Prometheus: the Michelangelo of Saturn


I’ve frequently said the Cassini spacecraft is an artist, so when Carolyn Porco, the mission’s imaging team lead, mentioned on Twitter that Saturn’s moon Prometheus is akin to Michelangelo, I had to take a look. Wow, this gorgeous image is suitable for framing! Visible in the perturbed, thin F ring, is the potato-shaped Prometheus, and having performed the perturbing, it continues in its orbit. Click the image for the super-huge version.

Prometheus (148 kilometers, 92 miles across) periodically creates streamer-channels in the F ring, and the moon’s handiwork can be seen as the dark channels. Here’s a movie made from Cassini images showing this process:

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on June 1, 2010. A star is also visible through the rings near the center right of the image.

There are also some additional features in the F ring, courtesy of Prometheus.

This Cassini image shows icy particles in Saturn’s F ring clumping into giant snowballs as the moon Prometheus makes multiple swings by the ring. Scientists say that the gravitational pull of the moon sloshes ring material around, creating wake channels that trigger the formation of objects as large as 20 kilometers (12 miles) in diameter.

“Scientists have never seen objects actually form before,” said Carl Murray, a Cassini imaging team member based at Queen Mary, University of London. “We now have direct evidence of that process and the rowdy dance between the moons and bits of space debris.”

Read more about these fans and snowballs in this JPL article.


Mini Moons Are Buzzing Through Saturn’s Rings

Scientists for NASA’s Cassini mission noticed some weird-looking propeller-like shapes in the outer edge of Saturn’s A ring. What could be creating these unusual contours? A closer look revealed they were being formed by dozens of moving moonlets. Normally, these kilometer-sized moons would have been almost impossible to see, since they are embedded within the rings. “However, their presence is betrayed by the large tell-tale ‘propeller’ structures they generate in the ring material on either side of them,” said Carolyn Porco, leader of the Cassini imaging team, and co-author on a new paper on these propeller moons. In an email, Porco said similar features had been seen earlier in other locations in Saturn’s rings, but were “much smaller, harder to see, and so numerous that there was no hope of following any one of them. The new propellers, and the moonlets that create them, are some ten times larger and much easier to identify and follow from image to image and year to year.”


The team said the ability to watch as the embedded moons’ orbits evolve over time could give scientists valuable new clues about how planets form and grow around stars in young solar systems.

“What is outstanding about these new findings is the insight they ultimately will provide into the early stages of solar system formation,” said Porco, “when growing planets become large enough to open gaps in the ring material around them and ultimately truncate their own growth.”

The scientists have tracked eleven of these moons since 2006. Most are between one and several kilometers in diameter, too small to be imaged directly by Cassini’s cameras, but are only distinguishable by the unique double-armed propeller features.

The area in the middle of Saturn’s outermost dense A ring is now known as the “propeller belts,” and the new moonlets have been given appropriate names.

“You may find it amusing that these large propellers have unofficially been named after famous aviators,” Porco said. “Those flight enthusiasts among you will recognize Bleriot, Earhart, Santos-Dumont, and others.”

Cassini caught sight of Blériot (named after a French aviator) more than 100 times, allowing the researchers to map its path in detail. The propeller shape it created is several thousand kilometers long, or half the distance across the continental United States.

“You would expect any object that’s just orbiting Saturn on its own should stay in a constant path,” said lead author Matthew Tiscareno from Cornell University. “What we actually see is that the orbits are changing.”

The most likely explanation, he said, is that the moons are actually interacting with the disk: exchanging angular momentum with the ring particles around them either through gravity or by direct collisions.

Still, other explanations, like resonant interactions with more distant moons, have not been ruled out as causes.

Scientists will be keeping an eye on these wandering little moons in order to figure out if the disk itself is driving the changes, similar to the interactions that occur in young solar systems. If it is, Tiscareno said, this would be the first time such a measurement has been made directly.

Read the team’s paper.

More images at CICLOPS

Sources: NASA, Cornell, Porco email

Cassini the Artist: Shadows, Ringshine, Double Crescent Moons

I often ponder whether the Cassini spacecraft is a better scientist or artist. I found three recent images from Cassini that definitely give the nod to artist, but surely there’s lots of great science here as well. In this image, Saturn casts its shadow on the rings, but it also shows how the rings reflect sunlight onto the dark side of the planet. Here Saturn appears dimly illuminated by this ringshine. This view looks toward the southern, unilluminated side of the rings from about 10 degrees below the ringplane, and was taken on Jan. 2, 2010 when Cassini was about 2.3 million kilometers (1.4 million miles) from Saturn. Below: beautiful moons.

Two moons, with Saturn's rings. Image Credit: NASA/JPL/Space Science Institute

While this image is stunningly gorgeous, perhaps the most amazing thing is that it was snapped by Cassini’s cameras just yesterday (March 15, 2010) and beamed back to Earth today! This is a raw, uncalibrated image and the only details posted about it is that the camera was pointing toward Tethys at approximately 2,410,546 kilometers away. Can anyone guess what the second moon is?

Double crescent moons. Credit: NASA/JPL/Space Science Institute.

Another beauty, Dione and Titan make a smiling pair of crescent moons. This image was taken on March 12, 2010 and received on Earth March 13, 2010. The camera was pointing toward Dione at approximately 2,211,699 kilometers away.

For more great images see the Cassini website, or the CICLOPS website

Saturn’s Rings Have Gone Plaid

Are Saturn’s rings spinning at ludicrous speeds? It appears they have gone plaid! The Cassini spacecraft has actually spied two types of waves in Saturn’s A ring: a spiral density wave on the left of the image and a more pronounced spiral bending wave near the middle. And the “plaid” look comes from the slight pixelation visible near the brightest and darkest lines, which the Cassini team says is an unavoidable result of the size of the camera’s sensor and of image processing.

And if you don’t get the “plaid” reference, go watch Spaceballs.

The image was taken in visible green light with the Cassini spacecraft narrow-angle camera on Jan. 11, 2010 at a distance of approximately 279,000 kilometers (173,000 miles) from Saturn.

Source: Cassini

Scientists Find Water Ice Creates the Spokes in Saturn’s B Ring


The mysterious spokes that sometimes appear in Saturn’s largest ring, the B ring, have been unexplained. But new measurements from Cassini’s Visual Infrared Mapping spectrometer (VIMS) suggests the radial spokes that sometimes form across the ring are entirely composed of water ice. The existence of the spokes were unexpected and were first observed when the Voyager spacecraft flew by Saturn in 1980. When Cassini arrived at Saturn in 2004, the spokes were not visible, but later appeared in 2005; the VIMS instrument was not able to observe the spokes until 2008. Even with this new information, the spokes are still mysterious, as they appear to be a seasonal phenomenon and can become visible and then fade within a few hours. The process that creates and dissipates the spokes is unknown.

Another view from Cassini of spokes. Credit: Credit: NASA/JPL/Space Science Institute

Early hypotheses on the spokes speculated that gravitational forces and/or electrostatic repulsion between ring particles played a role in creating the spokes. One clue was that the spokes are more commonly observed when Saturn’s rings are more nearly edge on to the Sun. Other scientists had suggested ice, but believed the spokes were composed mainly of smaller ice grains. However, the new data show a large portion of the grains are larger than expected; a micrometer or more in radius.

E. D’Aversa and his team from the Institute for Interplanetary Space Physics in Rome, Italy used the VIMS instrument on Cassini to observe the infrared spectrum emitted by these spokes on July 9, 2008. These were the first measurements of the complete reflectance spectrum of the spokes in a wide spectral range (0.35–0.51 ?m). The team said that radiative transfer modeling supports a pure water ice composition for the spoke’s grains, but their size distribution is found to be wider than previously thought.

The preliminary results showed a modal value of about 1.90 ?m (reff = 3.5 ?m, veff = 0.3) and a number density of about 0.01–0.1 grains/cm3. The researchers say the unexpected abundance of micron-sized grains in the spokes may have implications for the formation models since the energy requirement increases by at least one order of magnitude. Future observations could help constrain the size as well as shed more light on the how the spokes form, evolve and change.

Paper: The spectrum of a Saturn ring spoke from Cassini/VIMS

The Sound of Saturn’s Rings

This wonderful video was posted by Jennifer Ouellette on Discovery News, and I just had to share it. The sounds are actual recordings picked up by the Cassini spacecraft. I have heard the eerie audio before, but never had previously seen it paired up with moving images from the mission. The radio emissions, called Saturn kilometric radiation, are generated along with Saturn’s auroras, or northern and southern lights. Cassini’s Radio and Plasma Wave Science (RPWS) instrument takes high-resolution measurements that allow scientists to convert the radio waves into audio recordings by shifting the frequencies down into the audio frequency range.
Continue reading “The Sound of Saturn’s Rings”

What are Saturn’s Rings Made Of?

Saturn is sometimes called the ”Jewel of the Solar System” because its ring system looks like a crown. The rings are well known, but often the question ”what are Saturn’s rings made of” arises. Those rings are made up of dust, rock, and ice accumulated from passing comets, meteorite impacts on Saturn’s moons, and the planet’s gravity pulling material from the moons. Some of the material in the ring system are as small as grains of sand, others are larger than tall buildings, while a few are up to a kilometer across. Deepening the mystery about the moons is the fact that each ring orbits at a different speed around the planet.

Saturn is not the only planet with a ring system. All of the gas giants have rings, in fact. Saturn’s rings stand out because they are the largest and most vivid. The rings have a thickness of up to one kilometer and they span up to 482,000 km from the center of the planet.

The rings are named in alphabetical order according to when they were discovered. That makes it a little confusing when listing them in order from the planet. Below is a list of the main rings and gaps between them along with distances from the center of the planet and their widths.

  • The D ring is closest to the planet. It is at a distance of 66,970 – 74,490 km and has a width of 7,500 km.
  • C ring is at a distance of 74,490 – 91,980 km and has a width of 17,500 km.
  • Columbo Gap is at a distance of 77,800 km and has a width of 100 km.
  • Maxwell Gap is at a distance of 87,500 km and has a width of 270 km.
  • Bond Gap is at a distance of 88,690 – 88,720 km and has a width of 30 km.
  • Dawes Gap is at a distance of 90,200 – 90,220 km and has a width 20 km.
  • B ring is at a distance of 91,980 – 117,580 km with a width: 25,500 km.
  • The Cassini Division sits at a distance of 117,500 – 122,050 km and has a width of 4,700 km.
  • Huygens gap starts at 117,680 km and has a width of 285 km – 440 km.
  • The Herschel Gap is at a distance of 118,183 – 118,285 km with a width of 102 km.
  • Russell Gap is at a distance of 118,597 – 118,630 km and has a width of 33 km.
  • Jeffreys Gap sits at a distance of 118,931 – 118,969 km with a width of 38 km.
  • Kuiper Gap ranges from 119,403 -119,406 km giving it a width of 3 km.
  • Leplace Gap is at a distance of 119,848 – 120,086 km and a width of 238 km.
  • Bessel Gap is at 120,305 – 120,318 km with a width of 10 km.
  • Barnard Gap is at a distance of 120,305 – 120,318 km giving it a width of 3 km.
  • A ring is at a distance of 122,050 – 136,770 km with a width of 14,600 km.
  • Encke Gap sits between 133,570-133,895 km for a width of 325 km.
  • Keeler Gap is at a distance of 136,530-136,565 km with a width of 35 km.
  • The Roche Division is at 136,770 – 139,380 km for a width 2600 km.
  • F ring is begins at 140,224 km, but debate remains as to whether it is 30 or 500 km in width.
  • G ring is between 166,000 – 174,000 km and has a width of 8,000 km.
  • Finally, we get to the E ring. It is between 180,000 – 480,000 km giving it a width of 300,000 km.

As you can see, a great deal of observation has been dedicated to understanding and defining Saturn’s rings. Hopefully, having the answer to ”what are Saturn’s rings made of” will inspire you to look more deeply into the topic.

We have written many articles about Saturn for Universe Today. Here’s an article about the orbit of Saturn, and here’s an article about the temperature of Saturn.

If you’d like more info on Saturn, check out Hubblesite’s News Releases about Saturn. And here’s a link to the homepage of NASA’s Cassini spacecraft, which is orbiting Saturn.

We have recorded two episodes of Astronomy Cast just about Saturn. The first is Episode 59: Saturn, and the second is Episode 61: Saturn’s Moons.

Source: NASA

Cassini Finds Patterns and Rhythm in Saturn’s Rings


Cassini has been orbiting around Saturn for almost four years, and amazingly, the spacecraft keeps discovering new and unexpected features about this world and its system of rings and moons. Recently, in two of Saturn’s rings, Cassini found orderly lines of densely grouped, boulder-size icy particles that extend outward across the rings like ripples from a rock dropped in a calm pond. Surprisingly, the distances between these ring particles stay relatively equal even though their velocities may change. This type of pattern is completely new, as normally, the distances between particles change with their velocity.

The pattern was detected when Cassini sent out three signals toward Earth. The signals crossed Saturn’s rings, and the frequencies were scattered from the passing ring particles. Once the signals were captured by Earth-based antennas of NASA’s Deep Space Network, Cassini scientists saw a regular pattern in the received signal frequencies.

“This particular feature is the smallest and most detailed of anything seen in Saturn’s rings so far,” said Cassini radio science team member Essam Marouf. “In the chaotic environment of the rings, to find such regularity in the most cramped areas is nothing short of amazing.” The regular structure can only be found in locations where particles are densely packed together, such as the B ring and the innermost part of the A ring. The signals were sent to capture a complete view of the rings.

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

Scientists call this pattern of particles “enormously extended natural diffraction grating.” A diffraction grating has parallel lines like a picket fence; when light hits this fence, it separates according to wavelength, from ultraviolet to infrared light.

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

Original News Source: Cassini Press Release