Saturn Archives

March 12, 2009December 24, 2015 by Anne Minard

Cassini Switches to Backup Thrusters

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NASA’s Cassini spacecraft successfully switched to a backup set of propulsion thrusters late Wednesday, which will allow the long-lived machine to continue scoping out Saturn and its moons.

The swap was performed because of degradation in the performance of the primary thrusters, which had been in use since Cassini’s launch in 1997. This is only the second time in Cassini’s 11 years of flight that the engineering teams have gone to a backup system.

299665main_pia11141a-516 — This natural color view was created from images collected shortly after Cassini began its extended Equinox Mission in July 2008. Credit: NASA

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. Since its launch four years ago, the mission sent the Huygens probe to Saturn’s largest moon, Titan, and has yielded copious data about Saturn, its rings and its many moons.

The thrusters are used for making small corrections to the spacecraft’s course, for some attitude control functions, and for making angular momentum adjustments in the reaction wheels, which also are used for attitude control. The redundant set is an identical set of eight thrusters. Almost all Cassini engineering subsystems have redundant backup capability.

Cassini has successfully completed its original four-year planned tour of Saturn and is now in extended mission operations.

Sources: NASA, here and here.

March 3, 2009December 24, 2015 by Nancy Atkinson

Moonlet Could Be Source of Saturn’s G Ring

This sequence of three images, obtained by NASA's Cassini spacecraft over the course of about 10 minutes, shows the path of a newly found moonlet in a bright arc of Saturn's faint G ring. Image credit: NASA/JPL/Space Science Institute

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Saturn’s G ring has been the ring without a moon, until now. In trying to understand the mysterious G ring, Cassini scientists have taken every opportunity they can to take a closer look at what could be creating the ring. In 2007, scientists identified a possible source of the G ring as relatively large, icy particles that resided within a bright arc on the ring’s inner edge. But the researchers thought there had to be more than just these particles “shepherding” the ring, and concluded that there had to be larger, yet-unseen bodies hiding in the arc. Their persistence has now paid off, as a small moonlet has been found within the ring. “Before Cassini, the G ring was the only dusty ring that was not clearly associated with a known moon, which made it odd,” said Matthew Hedman, a Cassini imaging team associate at Cornell University in Ithaca, N.Y. “The discovery of this moonlet, together with other Cassini data, should help us make sense of this previously mysterious ring.” The sequence of three images above, obtained by NASA’s Cassini spacecraft over the course of about 10 minutes, shows the path of the moonlet in a bright arc of Saturn’s faint G ring.

Cassini imaging scientists analyzing all the images acquired over the course of about 600 days found the tiny moonlet, about a half a kilometer (about a third of a mile) across, embedded within a partial ring, or ring arc, previously found by Cassini in Saturn’s tenuous G ring.

Scientists imaged the moonlet on Aug. 15, 2008, and then they confirmed its presence by finding it in two earlier images. They have since seen the moonlet on multiple occasions, most recently on Feb. 20, 2009. The moonlet is too small to be resolved by Cassini’s cameras, so its size cannot be measured directly. However, Cassini scientists estimated the moonlet’s size by comparing its brightness to another small Saturnian moon, Pallene.

Hedman and his collaborators also have found that the moonlet’s orbit is being disturbed by the larger, nearby moon Mimas, which is responsible for keeping the ring arc together.

This brings the number of Saturnian ring arcs with embedded moonlets found by Cassini to three. The new moonlet may not be alone in the G ring arc. Previous measurements with other Cassini instruments implied the existence of a population of particles, possibly ranging in size from 1 to 100 meters (about three to several hundred feet) across. “Meteoroid impacts into, and collisions among, these bodies and the moonlet could liberate dust to form the arc,” said Hedman.

Saturn’s rings were named in the order they were discovered. Working outward they are: D, C, B, A, F, G and E. The G ring is one of the outer diffuse rings. Within the faint G ring there is a relatively bright and narrow, 250-kilometer-wide (150-miles) arc of ring material, which extends 150,000 kilometers (90,000 miles), or one-sixth of the way around the ring’s circumference. The moonlet moves within this ring arc. Previous Cassini plasma and dust measurements indicated that this partial ring may be produced from relatively large, icy particles embedded within the arc, such as this moonlet.

Carl Murray, a Cassini imaging team member and professor at Queen Mary, University of London, said, “The moon’s discovery and the disturbance of its trajectory by the neighboring moon Mimas highlight the close association between moons and rings that we see throughout the Saturn system. Hopefully, we will learn in the future more about how such arcs form and interact with their parent bodies.”

Early next year, Cassini’s camera will take a closer look at the arc and the moonlet. The Cassini Equinox mission, an extension of the original four-year mission, is expected to continue until fall of 2010.

Source: JPL

February 27, 2009December 24, 2015 by Anne Minard

Titan Dunes Turn Climate Models Upside Down

Map of dunes on Titan, with arrows indicating the general wind direction. Dark areas without arrows might have dunes but have not yet been imaged with radar. Credit: NASA/JPL/Space Science Institute (Boulder, Colorado)

Scientists have mapped vast dune fields on Titan that may align with the wind on Saturn’s biggest moon — flowing opposite the way climate models had predicted.

The maps, as above, represent four years of radar data collected by the Cassini spacecraft. They reveal rippled dunes that are generally oriented east-west, which means Titan’s winds probably blow toward the east instead of the west. If so, Titan’s surface winds blow opposite the direction suggested by previous global circulation models. On the example above, the arrows indicate the general wind direction. The dark areas without arrows might have dunes but have not yet been imaged.

“At Titan there are very few clouds, so determining which way the wind blows is not an easy thing, but by tracking the direction in which Titan’s sand dunes form, we get some insight into the global wind pattern,” says Ralph Lorenz, Cassini radar scientist at Johns Hopkins University in Maryland. “Think of the dunes sort of like a weather vane, pointing us to the direction the winds are blowing.”

Titan’s dunes are believed to be made up of hydrocarbon sand grains likely derived from organic chemicals in Titan’s smoggy skies. The dunes wrap around high terrain, which provides some idea of their height. They accumulate near the equator, and may pile up there because drier conditions allow for easy transport of the particles by the wind. Titan’s higher latitudes contain lakes and may be “wetter” with more liquid hydrocarbons, not ideal conditions for creating dunes.

“Titan’s dunes are young, dynamic features that interact with topographic obstacles and give us clues about the wind regimes,” said Jani Radebaugh, from Brigham Young University in Utah. “Winds come at these dunes from at least a couple of different directions, but then combine to create the overall dune orientation.”

Researchers say the wind pattern is important for planning future Titan explorations that might involve balloon-borne experiments. Some 16,000 dune segments were mapped out from about 20 radar images, digitized and combined to produce the new map, which is available at http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini. A paper based on the new findings appeared in the Feb. 11 issue of Geophysical Research Letters.

Cassini, which launched in 1997 and is now in extended mission operations, continues to blaze its trail around the Saturn system and will visit Titan again on March 27. Seventeen Titan flybys are planned this year.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. NASA’s Jet propulsion Laboratory (JPL) in Pasadena, California manages the Cassini-Huygens mission. The Cassini orbiter was designed, developed and assembled at JPL. The radar instrument was built by JPL and the Italian Space Agency, working with team members from the United States and several European countries. The imaging operations center is based at the Space Science Institute in Boulder, Colorado.

LEAD IMAGE CREDIT: NASA/JPL/Space Science Institute (Boulder, Colorado)

Source: NASA

February 25, 2009December 24, 2015 by Anne Minard

Jupiter, Saturn Plowed Through Asteroids, Study Says

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When Mars and Jupiter migrated to their present orbits around 4 billion years ago, they left scars in the asteroids belt that are still visible today.

The evidence is unveiled in a new paper in this week’s issue of the journal Nature, by planetary scientists David Minton and Renu Malhotra from the University of Arizona in Tucson.

The asteroid belt has long been known to harbor gaps, called Kirkwood gaps, in distinct locations. Some of these gaps correspond to unstable zones, where the modern-day gravitational influence of Jupiter and Saturn eject asteroids. But for the first time, Minton and Malhotra have noticed that some clearings don’t fit the bill.

“What we found was that many regions are depleted in asteroids relative to other regions, not just in the previously known Kirkwood gaps that are explained by the current planetary orbits,” Minton wrote in an email. In an editorial accompanying the paper, author Kevin Walsh added, “Qualitatively, it looks as if a snow plough were driven through the main asteroid belt, kicking out asteroids along the way and slowing to a stop at the inner edge of the belt.”

Walsh hails from the Observatoire de la Côte d’Azur in France. In his News and Views piece, he explains that the known Kirkwood gaps, discovered by Daniel Kirkwood in 1867, “correspond to the location of orbital resonances with Jupiter — that is, of orbits whose periods are integer ratios of Jupiter’s orbital period.” For example, if an asteroid orbited the Sun three times for every time Jupiter did, it would be in a 3:1 orbital resonance with the planet, he wrote. Objects in resonance with a giant planet have inherently unstable orbits, and are likely to be ejected from the solar system. When planets migrated, astronomers believe objects in resonance with them also shifted, affecting different parts of the asteroid belt at different times.

“Thus, if nothing has completely reshaped the asteroid belt since the planets settled into their current orbits, signatures of past planetary orbital migration may still remain,” Walsh wrote. And that’s exactly what Minton and Malhotra sought.

The asteroid belt easily gave up its secrets, showing the lingering evidence of planetary billiards on the inner edge of the asteroid belt and at the outer edge of each Kirkwood gap. The new finding, based on computer models, lends additional support to the theory that the giant planets — Jupiter, Saturn, Uranus and Neptune — formed twice as close to the sun as they are now and in a tighter configuration, and moved slowly outward.

“The orbit of Pluto and other Kuiper belt objects that are trapped in [orbits that resonate] with Neptune can be explained by the outward migration of Neptune,” Minton and Malhotra write in the new study. “The exchange of angular momentum between planetesimals and the four giant planets caused the orbital migration of the giant planets until the outer planetesimal disk was depleted.” Planetesimals are rocky and icy objects left over from planet formation.

“As Jupiter and Saturn migrated,” the authors continue, they wreaked havoc on the young asteroid belt, “exciting asteroids into terrestrial planet-crossing orbits, thereby greatly depleting the asteroid belt population and perhaps also causing a late heavy bombardment in the inner Solar System.”

The late heavy bombardment is proposed to have occurred about 3.9 billion years ago, or 600 million years after the birth of the Solar System, and it’s believed to account for many of the Moon’s oldest craters. Walsh said a reasonable next step, to corroborate the theory about the newly described clearings in the asteroid belt, is to link them chronologically with the bombardment.

LEAD PHOTO CAPTION: Artist’s depiction of the asteroid belt between Mars and Jupiter. Credit: David Minton and Renu Malhotra

Source: Nature

February 18, 2009December 24, 2015 by Nancy Atkinson

Next Big Planetary Mission: To Jupiter and Its Moons

Artist concept of proposed missions to the Jupiter system (left) and the Saturn system (right). Image credit: NASA/JPL

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At a meeting last week between NASA and ESA, the two space agencies narrowed down the choices for the next big flagship planetary missons, which will be joint efforts between the US and Europe. A mission to Jupiter and its four largest moons will be the primary mission the two space agencies will focus on, while they continue to plan for another potential mission to visit Saturn’s largest moon Titan and Enceladus. The two missions, the Jupiter System Mission and the Titan Saturn System Mission, are the result of NASA and ESA merging their separate mission concepts.

“This joint endeavour is a wonderful new exploration challenge and will be a landmark of 21st Century planetary science,” said David Southwood, ESA Director of Science and Robotic Exploration. “What I am especially sure of is that the cooperation across the Atlantic that we have had so far and we see in the future, between America and Europe, NASA and ESA, and in our respective science communities is absolutely right. Let’s get to work.”

The Europa Jupiter System Mission would use two robotic orbiters to conduct detailed studies of the giant gaseous planet Jupiter and its moons Io, Europa, Ganymede and Callisto. NASA would build one orbiter, initially named Jupiter Europa. ESA would build the other orbiter, initially named Jupiter Ganymede. The probes would launch in 2020 on two separate launch vehicles from different launch sites. The orbiters would reach the Jupiter system in 2026 and spend at least three years conducting research.

Europa has a surface of ice, and scientists theorize it has an ocean of water beneath that could provide a home for living things. Ganymede, the largest moon in the solar system, is the only moon known to have its own internally generated magnetic field and is suspected to have a deep undersurface water ocean. Scientists long have sought to understand the causes of the magnetic field. Callisto’s surface is extremely heavily cratered and ancient, providing a clear indication of a record of events from the early history of the Solar System. Finally, Io is the most volcanically active body in the solar system.

“The decision means a win, win situation for all parties involved,” said Ed Weiler, associate administrator for NASA’s Science Mission Directorate in Washington. “Although the Jupiter system mission has been chosen to proceed to an earlier flight opportunity, a Saturn system mission clearly remains a high priority for the science community.”

The future Titan Saturn System Mission would consist of a NASA orbiter and an ESA lander and research balloon.

Both of these proposed missions will set the stage for future planetary science research. These outer planet flagship missions could eventually answer questions about how our solar system formed and whether life exists elsewhere in the universe.

Source: JPL

February 2, 2009December 24, 2015 by Nancy Atkinson

Cassini Will Switch to Back-up Thrusters

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In a move reminiscent of Star Trek’s Scotty fine-tuning the Enterprise’s performance, engineers working with the Cassini spacecraft will begin work to switch the spacecraft’s thrusters to a back-up set after noticing a degradation in performance from the main thrusters that have been in use for over 11 years, since the spacecraft launched in October of 1997. The thrusters are used for making small corrections to the spacecraft’s course and for attitude control. In mid-March, the current set of eight thrusters, referred to as branch A, will be swapped over to a redundant and identical set, branch B. In a forward thinking move, almost all Cassini engineering subsystems have redundant backup capability. And in a testament of the spacecraft’s robustness and reliability, this is only the second time during Cassini’s 11-year flight that the engineering teams have gone to a backup system.

“Ay, Captain. Auxiliary thrusters engaged!”

Cassini’s propulsion engineers began to see a lower performance from one of the thrusters on branch A in October, and recently a second branch A thruster also began now showing some degraded performance.

An extensive review with the propulsion system contractor, Lockheed Martin Space Systems, Denver, Colo., the thruster manufacturer, Aerojet, Sacramento, Calif., and propulsion experts at NASA’s Jet Propulsion Laboratory, Pasadena, Calif., was completed last week. The recommendation was made to swap to side B as soon as is practical.

Nine of Saturn's moons are in this image. Can you find them? Credit: NASA/JPL/Space Science Institute

Mid-March is the earliest practical opportunity to make the swap. This allows time for the team to properly test and prepare the sequence of commands that will be sent to the spacecraft. Science planners have identified a period where no high-priority science will be lost during the switch, which will be done over a seven-day window. It also is a time when no navigation maneuvers are required to maintain the spacecraft’s trajectory.

The swap involves commanding a latch valve to open hydrazine flow to the B side, and powering on some thruster control electronics. No pyrotechnic devices are involved in the swap, and the action is fully reversible if necessary.

A few years ago, the backup reaction wheel was brought online and is currently functioning as one of the three prime wheels.

Cassini successfully completed its four-year planned tour and is now in its “Equinox” extended mission operations.

Source: JPL

December 31, 2008December 24, 2015 by Nancy Atkinson

Stunning New Images of Saturn’s Rings

This mosaic combines 30 images -- 10 each of red, green and blue light -- taken over the course of approximately two hours as Cassini panned its wide-angle camera across the entire planet and ring system Credit: NASA/JPL/Space Science Institute

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The Cassini Equinox Mission released new images of Saturn, revealing stunning detail of the planet’s rings. As Saturn advances in its orbit toward equinox and the sun gradually moves northward on the planet, the motion of Saturn’s ring shadows and the changing colors of its atmosphere continue to transform the face of Saturn as seen by Cassini. While the Cassini spacecraft will always have good views of the rings, during 2009, Saturn’s rings will disappear from view on Earth. As Saturn approaches its equinox, the rings will be “on edge” from our vantage point, meaning that Saturn’s rings will appear thinner and thinner until on September 4th, 2009 the rings will seem to vanish! But don’t worry, they will reappear about three months later. But during that time, Cassini will track the changing light effects on the rings. Above, Cassini snapped a series of images during two hours in July that have been put together to create a full, natural color view of the planet, its rings, and six of its moons: Titan, Janus, Mimas, Pandora, Epimetheus and Enceladus. The image was taken over the course of approximately two hours as Cassini panned its wide-angle camera across the entire planet and ring system on July 23, 2008

But most impressive is a sweeping panorama of nearly the entire ring system, shown in natural color. See below!

Details of Saturns icy rings are visible in this sweeping view from Cassini of the planets glorious ring system. Credit: NASA/JPL/Space Science Institute

Click to “embiggen” (stolen phrase from the Bad Astronomer) to get the full glory and splendor of Saturn’s rings!

This natural color mosaic, taken from 10 degrees below the illuminated side of the rings, shows, from left to right, radially outward from Saturn, the C ring (with its Colombo and Maxwell gaps); the B ring and the Cassini division beyond, with the intervening Huygens gap; the A ring (with its Encke and Keeler gaps); and, on the far right, the narrow F ring. The total span covers approximately 65,700 kilometers (40,800 miles).

The photograph is a combination of 45 images taken over the course of about 4 hours on Nov. 26.

The F ring and outer edge of the A ring. Credit: NASA/JPL

The F ring and outer edge of the A ring can be seen in this image. A kink feature is visible in the F ring, probably caused by Prometheus or Pandora, the F ring’s shepherd moons.
Another moon, Daphnis, can be seen in the Keeler gap near the outer edge of the A ring, along with the waves Daphnis raises on that gap’s edges. Waves like these allow researchers to locate new moons in gaps and also estimate their masses.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Nov. 7, 2008 at a distance of approximately 992,000 kilometers (616,000 miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 48 degrees. Image scale is 6 kilometers (3 miles) per pixel.

And if you haven’t seen this one yet, this artwork was created by the Cassini Equinox Mission to wish everyone a happy holidays. Happy New Year from all of us here at Universe Today, too!

Source: Cassini

December 16, 2008December 24, 2015 by Nancy Atkinson

Possible Cryovolcanoes on Titan

Infrared Map of Titan’s Active Regions. Credit: NASA/JPL

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A cold volcano seems like an oxymoron, but active “cryovolcanoes” may actually be spewing a super-chilled liquid into the atmosphere of Saturn’s moon Titan. The beauty of Cassini’s long and now extended mission is the numerous flybys the spacecraft is able to take of several of Saturn’s most interesting moons. We reported yesterday how scientists have been able to see how Enceladus’ surface and its geysers are changing over time, and now data collected during several recent flybys of Titan show alternations in that moon’s surface as well. “Cassini data have raised the possibility that Titan’s surface is active,” said Jonathan Lunine, a Cassini interdisciplinary scientist from the Lunar and Planetary Laboratory, at the University of Arizona, Tucson . “This is based on evidence that changes have occurred on the surface of Titan, between flybys of Cassini, in regions where radar images suggest a kind of volcanism has taken place.”

Rather than erupting hot, molten rock, it is theorized that the cryovolcanoes of Titan would erupt volatiles such as water, ammonia and methane. Scientists have suspected cryovolcanoes might populate Titan, and the Cassini mission has collected data on several previous passes of the moon that suggest their existence. Imagery of the moon has included a suspect haze hovering over flow-like surface formations. Scientists point to these as signs of cryovolcanism there.

What led some Cassini scientists to believe that things are happening now were changes in brightness and reflectance detected at two separate and distinct regions of Titan. Reflectance is the ratio of light that radiates onto a surface to the amount reflected back. These changes were documented by Visible and Infrared Mapping Spectrometer data collected on Titan flybys from July 2004 to March 2006. In one of the two regions, the reflectance of the surface surged upward and remained higher than expected. In the other region, the reflectance shot up but then trended downward. There is also evidence that ammonia frost is present at one of the two changing sites. The ammonia was evident only at times when the region was inferred to be active. Watch a video of the changes.

“Ammonia is widely believed to be present only beneath the surface of Titan,” said Robert M. Nelson of JPL, a scientist for Cassini’s Visual and Infrared Mapping Spectrometer team. “The fact that we found it appearing at times when the surface brightened strongly suggests that material was being transported from Titan’s interior to its surface.”

Possible active Cryovolcanic Features on Titan. Credit: NASA/JPL

Some Cassini scientists indicate that such volcanism could release methane from Titan’s interior, which explains Titan’s seemingly continuous supply of fresh methane. Without replenishment, scientists say, Titan’s original atmospheric methane should have been exhausted long ago.

But other scientists aren’t certain that cryovolcanoes are responsible for the changes seen on Titan. Instead the changes might result from the transient appearances of ground “fogs” of ethane droplets very near Titan’s surface, driven by atmospheric rather than geophysical processes. Nelson has considered the ground fog option, stating, “There remains the possibility that the effect is caused by a local fog, but if so, we would expect it to change in size over time due to wind activity, which is not what we see.”

An alternative hypothesis to an active Titan suggests the Saturnian moon could be taking its landform evolution cues from a moon of Jupiter.

“Like Callisto, Titan may have formed as a relatively cold body, and may have never undergone enough tidal heating for volcanism to occur,” said Jeffrey Moore, a planetary geologist at the NASA Ames Research Center, Moffett Field, Calif. “The flow-like features we see on the surface may just be icy debris that has been lubricated by methane rain and transported downslope into sinuous piles like mudflows.”

But scientists will continue to analyze and collect more data in attempt to pinpoint exactly what is happening on Titan. Cassini’s next Titan flyby is scheduled for Dec. 21, when the spacecraft will come within 970 kilometers (603 miles) of its cloud-shrouded surface.

Source: JPL

December 15, 2008December 24, 2015 by Nancy Atkinson

Amazing Close-up Images Show Enceladus is Changing

Cassini came within 25 kilometers (15.6 miles) of the surface of Enceladus on Oct. 5, 2008. Image credit: NASA/JPL/Space Science Institute

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Saturn’s moon Enceladus not only has jets of water vapor spewing from vents on the southern hemisphere, but the moon’s surface in the same region shows evidence of changes over time, providing surprising indications of Earth-like tectonics. New high resolution images from the Cassini spacecraft’s recent flybys of Enceladus show close views of the moon’s distinctive “tiger stripe” fractures, yielding new insight into what may be happening inside the fractures. “Of all the geologic provinces in the Saturn system that Cassini has explored, none has been more thrilling or carries greater implications than the region at the southernmost portion of Enceladus,” said Carolyn Porco, Cassini imaging team leader.

A special spacecraft maneuver dubbed “the skeet shoot” was employed to make smear-free imaging at close range possible. The ground track of the camera’s pointing was selected to cut swaths across three tiger stripes, or sulci, the prominent rifts through which jets of water vapor and ice particles are actively jetting. The full-resolution images are absolutely astounding. Take a look at the large images and movies here.

Cassini’s flybys on Aug. 11 and Oct. 31 of this year targeted Enceladus’ fractured southern region, and an Oct. 9 flyby took the spacecraft deep into the plume of water vapor and ice shooting out of the moon’s vents. Interestingly, the plume is not constant varies over time. Scientists think that condensation from the jets erupting from the surface may create ice plugs that close off old vents and force new vents to open. The opening and clogging of vents also corresponds with measurements indicating the plume varies from month to month and year to year. This movie shows the locations of the vents on a “spinning” Enceladus.

“We see no obvious distinguishing markings on the surface in the immediate vicinity of each jet source, which suggests that the vents may open and close and thus migrate up and down the fractures over time,” Porco said. “Over time, the particles that rain down onto the surface from the jets may form a continuous blanket of snow along a fracture.”

The varying cloud of vapor and particles extends into space and has a far-reaching effect on the entire Saturn system by supplying the ring system with fresh material and loading ionized gas from water vapor into Saturn’s magnetosphere.

Tiger stripes magnified. Image credit: NASA/JPL/Space Science Institute

But most interesting is the evidence of movement of Enceladus’ surface, called “spreading.”

“Enceladus has Earth-like spreading of the icy crust, but with an exotic difference — the spreading is almost all in one direction, like a conveyor belt,” said Paul Helfenstein, Cassini imaging associate at Cornell University in Ithaca , N.Y. “Asymmetric spreading like this is unusual on Earth and not well understood.”

“Enceladus has asymmetric spreading on steroids,” Helfenstein added. “We are not certain about the geological mechanisms that control the spreading, but we see patterns of divergence and mountain-building similar to what we see on Earth, which suggests that subsurface heat and convection are involved.” This video demonstrates the observed tectonic spreading along tiger stripes in the South Polar Terrain of Enceladus.

The tiger stripes are analogous to the mid-ocean ridges on Earth’s seafloor where volcanic material wells up and creates new crust. Using Cassini-based digital maps of the south polar region of Enceladus, Helfenstein reconstructed a possible history of the tiger stripes by working backward in time and progressively snipping away older and older sections of the map. Each time he found that the remaining sections fit together like puzzle pieces.

With water vapor, organic compounds and excess heat emerging from Enceladus’ south polar terrain, scientists are intrigued by the possibility of a liquid-water-rich habitable zone beneath the moon’s south pole.

Cassini’s next flyby of Enceladus will be in November 2009.

The Cassini team presented their findings and recent images at the American Geophysical Union’s fall meeting in San Francisco.

Source: NASA, CICLOPS

November 26, 2008December 24, 2015 by Nancy Atkinson

Underground Water Reservoirs Power Geysers on Enceladus

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Saturn’s moon Enceladus may indeed hide an underground reservoir of water. Scientists analyzed the plumes seen spewing from the moon with the Cassini spacecraft, and found water vapor and ice. “There are only three places in the solar system we know or suspect to have liquid water near the surface,” said Joshua Colwell Cassini team scientist from the University of Central Florida. “Earth, Jupiter’s moon Europa and now Saturn’s Enceladus. Water is a basic ingredient for life, and there are certainly implications there. If we find that the tidal heating that we believe causes these geysers is a common planetary systems phenomenon, then it gets really interesting.”

Using data from Cassini’s Ultraviolet Imaging Spectrograph (UVIS), the team’s findings support a theory that the plumes observed are caused by a water source deep inside Enceladus. An Earth analog is Lake Vostok in Antarctica, where liquid water exists beneath thick ice.

Scientists suggest that in Enceladus’s case, the ice grains would condense from the vapor escaping from the water source and stream through the cracks in the ice crust before heading into space. That’s likely what Cassini’s instruments detected in 2005 and 2007, the basis for the team’s investigation.

The team’s work also suggests that another hypothesis is unlikely. That theory predicts that the plumes of gas and dust observed are caused by evaporation of volatile ice freshly exposed to space when Saturn’s tidal forces open vents in the south pole. But the team found more water vapor coming from the vents in 2007 at a time when the theory predicted there should have been less.

Instead, their results suggest that the behavior of the geysers supports a mathematical model that treats the vents as nozzles that channel water vapor from a liquid reservoir to the surface of the moon. By observing the flickering light of a star as the geysers blocked it out, the team found that the water vapor forms narrow jets. The authors theorize that only high temperatures close to the melting point of water ice could account for the high speed of the water vapor jets.

Although there is no solid conclusion yet, there may be one soon. Enceladus is a prime target of Cassini during its extended Equinox Mission, underway now through September 2010. Cassini launched from the Kennedy Space Center in 1997 and has been orbiting Saturn since July 2004.

The team’s findings are reported in the Nov. 27 issue of the journal Nature.

Source: EurekAlert