Image: Propeller-shaped structure on Saturn's rings
A close-up shot of one of the propeller-shaped structures in the rings of Saturday. The image, released July 8, 2010, was obtained by NASA's Cassini spacecraft of the unlit side of Saturn's rings.
updated 7/8/2010 4:55:47 PM ET 2010-07-08T20:55:47

Giant propeller-shaped structures have been discovered in the rings of Saturn and appear to be created by a new class of hidden moons, NASA announced Thursday.

NASA's Cassini spacecraft spotted the distinctive structures inside some of Saturn's rings, marking the first time scientists have managed to track the orbits of individual objects from within a debris disk like the one that makes up Saturn's complicated ring system.

"Observing the motions of these disk-embedded objects provides a rare opportunity to gauge how the planets grew from, and interacted with, the disk of material surrounding the early sun," said the study's co-author Carolyn Porco, one of the lead researchers on the Cassini imaging team based at the Space Science Institute in Boulder, Colo. "It allows us a glimpse into how the solar system ended up looking the way it does."

Photos of the propellers taken by Cassini show them to be huge structures several thousands of miles long. By understanding how they form, astronomers hope to glean insight into the debris disks around other stars as well, researchers said.

The results of the study are detailed in the July 8 issue of the journal Astrophysical Journal Letters.

Propellers at Saturn
Cassini scientists have seen double-armed propeller structures in Saturn's rings before, but on a smaller scale than the larger, newfound features. They were first spotted in 2006 in an area now known as the "propeller belt," which is located in the middle of Saturn's outermost dense ring the A ring.

The propellers are actually gaps in the ring material were created by a new class of objects, called moonlets, that are smaller than known moons but larger than the particles making up Saturn's rings. It is estimated that these moonlets could number in the millions, according to Cassini scientists.

The moonlets clear the space immediately around them to generate the propeller-like features, but are not large enough to sweep clear their entire orbit around Saturn, as seen with the moons Pan and Daphnis. (Photos of Saturn rings and moons.)

But in the new study, researchers a new legion of larger and rarer moons in a separate part of the A ring, farther out from Saturn. These much larger moons create propellers that are hundreds of times larger than those previously described, and these objects have been tracked for about four years.

The study was led by Cassini imaging team associate Matthew Tiscareno at Cornell University in Ithaca, N.Y.

The propeller features for these larger moons are up to thousands of miles long and several miles wide. The moons embedded in Saturn's rings appear to kick up ring material as high as 1,600 feet above and below the ring plane.

This is much greater than the typical ring thickness of about 30 feet, researchers said.

Hidden Saturn moons
Still, the Cassini spacecraft is too far away to see the moons amid the swirling ring material that surrounds them. Yet, scientists estimate that the moons measure approximately half a mile in diameter, based on the size of the propellers.

According to their research, Tiscareno and his colleagues estimate that there are dozens of these giant propellers. In fact, 11 of them were imaged multiple times between 2005 and 2009.

One such propeller, nicknamed Bleriot after the famous aviator Louis Bleriot, has shown up in more than 100 separate Cassini images and one ultraviolet imaging spectrograph observation during this time.

"Scientists have never tracked disk-embedded objects anywhere in the universe before now," said Tiscareno. "All the moons and planets we knew about before orbit in empty space. In the propeller belts, we saw a swarm in one image and then had no idea later on if we were seeing the same individual objects. With this new discovery, we can now track disk-embedded moons individually over many years."

Over their four years of observation, the researchers noticed shifts in the orbits of the giant propellers as they travel around Saturn, but the cause of these disturbances have not yet been determined.

The shifting orbits could be caused by collisions with other smaller ring particles, or could be responses to these particles' gravity, the researchers said. The orbital paths of these moonlets could also be altered due to the gravitational attraction of large moons outside of Saturn's rings.

Scientists will continue to monitor the moons to see if the disk itself is driving the chances, similar to the interactions that occur in young solar systems. If so, Tiscareno said, this would be the first time such a measurement has been made directly.

"Propellers give us unexpected insight into the larger objects in the rings," said Linda Spilker, Cassini project scientist based at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Over the next seven years, Cassini will have the opportunity to watch the evolution of these objects and to figure out why their orbits are changing."

NASA launched the Cassini probe in 1997 and it arrived at Saturn in 2004, where it dropped the European Huygens probe on the cloudy surface of Titan, Saturn's largest moon. Cassini was slated to be decommissioned in September of this year, but received a life extension that now runs through 2017.

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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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