LOS ANGELES
(AP) -- Scientists believe heat from radioactive decay inside a tiny, icy Saturn
moon shortly after it formed billions of years ago may explain why geysers are
erupting from the surface today. The Cassini spacecraft last year beamed back
dazzling images of Yellowstone-like geysers spewing from a warm section on
Enceladus, raising the possibility that the moon, which has an overall surface
temperature of about minus-330 degrees, may have an internal environment
suitable for primitive life.
However,
scientists have been stumped by the origin of Enceladus' interior heat. Now a
new model suggests ancient radioactive decay played a key role in shaping the
moon's warm south pole region, where plumes of water vapor and ice crystals
periodically vent.
According
to the theory, Enceladus formed some 4.5 billion years ago by the mixing of ice
and rock containing radioactive isotopes of aluminum and iron. Over a period of
several million years, the rapid decay of the isotopes produced a burst of heat
that resulted in a rocky core enclosed by an ice sheet. Over time, the
remaining decomposition in the core further warmed and melted the moon's
interior.
If
confirmed, the model suggests Enceladus possesses the necessary ingredients to
support life -- a stable heat source, organic materials and liquid water.
"It tells
us that conditions inside Enceladus either were or still are conducive to
biochemical reactions,'' project scientist Dennis Matson said in a telephone
interview.
Results
were presented Monday at the annual Lunar and Planetary Science Conference in Texas and will be published in the April issue of the astronomical journal Icarus.
The Cassini
team previously theorized that the geysers likely came from underground
reservoirs of water close to the surface, indicating a lasting heat source
inside. Matson said the latest model helps explain where the interior heat
might have come from.
Last year,
another research team published a study that cast doubt on the existence of
water near Enceladus' surface. That study suggested that buried ice clathrates --
not liquid water -- were responsible for releasing the plumes through a tectonic
shift in the crust. Clathrates are lattice-like molecular structures that trap
other types of molecules.
Cassini scientists
plan to measure the composition of the gas rising from the plume during an
Enceladus flyby in 2008.
The Cassini
mission is a project of NASA, the European Space Agency and the Italian Space
Agency. Launched in 1997, the spacecraft entered orbit around Saturn in 2004,
exploring its rings and moons.
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