December 12, 2007
(Source: Jet Propulsion Laboratory/University of Colorado at Boulder)

SAN FRANCISCO, Calif. -- New observations by NASA's Cassini spacecraft indicate the rings of Saturn, once thought to have formed during the age of the dinosaurs, instead may have been created roughly 4.5 billion years ago, when the solar system was still under construction.

Larry Esposito, principal investigator for Cassini's Ultraviolet Imaging Spectrograph at the University of Colorado, Boulder, said data from NASA's Voyager spacecraft in the 1970s, and later from NASA's Hubble Space Telescope, led scientists to believe Saturn's rings were relatively youthful and likely created by a comet that shattered a large moon, perhaps 100 million years ago.


Saturn's Recycling Rings.

Larry Esposito, principal investigator for Cassini's Ultraviolet Imaging Spectrograph at the University of Colorado, Boulder, said data from NASA's Voyager spacecraft in the 1970s, and later from NASA's Hubble Space Telescope, led scientists to believe Saturn's rings were relatively youthful and likely created by a comet that shattered a large moon, perhaps 100 million years ago.

But ring features seen by instruments on Cassini -- which arrived at Saturn in 2004 -- indicate the rings were not formed by a single cataclysmic event. The ages of the different rings appear to vary significantly, and the ring material is continually being recycled, Esposito said.

"The evidence is consistent with the picture that Saturn has had rings all through its history," said Esposito of the University of Colorado's Laboratory for Atmospheric and Space Physics. "We see extensive, rapid recycling of ring material, in which moons are continually shattered into ring particles, which then gather together and re-form moons."


"Staring Mittens"
+ View Related Movie


Esposito and colleague Miodrag Sremcevic, also with the University of Colorado, are presenting these findings today in a news briefing at the meeting of the American Geophysical Union in San Francisco.

"We have discovered that the rings probably were not created just yesterday in cosmic time, and in this scenario, it is not just luck that we are seeing planetary rings now," said Esposito. "They probably were always around but continually changing, and they will be around for many billions of years."

Scientists had previously believed rings as old as Saturn itself should be darker due to ongoing pollution by the "infall" of meteoric dust, leaving telltale spectral signatures, Esposito said. But the new Cassini observations indicate the churning mass of ice and rock within Saturn's gigantic ring system is likely much larger than previously estimated. This helps explain why the rings overall appear relatively bright to ground-based telescopes and spacecraft.


Clumpy Moons
+ View Related Movie

"The more mass there is in the rings, the more raw material there is for recycling, which essentially spreads this cosmic pollution around," he said. "If this pollution is being shared by a much larger volume of ring material, it becomes diluted and helps explain why the rings appear brighter and more pristine than we expected."

Esposito, who discovered Saturn's faint F ring in 1979 using data from NASA's Pioneer 11 spacecraft, said a paper by him and his colleagues appearing in an upcoming issue of the journal Icarus supports the theory that Saturn¿s ring material is being continually recycled. Observing the flickering of starlight passing through the rings in a process known as stellar occultation, the researchers discovered 13 objects in the F ring ranging in size from 27 meters to 10 kilometers (30 yards to six miles) across.

Since most of the objects were translucent -- indicating at least some starlight was passing through them -- the researchers concluded they probably are temporary clumps of icy boulders that are continually collecting and disbanding due to the competing processes of shattering and coming together again. The team tagged the clumpy moonlets with cat names like "Mittens" and "Fluffy" because they appear to come and go unexpectedly over time and have multiple lives, said Esposito.

Esposito stressed that Saturn's rings of the future won't be the same rings we see today, likening them to great cities around the world like San Francisco, Berlin or Beijing. "While the cities themselves will go on for centuries or millennia, the faces of people on the streets will always be changing due to continual birth and aging of new citizens."

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 in Washington, D.C.

For more information about the Cassini-Huygens mission, visit: _http://saturn.jpl.nasa.gov and _http://www.nasa.gov/cassini. To listen to a podcast of Esposito and view a short video animation of objects in Saturn's F ring shattering and re-forming, visit: _http://www.colorado.edu/news/reports/space/.

Contacts:
Carolina Martinez 818-354-9382
Jet Propulsion Laboratory, Pasadena, Calif.
carolina.martinez@jpl.nasa.gov

Jim Scott 303-492-3114
University of Colorado, Boulder
jim.scott@colorado.edu


NEWS RELEASE: 2007-149


Source: NASA/JPL - Cassini - News Release

Saturn's Recycling Rings
December 12, 2007

This is an artist concept of a close-up view of Saturn's ring particles. The planet Saturn is seen in the background (yellow and brown). The particles (blue) are composed mostly of ice, but are not uniform. They clump together to form elongated, curved aggregates, continually forming and dispersing. The space between the clumps is mostly empty. The largest individual particles shown are a few meters (yards) across.

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. The ultraviolet imaging spectrograph was designed and built at, and the team is based at the University of Colorado, Boulder.

For more information about the Cassini-Huygens mission, visit: _http://saturn.jpl.nasa.gov/home/index.cfm. The ultraviolet imaging spectrograph team home page is at: _http://lasp.colorado.edu/cassini.

Credit: NASA/JPL/University of Colorado

Source: NASA/JPL - Cassini

"Staring Mittens"
December 12, 2007

This is an artist concept and movie of the view from Cassini during the star occultation that detected "Mittens," the small object to the right of the star. As Cassini watched the star pass behind Saturn's F ring (foreground), the star blinked out when Mittens blocked it, indicating it may be a solid moonlet.

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. The ultraviolet imaging spectrograph was designed and built at, and the team is based at the University of Colorado, Boulder.

For more information about the Cassini-Huygens mission, visit: _http://saturn.jpl.nasa.gov/home/index.cfm. The ultraviolet imaging spectrograph team home page is at: _http://lasp.colorado.edu/cassini.

Credit: NASA/JPL/University of Colorado

Source: NASA/JPL - Cassini

Clumpy Moons
December 12, 2007

This is a computer simulation of the final stage of the growth of a "clump" in Saturn's rings. The gravity from a hypothesized moonlet (solid gray sphere in frame center) has collected smaller ring particles (black) to form a temporary aggregation. The particles shown in the simulation are from centimeters to meters (inches to yards) across. The gray moonlet is 61 meters (200 feet) across.

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. The ultraviolet imaging spectrograph was designed and built at, and the team is based at the University of Colorado, Boulder.

For more information about the Cassini-Huygens mission, visit: _http://saturn.jpl.nasa.gov/home/index.cfm. The ultraviolet imaging spectrograph team home page is at: _http://lasp.colorado.edu/cassini.

Credit: NASA/JPL/University of Colorado

Source: NASA/JPL - Cassini

Jan. 31, 2008
(Source: ESA)

Order can be found in the most unexpected places, as demonstrated by our neighbor three planets down. Two of Saturn's rings have been found by NASA's Cassini spacecraft to contain orderly lines of densely grouped, boulder-size icy particles that extend outward across the rings like ripples from a rock dropped in a calm pond.


Artist concept showing the descent and landing
of Huygens.
Image credit: NASA/JPL/ESA

Order can be found in the most unexpected places, as demonstrated by our neighbor three planets down. Two of Saturn's rings have been found by NASA's Cassini spacecraft to contain orderly lines of densely grouped, boulder-size icy particles that extend outward across the rings like ripples from a rock dropped in a calm pond.

"Imagine going to a town that stretches from San Francisco to Los Angeles and seeing buildings spaced the same distance apart on every block," said Cassini radio science team member Essam Marouf of San Jose State University, San Jose, Calif. "All of these groups of particles within the rings are very close together, and the space between them is extremely small, only 100 to 250 meters (320 feet to 820 feet) wide, depending on where they are in the ring."

Normally, the distances between particles change with their velocity. In the case of Saturn's rings, the distances between these ring particles stay relatively equal even though their velocities may change. This type of pattern is completely new, according to Marouf.

"This particular feature is the smallest and most detailed of anything seen in Saturn's rings so far," Marouf said. "In the chaotic environment of the rings, to find such regularity in the most cramped areas is nothing short of amazing." The regular structure can only be found in locations where particles are densely packed together, such as the B ring and the innermost part of the A ring.

The unexpected pattern within Saturn's rings may give scientists some new ideas of what to expect from other similar planets and solar systems.

The pattern was detected when the radio on board the Cassini spacecraft sent out three signals toward Earth. The signals crossed the Saturn's rings, and their frequencies were separated by scattering from the ring particles. Once the signals were captured by Earth-based antennas of NASA's Deep Space Network, Cassini scientists saw a regular pattern in the received signal frequencies.

"The signals showed that the particle groups were arranged in an unexpectedly regular formation that had 'rhythm within the rings of Saturn'", said Marouf. "Each particle is in its own orbit, and sometimes they collide and move apart as their velocities change. As a result, you have particles bunched together into dense groups that extend across the ring in harmony with each other."


Huygens on Titan
Image credit: ESA

The pattern of particles is described as an enormously extended natural diffraction grating. A diffraction grating has parallel lines like a picket fence; when light hits this fence, it separates according to wavelength, from ultraviolet to infrared light.

The same thing happened when Cassini's radio signals hit the fencelike pattern of ring particles. The signals, sent out in 2005, were meant to capture a complete view of the rings.

The same thing happened when Cassini's radio signals hit the fencelike pattern of ring particles. The signals, sent out in 2005, were meant to capture a complete view of the rings.

This research appears as a cover story in the Dec. 28 issue of Geophysical Research Letters.

For more information:

Written by: Diya Chacko

Media Relations Contact: Carolina Martinez 818-354-9382

Source: NASA/JPL - Cassini - Feature

Saturn's Ring Rhythm
January 31, 2008

Radio signals sent by NASA's Cassini spacecraft to Earth through Saturn's rings revealed the presence of highly unusual regular formations of densely grouped ring particles. The harmonic ring structure caused the radio signal frequency to separate into three distinct components. The observed frequencies determine the regular spacing to be as small as 100 meters (320 feet), the finest-scale ring structure observed so far.
The regularly spaced yellow grid depicts the harmonic structure in Saturn's inner Ring A, and the image on the bottom right shows an actual observed frequency pattern (spectrogram). Color represents the observed signal strength. The structure acts like an enormously extended natural diffraction grating that separates the signal frequency into the three distinct components shown. The frequencies determine the regular spacing of the diffraction grating, 160 meters (500 feet) in this case. The image of Saturn was taken with Cassini's cameras and is shown here to illustrate the occultation. For additional information on the radio observations see Saturn's Ring Rhythm #2.

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. The radio science team is based 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. For more information on the radio science team visit _http://saturn.jpl.nasa.gov/spacecraft/instruments-cassini-rss.cfm. The Cassini imaging team homepage is at _http://ciclops.org.

Credit: NASA/JPL/Space Science Institute

Source: NASA/JPL - Cassini

Saturn's Ring Rhythm #2
January 31, 2008

For an Earth observer on May 3, 2005, the Cassini spacecraft appeared to pass behind the rings, then Saturn, then the rings again (the red line). The discovered harmonic structure was found on both the way in and out, but only in locations where particles are densely packed together, such as the B ring and the innermost part of the A ring.
The May 3 radio experiment and several others to follow in 2005 showed that the regular spacing of the harmonic structure vary from 100 to 250 meters (320 to 820 feet), depending on the location in the rings. To see an illustration of this occultation see Saturn's Ring Rhythm.

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. The radio science team is based 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. For more information on the radio science team visit _http://saturn.jpl.nasa.gov/spacecraft/instruments-cassini-rss.cfm.

Credit: NASA/JPL/Space Science Institute

Source: NASA/JPL - Cassini

One of Saturn's rings does housecleaning, soaking up material gushing from the fountains on Saturn's tiny ice moon Enceladus, according to new observations from the Cassini spacecraft.


Image above: This is a false-color image of jets
(blue areas) in the southern hemisphere of Enceladus
taken with the Cassini spacecraft narrow-angle
camera on Nov. 27, 2005. It has been processed
to reveal the individual jets that comprise the
plume.
Click image for enlargement.
Credit: NASA/JPL/Space Science Institute


"Saturn's A-ring and Enceladus are separated by 100,000 kilometers (62,000 miles), yet there’s a physical connection between the two," says Dr. William Farrell of NASA's Goddard Space Flight Center in Greenbelt, Md. "Prior to Cassini, it was believed that the two bodies were separate and distinct entities, but Cassini’s unique observations indicate that Enceladus is actually delivering a portion of its mass directly to the outer edge of the A-ring." Farrell is lead author of a paper on this discovery that appeared in Geophysical Research Letters January 23.

This is the latest surprising phenomenon associated with the ice geysers of Enceladus to be discovered or confirmed by Cassini scientists. Earlier, the geysers were found to be responsible for the content of the E-ring. Next, the whole magnetic environment of Saturn was found to be weighed down by the material spewing from Enceladus, which becomes plasma -- a gas of electrically charged particles. Now, Cassini scientists confirm that the plasma, which creates a donut-shaped cloud around Saturn, is being snatched by Saturn’s A-ring, which acts like a giant sponge where the plasma is absorbed.

Shot from Enceladus’ interior, the gas particles become electrically charged (ionized) by sunlight and collisions with other atoms and electrons. Once electrically charged, the particles feel magnetic force and are swept into the space around Saturn dominated by the planet's powerful magnetic field. There, they are trapped by Saturn’s magnetic field lines, bouncing back and forth from pole-to-pole. The fun ends, however, if their bouncing path carries them inward toward Saturn to the A-ring. There they stick, in essence becoming part of the ring. "Once they get to the outer A-ring, they are stuck," says Farrell.

"This is an example of how Saturn’s rings mitigate the overall radiation environment around the planet, sponging up low- and high-energy particles," says Farrell. By contrast, Jupiter has no dense rings to soak up high-energy particles, so that planet’s extremely high radiation environment persists.

The Cassini observations confirm a prediction by Dr. John Richardson and Dr. Slobodan Jurac of the Massachusetts Institute of Technology. In the early 1990’s, Hubble Space Telescope observations revealed the presence of a large body of water-related molecules in orbit about 240,000 km (almost 150,000 miles) from the planet. Richardson and Jurac modeled this water cloud and demonstrated it could migrate inward to the A-ring. "We relied on their predictions to help us interpret our data," said Farrell. "They predicted it, and we were seeing it."


Image above: Enceladus is seen here as a white
disk across the unilluminated side of Saturn's rings
(black and white stripes across the bottom of the
image). This image was taken with the Cassini
spacecraft narrow-angle camera on Oct. 27, 2007.
Click image for enlargement.
Credit: NASA/JPL/Space Science Institute

At the time of their prediction, the source of the water cloud was unknown. The source was not identified until 2005 when Cassini discovered the stunning geysers emitted from Enceladus.

Data for the discovery that Saturn's A-ring acts like a sponge were collected in July 2004 when Cassini arrived in orbit around Saturn, making its closest flyby over the A-ring. "We skimmed over the top of that ring fairly close," said Farrell.

Hot spots on the inside wall of the plasma donut -- the part colliding with the A-ring -- were emitting radio signals. These signals behaved as a sort of natural radio beacon, indicating the local plasma density at the inner edge of the donut. The signals were detected by Cassini's Radio and Plasma Wave instrument. The team used these signals to monitor the density of the plasma (the higher the frequency, the greater the density) and hence witness the change in gas density with time.

"As we approached the A-ring, the frequency dropped, implying that the plasma density was going down because it was being absorbed by the ring," said Farrell. "What really drove this home was what happened to the signal when we passed over a gap in the rings, called the Cassini division. There, the frequency went higher, implying that the plasma density was going up because plasma was leaking through the gap."

The research was funded by NASA through the Cassini-Huygens project. Cassini-Huygens is an international collaboration among NASA, the European Space Agency, and the Italian Space Agency. The Cassini orbiter was built and is managed by NASA's Jet Propulsion Laboratory, Pasadena, Calif.

Bill Steigerwald
NASA's Goddard Space Flight Center

Source: NASA/GSFC - News

Feb. 19, 2008
(Source: JPL)

Gaps in the soup of high energy particles near the orbits of two of Saturn's tiny moons indicate that Saturn may be surrounded by undiscovered, near-invisible partial rings. A paper in the February issue of the journal Icarus suggests the larger Saturnian moons may not be the only ones contributing material to Saturn's ring system.


The 60th moon of Saturn reveals itself in a
sequence of images. The discovery suggests
that the new moon, along with its neighbors
Methone and Pallene (discovered by the
Cassini imaging team in 2004), may form
part of a larger group of moons in this region.
The movie spans six hours.
+ Animation and caption
Image Credit: NASA/JPL/Space Science Institute
----------------------------------------------------

A team of scientists has detected two peculiar breaks in the near-constant rain of high energy electrons that bombard Cassini when near Saturn. They made the discovery using Cassini's Low Energy Magnetospheric Measurement System, a part of the Magnetospheric Imaging Instrument. The gaping holes fall along the orbits of two newly discovered moons, Methone and Anthe. Methone, discovered by Cassini in 2004, is about 3 kilometers across (2 miles), while Anthe, discovered in Cassini images in 2007, is about 2 kilometers wide (1 mile). Both moons are located between the orbits of Mimas and Enceladus.

"These observations tell us that even Saturn's smallest moons could be a source of dust in the Saturnian system," said Elias Roussos, the paper's lead author from the Max Planck Institute for Solar System Research in Katlenburg-Lindau, Germany.

If the tiny moons are indeed feeding dust into the rings, Roussos says possible future detection and characterization of these rings by more Cassini sensors could provide information about the surface of the moons Methone and Anthe, which are difficult to observe due to their small size.

Moons are known to absorb high energy particles. The fact that particles are missing is sensed by Cassini in the same way there are brief moments without rain falling on the windshield when driving under a bridge. These gaps in the flow of electrons showed that something wide was absorbing the charged particles. However, the gaps Cassini saw at Methone and Anthe are so wide, about 1,000 to 3,000 kilometers (600 to 1,900 miles) across, that they cannot be explained solely by the presence of such tiny moons. Instead, the measurements may indicate that the two moons are losing dust from their surface, building up one or more arcs of material along their orbits. Each ring arc is expected to be a few thousand kilometers wide and to comprise large dust grains or dust clumps.

"The released material may develop into ring arcs due to the gravitational 'tug of war' between Saturn's larger moons, such as Mimas," added Roussos. "A similar process has been found to take place at the arc within Saturn's G-ring."

Meteoroid impacts on Methone and Anthe are the most likely cause of the release of this material from their surfaces. The same process is thought to have formed Jupiter's faint rings at the orbits of the moons Amalthea, Thebe, Metis and Adrastea. The same situation might be happening at Saturn. In fact, rings of similar origin have also recently been detected in Cassini images along the orbits of the Saturnian moons Janus, Epimetheus and Pallene.

"What's odd is that these inferred ring arcs still remain undetected in Cassini images, while the rings at Janus, Epimetheus and Pallene orbits, thought to form under the same process, are visible," said Roussos. "This means the dust grains making up these two different classes of rings have different characteristics and sizes. However the reason behind this difference is a mystery."

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.

Media Relations Contact: Carolina Martinez (JPL) 818-354-9382

Source: NASA/JPL - Cassini - Feature

Unrolling the F-ring
April 23, 2008

The complex structure of Saturn's quirky F ring is unfurled in this mosaic made up of images taken by NASA's Cassini spacecraft.

The mosaic covers 255 degrees of longitude within the F ring, which represents about 70 percent of the ring's circumference around Saturn. From top to bottom, the mosaic represents an area 1,500 kilometers (930 miles) in radial width.

The 107 images used to create the mosaic were processed to make the ring appear as if it has been straightened, making it easier to see the ring's structure. Here, the vertical axis represents distance from Saturn and the horizontal axis represents longitude around Saturn. This frame of reference is centered on the bright core of the F ring, at the vertical center of the mosaic. In this system, the core is considered to be stationary; objects closer to Saturn (or below vertical center) move toward left, and objects farther from Saturn (here, above the core) move toward right.

Ring scientists now understand a great deal about what causes the various features in the ring. In addition to the powerful perturbing effect of the moon Prometheus (see The Prometheus Effect), there is thought to be a population of small objects in the F-ring region that interact with the ring's core to produce the structures seen (see The Clump/Moon Mystery). Two of the images had flaws, which caused the vertical lines seen on the right side of the mosaic. There is also a faint, roughly vertical, wavelike pattern in the view, which is an artifact of the process used to straighten the ring's shape.

The clear spectral filter images in this mosaic were obtained with the Cassini spacecraft narrow-angle camera on March 31, 2007, at a distance of about 2 million kilometers (1.2 million miles) from 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 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

September 5, 2008
(Source: NASA/JPL/Space Science Institute)

PASADENA, Calif. -- NASA's Cassini spacecraft has detected a faint, partial ring orbiting with one small moon of Saturn, and has confirmed the presence of another partial ring orbiting with a second moon. This is further evidence that most of the planet's small, inner moons orbit within partial or complete rings.


In this image, most of the visible material
in the arc lies ahead of Anthe in its orbit.
However, over time the moon drifts slowly
back and forth with respect to the arc.
----------------------------------------------------

Recent Cassini images show material, called ring arcs, extending ahead of and behind the small moons Anthe and Methone in their orbits. The new findings indicate that the gravitational influence of nearby moons on ring particles might be the deciding factor in whether an arc or complete ring is formed.

Both Anthe and Methone orbit Saturn in locations, called resonances, where the gravity of the nearby larger moon Mimas disturbs their orbits. Gravitational resonances are also responsible for many of the structures in Saturn's magnificent rings. Mimas provides a regular gravitational tug on each moon, which causes the moons to skip forward and backward within an arc-shaped region along their orbital paths, according to Nick Cooper, a Cassini imaging team associate from Queen Mary, University of London. "When we realized that the Anthe and Methone ring arcs were very similar in appearance to the region in which the moons swing back and forth in their orbits due to their resonance with Mimas, we knew we had a possible cause-and-effect relationship," Cooper said.

Scientists believe the faint ring arcs from Anthe and Methone likely consist of material knocked off these small moons by micrometeoroid impacts. This material does not spread all the way around Saturn to form a complete ring, because of the gravitational resonance with Mimas. That interaction confines the material to a narrow region along the orbits of the moons.


Arrows indicate the positions of Anthe, at
top left, and Methone, at bottom right.
Micrometeoroid impacts on the moons are
the likely source of the arc material.
----------------------------------------------------

This is the first detection of an arc of material near Anthe. The Methone arc was previously detected by Cassini's Magnetospheric Imaging Instrument, and the new images confirm its presence. Previous Cassini images show faint rings connected with other small moons either embedded within or near the outskirts of Saturn's main ring system, such as Pan, Janus, Epimetheus and Pallene. Cassini had also previously observed an arc in the G ring, one of Saturn's faint, major rings.

"This is probably the same mechanism responsible for producing the arc in the G ring," said Matthew Hedman, a Cassini imaging team associate at Cornell University in Ithaca, N.Y. Hedman and his Cassini imaging team colleagues previously determined that the G-ring arc is maintained by a gravitational resonance with Mimas, much like the new, small moon arcs. "Indeed, the Anthe arc may be similar to the debris we see in the G-ring arc, where the largest particles are clearly visible. One might even speculate that if Anthe were shattered, its debris might form a structure much like the G ring," Hedman said.

Additional analysis by scientists indicates that, while the gravitational influence of Mimas keeps the Anthe, Methone and G-ring arcs in place, the material that orbits with the moons Pallene, Janus and Epimetheus is not subject to such powerful resonant forces and is free to spread out around the planet, forming complete rings without arcs.

The intricate relationships between these ring arcs and the moons are just one of many such mechanisms that exist in the Saturn system. Cassini Imaging Team Member and Professor Carl Murray, also from Queen Mary, University of London, said, "There are many examples in the Saturn system of moons creating structures in the rings and disturbing the orbits of other moons. Understanding these interactions and learning about their origins can help us to make sense of what we are seeing in the Cassini images."

Images of Anthe and Methone with their ring arcs are available at: http://www.nasa.gov/cassini, http://saturn.jpl.nasa.gov and http://ciclops.org.

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.

Contacts:
Carolina Martinez 818-354-9382
Jet Propulsion Laboratory, Pasadena, Calif.
carolina.martinez@jpl.nasa.gov

Preston Dyches 720-974-5859
Space Science Institute, Boulder, Colo.
media@ciclops.org

Julia Maddock +44 (0)1793 442 094
Science and Technology Facilities Council
julia.maddock@stfc.ac.uk

NEWS RELEASE: 2008-172

Source: NASA/JPL - Cassini - Significant events

The Anthe Arc
September 5, 2008

Cassini images reveal the existence of a faint arc of material orbiting with Saturn's small moon Anthe.

The moon is moving downward and to the right in this perspective. In this image, most of the visible material in the arc lies ahead of Anthe (2 kilometers, or 1 mile across) in its orbit. However, over time the moon drifts slowly back and forth with respect to the arc. The arc extends over about 20 degrees in longitude (about 5.5 percent of Anthe's orbit) and appears to be associated with a gravitational resonance caused by the moon Mimas. Micrometeoroid impacts on Anthe are the likely source of the arc material. The orbit of Anthe lies between the larger moons Mimas and Enceladus. Anthe shares this region with two other small moons, Pallene (4 kilometers, or 3 miles across) and Methone (3 kilometers, or 2 miles across). Methone also possesses an arc (see Anthe and Methone Arcs), while Pallene is known to orbit within a faint, complete ring of its own (see Moon-Made Rings).

Cassini imaging scientists believe the process that maintains the Anthe and Methone arcs is similar to that which maintains the arc in the G ring (see Rounding the Corner). The general brightness of the image (along with the faint horizontal banding pattern) results from the long exposure time of 32 seconds required to capture the extremely faint ring arc and the processing needed to enhance its visibility (which also enhances the digital background noise in the image). The image was digitally processed to remove most of the background noise. The long exposure also produced star trails in the background. This view looks toward the un-illuminated side of the rings from about 3 degrees above the ringplane.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on July 3, 2008. The view was obtained at a distance of approximately 1.2 million kilometers (739,000 miles) from Anthe and at a sun-Anthe-spacecraft, or phase, angle of 12 degrees. Image scale is 7 kilometers (4 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

Anthe and Methone Arcs
September 5, 2008

Recent Cassini images show arcs of material co-orbiting with the Saturnian moons Anthe and Methone.

Arrows indicate the positions of Anthe, at top left, and Methone, at bottom right. Micrometeoroid impacts on the moons are the likely source of the arc material.

Cassini imaging scientists believe the process that maintains the Anthe and Methone arcs is similar to that which maintains the arc in the G ring (see Rounding the Corner). TThe general brightness of the image (along with the faint horizontal banding pattern) results from the long exposure time of 15 seconds required to capture the extremely faint ring arc and the processing needed to enhance its visibility (which also enhances the digital background noise in the image). The image was digitally processed to remove most of the background noise. This view looks toward the un-illuminated side of the rings from about 2 degrees above the ringplane.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Oct. 29, 2007. The view was acquired at a distance of approximately 2.3 million kilometers (1.4 million miles) from Anthe and 2.2 million kilometers (1.4 million miles) from Methone. Image scale is 14 kilometers (9 miles) per pixel on Anthe and 13 kilometers (8 miles) on Methone.

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

Anthe's Faint Arc
September 5, 2008

Cassini images reveal the existence of a faint arc of material orbiting with Saturn's small moon Anthe.

The moon is moving in a counterclockwise direction in this perspective, and is about to reach the ansa -- the point of maximum elongation -- as seen by the viewer, in its curving path around Saturn.

In this image, most of the visible material in the arc lies ahead of Anthe (2 kilometers, or 1 mile across) in its orbit. However, over time the moon drifts slowly back and forth with respect to the arc. Also ahead of the moon is a dark channel where the arc appears split into two strands, and these then merge farther around the orbital path. The arc extends over about 20 degrees in longitude (about 5.5 percent of Anthe's orbit) and appears to be associated with a gravitational resonance caused by Mimas. Micrometeoroid impacts on Anthe are the likely source of the arc material. The orbit of Anthe lies between the larger moons Mimas and Enceladus. Anthe shares this region with two other small moons, Pallene (4 kilometers, or 3 miles across) and Methone (3 kilometers, or 2 miles across). Methone also possesses an arc (see Anthe and Methone Arcs), while Pallene is known to orbit within a faint, complete ring of its own (see Moon-Made Rings).

Cassini imaging scientists believe the process that maintains the Anthe and Methone arcs is similar to that which maintains the arc in the G ring (see Rounding the Corner). This view looks toward the un-illuminated side of the rings from about 3 degrees above the ringplane. The view has been rotated so that Saturn's north pole would point upward. The general brightness of the image (along with the faint horizontal and vertical banding pattern) results from the long exposure time of 32 seconds required to capture the extremely faint ring arc and the processing needed to enhance its visibility (which also enhances the digital background noise in the image). The image was digitally processed to remove most of the background noise. The long exposure also produced star trails in the background.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on April 4, 2008. The view was acquired at a distance of approximately 1.2 million kilometers (746,000 miles) from Anthe and at a sun-Anthe-spacecraft, or phase, angle of 23 degrees. Image scale is 7 kilometers (4 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