This
set of images from NASA's Cassini mission shows the difference in the
amount of spray emanating from Saturn's moon Enceladus.Image Credit: NASA/JPL-Caltech/University of Arizona/Cornell. › Full image and caption
Cassini
imaging scientists used views like this one to help them identify the
source locations for individual jets spurting ice particles, water vapor
and trace organic compounds from the surface of Saturn's moon
Enceladus. Image Credit: NASA/JPL/Space Science Institute. › Full image and caption
Dramatic
plumes, both large and small, spray water ice out from many locations
along the famed "tiger stripes" near the south pole of Saturn's moon
Enceladus. Image Credit: NASA/JPL/Space Science Institute. › Full image and caption
PASADENA, Calif. -- The intensity of the jets of water ice and organic
particles that shoot out from Saturn's moon Enceladus depends on the
moon's proximity to the ringed planet, according to data obtained by
NASA's Cassini spacecraft.
The finding adds to evidence that a liquid water reservoir or ocean
lurks under the icy surface of the moon. This is the first clear
observation the bright plume emanating from Enceladus' south pole varies
predictably. The findings are detailed in a scientific paper in this
week's edition of Nature.
"The jets of Enceladus apparently work like adjustable garden hose
nozzles," said Matt Hedman, the paper's lead author and a Cassini team
scientist based at Cornell University in Ithaca, N.Y. "The nozzles are
almost closed when Enceladus is closer to Saturn and are most open when
the moon is farthest away. We think this has to do with how Saturn
squeezes and releases the moon with its gravity."
Cassini, which has been orbiting Saturn since 2004, discovered the jets
that form the plume in 2005. The water ice and organic particles spray
out from several narrow fissures nicknamed "tiger stripes."
"The way the jets react so responsively to changing stresses on
Enceladus suggests they have their origins in a large body of liquid
water," said Christophe Sotin, a co-author and Cassini team member at
NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Liquid water was
key to the development of life on Earth, so these discoveries whet the
appetite to know whether life exists everywhere water is present."
For years scientists hypothesized the intensity of the jets likely
varied over time, but no one had been able to show they changed in a
recognizable pattern. Hedman and colleagues were able to see the changes
by examining infrared data of the plume as a whole, obtained by
Cassini's visual and infrared mapping spectrometer (VIMS), and looking
at data gathered over a long period of time.
The VIMS instrument, which enables the analysis of a wide range of
data including the hydrocarbon composition of the surface of another
Saturnian moon, Titan, and the seismological signs of Saturn's
vibrations in its rings, collected more than 200 images of the Enceladus
plume from 2005 to 2012.
These data show the plume was dimmest when the moon was at the
closest point in its orbit to Saturn. The plume gradually brightened
until Enceladus was at the most distant point, where it was three to
four times brighter than the dimmest detection. This is comparable to
moving from a dim hallway into a brightly lit office.
Adding the brightness data to previous models of how Saturn squeezes
Enceladus, the scientists deduced the stronger gravitational squeeze
near the planet reduces the opening of the tiger stripes and the amount
of material spraying out. They think the relaxing of Saturn's gravity
farther away from planet allows the tiger stripes to be more open and
for the spray to escape in larger quantities.
"Cassini's time at Saturn has shown us how active and kaleidoscopic
this planet, its rings and its moons are," said Linda Spilker, Cassini
project scientist at JPL. "We've come a long way from the placid-looking
Saturn that Galileo first spied through his telescope. We hope to learn
more about the forces at work here as a microcosm for how our solar
system formed."
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, Pasadena, manages the mission
for NASA's Science Mission Directorate in Washington. The VIMS team is
based at the University of Arizona in Tucson.
For more information about the Cassini mission, visit: http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov .
Jia-Rui C. Cook 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif.
jccook@jpl.nasa.gov
Dwayne Brown 202-358-1726
NASA Headquarters, Washington
dwayne.c.brown@nasa.gov
