Cassini spacecraft image: Saturn's moons Tethys, Hyperion and Prometheus

The Cassini spacecraft captures a rare family photo of three of Saturn's moons that couldn't be more different from each other!

As the largest of the three, Tethys (image center) is round and has a variety of terrains across its surface.

Meanwhile, Hyperion (to the upper-left of Tethys) is the "wild one" with a chaotic spin and Prometheus (lower-left) is a tiny moon that busies itself sculpting the F ring.

To learn more about the surface of Tethys (660 miles, or 1,062 kilometers across), see PIA17164.

More on the chaotic spin of Hyperion (168 miles, or 270 kilometers across) can be found at PIA07683, and discover more about the role of Prometheus (53 miles, or 86 kilometers across) in shaping the F ring in PIA12786.

This view looks toward the sunlit side of the rings from about 1 degree above the ringplane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on July 14, 2014.

The view was acquired at a distance of approximately 1.2 million miles (1.9 million kilometers) from Tethys and at a Sun-Tethys-spacecraft, or phase, angle of 22 degrees.

Image scale is 7 miles (11 kilometers) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency.

The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C.

The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL.

The imaging operations center is based at the Space Science Institute in Boulder, Colo.

Moonlets created and destroyed in Saturn's F ring

Cassini spied just as many regular, faint clumps in Saturn's narrow F ring (the outermost, thin ring), like those pictured here, as Voyager did but it saw hardly any of the long, bright clumps that were common in Voyager images. 

Credit: NASA /JPL-Caltech /SSI

There is an ongoing drama in the Saturnian ring system that causes small moons to be born and then destroyed on time scales that are but an eyeblink in the history of the solar system.

SETI Institute scientists Robert French and Mark Showalter have examined photos made by NASA's Cassini spacecraft and compared them to 30 year-old pictures made by the Voyager mission.

They find that there is a marked difference in the appearance of one of the rings, even over this cosmologically short interval, a difference that can be explained by the brief strut and fret of small moons.

"The F ring is a narrow, lumpy feature made entirely of water ice that lies just outside the broad, luminous rings A, B, and C," notes French.

"It has bright spots. But it has fundamentally changed its appearance since the time of Voyager. Today, there are fewer of the very bright lumps."

The bright spots come and go over the course of hours or days, a mystery that the two SETI Institute astronomers think they have solved.

"We believe the most luminous knots occur when tiny moons, no bigger than a large mountain, collide with the densest part of the ring," says French.

"These moons are small enough to coalesce and then break apart in short order."

The F ring is at a special place in the ring system, at a distance known as the Roche limit, named for French astronomer Edouard Roche who first pointed out that if a moon orbits too close to a planet, the difference in gravitational tug on its near and far side can tear it apart.

This happens at a distance dependent on the mass of the planet, and in the case of Saturn, happens to be at the location of the F ring.

Consequently, material here is caught between the yin and yang of forming small moons, and having them pulled apart.

The moons in question are typically no more than 3 miles (5 km) in size, and consequently can come together quickly.

This chaotic region is given additional stir by Prometheus, a moon that's roughly 60 miles (100 km) in size that orbits just inside the F ring.

Every 17 years, Prometheus aligns with the F ring in a way that emphasises its gravitational influence on the ring's particles, precipitating the formation of the mini-moons, or moonlets.

"These newborn moonlets will repeatedly crash through the F ring, like bumper cars, producing bright clumps as they careen through lanes of material," says Showalter.

"But this is self-destructive behaviour, and the moons, being just at the Roche limit, are barely stable and quickly fragmented."

This scenario can explain the rapid variation in the number of bright clumps in the F ring, but is it true?

If the periodic influence of Prometheus is causing the waxing and waning of the clumps, then there should be an increase in their prevalence over the next few years, a prediction that the astronomers will be checking with Cassini data.

In addition to the drama of moons that come and go over less than a human lifetime, studies of the ring system give insight into how solar systems in general are built.

"The sort of processes going on around Saturn are very similar to those that took place here 4.6 billion years ago, when the Earth and the other large planets were formed," notes French. "It's an important process to understand."

This research was published in the online edition of the journal Icarus on July 15, 2014.

More information: Robert S. French, Shannon K. Hicks, Mark R. Showalter, Adrienne K. Antonsen, Douglas R. Packard, "Analysis of clumps in Saturn's F ring from Voyager and Cassini," Icarus, Volume 241, October 2014, Pages 200-220, ISSN 0019-1035, dx.doi.org/10.1016/j.icarus.2014.06.035 . Preprint: arxiv.org/abs/1408.2548

NASA Cassini Image: Saturn’s moon Pandora and the F Ring

Saturn’s moon Pandora (at right center) helps shape the narrow F ring. 

Pandora (50 miles, or 81 kilometers across) orbits outside the F ring. 

Another shepherd moon Prometheus (53 miles, or 86 kilometers across), orbits inside, both helping to prevent the ring from spreading. 

Cassini spacecraft took the image in visible light with the wide-angle camera on March 8, 2014. 

Image released Aug. 11, 2014.

Credit: NASA

Saturn's Moon Prometheus causes turbulence in it's F ring - video

Prometheus is caught in the act of creating gores and streamers in the F ring. 

Scientists believe that Prometheus and its partner-moon Pandora are responsible for much of the structure in the F ring.

Image Credit: NASA /JPL-Caltech /Space Science Institute (SSI)

The orbit of Prometheus (53 miles, or 86 kilometers across) regularly brings it into the F ring.

When this happens, it creates gores, or channels, in the ring where it entered. 

Prometheus then draws ring material with it as it exits the ring, leaving streamers in its wake.

This process creates the pattern of structures seen in this image.

This process is described in detail, along with a movie of Prometheus creating one of the streamer/channel features, in the image PIA08397.

This view looks toward the sunlit side of the rings from about 8.6 degrees above the ringplane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Feb. 11, 2014.

The view was acquired at a distance of approximately 1.3 million miles (2.1 million kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 147 degrees. Image scale is 8 miles (13 kilometers) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency.

The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission. You can also visit the Cassini imaging team homepage.

NASA Cassini Image: Prometheus practices its pull

NASA Cassini Image shows Shepherd moon Prometheus hovering just inside the reflective F ring. 

Credit: NASA /JPL-Caltech /Space Science Institute.

Lit by eerie, reflected light from Saturn's F ring (and a casting a faint shadow through a haze of icy "mist") Saturn's moon Prometheus can be seen in the raw image above, captured by Cassini's narrow-angle camera on Feb. 5 from a distance of 667,596 miles (1,074,392 km).

It's also receiving some light reflected off Saturn, which is off frame at the top (where the outermost edge of the A ring and the Keeler gap can be seen.)

As the potato-shaped Prometheus approaches the ring it yanks fine, icy material in towards itself, temporarily stretching the bright particles into long streamers and gaps and even kicking up bright clumps in the ring. It's a visual demonstration of gravity at work.

At its longest Prometheus is about 92 miles (148 km) across, but only 42 miles (68 km) in width.

It circles Saturn in a wave-shaped, scalloping orbit once every 14.7 hours.

NASA Cassini: Saturn's moon Prometheus sculpting the F Ring

Saturn's moons create art on the canvas of Saturn's rings with gravity as their tool. 

Here Prometheus is seen sculpting the F ring while Daphnis (too small to discern in this image) raises waves on the edges of the Keeler gap.

Prometheus (53 miles, or 86 kilometers across) is just above image center while Daphnis (5 miles, or 8 kilometers across), although too small to see in its location in the Keeler gap just to the right of center, can be located by the waves it creates on the edges of the gap. 

Prometheus and stars have been brightened by a factor of 2 relative to the rest of the image to enhance their visibility.

There are 20 stars visible in this image.

This view looks toward the unilluminated side of the rings from about 53 degrees below the ringplane. 

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Aug. 25, 2013.

The view was acquired at a distance of approximately 1.2 million miles (1.9 million kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 111 degrees. 

Image scale is 7 miles (11 kilometers) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. 

The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C.

The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL.

The imaging operations center is based at the Space Science Institute in Boulder, Colo.

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

The Cassini imaging team homepage is at ciclops.org .

Image credit: NASA/JPL-Caltech/Space Science Institute

NASA Cassini: Snowballs caught crashing into Saturn's weirdest ring

Saturn's weirdest ring is known for its sparkling displays, but now it's been caught in the act. NASA's Cassini spacecraft has captured the first video of snowballs crashing into the planet's distant F-ring, creating a mini-jet of sparkling ice crystals.

The event was captured while Cassini was filming Saturn's moon Prometheus approaching the ring. The moon, which orbits just inside the F-ring, following an elliptical path, brushes up against it every 17 years. During its approach, it's thought to create a ripple in the icy ring's geometry which causes snowball-like pieces to break off. These icy fragments are then thought to quickly crash back into it causing a sparkling mini-jet.

Based on the video, researchers were able to calculate the orbital direction and speed of the snowballs. Results indicate that they followed a very similar orbit to Prometheus and hit at a slow speed of about one meter per second. This points to the culprit being small snowballs created during the moon's previous approach, which survived and went on to strike through the F-ring itself.

"We had seen these mini-jets right from day one but, like most things with the F-ring, it's trying to understand what you're seeing," says Carl Murray, a Cassini imaging team member based at University of London in the UK. The group has found 500 such mini-jets after looking through 25 images of the F-ring. They now plan to examine them more closely to see if they fit the same description as the one caught on film.

NASA Cassini: Flaring fairy lights of Saturn's F ring

One of Saturn's rings is flaring and fading in a very strange fashion.

When Voyager 1 visited the planet in 1980, the ring was faint, but it sparkled with bright spots.

By the time the Cassini mission arrived in 2004, the spots were gone – but the ring as a whole had grown twice as bright.

Saturn's F ring has been a puzzle since it was discovered by the Pioneer 11 spacecraft in 1979.

While most of the inner rings have clear, well-defined edges, the F ring, which is the outermost of Saturn's main rings, has a thin central core surrounded by a diffuse skirt of smoke-sized ice particles.

That swirl of smoke forms kinks and knots, and some of it winds around the ring's core in a spiral.

Most of these funny features can be blamed on the little moon Prometheus, which orbits just inside the F ring.

As its elliptical orbit brings Prometheus towards and away from the ring on a 17-year cycle, the moon contorts the ring with its gravity.

It even steals material from the ring when it comes too close, as its mythical namesake stole fire from the gods.

"We knew the F ring changed on a day to day and even hour to hour basis because of interactions with Prometheus," says Robert French, a research assistant at the SETI Institute in Mountain View, California.

"But people always assumed it was stable over the longer term, over decades if not millennia."

So French and colleagues got a surprise when they compared images from the Voyager 1 and 2 missions, which zipped past Saturn in 1980 and 1981, with images from the Cassini spacecraft, which has been orbiting the planet since July 2004.

They found that the ring was twice as bright in 2004 as it was in 1980. It had also grown three times as wide and twice as opaque.

"All of that means there's a lot more dust today than there used to be," French says. Those tiny particles scatter sunlight, so when there are more of them the whole ring shines more brightly.

French's first thought was to blame Prometheus. But while Prometheus's orbit brought it closer to the F ring over the first 5 years of Cassini's stay in the Saturn system, the ring didn't change.

"That's very puzzling," French says. "People usually think of Prometheus as the cause of changes in the F ring, and Prometheus was making large changes in how it interacted with the F ring. Yet the F ring wasn't changing."

Cassini Image: Saturn's Rings and Prometheus

A crescent Saturn appears nestled within encircling rings in this Cassini spacecraft image.

Clouds swirl through the atmosphere of the planet and a barely visible Prometheus orbits between the planet's main rings and its the thin F ring.

Saturn's moon Prometheus appears as a speck above the rings near the middle of the image.

This view looks toward the southern, unilluminated side of the rings from about 3 degrees below the ringplane.

The image was taken with the Cassini spacecraft's wide-angle camera on Sept. 14, 2010, and was obtained at a distance of approximately 1.6 million miles, or 2.6 million kilometers, from Saturn and at a sun-Saturn-spacecraft, or phase, angle of 100 degrees.

Image Credit: NASA/JPL/Space Science Institute

Prometheus: Violent History Of Saturn's White Whale Moon

Saturn's potato-shaped moon Prometheus is rendered in 3D in this close-up from Cassini. Image credit: NASA/JPL/Space Science Institute

Like the battered white whale Moby Dick taunting Captain Ahab, Saturn's moon Prometheus surges toward the viewer in a 3-D image from NASA's Cassini spacecraft.

The image exposes the irregular shape and circular surface scars on Prometheus, pointing to a violent history. These craters are probably the remnants from impacts long ago.

Prometheus is one of Saturn's innermost moons. It orbits the gas-giant at a distance of about 140,000 kilometers (86,000 miles) and is 86 kilometers (53 miles) across at its widest point. The porous, icy world was originally discovered in images taken by NASA's Voyager 1 spacecraft back in 1980.

Cassini's narrow-angle camera captured two black-and-white images of the moon on Dec. 26, 2009, and the imaging team combined the images to make this new stereo view.

It looks different from the "egg-cellent" raw image of Prometheus obtained on Jan. 27 because that view shows one of the short ends of the oddly shaped moon. In this 3-D image, the sun illuminates Prometheus at a different angle, making the moon's elongated body visible.

NASA Prometheus acting on Saturn's Rings

The effects of the small moon Prometheus loom large on two of Saturn's rings in this image released by NASA.

The gravity of Prometheus periodically creates streamer-channels in the F ring.The image was taken in visible light with the Cassini spacecraft narrow-angle camera.

The view was acquired at a distance of approximately 1.8 million kilometres (1.1 million miles) from Saturn

Picture: AFP/GETTY / NASA

Cassini snaps Prometheus

Prometheus is one of Saturn's innermost moons.

Looking for all intents and purposes like a celestial egg after a session in Saturn's skillet, Prometheus displayed its pockmarked, irregular surface for NASA's Cassini spacecraft on Jan. 27, 2010.

It orbits the gas-giant at a distance of 139,353 kilometers (85,590 miles) and is 86 kilometers (53 miles) across at its widest point.

The porous, icy-bodied world was originally discovered by images taken by Voyager 1 back in 1980.

You could say this latest "egg-cellent" view has the Cassini science team licking their chops at the thought of future Prometheus images.

This raw, unprocessed image of Prometheus [pro-MEE-thee-us] , taken in visible light, was obtained by Cassini's narrow-angle camera at a distance of approximately 36,000 kilometers (23,000 miles).