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Author Topic:   NASA's / ESA's Cassini-Huygens to Saturn-Titan
Robert Pearlman
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Cassini-Huygens to Saturn-Titan

Cassini launched in October 1997 with the European Space Agency's (ESA) Huygens probe. The probe was equipped with six instruments to study Titan, Saturn's largest moon. It landed on Titan's surface on Jan. 14, 2005, and returned spectacular results.

Meanwhile, Cassini's 12 instruments have returned a daily stream of data from Saturn's system since arriving at Saturn in 2004.

Among the most important targets of the mission are the moons Titan and Enceladus, as well as others of Saturn's icy moons. Towards the end of the mission, Cassini will make closer studies of the planet and its rings.

Robert Pearlman
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NASA release
NASA Cassini's Flyby of Phoebe Shows a Moon with a Battered Past

First images from the Cassini flyby of Phoebe reveal it to be a scarred, cratered outpost with a very old surface and a mysterious past, and a great deal of variation in surface brightness across its surface.

"What spectacular images," said Dr. Carolyn Porco, Cassini Imaging Team leader at the Space Science Institute in Boulder, Colo. "So sharp and clear and showing a great many geological features, large and small. It's obvious a lot of new insights into the origin of this strange body will come as a result of all this."

"What we are seeing is very neat. Phoebe is a heavily cratered body. We might be seeing one of the chunks from the formation of the solar system, 4.5 billion years ago. It's too soon to say," said Dr. Torrence Johnson, Cassini imaging team member at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "It's important to see the big picture from all of the other instruments to get the global view on this tiny moon."

Dr. Gerhard Neukum, an imaging team member from Freie University in Berlin, said, "It is very interesting and quite clear that a lot of craters smaller than a kilometer are visible. This means, besides the big-ones, lots of projectiles smaller than 100 meters (328 feet) have hit Phoebe." Whether these projectiles came from outside or within the Saturn system is debatable.

There is a suspicion that Phoebe, the largest of Saturn's outer moons, might be parent to the other, much smaller retrograde outer moons that orbit Saturn.

Dr. Joseph Burns, an imaging team member and professor at Cornell University, Ithaca, N.Y. said, "Looking at those big 50 kilometers (31 mile) craters, one has to wonder whether their impact ejecta might be the other tiny moons that orbit Saturn on paths much like Phoebe's."

All planned 11 instruments operated as expected and all data was acquired. Scientists plan to use the data to create global maps of the cratered moon, and to determine Phoebe's composition, mass and density. It will take scientists several days to pour over the data to make more concrete conclusions.

Cassini came within approximately 2,068 kilometers (about 1,285 miles) of the dark moon on Friday, June 11. The spacecraft was pointing its instruments at the moon during the flyby. Several hours later it turned to point its antenna to Earth. The signal was received through the Deep Space Network antennas in Madrid, Spain and Goldstone, in California's Mojave Desert, at 7:52 a.m. PDT today. Cassini was traveling at a relative speed of 20,900 kilometers per hour (13,000 miles per hour) relative to Saturn. It's been 23 years since a spacecraft last visited Phoebe. The Voyager 2 flyby in 1981 was at a distance from 2.2 million kilometers, (about 1.4 million miles), 1,000 times farther away.

With the Phoebe accomplished, Cassini is on course for Saturn. A trajectory correction maneuver is scheduled for June 16. Cassini will conduct a critical 96-minute burn before going into orbit around Saturn on June 30 (July 1 Universal Time). During Cassini's planned four-year tour it will conduct 76 orbits around the Saturn system and execute 52 close encounters with seven of Saturn's 31 known moons.

Robert Pearlman
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NASA Release:
Cassini Spacecraft Arrives at Saturn

The international Cassini-Huygens mission has successfully entered orbit around Saturn. At 9:12 p.m. PDT on Wednesday, flight controllers received confirmation that Cassini had completed the engine burn needed to place the spacecraft into the correct orbit. This begins a four-year study of the giant planet, its majestic rings and 31 known moons.

"This is a tribute to the team at NASA and our partners at the European Space Agency and the Italian Space Agency, to accomplish this feat taking place 934 million miles [1.5 billion kilometers] away from Earth," said Dr. Ed Weiler, associate administrator for space science at NASA Headquarters, Washington, D.C. "What Cassini-Huygens will reveal during its tour of Saturn and its many moons, including Titan, will astonish scientists and the public. Everyone is invited to come along for the ride and see all this as it is happening. It truly is a voyage of discovery."

Members of the Cassini-Huygens mission at NASA's Jet Propulsion Laboratory, Pasadena, Calif., broke into cheers and high-fives as NASA's Deep Space Network confirmed receipt of the signal indicating successful entry into orbit.

"We didn't expect anything less and couldn't have asked for anything more from the spacecraft and the team," said Robert T. Mitchell, program manager for the Cassini-Huygens mission at JPL. "This speaks volumes to the tremendous team that made it all happen."

Dr. Charles Elachi, JPL director and team leader on the radar instrument onboard Cassini, said, "It feels awfully good to be in orbit around the lord of the rings. This is the result of 22 years of effort, of commitment, of ingenuity, and that's what exploration is all about."

The mission will face another dramatic challenge in December, when the spacecraft will release the piggybacked Huygens probe - provided by the European Space Agency - which will plunge through the hazy atmosphere of Saturn's largest moon, Titan.

"This was America's night. This was NASA doing it right," said Dr. David Southwood, director of scientific programs for the European Space Agency. "They really gave those of us in Europe a challenge. We've got six months to go until we land on Titan. We're just praying that everything will go as well."

Julie Webster, Cassini-Huygens spacecraft team chief, said, "The spacecraft has been an incredible joy to fly. We stand on the shoulders of people who had 40 years of experience building and designing spacecraft."

Saturn is the sixth planet from the Sun. It is the second largest planet in our solar system, after Jupiter. The planet and ring system serve as a miniature model of the disc of gas and dust surrounding our early Sun that eventually formed the planets. Detailed knowledge of the dynamics of interactions among Saturn's elaborate rings and numerous moons will provide valuable data for understanding how each of the solar system's planets evolved.

Cassini traveled nearly 3.5 billion kilometers (2.2 billion miles) to reach Saturn after its launch from Cape Canaveral Air Force Station, Fla., on Oct. 15, 1997. During Cassini's four-year mission, it will execute 52 close encounters with seven of Saturn's 31 known moons.

The first images are expected to return Thursday morning. Science measurements gathered Wednesday are the closest ever obtained of Saturn. Those measurements may reveal details of the gravitational and magnetic fields that tell scientists about Saturn's interior.

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NASA release
Cassini Discovers Ring and One, Possibly Two, Objects at Saturn

Scientists examining Saturn's contorted F ring, which has baffled them since its discovery, have found one small body, possibly two, orbiting in the F ring region, and a ring of material associated with Saturn's moon Atlas.

A small object was discovered moving near the outside edge of the F ring, interior to the orbit of Saturn's moon Pandora. The object was seen by Dr. Carl Murray, imaging team member at Queen Mary, University of London, in images taken on June 21, 2004, just days before Cassini arrived at Saturn. "I noticed this barely detectable object skirting the outer part of the F ring. It was an incredible privilege to be the first person to spot it," he said. Murray's group at Queen Mary then calculated an orbit for the object.

Scientists cannot yet definitively say if the object is a moon or a temporary clump. If it is a moon, its diameter is estimated at four to five kilometers (two to three miles) and it is located 1,000 kilometers (620 miles) from the F ring, Saturn's outmost ring. It is at a distance of approximately 141,000 kilometers (86,000 miles) from the center of Saturn and within 300 kilometers (190 miles) of the orbit of the moon Pandora. The object has been provisionally named S/2004 S3.

Scientists are not sure if the object is alone. This is because of results from a search through other images that might capture the object to pin down its orbit. The search by Dr. Joseph Spitale, a planetary scientist working with team leader Dr. Carolyn Porco at the Space Science Institute in Boulder, Colo., revealed something strange. Spitale said, "When I went to look for additional images of this object to refine its orbit, I found that about five hours after first being sighted, it seemed to be orbiting interior to the F ring," said Spitale. "If this is the same object then it has an orbit that crosses the F ring, which makes it a strange object." Because of the puzzling dynamical implications of having a body that crosses the ring, the inner object sighted by Spitale is presently considered a separate object with the temporary designation S/2004 S 4. S4 is roughly the same size as S3.

In the process of examining the F ring region, Murray also detected a previously unknown ring, S/2004 1R, associated with Saturn's moon, Atlas. "We knew from Voyager that the region between the main rings and the F ring is dusty, but the role of the moons in this region was a mystery," said Murray. "It was while studying the F ring in these images that I discovered the faint ring of material. My immediate hunch was that it might be associated with the orbit of one of Saturn's moons, and after some calculation I identified Atlas as the prime suspect."

The ring is located 138,000 kilometers (86,000 miles) from the center of Saturn in the orbit of the moon Atlas, between the A ring and the F ring. The width of the ring is estimated at 300 kilometers (190 miles). The ring was first spotted in images taken after orbit insertion on July 1, 2004. There is no way of knowing yet if it extends all the way around the planet.

"We have planned many images to search the region between the A and F rings for diffuse material and new moons, which we have long expected to be there on the basis of the peculiar behavior of the F ring," said Porco. "Now we have found something but, as is usual for the F ring, what we see is perplexing."

Searches will continue for further detections of the newfound body or bodies seen in association with the F ring. If the two objects indeed turn out to be a single moon, it will bring the Saturn moon count to 34. The newfound ring adds to the growing number of narrow ringlets around Saturn.

Robert Pearlman
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European Space Agency release
Huygens away!

The European Space Agency's Huygens probe successfully detached from NASA's Cassini orbiter today to begin a three-week journey to Saturn's moon Titan. NASA's Deep Space Network tracking stations in Madrid, Spain and Goldstone, Calif., received the signal at 7:24 p.m. (PST). All systems performed as expected and there were no problems reported with the Cassini spacecraft.

The Huygens probe, built and managed by the European Space Agency, was bolted to Cassini and has been riding along during the nearly seven-year journey to Saturn largely in a "sleep" mode. Huygens will be the first human-made object to explore on-site the unique environment of Titan, whose chemistry is assumed to be very similar to that of early Earth before life formed. Huygens will tell us whether this assumption is correct.

"We wish to congratulate our European partners as their journey begins and wish them well on their descent to Titan," said Robert T. Mitchell, Cassini program manager at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "We are very excited to see the probe off and to have accomplished this part of our job. Now we're ready to finish our part -- receiving and relaying the Huygens data back to Earth."

"Today's release is another successful milestone in the Cassini-Huygens odyssey," said Dr. David Southwood, director of science program for the European Space Agency. "This was an amicable separation after seven years of living together. Our thanks to our partners at NASA for the lift. Each spacecraft will now continue on its own but we expect they'll keep in touch to complete this amazing mission. Now all our hopes and expectations are focused on getting the first in-situ data from a new world we've been dreaming of exploring for decades."

The Huygens probe will remain dormant until the onboard timer wakes it up just before the probe reaches Titan's upper atmosphere on Jan. 14, 2005. Then it will be begin a dramatic plunge through Titan's murky atmosphere, tasting its chemical makeup and composition as it descends to touch down on its surface. The data gathered during this 2-1/2 hour descent will be transmitted from the probe to the Cassini orbiter. Afterward, Cassini will point its antenna to Earth and relay the data through NASA's Deep Space Network to JPL and on to the European Space Agency's Space Operations Center in Darmstadt, Germany, which serves as the operations center for the Huygens probe mission. From this control center, ESA engineers will be tracking the probe and scientists will be standing by to process the data from the probe's six instruments.

On Monday, Dec. 27, the Cassini orbiter will perform a deflection maneuver to keep it from following Huygens into Titan's atmosphere. This maneuver will also establish the required geometry between the probe and the orbiter for radio communications during the probe descent.

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European Space Agency release
Radio astronomers confirm Huygens entry in the atmosphere of Titan

At 11:25 CET the Robert C. Byrd Green Bank Telescope (GBT) of the National Radio-astronomy Observatory in West Virginia, USA, a part of the global network of radio telescopes involved in tracking the Huygens Titan probe, has detected the probe's 'carrier' (tone) signal.

The detection occurred between 11:20 and 11:25 CET, shortly after the probe began its parachute descent through Titan's atmosphere. The extremely feeble signal was first picked up by the Radio Science Receiver supplied by the NASA Jet Propulsion Laboratory. This signal is an important indication that the Huygens probe is 'alive'. However, it does not contain yet any substance; the latter is expected to come a few hours later via the Cassini spacecraft.

What the Green Bank radio telescope has detected is only a 'carrier' signal. It indicates that the back cover of Huygens must have been ejected, the main parachute must have been deployed and that the probe has begun to transmit, in other words, the probe is 'alive'. This, however, still does not mean that any data have been acquired, nor that they have been received by Cassini. The carrier signal is sent continuously throughout the descent and as such does not contain any scientific data. It is similar to the tone signal heard in a telephone handset once the latter is picked up.

Only after having received the data packets at ESOC will it be possible to say with certainty whether data were properly acquired. The first data set from Cassini will reach ESOC in the afternoon. Additional downlinks will follow throughout the evening and night for redundancy.

Further analysis of the signals will be conducted using other three independent data acquisition systems at the Green Bank Telescope. In addition to the GBT, sixteen other radio telescopes in Australia, China, Japan and the USA are involved in tracking the Huygens probe.

The ultimate goal of the tracking experiment is to reconstruct the probe's descent trajectory with an unprecedented accuracy of the order of one kilometre. The measurements will be conducted using Very Long Baseline Interferometry (VLBI) and Doppler tracking techniques. This would enable studies of the dynamics of Titan's atmosphere, which is considered to be a 'frozen' copy of that of the early Earth.

The VLBI component of the tracking experiment is coordinated by the Joint Institute for VLBI in Europe (JIVE) and ESA; the Doppler measurements are conducted by the Jet Propulsion Laboratory.

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European Space Agency release
First Landing, Outer Solar System

Today, after its seven-year journey through the Solar System on board the Cassini spacecraft, ESA's Huygens probe has successfully descended through the atmosphere of Titan, Saturn's largest moon, and safely landed on its surface.

The first scientific data arrived at the European Space Operations Centre (ESOC) in Darmstadt, Germany, this afternoon at 17:19 CET. Huygens is mankind's first successful attempt to land a probe on another a world in the outer Solar System. "This is a great achievement for Europe and its US partners in this ambitious international endeavour to explore the Saturnian system," said Jean-Jacques Dordain, ESA's Director General.

Following its release from the Cassini mothership on 25 December, Huygens reached Titan's outer atmosphere after 20 days and a 4 million km cruise. The probe started its descent through Titan's hazy cloud layers from an altitude of about 1270 km at 11:13 CET. During the following three minutes Huygens had to decelerate from 18 000 to 1400 km per hour.

A sequence of parachutes then slowed it down to less than 300 km per hour. At a height of about 160 km the probe's scientific instruments were exposed to Titan's atmosphere. At about 120 km, the main parachute was replaced by a smaller one to complete the descent, with an expected touchdown at 13:34 CET. Preliminary data indicate that the probe landed safely, likely on a solid surface.

The probe began transmitting data to Cassini four minutes into its descent and continued to transmit data after landing at least as long as Cassini was above Titan's horizon. The certainty that Huygens was alive came already at 11:25 CET today, when the Green Bank radio telescope in West Virginia, USA, picked up a faint but unmistakable radio signal from the probe. Radio telescopes on Earth continued to receive this signal well past the expected lifetime of Huygens.

Huygens data, relayed by Cassini, were picked up by NASA's Deep Space Network and delivered immediately to ESA's European Space Operation Centre in Darmstadt, Germany, where the scientific analysis is currently taking place.

"Titan was always the target in the Saturn system where the need for 'ground truth' from a probe was critical. It is a fascinating world and we are now eagerly awaiting the scientific results," says Professor David Southwood, Director of ESA's scientific programmme.

"The Huygens scientists are all delighted. This was worth the long wait," says Dr Jean-Pierre Lebreton, ESA Huygens Mission Manager. Huygens is expected to provide the first direct and detailed sampling of Titan's atmospheric chemistry and the first photographs of its hidden surface, and will supply a detailed 'weather report'.

One of the main reasons for sending Huygens to Titan is that its nitrogen atmosphere, rich in methane, and its surface may contain many chemicals of the kind that existed on the young Earth. Combined with the Cassini observations, Huygens will afford an unprecedented view of Saturn's mysterious moon.

"Descending through Titan was a once-in-a-lifetime opportunity and today's achievement proves that our partnership with ESA was an excellent one," says Alphonso Diaz, NASA Associate Administrator of Science.

The Cassini-Huygens mission is a cooperation between NASA, the European Space Agency and ASI, the Italian space agency. The Jet Propulsion Laboratory (JPL), a division of the California Institute of Technology in Pasadena, is managing the mission for NASA's Office of Space Science, Washington. JPL designed, developed and assembled the Cassini orbiter.

"The teamwork in Europe and the USA, between scientists, industry and agencies has been extraordinary and has set the foundation for today's enormous success," concludes Jean-Jacques Dordain.

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NASA release
NASA's Cassini Discovers Potential Liquid Water on Enceladus

NASA's Cassini spacecraft may have found evidence of liquid water reservoirs that erupt in Yellowstone-like geysers on Saturn's moon Enceladus. The rare occurrence of liquid water so near the surface raises many new questions about the mysterious moon.

"We realize that this is a radical conclusion - that we may have evidence for liquid water within a body so small and so cold," said Carolyn Porco, Cassini imaging team leader at the Space Science Institute, Boulder, Colo. "However, if we are right, we have significantly broadened the diversity of solar system environments where we might possibly have conditions suitable for living organisms."

High-resolution Cassini images show icy jets and towering plumes ejecting large quantities of particles at high speed. Scientists examined several models to explain the process. They ruled out the idea the particles are produced or blown off the moon's surface by vapor created when warm water ice converts to a gas. Instead, scientists have found evidence for a much more exciting possibility. The jets might be erupting from near-surface pockets of liquid water above 0 degrees Celsius (32 degrees Fahrenheit), like cold versions of the Old Faithful geyser in Yellowstone.

"We previously knew of at most three places where active volcanism exists: Jupiter's moon Io, Earth, and possibly Neptune's moon Triton. Cassini changed all that, making Enceladus the latest member of this very exclusive club, and one of the most exciting places in the solar system," said John Spencer, Cassini scientist, Southwest Research Institute, Boulder.

"Other moons in the solar system have liquid-water oceans covered by kilometers of icy crust," said Andrew Ingersoll, imaging team member and atmospheric scientist at the California Institute of Technology, Pasadena, Calif. "What's different here is that pockets of liquid water may be no more than tens of meters below the surface."

"As Cassini approached Saturn, we discovered the Saturnian system is filled with oxygen atoms. At the time we had no idea where the oxygen was coming from," said Candy Hansen, Cassini scientist at NASA's Jet Propulsion Laboratory (JPL) in Pasadena. "Now we know Enceladus is spewing out water molecules, which break down into oxygen and hydrogen."

Scientists still have many questions. Why is Enceladus so active? Are other sites on Enceladus active? Might this activity have been continuous enough over the moon's history for life to have had a chance to take hold in the moon's interior?

In the spring of 2008, scientists will get another chance to look at Enceladus when Cassini flies within 350 kilometers (approximately 220 miles), but much work remains after the spacecraft's four-year prime mission is over.

"There's no question, along with the moon Titan, Enceladus should be a very high priority for us. Saturn has given us two exciting worlds to explore," said Jonathan Lunine, Cassini interdisciplinary scientist, University of Arizona, Tucson, Ariz.

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NASA feature
Titan Descent Data Movie with Bells and Whistles

This movie, built with data collected during the European Space Agency's Huygens probe on Jan. 14, 2005, shows the operation of the Descent Imager/Spectral Radiometer camera during its descent and after touchdown. The camera was funded by NASA.

The almost four-hour-long operation of the camera is shown in less than five minutes. That's 40 times the actual speed up to landing and 100 times the actual speed thereafter.

The first part of the movie shows how Titan looked to the camera as it acquired more and more images during the probe's descent. Each image has a small field of view, and dozens of images were made into mosaics of the whole scene...

Sounds from a left speaker trace Huygens' motion, with tones changing with rotational speed and the tilt of the parachute. There also are clicks that clock the rotational counter, as well as sounds for the probe's heat shield hitting Titan's atmosphere, parachute deployments, heat shield release, jettison of the camera cover and touchdown.

Sounds from a right speaker go with the Descent Imager/Spectral Radiometer activity. There's a continuous tone that represents the strength of Huygens' signal to Cassini. Then there are 13 different chimes - one for each of instrument's 13 different science parts - that keep time with flashing-white-dot exposure counters. During its descent, the Descent Imager/Spectral Radiometer took 3,500 exposures.

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CICLOPS release
Inspiring Views Celebrate Cassini's Diamond Anniversary

Ten years ago today, NASA's Cassini spacecraft departed planet Earth from Cape Canaveral, Florida, and embarked on a seven-year long, circuitous journey of several billion miles across the solar system to the planet Saturn.

To celebrate this special occasion, the mission's imaging team is releasing today a spate of captivating new images and movies of the ringed planet and some of its most photogenic companions.

Headlining this bounty are two expansive and stunning natural color mosaics of Saturn and its rings. One of these is the view seen by the spacecraft as it looked back towards Saturn from its close encounter with the moon Iapetus last month, and shows the shadow-draped planet surrounded by its rings and many of its major icy moons. Another view peers down onto the planet's swirling blue and gold clouds and its splendid rings from a vantage point high above Saturn's equator.

Along with several other colorful views of the planet, there are dramatic vistas (including one stereo image, or anaglyph) of the cratered faces of a few of the planet's icy moons, a high resolution survey of the main ring system in natural color, colorful glimpses of Titan and an updated black-and-white map of Titan's surface.

Two exciting movies from Cassini also make their debut today. One sequence shows the detailed motions of the F-ring as its shepherd moon Prometheus approaches the ring, draws material from it, and gouges a channel in the dust-sized material remaining there.

But by far the most thrilling offering of all is a breathtaking flyover movie of the awesome 10-kilometer (6-mile) high equatorial ridge on Iapetus, acquired when Cassini was only a few thousand kilometers about the surface.

Imaging team leader Carolyn Porco at CICLOPS in Boulder, Colo. said, "To the thousands upon thousands of fellow explorers who have traveled along with us since we departed Earth 10 years ago today, who have followed our adventures across the solar system and into orbit around Saturn and who have since been as awestruck as we have at our findings there, we say, 'Happy Anniversary! It's been a pleasure flying with you.'"

The new images and movies are available at the CICLOPS, NASA and Jet Propulsion Laboratory websites.

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NASA release
Cassini Spacecraft Finds Ocean May Exist Beneath Titan's Crust

NASA's Cassini spacecraft has discovered evidence that points to the existence of an underground ocean of water and ammonia on Saturn's moon Titan. The findings made using radar measurements of Titan's rotation will appear in the March 21 issue of the journal Science.

"With its organic dunes, lakes, channels and mountains, Titan has one of the most varied, active and Earth-like surfaces in the solar system," said Ralph Lorenz, lead author of the paper and Cassini radar scientist at the Johns Hopkins Applied Physics Laboratory in Laurel, Md., "Now we see changes in the way Titan rotates, giving us a window into Titan's interior beneath the surface."

Members of the mission's science team used Cassini's Synthetic Aperture Radar to collect imaging data during 19 separate passes over Titan between October 2005 and May 2007. The radar can see through Titan's dense, methane-rich atmospheric haze, detailing never-before-seen surface features and establishing their locations on the moon's surface.

Using data from the radar's early observations, the scientists and radar engineers established the locations of 50 unique landmarks on Titan's surface. They then searched for these same lakes, canyons and mountains in the reams of data returned by Cassini in its later flybys of Titan. They found prominent surface features had shifted from their expected positions by up to 19 miles. A systematic displacement of surface features would be difficult to explain unless the moon's icy crust was decoupled from its core by an internal ocean, making it easier for the crust to move.

"We believe that about 62 miles beneath the ice and organic-rich surface is an internal ocean of liquid water mixed with ammonia," said Bryan Stiles of NASA's Jet Propulsion Laboratory (JPL) in, Pasadena, Calif. Stiles also is a contributing author to the paper.

The study of Titan is a major goal of the Cassini-Huygens mission because it may preserve, in deep-freeze, many of the chemical compounds that preceded life on Earth. Titan is the only moon in the solar system that possesses a dense atmosphere. The moon's atmosphere is 1.5 times denser than Earth's. Titan is the largest of Saturn's moons, bigger than the planet Mercury.

"The combination of an organic-rich environment and liquid water is very appealing to astrobiologists," Lorenz said. "Further study of Titan's rotation will let us understand the watery interior better, and because the spin of the crust and the winds in the atmosphere are linked, we might see seasonal variation in the spin in the next few years."

Cassini scientists will not have long to wait before another go at Titan. On March 25, just prior to its closest approach at an altitude of 620 miles, Cassini will employ its Ion and Neutral Mass Spectrometer to examine Titan's upper atmosphere. Immediately after closest approach, the spacecraft's Visual and Infrared Mapping Spectrometer will capture high-resolution images of Titan's southeast quadrant.

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NASA release
NASA Extends Cassini's Grand Tour of Saturn

NASA is extending the international Cassini-Huygens mission by two years. The historic spacecraft's stunning discoveries and images have revolutionized our knowledge of Saturn and its moons.

Cassini's mission originally had been scheduled to end in July 2008. The newly-announced two-year extension will include 60 additional orbits of Saturn and more flybys of its exotic moons. These will include 26 flybys of Titan, seven of Enceladus, and one each of Dione, Rhea and Helene. The extension also includes studies of Saturn's rings, its complex magnetosphere, and the planet itself.

"This extension is not only exciting for the science community, but for the world to continue to share in unlocking Saturn's secrets," said Jim Green, director, Planetary Science Division, NASA Headquarters, Washington. "New discoveries are the hallmarks of its success, along with the breathtaking images beamed back to Earth that are simply mesmerizing."

"The spacecraft is performing exceptionally well and the team is highly motivated, so we're excited at the prospect of another two years," said Bob Mitchell, Cassini program manager at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

Based on findings from Cassini, scientists think liquid water may be just beneath the surface of Saturn's moon, Enceladus. That's why the small moon, only one-tenth the size of Titan and one-seventh the size of Earth's moon, is one of the highest-priority targets for the extended mission.

Cassini discovered geysers of water-ice jetting from the Enceladus' surface. The geysers, which shoot out at a distance three times the diameter of Enceladus, feed particles into Saturn's most expansive ring. In the extended mission, the spacecraft may come as close as 15 miles from the moon's surface.

Cassini's observations of Saturn's largest moon, Titan, have given scientists a glimpse of what Earth might have been like before life evolved. They now believe Titan possesses many parallels to Earth, including lakes, rivers, channels, dunes, rain, snow, clouds, mountains and possibly volcanoes.

"When we designed the original tour, we really did not know what we would find, especially at Enceladus and Titan," said Dennis Matson, the JPL Cassini project scientist. "This extended tour is responding to these new discoveries and giving us a chance to look for more."

Unlike Earth, Titan's lakes, rivers and rain are composed of methane and ethane, and temperatures reach a chilly minus 290 degrees Fahrenheit. Although Titan's dense atmosphere limits viewing the surface, Cassini's high-resolution radar coverage and imaging by the infrared spectrometer have given scientists a better look.

Other activities for Cassini scientists will include monitoring seasons on Titan and Saturn, observing unique ring events, such as the 2009 equinox when the sun will be in the plane of the rings, and exploring new places within Saturn's magnetosphere.

Cassini has returned a daily stream of data from Saturn's system for almost four years. Its travel scrapbook includes nearly 140,000 images and information gathered during 62 revolutions around Saturn, 43 flybys of Titan and 12 close flybys of the icy moons.

More than 10 years after launch and almost four years after entering into orbit around Saturn, Cassini is a healthy and robust spacecraft. Three of its science instruments have minor ailments, but the impact on science-gathering is minimal. The spacecraft will have enough propellant left after the extended mission to potentially allow a third phase of operations. Data from the extended mission could lay the groundwork for possible new missions to Titan and Enceladus.

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NASA photo release
Enceladus Rev 80 Flyby Skeet Shoot #4
Full-Res: PIA11109

This image is the fourth skeet-shoot footprint taken during Cassini's very close flyby of Enceladus on Aug. 11, 2008. Cairo Sulcus is shown crossing the upper left portion of the image. An unnamed fracture curves around the lower right corner. (The image is upside down from the skeet-shoot footprint shown here.) The image was taken with the Cassini spacecraft narrow-angle camera on Aug. 11, 2008, a distance of approximately 2,621 kilometers (1,629 miles) above the surface of Enceladus. Image scale is approximately 20 meters (66 feet) per pixel.

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NASA/JPL release (June 24, 2009)
Salt Finding From NASA's Cassini Hints at Ocean Within Saturn Moon

For the first time, scientists working on NASA's Cassini mission have detected sodium salts in ice grains of Saturn's outermost ring. Detecting salty ice indicates that Saturn's moon Enceladus, which primarily replenishes the ring with material from discharging jets, could harbor a reservoir of liquid water -- perhaps an ocean -- beneath its surface.

Cassini discovered the water-ice jets in 2005 on Enceladus. These jets expel tiny ice grains and vapor, some of which escape the moon's gravity and form Saturn's outermost ring. Cassini's cosmic dust analyzer has examined the composition of those grains and found salt within them.

"We believe that the salty minerals deep inside Enceladus washed out from rock at the bottom of a liquid layer," said Frank Postberg, Cassini scientist for the cosmic dust analyzer at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. Postberg is lead author of a study that appears in the June 25 issue of the journal Nature.

Scientists on Cassini's cosmic dust detector team conclude that liquid water must be present because it is the only way to dissolve the significant amounts of minerals that would account for the levels of salt detected. The process of sublimation, the mechanism by which vapor is released directly from solid ice in the crust, cannot account for the presence of salt.

"Potential plume sources on Enceladus are an active area of research with evidence continuing to converge on a possible salt water ocean," said Linda Spilker, Cassini deputy project scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Our next opportunity to gather data on Enceladus will come during two flybys in November."

The makeup of the outermost ring grains, determined when thousands of high-speed particle hits were registered by Cassini, provides indirect information about the composition of the plume material and what is inside Enceladus. The outermost ring particles are almost pure water ice, but nearly every time the dust analyzer has checked for the composition, it has found at least some sodium within the particles.

"Our measurements imply that besides table salt, the grains also contain carbonates like soda. Both components are in concentrations that match the predicted composition of an Enceladus ocean," Postberg said. "The carbonates also provide a slightly alkaline pH value. If the liquid source is an ocean, it could provide a suitable environment on Enceladus for the formation of life precursors when coupled with the heat measured near the moon's south pole and the organic compounds found within the plumes."

However, in another study published in Nature, researchers doing ground-based observations did not see sodium, an important salt component. That team notes that the amount of sodium being expelled from Enceladus is actually less than observed around many other planetary bodies. These scientists were looking for sodium in the plume vapor and could not see it in the expelled ice grains. They argue that if the plume vapor does come from ocean water, the evaporation must happen slowly deep underground, rather than as a violent geyser erupting into space.

"Finding salt in the plume gives evidence for liquid water below the surface," said Sascha Kempf, also a Cassini scientist for the cosmic dust analyzer from the Max Planck Institute for Nuclear Physics. "The lack of detection of sodium vapor in the plume gives hints about what the water reservoir might look like."

Determining the nature and origin of the plume material is a top priority for Cassini during its extended tour, called the Cassini Equinox Mission.

"The original picture of the plumes as violently erupting Yellowstone-like geysers is changing," said Postberg."They seem more like steady jets of vapor and ice fed by a large water reservoir. However, we cannot decide yet if the water is currently 'trapped' within huge pockets in Enceladus' thick ice crust or still connected to a large ocean in contact with the rocky core."

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NASA release
Cassini Reveals New Ring Quirks, Shadows During Saturn Equinox

NASA scientists are marveling over the extent of ruffles and dust clouds revealed in the rings of Saturn during the planet's equinox last month. Scientists once thought the rings were almost completely flat, but new images reveal the heights of some newly discovered bumps in the rings are as high as the Rocky Mountains. NASA released the images Monday.

"It's like putting on 3-D glasses and seeing the third dimension for the first time," said Bob Pappalardo, Cassini project scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "This is among the most important events Cassini has shown us."

On Aug. 11, sunlight hit Saturn's rings exactly edge-on, performing a celestial magic trick that made them all but disappear. The spectacle occurs twice during each orbit Saturn makes around the sun, which takes approximately 10,759 Earth days, or about 29.7 Earth years. Earth experiences a similar equinox phenomenon twice a year; the autumnal equinox will occur Sept. 22, when the sun will shine directly over Earth's equator.

For about a week, scientists used the Cassini orbiter to look at puffy parts of Saturn's rings caught in white glare from the low-angle lighting. Scientists have known about vertical clumps sticking out of the rings in a handful of places, but they could not directly measure the height and breadth of the undulations and ridges until Saturn's equinox revealed their shadows.

"The biggest surprise was to see so many places of vertical relief above and below the otherwise paper-thin rings," said Linda Spilker, deputy project scientist at JPL. "To understand what we are seeing will take more time, but the images and data will help develop a more complete understanding of how old the rings might be and how they are evolving."

The chunks of ice that make up the main rings spread out 140,000 kilometers (85,000 miles) from the center of Saturn, but they had been thought to be only around 10 meters (30 feet) thick in the main rings, known as A, B, C, and D.

In the new images, particles seemed to pile up in vertical formations in each of the rings. Rippling corrugations -- previously seen by Cassini to extend approximately 804 kilometers (500 miles) in the innermost D ring -- appear to undulate out to a total of 17,000 kilometers (11,000 miles) through the neighboring C ring to the B ring.

The heights of some of the newly discovered bumps are comparable to the elevations of the Rocky Mountains. One ridge of icy ring particles, whipped up by the gravitational pull of Saturn's moon Daphnis as it travels through the plane of the rings, looms as high as about 4 kilometers (2.5 miles). It is the tallest vertical wall seen within the rings.

"We thought the plane of the rings was no taller than two stories of a modern-day building and instead we've come across walls more than 2 miles [3 kilometers] high," said Carolyn Porco, Cassini imaging team leader at the Space Science Institute in Boulder, Colo. "Isn't that the most outrageous thing you could imagine? It truly is like something out of science fiction."

Scientists also were intrigued by bright streaks in two different rings that appear to be clouds of dust kicked up in collisions between small space debris and ring particles. Understanding the rate and locations of impacts will help build better models of contamination and erosion in the rings and refine estimates of their age. The collision clouds were easier to see under the low-lighting conditions of equinox than under normal lighting conditions.

At the same time Cassini was snapping visible-light photographs of Saturn's rings, the Composite Infrared Spectrometer instrument was taking the rings' temperatures. During equinox, the rings cooled to the lowest temperature ever recorded. The A ring dropped down to a frosty 43 Kelvin (382 degrees below zero Fahrenheit). Studying ring temperatures at equinox will help scientists better understand the sizes and other characteristics of the ring particles.

The Cassini spacecraft has been observing Saturn, its moons and rings since it entered the planet's orbit in 2004. The spacecraft's instruments have discovered new rings and moons and have improved our understanding of Saturn's ring system.

The Cassini-Huygens mission is a cooperative project of NASA and the European and Italian Space Agencies. JPL manages the mission for the Science Mission Directorate at NASA Headquarters in Washington. JPL also designed, developed and assembled the Cassini orbiter and its two onboard cameras. The imaging team is based at the Space Science Institute. The Composite Infrared Spectrometer team is based at NASA's Goddard Space Flight Center in Greenbelt, Md.


NASA/JPL/Space Science Institute

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Caltech release
Caltech Scientists Discover Fog on Titan

Saturn's largest moon, Titan, looks to be the only place in the solar system -- aside from our home planet, Earth -- with copious quantities of liquid (largely, liquid methane and ethane) sitting on its surface. According to planetary astronomer Mike Brown of the California Institute of Technology (Caltech), Earth and Titan share yet another feature, which is inextricably linked with that surface liquid: common fog.


Credit: Mike Brown/Caltech

Fingers of fog can be seen moving across the south pole of Titan in this image constructed by Mike Brown and his colleagues using data from the Cassini spacecraft. The fog shows regions where pools of liquid methane sitting on the surface of Titan are evaporating into the atmosphere. After a long summer of frequent clouds and rain at the south pole, it appears in this late summer image that evaporating liquid methane covers large areas of the pole.

The presence of fog provides the first direct evidence for the exchange of material between the surface and the atmosphere, and thus of an active hydrological cycle, which previously had only been known to exist on Earth.

In a talk to be delivered December 18 at the American Geophysical Union's 2009 Fall Meeting in San Francisco, Brown, the Richard and Barbara Rosenberg Professor and professor of planetary astronomy, details evidence that Titan's south pole is spotted "more or less everywhere" with puddles of methane that give rise to sporadic layers of fog. (Technically, fog is just a cloud or bank of clouds that touch the ground).

Brown and his colleagues also describe their findings in a recent paper published in The Astrophysical Journal Letters.

The researchers made their discovery using data from the Visual and Infrared Mapping Spectrometer (VIMS) onboard the Cassini spacecraft, which has been observing Saturn's system for the past five years.

The VIMS instrument provides "hyperspectral" imaging, covering a large swath of the visible and infrared spectrum. Brown and his colleagues -- including Caltech undergraduate students Alex Smith and Clare Chen, who were working with Brown as part of a Summer Undergraduate Research Fellowship (SURF) project -- searched public online archives to find all Cassini data collected over the moon's south pole from October 2006 through March 2007. They filtered the data to separate out features occurring at different depths in the atmosphere, ranging from 20 kilometers (12.4 miles) to .25 kilometers (820 feet) above the surface. Using other filters, they homed in on "bright" features caused by the scattering of light off small particles -- such as the methane droplets present in clouds.

In this way, they isolated clouds located about 750 meters (less than a half-mile) above the ground. These clouds did not extend into the higher altitudes -- into the moon's troposphere, where regular clouds form. In other words, says Brown, they had found fog.

"Fog -- or clouds, or dew, or condensation in general -- can form whenever air reaches about 100 percent humidity," Brown says. "There are two ways to get there. The first is obvious: add water (on Earth) or methane (on Titan) to the surrounding air. The second is much more common: make the air colder so it can hold less water (or liquid methane), and all of that excess needs to condense."

This, he explains, is the same process that causes water droplets to form on the outside of a cool glass.

On Earth, this is the most common method of making fog, Brown says. "That fog you often see at sunrise hugging the ground is caused by ground-level air cooling overnight, to the point where it cannot hang onto its water. As the sun rises and the air heats, the fog goes away."

Similarly, fog can form when wet air passes over cold ground; as the air cools, the water condenses. And mountain fog occurs when air gets pushed up the side of a mountain and cools, causing the water to condense.

However, none of these mechanisms work on Titan.

The reason is that Titan's muggy atmosphere takes a notoriously long time to cool (or warm). "If you were to turn the sun totally off, Titan's atmosphere would still take something like 100 years to cool down," Brown says. "Even the coldest parts of the surface are much too warm to ever cause fog to condense."

Mountain fog is also out of the question, he adds. "A Titanian mountain would have to be about 15,000 feet high before the air would get cold enough to condense," he says. And yet the tallest mountains the moon could possibly carry (because of its fragile, icy crust) would be no more than 3000 feet high.

The only possible way to make Titanian fog, then, is to add humidity to the air. And the only way to do that, Brown says, is by evaporating liquid -- in this case, methane, the most common hydrocarbon on the moon, which exists in solid, liquid, and gaseous forms.

Brown notes that evaporating methane on Titan "means it must have rained, and rain means streams and pools and erosion and geology. The presence of fog on Titan proves, for the first time, that the moon has a currently active methane hydrological cycle."

The presence of fog also proves that the moon must be dotted with methane pools, Brown says. That's because any ground-level air, after becoming 100 percent humid and turning into fog, would instantly rise up into the atmosphere like a giant cumulus cloud. "The only way to make the fog stick around on the ground is to both add humidity and cool the air just a little," he explains. "The way to cool the air just a little is to have it in contact with something cold, like a pool of evaporating liquid methane."

In addition to Smith and Chen, The Astrophysical Journal Letters paper, "Discovery of Fog at the South Pole of Titan," was coauthored by Mate Adamkovics from the University of California, Berkeley. The work was funded by a grant from the National Science Foundation's Planetary Astronomy program.

For more information about the discovery, go to Brown's blog.

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NASA release
NASA Extends Cassini's Tour of Saturn, Continuing International Cooperation for World Class Science

NASA will extend the international Cassini-Huygens mission to explore Saturn and its planets to 2017. The agency's fiscal year 2011 budget provides a $60 million per year extension for continued study of the ringed planet.

"This is a mission that never stops providing us surprising scientific results and showing us eye popping new vistas," said Jim Green, director of NASA's planetary science division at NASA Headquarters in Washington. "The historic traveler's stunning discoveries and images have revolutionized our knowledge of Saturn and its moons."

Cassini launched in October 1997 with the European Space Agency's Huygens probe. The spacecraft arrived at Saturn in 2004. The probe was equipped with six instruments to study Titan, Saturn's largest moon. Cassini's 12 instruments have returned a daily stream of data from Saturn's system for nearly six years. The project was scheduled to end in 2008, but the mission received a 27-month extension to Sept. 2010.

"The extension presents a unique opportunity to follow seasonal changes of an outer planet system all the way from its winter to its summer," said Bob Pappalardo, Cassini project scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Some of Cassini's most exciting discoveries still lie ahead."

This second extension, called the Cassini Solstice Mission, enables scientists to study seasonal and other long-term weather changes on the planet and its moons. Cassini arrived just after Saturn's northern winter solstice, and this extension continues until a few months past northern summer solstice in May 2017. The northern summer solstice marks the beginning of summer in the northern hemisphere and winter in the southern hemisphere.

A complete seasonal period on Saturn has never been studied at this level of detail. The Solstice mission schedule calls for an additional 155 orbits around the planet, 54 flybys of Titan and 11 flybys of the icy moon Enceladus.

The mission extension also will allow scientists to continue observations of Saturn's rings and the magnetic bubble around the planet known as the magnetosphere. The spacecraft will make repeated dives between Saturn and its rings to obtain in depth knowledge of the gas giant. During these dives, the spacecraft will study the internal structure of Saturn, its magnetic fluctuations and ring mass.

The mission will be evaluated periodically to ensure the spacecraft has the ability to achieve new science objectives for the entire extension.

"The spacecraft is doing remarkably well, even as we endure the expected effects of age after logging 2.6 billion miles on its odometer," said Bob Mitchell, Cassini program manager at JPL. "This extension is important because there is so much still to be learned at Saturn. The planet is full of secrets, and it doesn't give them up easily."

Cassini's travel scrapbook includes more than 210,000 images; information gathered during more than 125 revolutions around Saturn; 67 flybys of Titan and eight close flybys of Enceladus. Cassini has revealed unexpected details in the planet's signature rings, and observations of Titan have given scientists a glimpse of what Earth might have been like before life evolved.

Scientists hope to learn answers to many questions that have developed during the course of the mission, including why Saturn seems to have an inconsistent rotation rate and how a probable subsurface ocean feeds the Enceladus' jets.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL manages the project for NASA's Science Mission Directorate in Washington. The Cassini orbiter was designed, developed and assembled at JPL.

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NASA release
Cassini Data Show Ice and Rock Mixture Inside Titan

By precisely tracking NASA's Cassini spacecraft on its low swoops over Saturn's moon Titan, scientists have determined the distribution of materials in the moon's interior. The subtle gravitational tugs they measured suggest the interior has been too cold and sluggish to split completely into separate layers of ice and rock.

The finding, to be published in the March 12 issue of the journal Science, shows how Titan evolved in a different fashion from inner planets such as Earth, or icy moons such as Jupiter's Ganymede, whose interiors have split into distinctive layers.

"These results are fundamental to understanding the history of moons of the outer solar system," said Cassini Project Scientist Bob Pappalardo, commenting on his colleagues' research. Pappalardo is with NASA's Jet Propulsion Laboratory in Pasadena, Calif. "We can now better understand Titan's place among the range of icy satellites in our solar system."

Scientists have known that Titan, Saturn's largest moon, is about half ice and half rock, but they needed the gravity data to figure out how the materials were distributed. It turns out Titan's interior is a sorbet of ice studded with rocks that probably never heated up beyond a relatively lukewarm temperature. Only in the outermost 500 kilometers (300 miles) is Titan's ice devoid of any rock, while ice and rock are mixed to various extents at greater depth.

"To avoid separating the ice and the rock, you must avoid heating the ice too much," said David J. Stevenson, one of the paper's co-authors and a professor of planetary science at the California Institute of Technology in Pasadena. "This means that Titan was built rather slowly for a moon, in perhaps around a million years or so, back soon after the formation of the solar system."

This incomplete separation of ice and rock makes Titan less like Jupiter's moon Ganymede, where ice and rock have fully separated, and perhaps more like another Jovian moon, Callisto, which is believed to have a mixed ice and rock interior. Though the moons are all about the same size, they clearly have diverse histories.

The Cassini measurements help construct a gravity map, which may help explain why Titan has a stunted topography, since interior ice must be warm enough to flow slowly in response to the weight of heavy geologic structures, such as mountains.

Creating the gravity map required tracking minute changes in Cassini's speed along a line of sight from Earth to the spacecraft as it flew four close flybys of Titan between February 2006 and July 2008. The spacecraft took paths between about 1,300 to 1,900 kilometers (800 to 1,200 miles) above Titan.

"The ripples of Titan's gravity gently push and pull Cassini along its orbit as it passes by the moon and all these changes were accurately recorded by the ground antennas of the Deep Space Network within 5 thousandths of a millimeter per second [0.2 thousandths of an inch per second] even as the spacecraft was over a billion kilometers [more than 600 million miles] away," said Luciano Iess, a Cassini radio science team member at Sapienza University of Rome in Italy, and the paper's lead author. "It was a tricky experiment."

The results don't speak to whether Titan has an ocean beneath the surface, but scientists say this hypothesis is very plausible and they intend to keep investigating. Detecting tides induced by Saturn, a goal of the radio science team, would provide the clearest evidence for such a hidden water layer.

A Cassini interdisciplinary investigator, Jonathan Lunine, said of his colleagues' findings, "Additional flybys may tell us whether the crust is thick or thin today." Lunine is with the University of Rome, Tor Vergata, Italy, and the University of Arizona, Tucson. "With that information we may have a better understanding of how methane, the ephemeral working fluid of Titan's rivers, lakes and clouds, has been resupplied over geologic time. Like the history of water on Earth, this is fundamental to a deep picture of the nature of Titan through time."

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 project for NASA's Science Mission Directorate in Washington. The Cassini orbiter was designed, developed and assembled at JPL. Cassini's radio science subsystem has been jointly developed by NASA and the Italian Space Agency (ASI).

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NASA release
Flash: NASA's Cassini Spacecraft Sees Lightning On Saturn

NASA's Cassini spacecraft has captured images of lightning on Saturn. The images have allowed scientists to create the first movie showing lightning flashing on another planet.

After waiting years for Saturn to dim enough for the spacecraft's cameras to detect bursts of light, scientists were able to create the movie, complete with a soundtrack that features the crackle of radio waves emitted when lightning bolts struck.

"This is the first time we have the visible lightning flash together with the radio data," said Georg Fischer, a radio and plasma wave science team associate based at the Space Research Institute in Graz, Austria. "Now that the radio and visible light data line up, we know for sure we are seeing powerful lightning storms."


Credit: NASA/JPL-Caltech/SSI

The movie and radio data suggest extremely powerful storms with lightning that flashes as brightly as the brightest super-bolts on Earth, according to Andrew Ingersoll, a Cassini imaging science subsystem team member at the California Institute of Technology in Pasadena. "What's interesting is that the storms are as powerful -- or even more powerful -- at Saturn as on Earth," said Ingersoll. "But they occur much less frequently, with usually only one happening on the planet at any given time, though it can last for months."

The first images of the lightning were captured in August 2009, during a storm that churned from January to October 2009 and lasted longer than any other observed lightning storm in the solar system. Results are described in an article accepted for publication in the journal Geophysical Research Letters.

To make a video, scientists needed more pictures with brighter lightning and strong radio signals. Data were collected during a shorter subsequent storm, which occurred from November through mid-December 2009. The frames in the video were obtained over 16 minutes on Nov. 30, 2009. The flashes lasted less than one second. The images show a cloud as long as 1,900 miles across and regions illuminated by lightning flashes about 190 miles in diameter. Scientists use the width of the flashes to gauge the depth of the lightning below the cloud tops.

When lightning strikes on Earth and on Saturn, it emits radio waves at a frequency that can cause static on an AM radio. The sounds in the video approximate that static sound, based on Saturn electrostatic discharge signals detected by Cassini's radio and plasma wave science instrument.

Cassini, launched in 1997, and NASA's Voyager mission, launched in 1977, previously had captured radio emissions from storms on Saturn. A belt around the planet where Cassini has detected radio emissions and bright, convective clouds earned the nickname "storm alley." Cassini's cameras, however, had been unable to get pictures of lightning flashing.

Since Cassini's arrival at Saturn in 2004, it has been difficult to see the lightning because the planet is very bright and reflective. Sunlight shining off Saturn's enormous rings made even the night side of Saturn brighter than a full-moon night on Earth. Equinox, the period around August 2009 when the sun shone directly over the planet's equator, finally brought the needed darkness. During equinox, the sun lit the rings edge-on only and left the bulk of the rings in shadow.

Seeing lightning was another highlight of the equinox period, which already enabled scientists to see clumps in the rings as high as the Rocky Mountains.

"The visible-light images tell us a lot about the lightning," said Ulyana Dyudina, a Cassini imaging team associate based at Caltech, who was the first to see the flashes. "Now we can begin to measure how powerful these storms are, where they form in the cloud layer and how the optical intensity relates to the total energy of the thunderstorms."

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. NASA's Jet Propulsion Laboratory in Pasadena manages the mission for NASA's Science Mission Directorate in Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL.

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NASA release
Cassini Bags Enceladus 'Tigers'

NASA's Cassini spacecraft has successfully completed its flyby over the "tiger stripes" in the south polar region of Saturn's moon Enceladus and has sent back images of its passage. The spacecraft also targeted the moon Tethys.

The tiger stripes are actually giant fissures that spew jets of water vapor and organic particles hundreds of kilometers, or miles, out into space. While the winter is darkening the moon's southern hemisphere, Cassini has its own version of "night vision goggles" -- the composite infrared spectrometer instrument - to track heat even when visible light is low. It will take time for scientists to assemble the data into temperature maps of the fissures.

More raw images from the Enceladus flyby, dubbed "E11," are available here.

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NASA Jet Propulsion Laboratory release
Engineers Assessing Cassini Spacecraft

Engineers at NASA's Jet Propulsion Laboratory, Pasadena, Calif., are working to understand what caused NASA's Cassini spacecraft to put itself into "safe mode," a precautionary standby mode. Cassini entered safe mode around 4 p.m. PDT (7 p.m. EDT) on Tuesday, Nov. 2.

Since going into safe mode, the spacecraft has performed as expected, suspending the flow of science data and sending back only data about engineering and spacecraft health. Cassini is programmed to put itself into safe mode automatically any time it detects a condition on the spacecraft that requires action from mission controllers on the ground.

Engineers say it is not likely that Cassini will be able to resume full operations before a planned Nov. 11 flyby of Saturn's moon Titan. But Cassini has 53 more Titan flybys planned in its extended mission, which lasts until 2017.

"The spacecraft responded exactly as it should have, and I fully expect that we will get Cassini back up and running with no problems," said Bob Mitchell, Cassini program manager based at JPL. "Over the more than six years we have been at Saturn, this is only the second safing event. So considering the complexity of demands we have made on Cassini, the spacecraft has performed exceptionally well for us."

Since Cassini launched in 1997, Cassini has put itself into safe mode a total of six times.

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NASA Jet Propulsion Laboratory release
Status Update: Cassini to Resume Nominal Operations

Engineers at NASA's Jet Propulsion Laboratory, Pasadena, Calif., expect the Cassini spacecraft will resume normal operations on Nov. 24. They have traced the steps taken by an onboard computer before Cassini put itself in precautionary "safe mode" last week.

Mission managers determined that the spacecraft went into safe mode because of a flip of a bit in the command and data system computer. The bit flip prevented the computer from registering an important instruction, and the spacecraft, as programmed, went into the standby mode. Engineers are still working to understand why the bit flipped.

Since the spacecraft went into safe mode on Nov. 2, the onboard computer with the bit flip has been reset and one of the science instruments has been turned back on to keep it warm. Over the next week or so, engineers will bring the rest of the science instruments back online.

Playback from the computer's memory is enabling engineers to extract science data collected before the spacecraft entered safe mode. The flow of science data is expected to resume when the instruments are powered back on next week.

"The bit flip happened in exactly the wrong location -- almost any place else would have merely resulted in a rejected command -- but the spacecraft responded exactly as programmed," said Bob Mitchell, Cassini program manager at JPL. "Cassini is in excellent shape, and we are looking forward to the next seven years of this mission."

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posted 03-21-2012 06:00 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
NASA Jet Propulsion Laboratory release
Cassini Plasma Spectrometer Resumes Operations

The Cassini plasma spectrometer instrument aboard NASA's Cassini spacecraft at Saturn has resumed operations. Mission managers received confirmation on Friday, March 16, that it was turned on. They plan to monitor the instrument for any unusual behavior.

Last June, short circuits in the instrument led to unexpected voltage shifts on the spacecraft. As a precaution, mission managers turned off the CAPS instrument while engineers investigated the issue.

The investigation led to the conclusion that tin plating on electronics components had grown "whiskers." The whiskers were very small, less than the diameter of a human hair, but they were big enough to contact another conducting surface and carry electrical current.

Researchers are still trying to understand why whiskers grow on tin and other metals, but they know now that whiskers can grow in space and on Earth. It is believed that these or additional tin whiskers that may grow on Cassini cannot carry enough current to cause problems, but will burn out on their own like a lightweight fuse.

Robert Pearlman
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posted 04-23-2012 05:33 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
NASA Jet Propulsion Laboratory release
Cassini Sees Objects Blazing Trails in Saturn Ring

Scientists working with images from NASA's Cassini spacecraft have discovered strange half-mile-sized (kilometer-sized) objects punching through parts of Saturn's F ring, leaving glittering trails behind them. These trails in the rings, which scientists are calling "mini-jets," fill in a missing link in our story of the curious behavior of the F ring. The results will be presented tomorrow at the European Geosciences Union meeting in Vienna, Austria.

"I think the F ring is Saturn's weirdest ring, and these latest Cassini results go to show how the F ring is even more dynamic than we ever thought," said Carl Murray, a Cassini imaging team member based at Queen Mary University of London, England. "These findings show us that the F ring region is like a bustling zoo of objects from a half mile [kilometer] to moons like Prometheus a hundred miles [kilometers] in size, creating a spectacular show."

Scientists have known that relatively large objects like Prometheus (as long as 92 miles, or 148 kilometers, across) can create channels, ripples and snowballs in the F ring. But scientists didn't know what happened to these snowballs after they were created, Murray said. Some were surely broken up by collisions or tidal forces in their orbit around Saturn, but now scientists have evidence that some of the smaller ones survive, and their differing orbits mean they go on to strike through the F ring on their own.

These small objects appear to collide with the F ring at gentle speeds - something on the order of about 4 mph (2 meters per second). The collisions drag glittering ice particles out of the F ring with them, leaving a trail typically 20 to 110 miles (40 to 180 kilometers) long. Murray's group happened to see a tiny trail in an image from Jan. 30, 2009 and tracked it over eight hours. The long footage confirmed the small object originated in the F ring, so they went back through the Cassini image catalog to see if the phenomenon was frequent.

"The F ring has a circumference of 550,000 miles [881,000 kilometers], and these mini-jets are so tiny they took quite a bit of time and serendipity to find," said Nick Attree, a Cassini imaging associate at Queen Mary. "We combed through 20,000 images and were delighted to find 500 examples of these rogues during just the seven years Cassini has been at Saturn."

In some cases, the objects traveled in packs, creating mini-jets that looked quite exotic, like the barb of a harpoon. Other new images show grand views of the entire F ring, showing the swirls and eddies that ripple around the ring from all the different kinds of objects moving through and around it.

"Beyond just showing us the strange beauty of the F ring, Cassini's studies of this ring help us understand the activity that occurs when solar systems evolve out of dusty disks that are similar to, but obviously much grander than, the disk we see around Saturn," said Linda Spilker, Cassini project scientist based at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "We can't wait to see what else Cassini will show us in Saturn's rings."

cspg
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posted 04-03-2014 10:53 PM     Click Here to See the Profile for cspg   Click Here to Email cspg     Edit/Delete Message   Reply w/Quote
NASA release
NASA Space Assets Detect Ocean inside Saturn Moon

NASA's Cassini spacecraft and Deep Space Network have uncovered evidence Saturn's moon Enceladus harbors a large underground ocean of liquid water, furthering scientific interest in the moon as a potential home to extraterrestrial microbes.

Researchers theorized the presence of an interior reservoir of water in 2005 when Cassini discovered water vapor and ice spewing from vents near the moon's south pole. The new data provide the first geophysical measurements of the internal structure of Enceladus, consistent with the existence of a hidden ocean inside the moon. Findings from the gravity measurements are in the Friday, April 4 edition of the journal Science.

"The way we deduce gravity variations is a concept in physics called the Doppler Effect, the same principle used with a speed-measuring radar gun," said Sami Asmar of NASA's Jet Propulsion Laboratory in Pasadena, Calif., a coauthor of the paper. "As the spacecraft flies by Enceladus, its velocity is perturbed by an amount that depends on variations in the gravity field that we're trying to measure. We see the change in velocity as a change in radio frequency, received at our ground stations here all the way across the solar system."

The gravity measurements suggest a large, possibly regional, ocean about 6 miles (10 kilometers) deep, beneath an ice shell about 19 to 25 miles (30 to 40 kilometers) thick. The subsurface ocean evidence supports the inclusion of Enceladus among the most likely places in our solar system to host microbial life. Before Cassini reached Saturn in July 2004, no version of that short list included this icy moon, barely 300 miles (500 kilometers) in diameter.

"This then provides one possible story to explain why water is gushing out of these fractures we see at the south pole," said David Stevenson of the California Institute of Technology, Pasadena, one of the paper's co-authors.
Cassini has flown near Enceladus 19 times. Three flybys, from 2010 to 2012, yielded precise trajectory measurements. The gravitational tug of a planetary body, such as Enceladus, alters a spacecraft's flight path. Variations in the gravity field, such as those caused by mountains on the surface or differences in underground composition, can be detected as changes in the spacecraft's velocity, measured from Earth.

The technique of analyzing a radio signal between Cassini and the Deep Space Network can detect changes in velocity as small as less than one foot per hour (90 microns per second). With this precision, the flyby data yielded evidence of a zone inside the southern end of the moon with higher density than other portions of the interior.

The south pole area has a surface depression that causes a dip in the local tug of gravity. However, the magnitude of the dip is less than expected given the size of the depression, leading researchers to conclude the depression's effect is partially offset by a high-density feature in the region, beneath the surface.

"The Cassini gravity measurements show a negative gravity anomaly at the south pole that however is not as large as expected from the deep depression detected by the onboard camera," said the paper's lead author, Luciano Iess of Sapienza University of Rome. "Hence the conclusion that there must be a denser material at depth that compensates the missing mass: very likely liquid water, which is seven percent denser than ice. The magnitude of the anomaly gave us the size of the water reservoir."

There is no certainty the subsurface ocean supplies the water plume spraying out of surface fractures near the south pole of Enceladus, however, scientists reason it is a real possibility. The fractures may lead down to a part of the moon that is tidally heated by the moon's repeated flexing, as it follows an eccentric orbit around Saturn.

Much of the excitement about the Cassini mission's discovery of the Enceladus water plume stems from the possibility that it originates from a wet environment that could be a favorable environment for microbial life.

"Material from Enceladus’ south polar jets contains salty water and organic molecules, the basic chemical ingredients for life," said Linda Spilker, Cassini's project scientist at JPL. "Their discovery expanded our view of the 'habitable zone' within our solar system and in planetary systems of other stars. This new validation that an ocean of water underlies the jets furthers understanding about this intriguing environment."

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