[meteorite-list] NASA-Funded Study Says Saturn's Moon Enceladus Rolled Over

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed May 31 16:47:47 2006
Message-ID: <200605311846.LAA23280_at_zagami.jpl.nasa.gov>

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NEWS RELEASE: 2006-080 May 31, 2006
                   
NASA-Funded Study Says Saturn's Moon Enceladus Rolled Over
 
Saturn's moon Enceladus - an active, icy world with an unusually
warm south pole - may have performed an unusual trick for a
planetary body. New research shows Enceladus rolled over,
literally, explaining why the moon's hottest spot is at the south
pole.

Enceladus recently grabbed scientists' attention when the Cassini
spacecraft observed icy jets and plumes indicating active geysers
spewing from the tiny moon's south polar region.

"The mystery we set out to explain was how the hot spot could
end up at the pole if it didn't start there," said Francis Nimmo,
assistant professor of Earth sciences, University of California,
Santa Cruz.

The researchers propose the reorientation of the moon was driven
by warm, low-density material rising to the surface from within
Enceladus. A similar process may have happened on Uranus' moon
Miranda, they said. Their findings are in this week's journal
Nature.

"It's astounding that Cassini found a region of current geological
activity on an icy moon that we would expect to be frigidly cold,
especially down at this moon's equivalent of Antarctica," said
Robert Pappalardo, co-author and planetary scientist at NASA's Jet
Propulsion Laboratory in Pasadena, Calif. "We think the moon
rolled over to put a deeply seated warm, active area there."
Pappalardo worked on the study while at the University of
Colorado.

Rotating bodies, including planets and moons, are stable if more
of their mass is close to the equator. "Any redistribution of
mass within the object can cause instability with respect to the
axis of rotation. A reorientation will tend to position excess
mass at the equator and areas of low density at the poles," Nimmo
said. This is precisely what happened to Enceladus.

Nimmo and Pappalardo calculated the effects of a low-density blob
beneath the surface of Enceladus and showed it could cause the
moon to roll over by up to 30-degrees and put the blob at the
pole.
 
Pappalardo used an analogy to explain the Enceladus rollover. "A
spinning bowling ball will tend to roll over to put its holes --
the axis with the least mass -- vertically along the spin axis.
Similarly, Enceladus apparently rolled over to place the portion
of the moon with the least mass along its vertical spin axis," he
said.

The rising blob (called a "diapir") may be within either the icy
shell or the underlying rocky core of Enceladus. In either case,
as the material heats up it expands and becomes less dense, then
rises toward the surface. This rising of warm, low-density
material could also help explain the high heat and striking
surface features, including the geysers and "tiger-stripe" region
suggesting fault lines caused by tectonic stress.

Internal heating of Enceladus probably results from its eccentric
orbit around Saturn. "Enceladus gets squeezed and stretched by
tidal forces as it orbits Saturn, and that mechanical energy is
transformed into heat energy in the moon's interior," added
Nimmo.
 
Future Cassini observations of Enceladus may support this model.
 Meanwhile, scientists await the next Enceladus flyby in 2008
for more clues.
 
This research was supported by grants from NASA. The
Cassini-Huygens mission is a cooperative project of NASA, the
European Space Agency and the Italian Space Agency. JPL, a
division of Caltech, manages the mission for NASA's Science
Mission Directorate. 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 .

-end-
Received on Wed 31 May 2006 02:46:21 PM PDT