Cassini Captures Ocean-Like Spray at Saturn Moon

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Jia-Rui Cook 818-354-0850
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Dwayne C. Brown 202-358-1726
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Markus Bauer 011-31-71-565-6799
European Space Agency, Noordwijk, the Netherlands
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News release: 2011-190 June 22, 2011

Cassini Captures Ocean-Like Spray at Saturn Moon

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2011-190&cid=release_2011-190

PASADENA, Calif. – NASA's Cassini spacecraft has discovered the best evidence yet for a large-
scale saltwater reservoir beneath the icy crust of Saturn's moon Enceladus. The data came from the
spacecraft's direct analysis of salt-rich ice grains close to the jets ejected from the moon.

Data from Cassini's cosmic dust analyzer show the grains expelled from fissures, known as tiger
stripes, are relatively small and predominantly low in salt far away from the moon. But closer to the
moon's surface, Cassini found that relatively large grains rich with sodium and potassium dominate
the plumes. The salt-rich particles have an "ocean-like" composition and indicate that most, if not all,
of the expelled ice and water vapor comes from the evaporation of liquid salt water. The findings
appear in this week's issue of the journal Nature.

"There currently is no plausible way to produce a steady outflow of salt-rich grains from solid ice
across all the tiger stripes other than salt water under Enceladus's icy surface," said Frank Postberg, a
Cassini team scientist at the University of Heidelberg, Germany, and the lead author on the paper.
When water freezes, the salt is squeezed out, leaving pure water ice behind. If the plumes emanated
from ice, they should have very little salt in them.

The Cassini mission discovered Enceladus' water-vapor and ice jets in 2005. In 2009, scientists
working with the cosmic dust analyzer examined some sodium salts found in ice grains of Saturn's E
ring, the outermost ring that gets its material primarily from Enceladean jets. But the link to
subsurface salt water was not definitive.

The new paper analyzes three Enceladus flybys in 2008 and 2009 with the same instrument, focusing
on the composition of freshly ejected plume grains. The icy particles hit the detector target at speeds
between 15,000 and 39,000 mph (23,000 and 63,000 kilometers per hour), vaporizing instantly.
Electrical fields inside the cosmic dust analyzer separated the various constituents of the impact
cloud.

The data suggest a layer of water between the moon's rocky core and its icy mantle, possibly as deep
as about 50 miles (80 kilometers) beneath the surface. As this water washes against the rocks, it
dissolves salt compounds and rises through fractures in the overlying ice to form reserves nearer the
surface. If the outermost layer cracks open, the decrease in pressure from these reserves to space
causes a plume to shoot out. Roughly 400 pounds (200 kilograms) of water vapor is lost every second
in the plumes, with smaller amounts being lost as ice grains. The team calculates the water reserves
must have large evaporating surfaces, or they would freeze easily and stop the plumes.

"This finding is a crucial new piece of evidence showing that environmental conditions favorable to
the emergence of life can be sustained on icy bodies orbiting gas giant planets," said Nicolas
Altobelli, the European Space Agency's project scientist for Cassini.

Cassini's ultraviolet imaging spectrograph also recently obtained complementary results that support
the presence of a subsurface ocean. A team of Cassini researchers led by Candice Hansen of the
Planetary Science Institute in Tucson, Ariz., measured gas shooting out of distinct jets originating in
the moon's south polar region at five to eight times the speed of sound, several times faster than
previously measured. These observations of distinct jets, from a 2010 flyby, are consistent with
results showing a difference in composition of ice grains close to the moon's surface and those that
made it out to the E ring. That paper was published in the June 9 issue of Geophysical Research
Letters.

"Without an orbiter like Cassini to fly close to Saturn and its moons -- to taste salt and feel the
bombardment of ice grains -- scientists would never have known how interesting these outer solar
system worlds are," said Linda Spilker, NASA's Cassini project scientist at the Jet Propulsion
Laboratory in Pasadena, Calif.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the
Italian Space Agency. The mission is managed by JPL for NASA's Science Mission Directorate in
Washington. JPL is a division of the California Institute of Technology, Pasadena.

For more information about Cassini, visit: http://www.nasa.gov/cassini and
http://saturn.jpl.nasa.gov .

-end-

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