Image: Saturn rings
NASA / JPL / SSI
The Cassini spacecraft's ultraviolet imaging spectrograph found that parts of Saturn's B ring are packed with clumps, called self-gravity wakes, separated by nearly empty gaps. The wakes are most pronounced in the blue areas of this false-color image. The yellow areas are so dense that starlight cannot pass through them.
updated 5/22/2007 3:47:17 PM ET 2007-05-22T19:47:17

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

The research also suggests that 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 at 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 that 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 compared 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.

Slideshow: From Earth to stars 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's data showed that 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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Photos: Best of Cassini

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  1. Starring Saturn

    This backlit view of Saturn was voted the favorite image to come from the Cassini orbiter - and it has been described as "perhaps the most stunning photograph ever taken." The image, captured on Sept. 15, 2006, shows two faint rings that were discovered by the Cassini team. And at the highest resolution, Earth itself appears as a pale blue dot just to the left of the brightest rings, at about the 10 o'clock position. (NASA / JPL / Space Science Institute) Back to slideshow navigation
  2. Dark rings

    An infrared image from the Cassini orbiter, acquired May 24, 2007, reveals clouds beneath the hazes in Saturn's atmosphere, as well as the unilluminated side of the giant planet's rings. The shadows of the rings fall upon the planet's cloud layer. This image shares the honors as the favorite black-and-white picture from Cassini. (NASA / JPL / Space Science Institute) Back to slideshow navigation
  3. Abstract art

    A Cassini image from May 10, 2006, shows the shaded edge of Saturn's disk, rounded by dark rings seen nearly edge-on. The crescent disk of Titan, Saturn's largest moon, can be seen in the background beyond the rings. This image shares the honors as the favorite black-and-white image from Cassini. (NASA / JPL / Space Science Institute) Back to slideshow navigation
  4. Pearly moons

    Two of Saturn's moons - Tethys and Enceladus - look like pearls backdropped by the planet's disk in this image, captured on July 24, 2007. The thin "string" connecting the pearls is actually the plane of the planet's rings, seen edge-on. The rings cast a dark shadow on Saturn's disk. Two other moons appear in this image, although they can barely be made out at the highest resolution: Hyperion is near the lower left corner of the image, and Epimetheus is the slightest of specks between Tethys and Enceladus. (NASA / JPL / Space Science Institute) Back to slideshow navigation
  5. Saturn from on high

    The Cassini spacecraft provides a high-contrast view of Saturn and its rings, as seen from above. This portrait is actually a mosaic of 36 images taken on Jan. 19, 2007, from about 40 degrees above the plane of the rings. (NASA / JPL / Space Science Institute) Back to slideshow navigation
  6. Shadows on clouds

    Saturn's darkened rings cast shadows on the planet's blue and gold cloud tops, while the moon Dione hangs like a dot in the black sky beyond. This image was taken by the Cassini spacecraft on Feb. 4, 2007, from a distance of about 800,000 miles. (NASA / JPL / Space Science Institute) Back to slideshow navigation
  7. View from below

    Cassini coasts beneath giant Saturn, staring upward at its gleaming crescent and icy rings. A great bull's-eye pattern is centered on the south pole, where a vast, hurricane-like storm spins. This view, obtained on Jan. 30, 2007, looks toward the lit side of the rings from about 26 degrees below the ring plane. (NASA / JPL / Space Science Institute) Back to slideshow navigation
  8. Pastel planet

    Dark and sharply defined ring shadows appear to constrict the flow of color from Saturn's warmly hued south to the bluish northern latitudes. Scientists studying Saturn are not yet sure about the precise cause of the color change from north to south. The different colors may be due to seasonal effects on the atmosphere. The images that went into this mosaic were obtained by the Cassini spacecraft on Feb. 4, 2007. (NASA / JPL / Space Science Institute) Back to slideshow navigation
  9. Ringing success

    This ultraviolet image from the Cassini spacecraft shows the detailed composition of Saturn's outer C and inner B rings from left to right, with the inner B ring beginning a little more than halfway across the image. The general pattern is from "dirty" red particles to the denser ice shown in turquoise as the ringlets spread outward. (University Of Colorado, LASP / AP) Back to slideshow navigation
  10. A is for amazing

    This ultraviolet image shows the A ring, beginning with a 'dirty' interior of red followed by a general pattern of more turquoise as it spreads away from the planet, indicating a denser material made up of ice. The red band roughly three-fourths of the way outward in the A ring is known as the Encke gap. (University Of Colorado, LASP - NASA / Reuters) Back to slideshow navigation
  11. Casting a shadow

    This image taken by Cassini shows the planet Saturn casting a shadow over its rings. (NASA - JPL - Caltech / Reuters) Back to slideshow navigation
  12. Titan revealed

    This is an infrared image of Titan, one of Saturn's moons, mapping the surface hidden beneath the moon's opaque atmosphere. Green areas represent water ice, while yellow areas have higher concentrations of hydrocarbons. The white spot is a methane cloud. (NASA) Back to slideshow navigation
  13. Ripples in the ring

    Scallops in the ring on the left side of this image were likely caused by a Saturnian moon rolling along the edge. One bright ringlet is visible within the gap, and at least one other faint ringlet can be made out. "This is textbook ring physics, right there, in one image," says Cassini imaging team leader Carolyn Porco. (NASA - SSI) Back to slideshow navigation
  14. Wisps in space

    A close-up of one of Saturn's rings shows a wispy pattern of ripples that may have been stirred up by a moonlet's orbit. Such unprecedented views of ring details are possible because of the Cassini camera's resolution. (NASA TV) Back to slideshow navigation
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