[meteorite-list] Cassini Finds Global Ocean in Saturn's Moon Enceladus
From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue, 15 Sep 2015 17:21:47 -0700 (PDT)
September 15, 2015
Cassini Finds Global Ocean in Saturn's Moon Enceladus
A global ocean lies beneath the icy crust of Saturn's geologically active
moon Enceladus, according to new research using data from NASA's Cassini
Researchers found the magnitude of the moon's very slight wobble, as it
orbits Saturn, can only be accounted for if its outer ice shell is not frozen
solid to its interior, meaning a global ocean must be present.
The finding implies the fine spray of water vapor, icy particles and simple
organic molecules Cassini has observed coming from fractures near the moon's
south pole is being fed by this vast liquid water reservoir. The research is
presented in a paper published online this week in the journal Icarus.
Previous analysis of Cassini data suggested the presence of a lens-shaped
body of water, or sea, underlying the moon's south polar region. However,
gravity data collected during the spacecraft's several close passes over the
south polar region lent support to the possibility the sea might be global.
The new results -- derived using an independent line of evidence based on
Cassini's images -- confirm this to be the case.
"This was a hard problem that required years of observations, and
calculations involving a diverse collection of disciplines, but we are
confident we finally got it right," said Peter Thomas, a Cassini imaging team
member at Cornell University, Ithaca, New York, and lead author of the paper.
Cassini scientists analyzed more than seven years' worth of images of
Enceladus taken by the spacecraft, which has been orbiting Saturn since
mid-2004. They carefully mapped the positions of features on Enceladus --
mostly craters -- across hundreds of images, in order to measure changes in
the moon's rotation with extreme precision.
As a result, they found Enceladus has a tiny, but measurable wobble as it
orbits Saturn. Because the icy moon is not perfectly spherical -- and because
it goes slightly faster and slower during different portions of its orbit
around Saturn -- the giant planet subtly rocks Enceladus back and forth as it
The team plugged their measurement of the wobble, called a libration, into
different models for how Enceladus might be arranged on the inside, including
ones in which the moon was frozen from surface to core.
"If the surface and core were rigidly connected, the core would provide so
much dead weight the wobble would be far smaller than we observe it to be,"
said Matthew Tiscareno, a Cassini participating scientist at the SETI
Institute, Mountain View, California, and a co-author of the paper. "This
proves that there must be a global layer of liquid separating the surface
from the core," he said.
The mechanisms that might have prevented Enceladus' ocean from freezing
remain a mystery. Thomas and his colleagues suggest a few ideas for future
study that might help resolve the question, including the surprising
possibility that tidal forces due to Saturn's gravity could be generating
much more heat within Enceladus than previously thought.
"This is a major step beyond what we understood about this moon before, and
it demonstrates the kind of deep-dive discoveries we can make with long-lived
orbiter missions to other planets," said co-author Carolyn Porco, Cassini
imaging team lead at Space Science Institute (SSI), Boulder, Colorado, and
visiting scholar at the University of California, Berkeley. "Cassini has been
exemplary in this regard."
The unfolding story of Enceladus has been one of the great triumphs of
Cassini's long mission at Saturn. Scientists first detected signs of the
moon's icy plume in early 2005, and followed up with a series of discoveries
about the material gushing from warm fractures near its south pole. They
announced strong evidence for a regional sea in 2014, and more recently, in
2015, they shared results that suggest hydrothermal activity is taking place
on the ocean floor.
Cassini is scheduled to make a close flyby of Enceladus on Oct. 28, in the
mission's deepest-ever dive through the moon's active plume of icy material.
The spacecraft will pass a mere 30 miles (49 kilometers) above the moon's
The Cassini-Huygens mission is a cooperative project of NASA, ESA (European
Space Agency) and the Italian Space Agency. NASA's Jet Propulsion Laboratory
(JPL) in Pasadena, California, manages the mission for the agency's Science
Mission Directorate in Washington. JPL is a division of the California
Institute of Technology in Pasadena, California. The Cassini imaging
operations center is based at Space Science Institute.
For more information about Cassini, visit:
Dwayne Brown / Laurie Cantillo
202-358-1726 / 202-358-1077
dwayne.c.brown at nasa.gov / laura.l.cantillo at nasa.gov
Jet Propulsion Laboratory, Pasadena, Calif.
preston.dyches at jpl.nasa.gov
Received on Tue 15 Sep 2015 08:21:47 PM PDT