Cassini Pinpoints Source of Jets on Saturn's Moon Enceladus
PASADENA, Calif. -- In a feat of interplanetary sharpshooting,
NASA's Cassini spacecraft has pinpointed precisely where the
icy jets erupt from the surface of Saturn's geologically active
New carefully targeted pictures reveal exquisite details in the
prominent south polar "tiger stripe" fractures from which the
jets emanate. The images show the fractures are about 300 meters
(980 feet) deep, with V-shaped inner walls. The outer flanks of
some of the fractures show extensive deposits of fine material.
Finely fractured terrain littered with blocks of ice tens of
meters in size and larger (the size of small houses) surround
"This is the mother lode for us," said Carolyn Porco, Cassini
imaging team leader at the Space Science Institute, Boulder, Colo.
"A place that may ultimately reveal just exactly what kind of
environment -- habitable or not -- we have within this tortured little moon."
One highly anticipated result of this flyby was finding the location
within the fractures from which the jets blast icy particles, water
vapor and trace organics into space. Scientists are now studying the
nature and intensity of this process on Enceladus, and its effects
on surrounding terrain. This information, coupled with observations
by Cassini's other instruments, may answer the question of whether
reservoirs of liquid water exist beneath the surface.
The high-resolution images were acquired during an Aug. 11, 2008,
flyby of Enceladus, as Cassini sped past the icy moon at 64,000
kilometers per hour (40,000 miles per hour). A special technique,
dubbed "skeet shooting" by the imaging team, was developed to cancel
out the high speed of the moon relative to Cassini and obtain the
"Knowing exactly where to point, at just the right time, was critical
to this event," said Paul Helfenstein, Cassini imaging team associate
at Cornell University, Ithaca, NY., who developed and used the skeet-shoot
technique to design the image sequence. "The challenge is equivalent
to trying to capture a sharp, unsmeared picture of a distant roadside
billboard with a telephoto lens out the window of a speeding car."
Helfenstein said that from Cassini's point of view, "Enceladus was
streaking across the sky so quickly that the spacecraft had no hope
of tracking any feature on its surface. Our best option was to point
the spacecraft far ahead of Enceladus, spin the spacecraft and camera
as fast as possible in the direction of Enceladus' predicted path,
and let Enceladus overtake us at a time when we could match its motion
across the sky, snapping images along the way."
For scientists, having the combination of high-resolution snapshots
and broader images showing the whole region is critical for understanding
what may be powering the activity on Enceladus.
"There appears to have been extensive fallout of icy particles to the ground,
along some of the fractures, even in areas that lie between two jet source
locations, though any immediate effects of presently active jets are subtle," said Porco.
Imaging scientists suggest that once warm vapor rises from underground
to the cold surface through narrow channels, the icy particles may
condense and seal off an active vent. New jets may then appear elsewhere
along the same fracture.
"For the first time, we are beginning to understand how freshly erupted
surface deposits differ from older deposits," said Helfenstein, an icy
moons expert. "Over geologic time, the eruptions have clearly moved up
and down the lengths of the tiger stripes."
The new images, with jet source locations labeled, are available at:
The Cassini-Huygens mission is a cooperative project of NASA, the European
Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory,
a division of the California Institute of Technology in Pasadena, manages
the Cassini-Huygens mission for NASA's Science Mission Directorate, Washington.
The Cassini orbiter and its two onboard cameras were designed, developed and
assembled at JPL. The imaging team is based at the Space Science Institute, Boulder, Colo.
Jet Propulsion Laboratory, Pasadena, Calif.
Preston Dyches 720-974-5859
Space Science Institute, Boulder, Colo.