This thread deals with Cassini's exploration of Enceladus. Discoveries about Saturn's moon Titan, can be found here: Exploration of Titan - Saturn's Largest Moon. Many of the images made using that spacecraft's optical camera's can be found in the Cassini - Images of Saturn & Its Moons thread. Infrared discoveries can be found in the Cassini - Infrared Images thread. Other major announcements and discoveries may be found in separate threads.

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May 31, 2006
(Source: Jet Propulsion Laboratory / University of Santa Cruz, Calif. / University of Colorado, Boulder)

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.

NEWS RELEASE: 2006-080

Source: NASA/JPL - Cassini - Press Release

Enceladus roll
May 31, 2006

This graphic illustrates the interior of Saturn's moon Enceladus. It shows warm, low-density material rising to the surface from within, in its icy shell (yellow) and/or its rocky core (red). A NASA-funded study says Enceladus might have rolled or rotated itself to place this area of low density at the south pole. This finding is in the June 1, 2006, issue of the journal Nature.

This graphic uses parts of visible-light images taken by the Cassini spacecraft camera that have been modified for the purpose of showing the interior structure. Cassini's cameras captured a giant plume blasting icy particles into space.

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 mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Credit: NASA/JPL/Space Science Institute

Source: NASA/JPL - Cassini

great topic to post waspie,... i know isnt that whole idea of a moon rotating upward and over a frillen trip or what.

i read of this night before last on a nother nasa link i beileved it was called near earth objects newsline. spacenews update or something a ma gig ? anyway im so glad you posted it because it blew me away.


thanks for the great picture too
Abecrombie

Thanks Abecrombie, but really it's NASA you should thank. I just do the re-posting.

A Moon's Telltale Tail
June 12, 2006

The plumes of Enceladus continue to gush icy particles into Saturn orbit, making this little moon one of a select group of geologically active bodies in the solar system.
Enceladus (505 kilometers, or 314 miles across) is seen here against the night side of Saturn. The extended exposure time used to image the plumes also makes the southern hemisphere, illuminated by ring-shine, appear bright.

The image was acquired in visible light with the Cassini spacecraft narrow-angle camera on May 4, 2006 at a distance of approximately 2.1 million kilometers (1.3 million miles) from Enceladus and 2.3 million kilometers (1.5 million miles) from Saturn. The image was taken at a Sun-Enceladus-spacecraft, or phase, angle of 159 degrees. Image scale is 13 kilometers (8 miles) per pixel on Enceladus.

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 mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Credit: NASA/JPL/Space Science Institute

Source: NASA/JPL - Cassini

We keep finding new ice everywhere. H2O seems to be perhapd the most common compound in the universe.

Scattered Ice, Scattered Light
June 14, 2006

An enhanced close-up view shows at least two distinct jets spraying a mist of fine particles from the south polar region of Enceladus. The particles in the plume scatter sunlight most effectively at high Sun-Enceladus-spacecraft angles, or phase angles, making the plumes appear bright.
This image shows the night side of Saturn and the active moon against dark sky. Enceladus is 505 kilometers (314 miles) across.

Some artifacts due to image compression and cosmic rays striking the camera's detector remain as noise in the image.

The image was acquired in polarized green light with the Cassini spacecraft narrow-angle camera on May 4, 2006 at a distance of approximately 2.1 million kilometers (1.3 million miles) from Enceladus and 2.3 million kilometers (1.4 million miles) from Saturn. The image was taken at a Sun-Enceladus-spacecraft, or phase, angle of 159 degrees. Image scale is 13 kilometers (8 miles) per pixel.

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 mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Credit: NASA/JPL/Space Science Institute

Source: NASA/JPL - Cassini

June 29, 2006
(Source: Jet Propulsion Laboratory)

Atomic oxygen could never be confused with expensive perfume. But just as a fragrance lingering in the air of an empty room offers hints about a previous occupant, the cloud of oxygen the Cassini spacecraft encountered as it first approached Saturn turned out to be a calling card from another celestial presence, the tiny moon Enceladus.


Cassini's ultraviolet imaging spectrograph
observed the star Gamma Orionis as
Enceladus crossed in front of the star. The
light of the star dimmed as it was obscured
by the atmosphere before being blocked
entirely by Enceladus itself.

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The oxygen was the first clue that much more is going on beneath Enceladus' icy surface than it first appeared. It took a while for scientists to get the message. Tracking down the oxygen's source led them to a most unusual spot in the solar system, a place that may possess one of the rarest and most sought-after substances in the universe - liquid water.

Now You See It, Now You Don't

Cassini's ultraviolet imaging spectrograph made its initial survey of Saturn's atmosphere late in December 2003 as the spacecraft neared the end of its seven-year voyage to the ringed planet. Along with the expected hydrogen, long known to be the gas giant's major component, the spectrograph detected the presence of oxygen. "We were the first to discover the oxygen in the Saturn system," says Dr. Larry Esposito of the University of Colorado, principal investigator for the instrument. Since Saturn's rings are made mostly of water ice, it wasn't surprising to find one ingredient of water, oxygen, in Saturn's atmosphere, he explains. The oxygen they observed was in the form of single oxygen atoms, called atomic oxygen, like that in water, H2O.

In January 2004, when it looked again at Saturn's atmosphere, it found a massive bubble of oxygen near Saturn's outermost ring, the E ring. Then just a few months later, much of the oxygen was gone. "What was surprising was the amount of oxygen we saw and how it changed," says Esposito. "This was the first sign that something unusual was going on."


A view of Enceladus showing largely the
southern hemisphere and the south polar
terrain at the bottom of the image.

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"Our first idea was that the collisions between small moons in the rings would release small puffs of ice and that ice would be broken down into its atoms, one of which would be atomic oxygen," Esposito explains. "We put out this hypothesis, but the idea didn't seem to be working out."

What did work out were a host of observations in spring 2005 showing that something very odd was taking place on Enceladus, which just happens to orbit within the E ring, where the mysterious cloud of oxygen was first discovered. Cassini's magnetometer showed that the moon had an atmosphere. Too small to have enough gravity to hold on to an atmosphere for very long, Enceladus had to have a steady source of gas, such as geysers, to keep an atmosphere going. The cosmic dust analyzer detected a stream of particles around Enceladus. The scientists wondered whether these particles could be coming from the moon or from the E ring and if, perhaps, the moon itself might be the source of ice particles for the E ring.

The Cassini science teams were eager to get a closer look. Mission navigators re-designed the spacecraft's trajectory to bring it closer to Enceladus than had been previously planned. "This is a big advantage of a mission like Cassini," according to Esposito. "You don't just fly by once, you can follow-up when something seems promising."

Ready for a Close-Up


The E ring, a ring feature now known to be
created by Enceladus.

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In July 2005, Cassini cruised only 175 kilometers (109 miles) from Enceladus. The spacecraft's instruments revealed that the large dark cracks, dubbed "tiger stripes," on the moon's south pole were warm and spewing out water vapor and ice particles.

The flyby occurred just when a star was moving behind the moon's southern pole. "As we watched the moon extinguish the light from the star, the spectrometer identified oxygen," says Esposito. "The starlight showed water molecules between us -- the spacecraft -- and the star. It showed a localized cloud of water near Enceladus."

"We were able to measure the shape of the cloud, estimate the amount of water it contained and the rate it would be destroyed and produce oxygen," says Esposito. The amount of water they saw, about a million tons, was exactly that needed to provide a cloud of oxygen like the one they had first observed near the E ring more than a year earlier. "This was a most pleasing result," says Esposito. "We measured two new distinct phenomena and found that they fit together."

The mystery of the atomic oxygen was solved. At the same time, its source, the diminutive Enceladus revealed itself to be completely different than the cold, dead icy moon it should have been. Small as it is, it has an internal heat source and is geologically active. Its geysers throw out enough water vapor and ice to maintain the moon's atmosphere, feed the vast E ring, and decompose into clouds of oxygen like the one first spotted by Cassini on its way to Saturn.

Not far beneath the moon's snowy white surface, scientists say, may be large pools of liquid water, warmed by the same heat source that powers its geysers. Its potential for water puts Enceladus into an elite group of places where life could exist. The Cassini spacecraft will swing back in 2008 for another look.

To learn more about Enceladus, visit http://saturn.jpl.nasa.gov/science/moons/moonDetails.cfm?pageID=83


Source: NASA/JPL - Cassini - News Feature

Boosting the Signal
July 21, 2006

The ice jets of Enceladus send particles streaming into space hundreds of kilometers above the south pole of this spectacularly active moon. Some of the particles escape to form the diffuse E ring around Saturn.
This color-coded image was processed to enhance faint signals, making the contours and extent of the fainter, larger-scale component of the plume easier to see.

The bright strip behind and above Enceladus (505 kilometers, 314 miles across) is the E ring, in which this intriguing body resides. The small round object at far left is a background star.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on March 24, 2006 at a distance of approximately 1.9 million kilometers (1.2 million miles) from Enceladus and at a Sun-Enceladus-spacecraft, or phase, angle of 162 degrees. Image scale is 11 kilometers (7 miles) per pixel.


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 mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Credit: NASA/JPL/Space Science Institute

Source: NASA/JPL - Cassini

Moon With a Warm Heart
August 22, 2006

Few large craters are to be found in the wrinkled terrain of Enceladus, where the surface has been reworked by geologic processes presumably resulting from the moon's inner warmth.
Cassini spied the bright crescent of Enceladus (505 kilometers, or 314 miles across) on July 23, 2006 at a distance of approximately 628,000 kilometers (391,000 miles). The image was taken in visible light with the Cassini spacecraft narrow-angle camera at a Sun-Enceladus-spacecraft, or phase, angle of 103 degrees. Image scale is 4 kilometers (2 miles) per pixel.

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 mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Credit: NASA/JPL/Space Science Institute

Source: NASA/JPL - Cassini

Living Moon
September 4, 2006

Enceladus continues to exhale water ice into Saturn orbit, keeping the E ring topped off with tiny particles.
Enceladus (505 kilometers, or 314 miles across) is a source of much interest for planetary scientists, being nearly seven times smaller than Earth's own moon, yet having active geology that appears to involve near-surface liquid water.

The image was taken in visible green light with the Cassini spacecraft narrow-angle camera on Aug. 11, 2006 at a distance of approximately 2.2 million kilometers (1.3 million miles) from Enceladus and at a Sun-Enceladus-spacecraft, or phase, angle of 164 degrees. Image scale is 13 kilometers (8 miles) per pixel

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 mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Credit: NASA/JPL/Space Science Institute

Source: NASA/JPL - Cassini

Enigma in Ice
September 28, 2006

Cassini spies the wrinkled, fractured and remarkably crater-poor terrain of Enceladus. Scientists are working to understand what causes the moon's surprising geologic activity (see Fountains of Enceladus).
North on Enceladus (505 kilometers, 314 miles across) is up and rotated 20 degrees to the left.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Sept. 8, 2006 at a distance of approximately 560,000 kilometers (348,000 miles) from Enceladus and at a Sun- Enceladus-spacecraft, or phase, angle of 103 degrees. Image scale is 3 kilometers (2 miles) per pixel.

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 mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Credit: NASA/JPL/Space Science Institute

Source: NASA/JPL - Cassini

A Folded Surface
October 4, 2006

The wrinkled border of Enceladus' south polar region snakes across this view, separating fresher, younger terrain from more ancient, cratered provinces.
This is the region of Enceladus (505 kilometers, or 314 miles across) that is known to be presently geologically active. At right are clearly visible ridges and troughs thought to be caused by compressional stresses across the icy surface.

The image was taken in polarized green light with the Cassini spacecraft narrow-angle camera on Sept. 9, 2006 at a distance of approximately 66,000 kilometers (41,000 miles) from Enceladus and at a Sun-Enceladus-spacecraft, or phase, angle of 104 degrees. Image scale is 396 meters (1,300 feet) per pixel.

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 mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Credit: NASA/JPL/Space Science Institute

Source: NASA/JPL - Cassini

Half-lit Enceladus
October 12, 2006

A world whose mysteries are just coming to light, Enceladus has enchanted scientists and non-scientists alike. With its potential for near-surface liquid water, the icy moon may be the latest addition to the list of possible abodes for life.
The view was acquired about two-and-a-half hours after A Folded Surface, during an encounter with Enceladus (505 kilometers, or 314 miles across).

The image was taken using a combination of spectral filters sensitive to wavelengths of polarized ultraviolet light. The Cassini spacecraft narrow-angle camera acquired the view on Sept. 9, 2006 at a distance of approximately 141,000 kilometers (877,000 miles) from Enceladus and at a Sun-Enceladus-spacecraft, or phase, angle of 96 degrees. Image scale is 850 meters (0.5 mile) per pixel.

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 mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Credit: NASA/JPL/Space Science Institute

Source: NASA/JPL - Cassini

That is an interesting cross pattern. I wonder what they think caused that?

Relaxing on Enceladus
November 17, 2006

Looking down onto the northern hemisphere of geologically complex Enceladus, the Cassini spacecraft spies softened, or "relaxed," craters and east-west trending fractures and faults.

The anti-Saturn hemisphere of Enceladus (505 kilometers, or 314 miles across) is lit here.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Oct. 12, 2006 at a distance of approximately 521,000 kilometers (324,000 miles) from Enceladus and at a Sun-Enceladus-spacecraft, or phase, angle of 101 degrees. Image scale is 3 kilometers (2 miles) per pixel.

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 mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Credit: NASA/JPL/Space Science Institute

Source: NASA/JPL - Cassini

Out of the Noise
December 5, 2006

A ghostly view of Enceladus reveals the specter of the moon's icy plume of fine particles. Scientists continue to monitor the plume, where mission planning allows, using the Cassini spacecraft's imaging cameras.

This view looks toward northern latitudes on the trailing hemisphere of Enceladus (505 kilometers, or 314 miles across). North is up.

The image was taken with the Cassini spacecraft narrow-angle camera using a spectral filter sensitive to wavelengths of ultraviolet light centered at 338 nanometers on Oct. 31, 2006. Cassini was then at a distance of approximately 1.4 million kilometers (900,000 miles) from Enceladus and at a Sun-Enceladus-spacecraft, or phase, angle of 148 degrees. Image scale is 8 kilometers (5 miles) per pixel.

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 mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Credit: NASA/JPL/Space Science Institute

Source: NASA/JPL - Cassini

Arabian Sulci
December 13, 2006

Enceladus shows off its tortured south polar terrain, which is crosscut by the roughly parallel furrows and ridges called sulci, or informally, "tiger stripes."

Several features on Enceladus were recently given names by the International Astronomical Union in accord with the naming convention for the icy moon, which draws from characters and places from The Arabian Nights. The four most prominent sulci are named Alexandria, Cairo, Baghdad and Damascus.

Lit terrain in this view is on the anti-Saturn side of Enceladus (505 kilometers, or 314 miles across).

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Nov. 8, 2006 at a distance of approximately 399,000 kilometers (248,000 miles) from Enceladus and at a Sun-Enceladus-spacecraft, or phase, angle of 75 degrees. Image scale is 2 kilometers (1 mile) per pixel.

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 mission for NASA\'s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Credit: NASA/JPL/Space Science Institute

Source: NASA/JPL - Cassini

Ice Fountains
December 29, 2006

Multiple jets of icy particles are blasted into space by the active venting on Saturn¿s moon Enceladus.

This image was acquired in a viewing geometry that makes the tiny particles in the Enceladus plume easy to see.

This view was taken in visible light with the Cassini spacecraft narrow-angle camera on Jan. 18, 2006, at a distance of approximately 930,000 kilometers (578,000 miles) from Enceladus and at a sun-Enceladus-spacecraft, or phase, angle of 154 degrees. Image scale is 6 kilometers (3 miles) per pixel.

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 mission for NASA\'s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Credit: NASA/JPL/Space Science Institute

Source: NASA/JPL - Cassini

Map of Enceladus - December 2006
December 29, 2006

This global digital map of Saturn's moon Enceladus was created using data taken by the Cassini spacecraft, with gaps in coverage filled in by NASA Voyager spacecraft data. The map is an equidistant projection and has a scale of 300 meters (980 feet) per pixel. Equidistant projections preserve distances on a body, with some distortion of area and direction.

The mean radius of Enceladus used for projection of this map is 252 kilometers (157 miles).

This map is an update to the version released in December 2005. See Map of Enceladus - December 2005.

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 mission for NASA\'s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Credit: NASA/JPL/Space Science Institute

Source: NASA/JPL - Cassini

Enceladus: Trailing Hemisphere
December 29, 2006

A variety of surface ages is revealed in this 16-image mosaic taken during Cassini's first close flyby of Enceladus, on Feb. 17, 2005.

This mosaic shows the trailing hemisphere of Enceladus -- the side of Enceladus that always faces away from the direction of the satellite's orbital motion. This hemisphere is dominated by Sarandib Planitia (just right of center), a region thought to be dominated by smooth plains in NASA Voyager 2 images taken in August 1981, but shown here in much higher resolution images to be covered in low ridges and troughs. Other major features seen in the region include Labtayt Sulci, a 1-kilometer- (0.6-mile-) deep canyon running northward from a cusp in the south polar terrain boundary (Cashmere Sulci) at lower right to a set of 1-kilometer-tall ridges (Cufa Dorsa and Ebony Dorsum) east of Sarandib Planitia (also seen in Enceladus Mosaic), as well as Samarkand Sulci, a band of ridges and troughs running along the western margin of Sarandib Planitia almost all the way north to Enceladus' north pole.

In contrast to the youthful terrain of Sarandib Planitia and the terrain south of it, the terrain north and west of Sarandib appears much older. These regions are covered with impact craters at various stages of degradation, either from viscous relaxation (which causes the craters to flatten over time), or from tectonic activity.

To create this single full-disk mosaic, the 16 images were reprojected into an orthographic projection centered at 2.3 degrees north latitude, 317.7 degrees west longitude with a pixel scale of 63 meters (207 feet) per pixel. The original images were taken by the Cassini spacecraft narrow-angle and wide-angle cameras from distances ranging from 10,850 to 29,750 kilometers (6,740 to 18,490 miles). The images had a phase, or sun-Enceladus-spacecraft, angle of 28 degrees.

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 mission for NASA\'s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Credit: NASA/JPL/Space Science Institute

Source: NASA/JPL - Cassini

Fractured World
December 29, 2006

Numerous blue-green fractures can be seen in this false-color mosaic taken during Cassini's second close flyby of Enceladus, on March 9, 2005.

The mosaic shows the anti-Saturnian hemisphere of Enceladus -- the side that always faces away from Saturn. This region contains a number of tectonic and impact features and shows how these two geologic forces interact on Enceladus. The center left portion of this mosaic is dominated by Diyar Planitia. Like Sarandib Planitia observed in the previous Enceladus flyby, the region is characterized by low ridges and troughs. Throughout this hemisphere, fractures of all sizes disrupt the previously existing cratered terrain and even the comparatively youthful Diyar Planitia.

Many of the younger fractures have blue-green walls, revealing coarse-grained water ice in the top layers of Enceladus' lithosphere, compared to the fine-grained ice that coats much of Enceladus' surface. The blue-green color is very similar to the coatings surrounding the south polar 'tiger stripes' (these appear greener than the features in the south polar mosaic released in 2005 (see Enceladus the Storyteller) due to the use of clear-filter images, instead of green, in that mosaic).

A higher resolution cropped section of this mosaic is available in Exploring Icy Canyons.

This mosaic consists of 25 false-color footprints (75 images total) taken by the Cassini spacecraft's narrow-angle camera. The mosaic uses an ultraviolet filter centered at 338 nanometers for blue, a green filter centered at 568 nanometers for green and a near-infrared filter centered at 930 nanometers for red--thus covering a wider spectrum region than the human eye. To create a single, full-disk mosaic, the images were reprojected into an orthographic projection centered at 1.5 degrees south latitude, 204 degrees west longitude with a pixel scale of 90 meters (295 feet) per pixel. The black strip seen at the top of the mosaic is an unfilled seam between two images.

The original images were taken from distances ranging from 4,300 to 31,800 kilometers (2,670 to 19,760 miles). The images have a phase, or sun-Enceladus-spacecraft, angle of 45 degrees.

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 mission for NASA\'s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Credit: NASA/JPL/Space Science Institute

Source: NASA/JPL - Cassini

Exploring Icy Canyons
December 29, 2006

Fine topographic detail and color variations are revealed in this 11-image, false color mosaic taken during Cassini's second close flyby of Saturn's moon Enceladus, on March 9, 2005.

This mosaic, a high-resolution cropped section of the full-disk mosaic available in Fractured World, shows the center of the anti-Saturnian hemisphere of Enceladus -- the side of Enceladus that always faces away from Saturn. The left portion of the mosaic is dominated by Diyar Planitia. Like Sarandib Planitia, observed in the previous Enceladus flyby of February 2005, the region is characterized by low ridges and troughs. Throughout this region, fractures of all sizes cut across Diyar Planitia and the older, cratered terrain at center and right.

Many of the younger fractures have blue-green walls, revealing coarse-grained water ice in the top layers of Enceladus' lithosphere, compared to the fine-grained ice that coats much of Enceladus' surface. The blue-green color is very similar to the coatings of the south polar "tiger stripes." The color here is greener than the features in the south polar mosaic released in 2005 (see Enceladus the Storyteller) due to the use of clear-filter images, instead of green, in the latter mosaic.

This mosaic consists of 11 false-color footprints (33 images total) taken by the Cassini spacecraft's narrow-angle camera. The mosaic uses an ultraviolet filter centered at 338 nanometers for blue, a green filter centered at 568 nanometers for green and a near-infrared filter centered at 930 nanometers for red, thus covering a wider spectrum region than the human eye. To create a single mosaic, the images were reprojected into an orthographic projection with a pixel scale of 45 meters per pixel. The region is centered at 3.9 degrees north latitude, 208.9 degrees west longitude and covers an area 233 kilometers (145 miles) by 154 kilometers (96 miles) in size.

The original images were taken by the Cassini spacecraft's narrow-angle camera from distances ranging from 4,300 to 27,050 kilometers (2,670 to 16,810 miles). The images have a phase, or sun-Enceladus-spacecraft, angle of 45 degrees. Image scale is 45 meters (150 feet) per pixel.

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 mission for NASA\'s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Credit: NASA/JPL/Space Science Institute

Source: NASA/JPL - Cassini

Brilliant Ice Dust
December 29, 2006

Lit by reflected light from Saturn, Enceladus appears to hover above the gleaming rings, its well-defined ice particle jets spraying a continuous hail of tiny ice grains. The fine particles coat the moon in a mantle as white as fresh snow and populate the torus, or doughnut-shaped E ring in which Enceladus resides.

Beyond Enceladus (505 kilometers, or 314 miles across), the fine particles in Saturn's other rings also glow brilliantly in scattered light in this viewing geometry. Running horizontally across the center of the image, between Enceladus and the dazzlingly bright F ring, are two faint rings--kin of the E ring. These are the G ring (top) and the recently discovered ring designated R/2006 S1 (bottom), which is also unofficially known as the Janus/Epimetheus ring.

This image was taken in visible light with the Cassini spacecraft narrow-angle camera on March 22, 2006, at a distance of approximately 1.303 million kilometers (810,000 miles) from Enceladus and at a sun-Enceladus-spacecraft, or phase, angle of 160 degrees. Image scale is 8 kilometers (5 miles) per pixel.

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 mission for NASA\'s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Credit: NASA/JPL/Space Science Institute

Source: NASA/JPL - Cassini

The University of Virginia press release is reproduced below:

Feb. 8, 2007 -- Astronomers from the University of Virginia and other institutions have found that Enceladus, the sixth-largest moon of Saturn, is a “cosmic graffiti artist,” pelting the surfaces of at least 11 other moons of Saturn with ice particles sprayed from its spewing surface geysers. This ice sandblasts the other moons, creating a reflective surface that makes them among the brightest bodies in the solar system (Enceladus, itself a ball of mostly ice, is the single most reflective body in our solar system).

“Enceladus’ art is a work-in-progress, constantly altering the surfaces of other moons orbiting within this moon’s beautiful swirl of ice particles,” said Anne Verbiscer, a research scientist in the astronomy department at the University of Virginia and the study’s lead investigator. “We’ve dubbed Enceladus a graffiti artist because of its ability to alter the appearance of the other moons.”

A paper about her and her colleagues’ findings appears in the Feb. 9 issue of the journal Science.

The ring of ice particles Enceladus forms around Saturn is known as the E-ring. At least 11 other moons orbit within the E-ring and are constantly subjected to high velocity collisions with Enceladus’s icy wake.


Wispy fingers of bright, icy material reach
tens of thousands of kilometers outward from
Saturn's moon Enceladus into the E ring,
while the moon's active south polar jets
continue to fire away
Photo courtesy NASA/JPL/Space Science Institute



Anne Verbischer
Photo by Dan Addison
(click on photo for high res version)

A series of geysers at Enceladus’s south pole continually erupt, ejecting ice particles, spewing a swirling wispy trail in the moon’s wake and ultimately forming a cloudy ring of ice particles. The ring is added to over and over as Enceladus repeats its orbit. The particles may persist for thousands of years, until they collide with one of the embedded moons, including Enceladus as it flows through its own emissions.

“We asked ourselves why those other moons in the E ring are so bright, though they are not geologically active like Enceladus? The answer, we now know, is that the other moons are being ‘sand-blasted’, so to speak, by the ice particles ejected from Enceladus,” Verbiscer said. “These are physical characteristics not previously known.”

Verbiscer added that Enceladus is of great interest to astrobiologists who believe primitive microorganisms could, in theory, exist beneath the surface of that moon because of the existence of liquid water below the surface.

Planetary astronomers are particularly interested in Enceladus because of its geological activity. At 314 miles in diameter, Enceladus is nearly seven times smaller than the Earth’s moon. But unlike our moon, Enceladus is continually changing as its geysers spew ice and liquid water, the likely result of heat and pressure deep within.

The surface of Enceladus is quite young, possibly less than 100 million years. It is the sixth largest moon of the more than thirty known moons that orbit Saturn. Because of its icy surface, Enceladus has the highest albedo, or surface reflectivity of any body in the solar system. Astronomer William Herschel discovered the moon in 1789.

The satellite’s surface of ice includes smooth areas of plains, ice vents, ridges and long lines of cracks at its south pole. The cracks are the source of the ice plumes released from the body that escape into its orbit, trailing and accumulating in its path, creating a highly visible cloudy ring around Saturn.

Enceladus is named for a Roman and Greek mythological giant who was considered responsible for volcanic fires on Mt. Etna in Sicily. “That analogy certainly holds true with the realization that Enceladus is geologically active and spraying ice particles out of its south pole,” Verbiscer said. “But we’ve extended the gigantic influence that it has, because of its ability to alter the appearance of its neighboring moons.”

Verbiscer’s co-investigators are Richard French of Wellesley College, Mark Showalter of the SETI Institute and Paul Helfenstein of Cornell University.

Source: U.Va. Press Release

Icy Outpost?
February 21, 2007

The Cassini spacecraft looks down under at the tortured south polar region of Enceladus, crossed by its "tiger stripes," or sulci, as the long, nearly parallel fractures are officially known. The use of enhanced color in this and other composite images makes the fractures and faults easier for the eye to detect.

The moon's excess warmth, water ice jets, and huge vapor plume laced with simple organic materials make it an excellent candidate for the search for pre-biotic chemistry, and possibly even life, beyond Earth. Enceladus is 505 kilometers (314 miles across).

This false-color view is a composite of images obtained using filters sensitive to ultraviolet, green and infrared light. The images were taken by the Cassini spacecraft narrow-angle camera on Jan. 16, 2007 at a distance of approximately 657,000 kilometers (408,000 miles) from Enceladus. Image scale is 4 kilometers (2 miles) per pixel.

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 mission for NASA\'s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Credit: NASA/JPL/Space Science Institute

Source: NASA/JPL - Cassini

March 12, 2007
(Source: Jet Propulsion Laboratory)

A hot start billions of years ago might have set into motion the forces that power geysers on Saturn's moon Enceladus.

"Deep inside Enceladus, our model indicates we've got an organic brew, a heat source and liquid water, all key ingredients for life," said Dr. Dennis Matson, Cassini project scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "And while no one is claiming that we have found life by any means, we probably have evidence for a place that might be hospitable to life."


From afar, Enceladus exhibits a bizarre mixture
of softened craters and complex, fractured terrains.

Since NASA's Voyager spacecraft first returned images of the moon's snowy white surface, scientists have suspected Enceladus had to have something unusual happening within that shell. Cameras on NASA's Cassini orbiter seemed to confirm that suspicion in 2005 when they spotted geysers on Enceladus ejecting water vapor and ice crystals from its south polar region. The challenge for researchers has been to figure out how this small ice ball could produce the levels of heat needed to fuel such eruptions.


The ice jets of Enceladus send particles
streaming into space hundreds of kilometers
above the south pole of
this spectacularly active moon.

A new model suggests the rapid decay of radioactive elements within Enceladus shortly after it formed may have jump-started the long-term heating of the moon's interior that continues today. The model provides support for another recent, related finding, which indicates that Enceladus' icy plumes contain molecules that require elevated temperatures to form.

"Enceladus is a very small body, and it's made almost entirely of ice and rock. The puzzle is how the moon developed a warm core," said Dr. Julie Castillo, the lead scientist developing the new model at JPL. "The only way to achieve such high temperatures at Enceladus is through the very rapid decay of some radioactive species."

The hot start model suggests Enceladus began as a mixed-up ball of ice and rock that contained rapidly decaying radioactive isotopes of aluminum and iron. The decomposition of those isotopes -- over a period of about 7 million years -- would produce enormous amounts of heat. This would result in the consolidation of rocky material at the core surrounded by a shell of ice. According to the theory, the remaining, more slowly decaying radioactivity in the core could continue to warm and melt the moon's interior for billions of years, along with tidal forces from Saturn's gravitational tug.


Plumes of icy material extend above the southern
polar region of Enceladus

Scientists have also found the model helpful in explaining how Enceladus might have produced the chemicals in the plume, as measured by Cassini's ion and neutral mass spectrometer. Matson is lead author of a new study of the plume's composition, which appears in the April issue of the journal Icarus. Although the plume is predominantly made up of water vapor, the spectrometer also detected within the plume minor amounts of gaseous nitrogen, methane, carbon dioxide, propane and acetylene.

Scientists were particularly surprised by the nitrogen because they don't think it could have been part of Enceladus' original makeup. Instead, Matson's team suggests it is the product of the decomposition of ammonia deep within the moon, where the warm core and surrounding liquid water meet.


The fountain-like sources of the fine spray
of material that towers over Enceladus' south
polar region.

The thermal decomposition of ammonia would require temperatures as high as 577 degrees Celsius (1070 degrees Fahrenheit), depending on whether catalysts such as clay minerals are present. And while the long-term decay of radioactive species and current tidal forces alone cannot account for such high temperatures, with the help of the hot start model, they can.

The scalding conditions are also favorable for the formation of simple hydrocarbon chains, basic building blocks of life, which Cassini's spectrometer detected in small amounts within Enceladus' plume. The team concludes that so far, all the findings and the hot start model indicate that a warm, organic-rich mixture was produced below the surface of Enceladus and might still be present today, making the moon a promising kitchen for the cooking of primordial soup.

To gather more information about the chemistry within Enceladus, the team plans to directly measure the gas emanating from the plume during a flyby scheduled for March 2008.

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 in Pasadena, manages the Cassini-Huygens mission for NASA's Science Mission Directorate, Washington. 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.

Contacts:
Carolina Martinez 818-354-9382
Jet Propulsion Laboratory, Pasadena, Calif.

NEWS RELEASE: 2007-025

Source: NASA/JPL - Cassini - News Release

22 March 2007

This 16-image mosaic of Enceladus was taken during Cassini's first close flyby of this moon of Saturn on 17 February 2005.

This mosaic shows the trailing hemisphere of Enceladus - the side of Enceladus that always faces away from the direction of the satellite's orbital motion. This hemisphere is dominated by Sarandib Planitia (just right of center), a region thought to be dominated by smooth plains in NASA Voyager 2 images taken in August 1981, but shown here in much higher resolution images to be covered in low ridges and troughs. Other major features seen in the region include Labtayt Sulci, a 1-kilometre deep canyon running northward from a cusp in the south polar terrain boundary (Cashmere Sulci) at lower right to a set of 1-kilometre-tall ridges (Cufa Dorsa and Ebony Dorsum) east of Sarandib Planitia, as well as Samarkand Sulci, a band of ridges and troughs running along the western margin of Sarandib Planitia almost all the way north to Enceladus' north pole.

In contrast to the youthful terrain of Sarandib Planitia and the terrain south of it, the terrain north and west of Sarandib appears much older. These regions are covered with impact craters at various stages of degradation, either from viscous relaxation (which causes the craters to flatten over time), or from tectonic activity.

To create this single full-disc mosaic, the 16 images were reprojected into an orthographic projection centered at 2.3 degrees north latitude, 317.7 degrees west longitude with a pixel scale of 63 metres per pixel. The original images were taken by the Cassini spacecraft narrow-angle and wide-angle cameras from distances ranging from 10 850 to 29 750 kilometres. The images had a phase, or sun-Enceladus-spacecraft, angle of 28 degrees.

Credits: NASA/JPL/Space Science Institute

In a David and Goliath story of Saturnian proportions, the little moon Enceladus is weighing down giant Saturn’s magnetic field so much that the field is rotating slower than the planet. This phenomenon makes it nearly impossible to measure the length of the Saturn day using techniques that work at the other giant planets.

“No one could have predicted that the little moon Enceladus would have such an influence on the radio technique that has been used for years to determine the length of the Saturn day,” said Dr. Don Gurnett of the University of Iowa, Iowa City. Gurnett is the principal investigator on the radio and plasma wave science experiment onboard NASA's Cassini spacecraft. The radio technique measures the rotation of the planet by taking its radio pulse rate - the rhythm of natural radio signals from the planet.

Geysers on Saturn's little moon Enceladus are throwing off Saturn's internal clock, making it hard to measure the length of Saturn's day.

Credits: NASA

A new study of Cassini data, reported this week in the online version of the journal Science, determined that Saturn’s magnetic field lines - invisible lines originating from the interior of a magnetized planet - are being forced to slip relative to the rotation of the planet by the weight of electrically charged particles originating from geysers spewing water vapor and ice from Enceladus. These results are based on joint observations by two Cassini instruments - the radio and plasma wave instrument (RPWS) and the magnetometer (MAG).

The neutral gas particles ejected from the geysers on Enceladus form a donut-like torus around Saturn. As these particles become electrically charged, they are captured by Saturn’s magnetic field, forming a disc of ionized gas, or plasma, which surrounds the planet near the equator. The particles weigh down the magnetic field so much that the rate of rotation of the plasma disc slows down slightly. This slippage causes the radio period, controlled by the plasma disc rotation, to be longer than the planet's actual rotation period.

Scientists conclude the period Cassini has been measuring from radio emission is not the length of the Saturn day, but rather the rotation period of the plasma disc. At present, because of Saturn’s cloud motion, no technique is known that can accurately measure the planet's actual internal rotation.

The image of Saturn's rings was taken with the Cassini wide-angle camera on 14 December 2004. It was taken at a distance of approximately 654 000 kilometres from Saturn through a filter sensitive to wavelengths of infrared light centred at 728 nanometres. The image scale is 35 kilometres per pixel.

Credits: NASA/JPL/Space Science Institute

Finding out the length of Saturn’s day has been a challenge because the gaseous planet has no surface or fixed point to clock its rotation rate. Initially, the approach was to use periodic regular radio signals, as has been done for Jupiter, Uranus and Neptune. However, Saturn’s radio period has turned out to be troubling in two ways.

It seems to be a pulsed signal rather than a rotating, lighthouse-like beam. Secondly, the period seems to be slowly changing over months to years. The day measured by Cassini is some six minutes longer than the day recorded by NASA’s Voyager spacecraft in the early 1980s, a change of nearly one percent.

“We have linked the pulsing radio signal to a rotating magnetic signal. Once each rotation of Saturn's magnetic field, an asymmetry in the field triggers a burst of radio waves,” said Prof. David Southwood, co-author, Imperial College London, and Director of Science at the European Space Agency. "We have then linked both signals to material that has come from Enceladus.”

The ice jets of Enceladus send particles streaming into space hundreds of kilometres above the south pole of this spectacularly active moon. Some of the particles escape to form the diffuse E ring around Saturn. This colour-coded image was processed to enhance faint signals, making the contours and extent of the fainter, larger-scale component of the plume easier to see.

The bright strip behind and above Enceladus (505 kilometres) is the E ring, in which this intriguing body resides. The small round object at far left is a background star.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on 24 March 2006 at a distance of approximately 1.9 million kilometres from Enceladus and at a Sun-Enceladus-spacecraft, or phase, angle of 162 degrees. Image scale is 11 kilometres per pixel.

Credits: NASA/JPL/Space Science Institute

Based on the new observations, scientists now think there are two possible reasons for the change in radio period. The first theory is that the geysers on Enceladus could be more active now than in Voyagers’ time. The second is that there may be seasonal variations as Saturn orbits the sun once every 29 years.

“One would predict that when the geysers are very active, the particles load down the magnetic field and increase the slippage of the plasma disc, thereby increasing the radio emission period even more. If the geysers are less active, there would be less of a load on the magnetic field, and therefore less slippage of the plasma disc, and a shorter period,” said Gurnett.

"The direct link between radio, magnetic field and deep planetary rotation has been taken for granted up to now. Saturn is showing we need to think further," said Michele Dougherty, principal investigator on Cassini’s magnetometer instrument, Imperial College London.


Note

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Cassini orbiter was designed, developed and assembled at JPL. The magnetometer (MAG) team is based at Imperial College London (UK). The radio and plasma wave science experiment (RPWS) team is based at the University of Iowa, Iowa City (US).

Source: ESA - News

Mar. 23

Strangely, astronomers don't know how long a day is on Saturn, because they can't get a firm footing on the problem given the giant planet's gaseous nature.

So they have long relied on radio measurements of the ringed planet's magnetic field to help estimate the length of the day. But that doesn't really work either, they realized, so estimates have remained loose. Now the scientists at least have a better handle on this aspect of the problem.

Geyser activity from Saturn's small moon Enceladus weighs down the big planet's magnetic field so much that the field rotates more slowly than Saturn itself, new observations reveal. The moon is a mere 310 miles (500 kilometers) wide.

Geysers on Saturn's little moon Enceladus are throwing off Saturn's internal clock, making it hard to measure the length of the Saturn day.

A day on Earth is determined by how long it takes the planet to spin once on its axis. That's pretty easy to measure, because Earth's surface is solid. Just sit there for about 24 hours, 3 minutes and 56.55 seconds, on average, and measure the time between two sunrises. (That works today, but eventually we will have more than 24 hours to get this job and others done. A lot more.
"No one could have predicted that the little moon Enceladus would have such an influence on the radio technique that has been used for years to determine the length of the Saturn day," said Don Gurnett of the University of Iowa.

Gurnett is the principal investigator on a radio and plasma wave science experiment on NASA's Cassini spacecraft. The idea has been to measure Saturn's rotation by taking its radio pulse. The technique works pretty well on the other giant planets.

But the new observations, reported online this week by the journal Science, show that the invisible magnetic field lines, which emanate from Saturn's poles and radiate out like a giant, skeletal pumpkin, slip in relation to the planet's rotation.

The slip owes to the collective weight of electrically charged particles that originate in Enceladus' remarkable geysers of water vapor and ice. Particles in the geysers encircle Saturn and become electrically charged, forming a disk around the equator of hot gas called plasma.

Meanwhile, measurements revealed last year that Saturn's day has gotten about six or eight minutes longer—now roughly 10 hours and 47 minutes—since the 1980s when measured by the Voyager missions. Nobody suspects the trend to continue forever (meaning the days would just get longer and longer at such a rapid rate), but they also don't know what's going on.

Either the geysers on Enceladus are more active now than in the '80s, the astronomers figure, or perhaps there are seasonal variations as Saturn orbits the Sun, a year that takes more than 29 Earth-years to complete.

"One would predict that when the geysers are very active, the particles load down the magnetic field and increase the slippage of the plasma disk, thereby increasing the radio emission period even more," Gurnett said Thursday. "If the geysers are less active, there would be less of a load on the magnetic field, and therefore less slippage of the plasma disk, and a shorter period."

"The direct link between radio, magnetic field and deep planetary rotation has been taken for granted up to now," said Michele Dougherty, a researcher at Imperial College London and principal investigator on Cassini's magnetometer instrument. "Saturn is showing we need to think further."

go

Astral Pearl
April 11, 2007

The high northern latitudes on Enceladus show little detail from Cassini's distant vantage point, nearly 50 degrees above the moon's equator.

The plume of icy material that jets from the south pole of Enceladus (505 kilometers, or 314 miles across) is not visible in this viewing geometry.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Feb. 26, 2007 at a distance of approximately 1.7 million kilometers (1.1 million miles) from Enceladus and at a Sun-Enceladus-spacecraft, or phase, angle of 95 degrees. Scale in the original image was 10 kilometers (6 miles) per pixel. The image was contrast enhanced and magnified by a factor of two.

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 mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov. The Cassini imaging team homepage is at http://ciclops.org.

Credit: NASA/JPL/Space Science Institute

Source: NASA/JPL - Cassini

Casting a Shadow
April 18, 2007
Sunlight makes visible the faint band called the E ring as two moons meet in the sky.

Blazing like an icy torch, the plume of Enceladus shines in scattered sunlight as the moon casts a shadow onto Saturn's E ring. Some of the tiny ice particles erupted from the moon's south polar region go into Saturn orbit, forming the doughnut-shaped ring, onto which the moon's shadow is cast in this view.

The shadow of Enceladus (505 kilometers, or 314 miles across) stretches away to the upper left at around the 10 o'clock position. The Sun-Enceladus-spacecraft, or phase, angle is 164 degrees here, with the Sun being located toward the lower right. This means that Enceladus' shadow extends toward the Cassini spacecraft -- through part of the E ring.

Some of the bright dots in this heavily processed view are background stars. Others are due to cosmic ray hits on the camera detector.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Aug. 11, 2006 at a distance of approximately 2.2 million kilometers (1.3 million miles) from Enceladus. Image scale is 13 kilometers (8 miles) per pixel.

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 mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov. The Cassini imaging team homepage is at http://ciclops.org.

Credit: NASA/JPL/Space Science Institute

Source: NASA/JPL - Cassini

May 16, 2007
(Source: Jet Propulsion Laboratory/University of Santa Cruz)

Pasadena, Calif.--Rubbing your hands together on a cold day generates a bit of heat, and the same process of frictional heating may be what powers the geysers jetting out from the surface of Saturn's moon Enceladus.

Tidal forces acting on fault lines in the moon's icy shell cause the sides of the faults to rub back and forth against each other, producing enough heat to transform some of the ice into plumes of water vapor and ice crystals, according to a new study published in the May 17 issue of the journal Nature.

Francis Nimmo, assistant professor of Earth and planetary sciences at the University of California, Santa Cruz, and his co-authors calculated the amount of heat that could be generated by this mechanism and concluded that it is the most likely explanation for the plumes and other features observed in the south polar region of Enceladus. This region is warmer than the rest of the frozen surface of Enceladus and has features called "tiger stripes" that look like tectonic fault lines.


Shear Heating on Enceladus

"We think the tiger stripes are the source of the plumes, and we made predictions of where the tiger stripes should be hottest that can be tested by future measurements," Nimmo said.

Driving the whole process is the moon's eccentric orbit, which brings it close to Saturn and then farther away, so that the gravitational attraction it feels changes over time.

"It's getting squeezed and stretched as it goes around Saturn, and those tidal forces cause the faults to move back and forth," Nimmo said.

Unlike some other proposals for the origin of the plumes, this mechanism does not require the presence of liquid water near the surface of Enceladus, noted co-author Robert Pappalardo of NASA's Jet Propulsion Laboratory in Pasadena, Calif.

"The heat is sufficient to cause ice to sublimate, like in a comet -- the ice evaporates into vapor, and the escaping vapor drags particles off into space," Pappalardo said.

The study does suggest, however, that Enceladus has a liquid ocean lying deep beneath the ice. That allows the ice shell to deform enough to produce the necessary movement in the faults. If the ice shell sat directly on top of the moon's rocky interior, tidal forces would not produce enough movement in the faults to generate heat, Nimmo said.

The frictional, or "shear heating," mechanism is consistent with an earlier study by Nimmo and Pappalardo which proposed that Enceladus reoriented itself to position its hot spot at the south pole (see earlier press release at http://press.ucsc.edu/text.asp?pid=878). In that study, the researchers described how the reorientation of Enceladus would result from a lower density of the thick ice shell in this region.

In the new paper, the researchers estimated the thickness of the ice shell to be at least 5 kilometers (3 miles) and probably several tens of kilometers or miles. They also estimated that the movement along the fault lines is about half a meter over the course of a tidal period.

In addition to Nimmo and Pappalardo, the co-authors of the paper include John Spencer of the Southwest Research Institute in Boulder, Colo., and McCall Mullen of the University of Colorado, Boulder. This study was funded by NASA's Planetary Geology and Geophysics and Outer Planets research programs.

Enceladus has sparked great interest among scientists, particularly since the discovery more than a year ago by NASA's Cassini spacecraft of the geysers shooting off its surface. This is one of two papers about Enceladus appearing in the May 17 issue of Nature. In the other paper, scientists explain how cracks in the icy surface of Enceladus open and close under Saturn's pull. Saturn's tides could control the timing of the geyser's eruptions, researchers suggest.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. NASA¿s Jet Propulsion Laboratory, a division of Caltech, 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.

More information on the Cassini mission is available at: http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov.

Contacts:
Carolina Martinez 818-354-9382
Jet Propulsion Laboratory, Pasadena, Calif.

Tim Stephens 831-459-2495
University of Santa Cruz, Calif.

NEWS RELEASE: 2007-060

Source: NASA/JPL - Cassini - News Release

Shear Heating on Enceladus
May 16, 2007

Plumes of water vapor and other gases escape at high velocity from the surface of Saturn's moon Enceladus, as shown in this artist concept.

The "shear heating" mechanism suggests that tidal forces acting on fault lines in the moon's icy shell cause the sides of the faults to rub back and forth against each other, producing enough heat to transform some of the ice into plumes of water vapor and ice crystals. Cold sub-surface ice (blue) becomes much warmer near the active fractures from which the plumes emanate.

Movement along the fault lines may be about half a meter (20 inches) over the course of the 1.37-day tidal period of Enceladus around Saturn.

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 mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov.

Credit: NASA/JPL/Space Science Institute

Source: NASA/JPL - Cassini

May 16, 2007
(Source: Goddard Space Flight Center)

Cracks in the icy surface of Saturn's moon Enceladus open and close daily under the pull of Saturn's gravity, according to new calculations by NASA-sponsored researchers.

"Tides generated by Saturn's gravity could control the timing of eruptions from cracks in the southern hemisphere of Enceladus," said Dr. Terry Hurford of NASA's Goddard Space Flight Center, Greenbelt, Md. Hurford is lead author of a paper on this research appearing in Nature May 17. This paper is one of two studies on Enceladus in this issue of Nature. The other paper explains that tidal forces cause the sides of the cracks to rub together and produce enough heat to vaporize ice into plumes that jettison off the moon, researchers suggest.


This is a mosaic of Enceladus compiled from
21 images taken by the Cassini spacecraft
as it swooped past the moon's south pole on
July 14, 2005. The Tiger Stripe region appears
as a series of long cracks toward the bottom.
The mosaic is in false color, and includes
images taken in various types of light, including
ultraviolet and infrared.
Credit: NASA/JPL/Space Science Institute

In 2005, the Cassini spacecraft flew by Enceladus and saw plumes of material erupting from the south pole of Enceladus. Scientists were surprised to see this because eruptions are powered by heat from an object's interior. Enceladus is tiny compared to most moons, only about 500 kilometers (310 miles) in diameter, so it should have lost its interior heat to the cold of space long ago.

A closer look by Cassini revealed a series of 120-kilometer (75-mile) long cracks in the south polar region of Enceladus, which were nicknamed "Tiger Stripes" because they resembled a tiger's distinctive marks. The stripes are warmer than their surroundings, so scientists believe they are the source of the eruptions. The Cassini observations also show the plumes consist of water vapor, so there is evidence for liquid water under the ice. Since liquid water is necessary to support known forms of life, Enceladus has become a promising place to look for extraterrestrial life.

Enceladus' 1.3-Earth-day orbit around Saturn is slightly elliptical (egg-shaped), so the moon's distance from Saturn changes regularly as it travels in its orbit. When Enceladus is closer to Saturn, the pull of Saturn's gravity is stronger, creating a larger tide; and when Enceladus is farther away, the pull is weaker, creating a smaller tide. Saturn's position in Enceladus' sky also changes slightly, moving the location of the tide on Enceladus' surface from east to west and back again with each orbit. These two effects combine to produce changing stress on the moon's icy surface. The team developed a computer model to calculate how the changing stress affects the Tiger Stripes.

"We found that because of the way the Tiger Stripes are oriented on the surface, when Enceladus is farthest from Saturn, the stresses in the region pull most of them open, and when Enceladus is closest to Saturn, the stresses force most of them to close," said Hurford. "Different stripes open at different times in the orbit. Assuming they erupt as soon as they open, exposing liquid water to the vacuum of space, we can predict which stripes will be erupting at certain times in the orbit. Also, because most of the stripes are open when Enceladus is farthest from Saturn, we expect the eruptive activity to be greatest at this time."

It has been hard to conclusively test the model so far because of the orientation of the stripes when Cassini took images of the eruptions. Cassini saw the eruptions when they appeared on the edge of Enceladus as they were backlit by the sun. From this viewpoint, the Tiger Stripes were lined up so that some were closer to the spacecraft and some were farther away. It is hard for the team to tell if an eruption was coming from a stripe in the foreground or from one in the background. However, future observations of the moon when Cassini is in a different location may provide a partial test by allowing the eruptions from one stripe to appear distinct from the rest.

The research was funded through NASA's Postdoctoral Program Fellowship. The team includes Hurford, Dr. Paul Helfenstein of Cornell University, Ithaca, N.Y., Dr. Greg Hoppa of Raytheon, Woburn, Mass., Dr. Richard Greenberg of the University of Arizona, Tucson, and Dr. Bruce Bills of the Scripps Institution of Oceanography, La Jolla, Calif., and Goddard. The Cassini-Huygens mission is a cooperative project among NASA, the European Space Agency, and the Italian Space Agency. JPL, 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 was designed, developed, and assembled at JPL.

Contacts:
Nancy Neal-Jones / Bill Steigerwald
NASA Goddard Space Flight Center
301 286 0039 / 5017

Source: NASA/JPL - Cassini - News Release

Icy Emanations
June 4, 2007

Peeking over the crescent of Enceladus, the Cassini spacecraft views the towering plume of ice particles erupting from the moon's south polar region.

Multiple components of the overall plume are visible in this view of Enceladus (505 kilometers, or 314 miles across).

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on April 24, 2007 at a distance of approximately 188,000 kilometers (117,000 miles) from Enceladus and at a Sun-Enceladus-spacecraft, or phase, angle of 153 degrees. Image scale is 1 kilometer (0.6 miles) per pixel.

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 Techno