More rings in Saturn's neighborhood

Saturn's moon Rhea could be a mini version of its ringed parent and the first moon known to have rings of its own.

Scientists detected hints of the rings when the Cassini spacecraft flew by the moon, Saturn's second largest, in November 2005.

Surprisingly, instruments aboard Cassini measured an absence of electrons around the moon where astronomers expected the charged particles to swarm.

"This showed that there was something unique going on," said Geraint Jones, a Cassini scientist. "We haven't seen anything like this at any of the other moons. The only thing we can come up with that fits what we see is that maybe there is some debris around Rhea. If it is correct this would be the first moon where we have evidence of rings."

Since Rhea lies within Saturn's magnetosphere, which traps ions and electrons, scientists expected the moon to be awash in these particles. Instead, they measured a gap in electrons in a swath of space surrounding Rhea.

A set of rings could explain the disappearing electrons because the material making up the rings — most likely chunks of water ice up to a centimeter or meter in diameter — would absorb electrons.

Rhea, named after the classical Greek titan goddess, the mother of Zeus, Hades, Hera and other Olympian deities, is a barren, icy world covered in craters. Its diameter is a little less than half that of our moon.

So far, Cassini has not been able to see the rings. If the spacecraft's mission is extended, the researchers hope it might glimpse them on a future close flyby of Rhea.

Saturn has dozens of moons; to date, 52 of them have been named.

Enceladus jets

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

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Geysers Gush from Cracks in Saturn's Moon

False color Cassini image illustrating the jets of fine icy particles erupting from the south polar region of Enceladus. Please credit: Cassini Imaging Team and NASA/JPL/SSI

Slushy geysers on Saturn's moon Enceladus erupt from fractures clustered around a hot spot at the satellite's south pole, scientists have now confirmed.

Using NASA's Cassini spacecraft, researchers recorded the location of jet events on Enceladus for two years. They found that the most prominent jets emanated from hot spots along four cracks, or "tiger stripes," on the moon's surface called Alexandria, Cairo, Baghdad and Damascus.

The monikers come from a naming convention created during the days of the Voyager spacecraft, which required features on Saturnian satellites be named after the myths and epics of the world. The fissures on Enceladus were named after cities in the Arabian story collection, "One Thousand and One Nights."

The discovery, detailed in the Oct. 11 issue of the journal Nature, is the first to directly link the tiger stripes and the jets.

"We suspected that the jets were coming from the fractures ... but this is now definitive proof," said study team member Carolyn Porco, leader of Cassini's imaging team at the Space Science Institute in Boulder, Colo.

The finding also provides new observational constraints for computer modelers attempting to simulate the geyser's underlying mechanisms, Porco said, and could help determine whether a vast liquid ocean—and possibly life—lies beneath Enceladus' crust.

An active moon

Geological activity on Enceladus was only confirmed about two years ago, when Cassini's infrared camera detected an anomalous hot spot on the moon's south pole and revealed that pale blue "veins" on the moon's surface were actually deep chasms spewing a mixture of liquid water, ice and organic compounds into space.

Scientists now think Enceladus' slushy ejecta are the source of Saturn's tenuous E-ring, and that other Saturnian moons passing through this ring are coated in the reflective substance, making them unusually bright.

Recently, scientists have theorized the geysers might be powered by the grinding of ice sheets against one another and the periodic opening and closing of gaps on the moon's surface.

Both mechanisms were thought to be driven by a process called tidal heating. Because Enceladus' path around Saturn is elliptical, it is pulled unevenly by the planet's gravity at different points along its orbit. This creates a bulge on the moon's surface that grows and shrinks depending on the moon's distance from Saturn.

The repetitive motion generates friction and heat, which scientists suspect drives the tiger stripes to open and close.

The new findings are generally consistent with the geyser mechanism models, except for one major discrepancy involving the tiger stripe Baghdad, said study team member Joseph Spitale, also of the Space Science Institute.

"They didn't predict almost any heating on [Baghdad], and we found our strongest sources there," Spitale told SPACE.com.

Future models will have to take Baghdad's activity into account, the researchers say.

The discrepancy "means that the people who are doing these kinds of models need to go and see if they can't tweak their parameters to try and match what we're observing," Porco said.

The go-to moon

Enceladus is only one of a handful of bodies in our solar system known to be geologically active, and, in Porco's opinion, is the go-to place to answer questions about astrobiology.

"Mars has been a candidate for a long time, but even the guys who study Mars will tell you—if they are being at all objective about this—that chances are there are no living organisms on Mars ... unless you go to the poles," she said.

Porco thinks Enceladus also has a leg up on Jupiter's satellite Europa, another leading contender in scientists' eyes as a life-harboring world, because many of the suspected requirements for life have already been confirmed on Enceladus.

"We've flown through the plumes. We've measured the presence of organics. We already know there's access heat" on Enceladus, Porco said. "The only outstanding question is, do these jets derive directly from liquid water or not?"

Saturn: Lapetus

Some NASA images of Lapetus: one of Saturns moons.

Length of Saturn's Day Revised

A day on Saturn just got a few minutes shorter, if new calculations are correct.

Using data collected by NASA's Cassini, Pioneer and Voyager spacecraft, scientists have revised the ringed planet's rotation period to 10 hours, 32 minutes and 35 seconds-about 15 minutes shorter than an estimate made only last year.

Those precious minutes could have big implications for how scientists think about Saturn and other gas giants.

"While that may seem like a small uncertainty for the average person, it makes an enormous difference in terms of how we can understand the interior of Saturn," said study team member Gerald Schubert of the University of California, Los Angeles.

If the new rotation rate, detailed in the Sept. 7 issue of the journal Science, is correct, then Saturn's winds blow slower than previously thought and instead of whooshing in only a single direction, can blow both east and west. The finding could also shed light on how gas giant planets in general form.

The problem with gas planets

Schubert and his colleague John Anderson of Global Aerospace in Pasadena, Calif., calculated Saturn's faster rotation using a combination of gravity, wind and deflected radio measurements collected by the three spacecraft.

The spin rate for rocky planets such as Earth can be determined by simply monitoring how fast a particular spot on the planet moves relative to other celestial objects. This doesn't work for gas planets like Jupiter and Saturn, however, because their solid cores are hidden by atmospheric clouds.

Scientists instead measure the rotation periods of the gas giants' magnetic fields, which are assumed to be closely tied to the spin rate of their solid interiors. For this to work, the rotation axis of a gas giant's magnetic field and the rotation axis around which the planet's solid core spins must differ.

But for Saturn, the two axes are nearly identical, so scientists have had to rely on even less direct measures to calculate its rotation rate. Using radio emissions data collected by the Voyager spacecraft in the 1980s, scientists initially determined a Saturnian day to be 10 hours, 39 minutes and 22 seconds.

That estimate was revised in 2004, using Cassini-collected data, to 10 hours, 45 minutes and 45 seconds. It was tweaked yet again last year to 10 hours, 47 minutes and 6 seconds.

Schubert admits that his and Anderson's estimate is only the latest educated guess. "We can't say with absolute certainty that this is Saturn's rotation rate," Schubert said. "At the moment, there's no way that anyone knows of to directly measure Saturn's rotation rate."

Slower winds

Knowing the length of a Saturnian day would help scientists better understand the planet's interior.

For example, if the new spin time is correct, it would change estimates of the planet's wind speed. To calculate wind speed, scientists subtract the speed at which clouds appear to move in the planet's atmosphere from the rotation speed of the planet's solid core.

"When people thought they knew Saturn's rotation rate, they did the subtraction to calculate wind speed and they got a pretty crazy result, huge wind speeds and all the winds were blowing in the same direction," Schubert said.

Those calculations don't match with Jupiter, which has significantly slower winds that blow both east and west.

"Now with this faster rotation rate, the wind speeds actually come down to Jupiter-like values," Schubert said in a telephone interview. "Those few minutes make a world of difference."

Gas planet formation

The new finding might also help scientists distinguish between two competing theories of gas planet formation. According to the "core accretion" model, gas giants form in a similar manner to rocky planets, by gradually accreting rocky debris until they become so large that they draw vast quantities of hydrogen and helium gas unto themselves.

In the competing "disk instability" model, gas planets form when large clumps of gas orbiting in debris disks around young stars collapse under their own gravity to eventually form planets.

Morris Podolak, an astronomer at Tel Aviv University in Israel who was not involved in the study, suggests in a related Science article that if Saturn's rotation rate is indeed faster than previously thought, then its internal core must also be smaller, which could in turn favor the disk instability model.

Alan Boss, a planet-formation theorist at the Carnegie Institution of Washington, and the main proponent of the disk instability model, is more skeptical. "I do not think that this result, while provocative, sheds much light on the debate over planet formation," Boss, who was not involved in the new study, told SPACE.com. "It mainly serves to show how little we can be certain about the interiors of the giant planets."

Schubert is reserving judgment for now, saying that while he thinks knowing Saturn's rotation rate is crucial to understanding the planet's interior, he is unsure whether it will have any bearing on choosing between the two hypotheses.

Mounting Mysteries at Saturn Keep Scientists Guessing

Humanity has known of Saturn since prehistory, but enigmas about this ringed world still abound-from new mysteries concerning a baffling hexagon of clouds on the planet to perennial puzzles concerning its famous rings.

Giant hexagon

The latest mystery is the giant hexagon circling Saturn's north pole. Scientists caught glimpses of it decades ago from the Voyager mission, but confirmed its existence with the Cassini spacecraft.

Nothing like the hexagon has ever been seen at any other planet, with each of its sides nearly 7,500 miles (12,500 kilometers) across-big enough to fit nearly four Earths inside. Thermal images show it reaches roughly 60 miles (100 kilometers) down into the planet's atmosphere. "It's a very bizarre object," said Kevin Baines, atmospheric expert and member of Cassini's visual and infrared mapping spectrometer team at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

Although water swirling inside a bucket can generate whirlpools possessing geometric holes, "there's no bucket here," Baines said. "You're not flinging fluid against some wall."

Scientists have bandied about several other ideas concerning the hexagon's origin. Perhaps a giant spinning cylinder of gas stretching thousands of kilometers into Saturn lies at the hexagon's center, and the hexagon's cloudy walls emerged from interactions with slower-spinning gas at the cylinder's edges that did not spin as fast, Baines said. Or perhaps the hexagon arises from a complex interaction between waves undulating through the atmosphere and gas churning up it.

"Hopefully we'll learn more about the hexagon when the seasons on Saturn change and the sun begins to shine on the hexagon about 18 months from now," Baines said. Cassini's eagle-eyed cameras should show details of the hexagon 80 times sharper than those currently available via the spacecraft's thermal imagers.

Lord of the rings

Strange features abound within the rings of Saturn. These include hundreds of "record grooves" or narrow fluctuations in the B ring, the most massive ring. These also include "plateaus" in the C ring, the innermost main ring-broad, dark, sharp-edged features thicker than elsewhere in the ring. "No one has a clue what causes them," Jeffrey Cuzzi, a planetary scientist at the NASA Ames Research Center in California, said of these grooves and plateaus.

Not only are the origins of these features mysterious, but so are those of the rings themselves.

Some researchers argue the rings are debris left over from Saturn's formation, making them roughly as old as the solar system itself, or about 4.5 billion years old. Others say that if they were that old, they should be polluted with dirty ice from comets, which are thought to rain down often on gas giants, as the comet Shoemaker-Levy illustrated when it smacked into Jupiter in 1994.

The fact that the rings seem be made of relatively clean and not dirty ice suggests they might be only a few hundred million years old, or "no more recent than the age of fish on Earth," Cuzzi said. In this idea, they're made of rubble perhaps from a moon that got ripped apart.

Future observations from Cassini might help really understand what the rings are made of, which scientists could then compare with the compositions of comets or Saturn's moons to find the better match-up, Cuzzi said.

More knowledge about the origins of the rings and their features could help scientists understand more of the dynamics involved in other kinds of astrophysical disks, "such as the one that formed the planets in our solar system," said Matthew Hedman, a research associate at Cornell University.

Time of day

The very length of the day on Saturn-that is, the rate at which the bulk of the planet spins-also remains a mystery. The planet's dense, cloudy atmosphere makes it impossible to simply peer down hundreds of miles to see how fast Saturn is actually spinning.

When measuring Jupiter's rate of spin, astronomers were helped by the fact that, like Earth, Jupiter's magnetic poles are not lined up with the axis on which it spins. This means when Jupiter spins, its magnetic poles move with it, and thus astronomers can determine how fast Jupiter is spinning by looking at its magnetic field.

However, Saturn's magnetic poles are lined up nearly perfectly with the axis on which it spins. This has led to confusing results, such as Saturn's day improbably lengthening by about six minutes in the past 26 years. One possible explanation was that puffs of water from the Saturnian moon Enceladus's geysers may have literally clouded Saturn's magnetic field with ionized particles that changed how we saw Saturn's magnetic field, Baines said.

The water molecules become ionized by charged particles they encounter in Saturn's magnetic field, and then become trapped for a time in the field, weighing and dragging it down a bit so that the field actually spins more slowly. Scientists hope that by comparing Enceladus's geyser activity with Saturn's magnetic field spin over the next few years-perhaps finding a span of time when there's a lull in that moon's eruptions-they might be able to finally determine the true rotation rate of Saturn.

Energy crisis

Saturn and the solar system's other giant planets also face what researchers call an "energy crisis"-their upper atmospheres are far hotter than can be explained by absorbed sunlight. Scientists had suspected the mechanism that causes the aurora borealis or Northern Lights on Earth might explain this heat. On Earth, super-hot particles from the solar wind collide with the planet's magnetic field exciting atoms in the atmosphere that shed light and thus create auroras.

However, atmospheric physicist Alan Aylward at University College London along with physicist Chris Smith and their colleagues found auroras could actually cool the upper atmospheres of gas giants, by forcing air closer to the equator down to lower, colder depths.

The extra heat astronomers see might get explained by energy from gravity waves, atmospheric oscillations up and down caused by the tug of war between the planet's gravity and the buoyancy of the atmosphere's gas. (These gravity waves differ from gravitational waves, or fluctuations in space-time itself.) Or Saturn's electric fields could be even more complex than before thought.

"We don't even understand the details of the electric fields on Earth, and those on Jupiter and Saturn are quite a bit farther away and of different compositions," Aylward said.

Mysterious Twist Found in Saturn's Electric Ring

Img 1. A Cassini image showing the energetic emission from Saturn’s ring current. Part of the lopsided ring rotates with the planet approximately every 10 hours and 47 minutes. Credit: NASA

Img 2. Earth’s ring current. The view is looking down on the planet’s north pole; the white lines show the Earth’s position and orientation. The ring doesn't rotate with the planet, but remains fixed relative to the Sun. Credit: NASA

An invisible donut of trapped, hot particles surrounding Saturn is all bent out of shape--a finding that astronomers can't yet explain.

A similar "ring current" phenomenon occurs around Earth as a relatively stable donut when present, but new Cassini spacecraft images show Saturn's loop is a lopsided mess.

"It's curious that Saturn's ring current isn't symmetric," said Don Mitchell, an astrophysicist at Johns Hopkins University who helped examine the images beamed back to Earth. "We think the solar wind is squishing the sunward side of the ring current, kind of like a wind sock."

Planets with magnetic fields can trap hot particles within their clutches to form giant electrified clouds-the ring currents-that are invisible to the naked eye.

Earth's ring current is made of hydrogen and appears during solar flares. Saturn's is made largely of oxygen and is always present. The saturnian moon Enceladus is responsible for the electric halo, as it consistently spews water vapor from its depths to feed the ring current with oxygen and hydrogen ions.

Because oxygen is far heavier than hydrogen, Mitchell said, Saturn's ring current can distort the planet's magnetic field and make for an odd shape.

"The heavier oxygen is like a rock on a string, stretching the magnetic field of Saturn," Mitchell said.

More mysterious to Mitchell and his colleagues, however, is a "clump" of electrified particles within the ring that rotates in sync with the planet roughly every 10 hours and 47 minutes.

Cassini's images show the bright clump orbits Saturn between 300,000 and 634,000 miles (485,000 and 1,000,000 kilometers) away from the planet's surface, but astronomers have not yet figured out what creates it nor why it moves so quickly.

"Saturn is a big fast rotator. The clump seems loosely hooked to the planet, yet rotates with it," Mitchell said. "It may be connected with Saturn's ring current, but we just don't know. This is something we're working very hard to figure out."

Stamatios Krimigis, also an astrophsycist at Johns Hopkins who examined the images, is presenting them Thursday at the European Planetary Science Congress in Potsdam, Germany.

Saturn's Mysterious G-ring Explained

This image of Saturn's G ring captures its single bright arc on the ring's inner edge. Credit: Cassini Imaging Team and NASA/JPL/SSI

A loosely knit band of roving ice boulders in orbit around Saturn could be providing the raw material for one of the planet's rings, scientists say.

The finding, detailed in the Aug. 3 issue of the journal Science, could solve the puzzle of what sustains Saturn's "G-ring" and might be evidence that a Saturnian moonlet was destroyed during an ancient collision.

The formation of Saturn's rings is a general mystery, but theorists figure they're the result of one or more breakups of icy objects in the past. In particular though, the G-ring has really puzzled scientists since its discovery in the late 1970s by the Voyager mission.

The odd ring

The G-ring is a faint and narrow circlet of debris located beyond Saturn's main set of rings. There is no obvious way it could have formed. Material for Saturn's E-ring is supplied by debris shed from the moon Enceladus, and the planet's F-ring is created by the shepherding actions of the moons Prometheus and Pandora, which act like snowplows to clear lanes on either side of the ring.

But Mimas, the G-ring's closest Saturnian moon, is located a relatively far 9,300 miles (15,000 kilometers) away from the ring.

In September 2006, NASA's Cassini spacecraft provided scientists with one of their best glimpses of the G-ring. Images revealed a bright, curved streak of material near the ring's inner edge composed of icy particles ranging in size from less than a centimeter to a meter in diameter.

"You don't normally expect in a ring system to see something confined to a range of latitudes around Saturn," said study team member Matthew Hedman of Cornell University in New York. "By definition, things should smear out and become a continuous ring all the way around the planet."

Scientists estimate the arc is about 155 miles (250 kilometers) wide and about 100,000 miles (170,000 kilometers) long, or about one-sixth the circumference of the G-ring. If all the material in the arc were gathered into a single body, it would form an icy moonlet more than 300 feet (100 meters) across.

And like a moon, the bright arc circles around Saturn, taking about 19 hours to make one complete orbit. It moves in a nearly synchronous orbit with Mimas, going around seven times for every six orbits that Mimas makes.

Orbital resonance

Despite Mimas's distant location from the G-ring, scientists think the moon's gravity helps herd in the larger pieces of debris in the arc, keeping them in a crescent shape as they go around Saturn.

Occasionally, these large chunks of ice smash into one another, releasing clouds of dust and fine ice crystals into space. The researchers speculate that the shed material gets bumped around by highly charged particles and electrons, called plasma, in Saturn's magnetosphere and eventually drift out of the confines of the arc to settle into a ring.

"The big [arc] particles only feel gravity, so they don't spread very much. They're all trapped in the arc," Hedman told SPACE.com. "But the little dust grains can interact with the plasma in Saturn's magnetosphere. Since they're smaller, they can feel those forces and [the interaction] can cause material to spread radially."

The origin of the arc's bigger particles is still a mystery. One idea is that they are remnants of a small satellite destroyed long ago through a collision with another object. "One possibility is that it was a moonlet that was broken up," Hedman said. "The trick is that it has to get into this configuration with Mimas, and we're still trying to understand how that could've happened in the first place."

VIDEO: The Source of Saturn's G-ring

New 60th Moon of Saturn Discovered

A still-frame from a movie taken by NASA's Cassini spacecraft of Saturn's newly discovered moon (in red square). Credit: NASA/JPL/Space Science Institute

A new moon of Saturn has been discovered, bringing the planet's satellite tally to 60.

Initial measurements suggest the new moon, which is still unnamed, is about 1.2 miles (2 kilometers) wide, and lies between the orbits of Mehone and Pallene, two Saturnian moons discovered by NASA's Cassini spacecraft in 2004. The newfound moon is about 1.09 million miles (1.76 million kilometers) from Saturn and could be part of a larger group of still undiscovered moons around the ringed planet.

The moon was observed by Cassini on May 30, 2007.

Saturn has the second largest tally of moons in the solar system next to Jupiter, which has 63. However, like the definition of "planet," there is an ongoing debate about what size a satellite must be and how it must behave to qualify as a moon. If very small and as-yet unfound objects are ultimately included, the moon tallies could soar into the hundreds or even thousands.

Constantly Colliding Clumps Found in Saturn's Rings

The newfound clumps in Saturn's B ring are 100 to 160 feet (30 to 50 meters) across. They are too small to be seen directly. However, scientists can map the distribution, shape and orientation of the clumps. Colors in this image indicate the orientation of clumps, and brightness indicates the density of ring particles. The formation of wakes is strongest in the bluer regions, where ring particles clump together in tilted wakes. Particles in the central yellow regions are too densely packed for any starlight to pass through. Credit: NASA/JPL/Space Science Institute

Saturn's largest ring might appear solid when viewed from Earth, but closer inspection by NASA's Cassini spacecraft reveals it is composed of tightly packed clumps of particles in constant collision with one another.

The research also suggests scientists have underestimated the total mass of Saturn's rings, which might actually be two or more times as massive than previously thought.

"The rings are different from the picture we had in our minds," said study leader Larry Esposito of the University of Colorado, Boulder. "If you were flying under Saturn's rings in an airplane, you would see these flashes of sunlight come through the gaps, followed by dark and so forth."

The findings, to be detailed in an upcoming issue of the journal Icarus, show Saturn's B ring particles are not uniformly distributed as previously thought.

A Saturn CAT scan

To measure the ring particles' distribution, scientists directed Cassini to observe the brightness of a background star as the rings passed in front of it multiple times. Study team member Josh Colwell of the University of Central Florida, Orlando compares the technique to a medical CAT scan.

"By studying the brightness of stars as the rings pass in front of them, we are able to map the ring structures in 3-D and learn more about the shape, spacing and orientation of clusters of particles," Colwell said.

This provided a measurement of the amount of ring material between the spacecraft and the star.

The observations confirmed that ring particles come together to form giant clumps called "self-gravity wakes" that can reach 100 to 160 feet (30 to 50 meters) across.

If the clumps were farther from Saturn, they might amass to form a moon, scientists say. But because they are so close to Saturn, the clumps' different speeds around the planet counteract the gravitational attraction they feel for each other and stretch them out like taffy.

Constantly colliding

Cassini also revealed the clumps in Saturn's B ring are neatly organized and constantly colliding, which surprised scientists.

It was previously thought the ring particles crashed into one another about twice every hour.

Instead, "at any given time, most particles are going to be in one of the clumps," Cowell said, "but the particles keep moving from clump to clump as clumps are destroyed and new ones are formed."

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Bizarre Hexagon Spotted on Saturn

That's weird alright. From Space.com:

One of the most bizarre weather patterns known has been photographed at Saturn, where astronomers have spotted a huge, six-sided feature circling the north pole.

Rather than the normally sinuous cloud structures seen on all planets that have atmospheres, this thing is a hexagon.

The honeycomb-like feature has been seen before. NASA's Voyager 1 and 2 spacecraft imaged it more than two decades ago. Now, having spotted it with the Cassini spacecraft, scientists conclude it is a long-lasting oddity.

"This is a very strange feature, lying in a precise geometric fashion with six nearly equally straight sides," said Kevin Baines, atmospheric expert and member of Cassini's visual and infrared mapping spectrometer team at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "We've never seen anything like this on any other planet. Indeed, Saturn's thick atmosphere, where circularly-shaped waves and convective cells dominate, is perhaps the last place you'd expect to see such a six-sided geometric figure, yet there it is."

The hexagon is nearly 15,000 miles (25,000 kilometers) across. Nearly four Earths could fit inside it. The thermal imagery shows the hexagon extends about 60 miles (100 kilometers) down into the clouds.

At Saturn's south pole, Cassini recently spotted a freaky human eye-like feature that resembles a hurricane.

"It's amazing to see such striking differences on opposite ends of Saturn's poles," said Bob Brown, team leader of the Cassini visual and infrared mapping spectrometer at the University of Arizona. "At the south pole we have what appears to be a hurricane with a giant eye, and at the north pole of Saturn we have this geometric feature, which is completely different."

The hexagon appears to have remained fixed with Saturn's rotation rate and axis since first glimpsed by Voyager 26 years ago. The actual rotation rate of Saturn is still uncertain, which means nobody knows exactly how long the planet's day is.

"Once we understand its dynamical nature, this long-lived, deep-seated polar hexagon may give us a clue to the true rotation rate of the deep atmosphere and perhaps the interior," Baines said.

• Video: The Hexagon on Saturn

Hubble Catches Saturn’s Orbital Dance in New Movies

W00t!

Astronomers have created three stunning movies of Saturn and its rings, using special techniques to extend still images taken by the Hubble Space Telescope into moving pictures that show the ringed planet in novel splendor.

Each movie highlights a different moment in the planet's 30-year orbit around the Sun.

• VIDEO: Hubble Space Telescope’s Saturnian Movies

Two of the movies (15 seconds long and 30 seconds long) show the motion of several of Saturn's moons when the planet's rings were tilted nearly edge-on towards the Earth and Sun. Such alignments happen about once every 15 years. The third movie, at 24-seconds long, shows a clear view of Saturn's southern hemisphere when the planet's rings were most tilted toward Earth.

Ray Villard of the Space Telescope Science Institute (STScI), which oversees the Hubble space telescope's research mission, said the movies show Saturn at very unique orientations relative to Earth.

"When Saturn's ring plane was edge-on to earth, the ring becomes a wafer-thin slice and that's a beautiful opportunity to see the moons very clearly," he said.

Another set of images used for the videos and from a similar orientation also impressed folks at STScI immediately, Villard said. "What's spectacular about that, which we noticed when the pictures first were taken, is that you can actually see the shadow from the moon skirting across the ring plane," he told Space.com. "That would only happen at a unique time, just like a setting sun."

Software was used to morph a dozen images, during each of these orbital slices of time, into the hundreds of images needed for the movies.

The images were taken by the Hubble's Wide Field Planetary Camera 2 in 1995 and the Advanced Camera for Surveys in 2003.

Movie details

The shortest edge-on ring movie shows the moons Titan and Tethys orbiting Saturn. The moons follow the rings' thin line in their orbit around Saturn. Titan's shadow is the first to appear, moving across Saturn's disk. Titan follows, with Tethys appearing on the left from behind the planet. The moons seem to move much faster than they actually do because several hours of viewing time (images were taken over a 10.5-hour span) were compressed to make the movie, which also shows bands of clouds that make up Saturn's atmosphere.

The longer edge-on ring movie shows the icy moons Mimas, Enceladus, Dione and Tethys rounding Saturn. Enceladus appears first with Mimas right behind. Both moons cast small shadows on the planet, and Enceladus casts a shadow on the rings. Mimas' orbit is too inclined to hit the rings. Dione then appears with a long shadow that tracks across the ring system. Tethys appears only briefly as it moves behind the planet on the right. The images for this movie were taken over a 9.5-hour span.

The maximum ring-tilt movie first shows Saturn spinning. Although the rings rotate with the planet, they appear to be stationary because the ring material is spread out so evenly. Saturn rotates on its axis every 10 hours, more than twice as fast as Earth.

Next, the movie offers a close-up of Saturn's southern hemisphere. Astronomers enhanced the contrast in this sequence to make Saturn's banded cloud structure more obvious. The images for this movie were taken over a 24-hour span.

NASA's Voyager and Cassini missions also have generated movies of Saturn. Cassini has been at Saturn since July 2004, studying the planet, its moons and its ring system.

"Cassini has shown us those moons are so diverse that it's like finding a little solar system unto itself," Villard said.

• VIDEO: Hubble Space Telescope’s Saturnian Movies
• VIDEO: The Cassini Probe Crosses Saturn’s Rings
• VIDEO: Enceladus – Saturn’s Old Faithful
• The Best Hubble Space Telescope Images
• Complete Coverage of the Hubble Space Telescope
• Hubble Gets Superb View of Saturn and Rings
• IMAGES: New Snapshots of Saturn
• IMAGES: Imagining Saturn and Titan
• All About Saturn

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Imagining Saturn and Titan

Pretty cool!
From Space.com:

A possible view of the Titan surface; shoreline of a small methane lake with haze and clouds above. Terrain made with Cassini radar data. (made with the grey scale map I made from the 'shoreline' Titan radar map). These artist renderings by Kees Veenenbos are based on real spacecraft data.