists were eager to take
a closer look at the ``cycloid`` cracks themselves -- giant fissures which
can stretch for thousands of miles and appear in some cases to be flanked
by some sort of orangey-brown residue.
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- ``We don`t know what that stuff is. But it sure looks
delicious,`` Greenberg said with a smile, adding in a serious aside that
it was far too early to suggest that the residue might be some sort of
organic material.
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- These and other questions about Europa may get clearer
answers in 2003, when NASA`s Europa Orbiter is due to visit the moon to
look for closer evidence of an ocean. More information about that mission
can be found at http://www.jpl.nasa.gov/ice
-- fire//europao.htm.
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