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Posted by baalke on March 12, 2007, 11:39 am
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http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=729
A Hot Start Might Explain Geysers on Enceladus
Contacts:
Carolina Martinez 818-354-9382
Jet Propulsion Laboratory, Pasadena, Calif.
NEWS RELEASE: 2007-025
March 12, 2007
A hot start billions of years ago might have set into motion the
forces
that power geysers on Saturn's moon Enceladus.
"Deep inside Enceladus, our model indicates we've got an organic brew,
a
heat source and liquid water, all key ingredients for life," said Dr.
Dennis Matson, Cassini project scientist at NASA's Jet Propulsion
Laboratory, Pasadena, Calif. "And while no one is claiming that we
have
found life by any means, we probably have evidence for a place that
might be hospitable to life."
Since NASA's Voyager spacecraft first returned images of the moon's
snowy white surface, scientists have suspected Enceladus had to have
something unusual happening within that shell. Cameras on NASA's
Cassini
orbiter seemed to confirm that suspicion in 2005 when they spotted
geysers on Enceladus ejecting water vapor and ice crystals from its
south polar region. The challenge for researchers has been to figure
out
how this small ice ball could produce the levels of heat needed to
fuel
such eruptions.
A new model suggests the rapid decay of radioactive elements within
Enceladus shortly after it formed may have jump-started the long-term
heating of the moon's interior that continues today. The model
provides
support for another recent, related finding, which indicates that
Enceladus' icy plumes contain molecules that require elevated
temperatures to form.
"Enceladus is a very small body, and it's made almost entirely of ice
and rock. The puzzle is how the moon developed a warm core," said Dr.
Julie Castillo, the lead scientist developing the new model at JPL.
"The
only way to achieve such high temperatures at Enceladus is through the
very rapid decay of some radioactive species."
The hot start model suggests Enceladus began as a mixed-up ball of ice
and rock that contained rapidly decaying radioactive isotopes of
aluminum and iron. The decomposition of those isotopes -- over a
period
of about 7 million years -- would produce enormous amounts of heat.
This
would result in the consolidation of rocky material at the core
surrounded by a shell of ice. According to the theory, the remaining,
more slowly decaying radioactivity in the core could continue to warm
and melt the moon's interior for billions of years, along with tidal
forces from Saturn's gravitational tug.
Scientists have also found the model helpful in explaining how
Enceladus
might have produced the chemicals in the plume, as measured by
Cassini's
ion and neutral mass spectrometer. Matson is lead author of a new
study
of the plume's composition, which appears in the April issue of the
journal Icarus. Although the plume is predominantly made up of water
vapor, the spectrometer also detected within the plume minor amounts
of
gaseous nitrogen, methane, carbon dioxide, propane and acetylene.
Scientists were particularly surprised by the nitrogen because they
don't think it could have been part of Enceladus' original makeup.
Instead, Matson's team suggests it is the product of the decomposition
of ammonia deep within the moon, where the warm core and surrounding
liquid water meet.
The thermal decomposition of ammonia would require temperatures as
high
as 577 degrees Celsius (1070 degrees Fahrenheit), depending on whether
catalysts such as clay minerals are present. And while the long-term
decay of radioactive species and current tidal forces alone cannot
account for such high temperatures, with the help of the hot start
model, they can.
The scalding conditions are also favorable for the formation of simple
hydrocarbon chains, basic building blocks of life, which Cassini's
spectrometer detected in small amounts within Enceladus' plume. The
team
concludes that so far, all the findings and the hot start model
indicate
that a warm, organic-rich mixture was produced below the surface of
Enceladus and might still be present today, making the moon a
promising
kitchen for the cooking of primordial soup.
To gather more information about the chemistry within Enceladus, the
team plans to directly measure the gas emanating from the plume during
a
flyby scheduled for March 2008.
The Cassini-Huygens mission is a cooperative project of NASA, the
European Space Agency and the Italian Space Agency. JPL, a division of
the California Institute of Technology in Pasadena, manages the
Cassini-Huygens mission for NASA's Science Mission Directorate,
Washington. The Cassini orbiter was designed, developed and assembled
at
JPL.
For images and information about the Cassini mission, visit:
http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov .
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