Revelations in Saturn's Rings Continue as Equinox Approaches

The Cassini spacecraft captured this image of a small object in the outer portion of Saturn's B ring. The Cassini spacecraft captured this image of a small object in the outer portion of Saturn's B ring casting a shadow on the rings as Saturn approaches its August 2009 equinox.
  • submit to reddit

August 07, 2009

Thanks to a special play of sunlight and shadow as Saturn continues its march towards its August 11 equinox, recent images captured by NASA’s Cassini spacecraft are revealing new three-dimensional objects and structures in the planet’s otherwise flat rings. The Cassini spacecraft captured this image of a small object in the outer portion of Saturn's B ring casting a shadow on the rings as Saturn approaches its August 2009 equinox.

This new moonlet, situated about 300 miles (480 kilometers), inward from the outer edge of the B ring, was found by detection of its shadow which stretches 25 miles, or 41 kilometers, across the rings. The shadow length implies the moonlet is protruding about 660 feet, or 200 meters, above the ring plane. If the moonlet is orbiting in the same plane as the ring material surrounding it, which is likely, it must be about 1,300 feet, or 400 meters, across. This object is not attended by a propeller feature, unlike the band of moonlets discovered in Saturn's A ring earlier by Cassini. The A ring moonlets, which have not been directly imaged, were found because of the propeller-like narrow gaps on either side of them that they create as they orbit within the rings. The lack of a propeller feature surrounding the new moonlet is likely because the B ring is dense, and the ring material in a dense ring would be expected to fill in any gaps around the moonlet more quickly than in a less dense region like the mid-A ring. Also, it may simply be harder in the first place for a moonlet to create propeller-like gaps in a dense ring.

The search for three-dimensional structures in Saturn's rings has been a major goal of the imaging team during Cassini's "Equinox Mission," the two-year period containing exact equinox -- that moment when the sun is seen directly overhead at noon at the planet's equator. This novel illumination geometry, which occurs every half-Saturn-year, or about 15 Earth years, lowers the sun's angle to the ring plane and causes out-of-plane structures to cast long shadows across the rings' broad expanse, making them easy to detect.

The new images can be found at http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini



Commotion at Ring's Edge May Be Effect of Small Icy Object NASA Cassini Images May Reveal Birth of a Saturn Moon

› Read more

In its next phase, NASA's Cassini spacecraft will perform 22 loops between Saturn and its innermost ring. Join in the Cassini Name Game

› Read more

Shadow Portrait of NASA Rover Opportunity on Martian Slope Cleaner NASA Rover Sees Its Shadow in Martian Spring

› Read more


Get JPL Updates
Sign Up for JPL UpdatesRegister today and receive up-to-the-minute e-mail alerts delivered directly to your inbox.
Sign Up for JPL Updates