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Enceladus 'Feeds' Ring

Tiny Icy Moon 'Feeds' Giant Saturn Ring

How did those beautiful rings of Saturn form?

This is one of the big mysteries people have wondered about since the rings were discovered. Answering this question is a key science objective for the Cassini mission. Cassini has found a partial answer by discovering that the moon Enceladus is 'feeding' Saturn's largest ring, the E-ring.

During a close flyby of Enceladus on July 14, 2005, Cassini's cosmic dust analyzer directly measured that Enceladus' south pole is spewing tiny ice grains that are being scooped up into the expansive E-ring. This flyby was so close, within 175 kilometers (109 miles), that it allowed the spacecraft to take a direct sniff at Enceladus and measure the distribution of the freshly produced grains within the E-ring. The instrument found that slow-moving dust grains cannot escape the moon's gravity and are trapped to form a cloud around the moon. But the faster dust grains get away from Enceladus and replenish Saturn's E ring.

One Ring to Rule Them All

This discovery is the first direct confirmation that the moons of Saturn are responsible for forming one of Saturn's rings. This information may play a key role in deciphering how the other rings of Saturn formed.

Diagram of Saturn's Rings
Saturn's Rings

Saturn's rings are an enormous, complex structure. From edge-to-edge, the ring system would not even fit in the distance between Earth and the Moon. The seven main rings are labeled in the order in which they were discovered. From the planet outward, they are D, C, B, A, F, G and E.

Saturn's remarkable E-ring is the largest planetary ring in our solar system, spanning all the way from Mimas' orbit to Titan's orbit, about 1 million kilometers (621,370 miles). It is by far the most extended ring around Saturn.

Making the Ring

Until recently scientists assumed that the dust at Enceladus was produced by a process similar to that observed at the Galilean moons of Jupiter: micrometeoroids striking the moon's surface blasting dust particles loose. However, the Cassini data show that the E ring is being replenished not only by dust particles from micrometeoroid hits on the surface of Enceladus but also from grains expelled from possible vents located in the south polar region. The possibility of vents is revealed by a higher surface temperature detected by Cassini's composite and infrared spectrometer, which detected temperature differences at the south pole.

Cassini's 'Bag of Tricks'

Zooming in on Enceladus

Cassini is proving that having multiple instruments, capable of in situ measurement and remote-sensing, is invaluable. Its entire bag of tricks is helping solve the Saturnian-ring puzzle. At Enceladus several instruments have detected a localized atmosphere at the south pole, while another has detected huge temperature differences. The discoveries have turned the picture of Enceladus from a dead, cold body into an active, warm moon. The next Enceladus flyby is March 2008.

The measurements that confirmed Enceladus as the source of the E-ring were performed using the high rate detector, a subsystem of the cosmic dust analyzer. The detector was developed by the University of Chicago. The cosmic dust analyzer is operated by scientists at the Max Planck Institute for nuclear physics in Heidelberg, Germany. Design and preliminary analysis of the measurements is based on models which were developed in the University of Potsdam, Germany.

Additional information on the Cassini mission is available at: and .

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. The Cassini orbiter was designed, developed and assembled at JPL.