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Saturn’s rings studied using stellar occultation

A stellar occultation occurs with the light from a star is blocked by an intervening body (such as a planet, moon, ring, or asteroid) from reaching an observer. The main reason for observing stellar occultations is that they can be used to probe ring systems and atmospheres in the outer solar system with spatial resolutions of a few kilometers-several orders of magnitude better than the resolution of any other Earth-based method.

Scientists from the University of Colorado at Boulder have used the technique to make observations of Saturn’s rings with tremendous clarity. Their insrtrument on the Cassini-Huygens spacecraft was pointed through the rings toward a star, Xi Ceti. The fluctuations of starlight passing through the rings provide information on the structure and dynamics of the particles within them.

The size of the ring particles varies from dust specks to mountains, with most ranging between marbles and boulders.

The Cassini observations show dramatic variations in the number of ring particles over very short distances. The particles in individual ringlets are bunched closely together, with the amount of material dropping abruptly at the ringlet edge.The sharp edges of small ringlets are especially evident in the C ring and in the so-called Cassini Division on either side of the bright B ring, Saturn’s largest ring.

The Cassini observations show that the distance between the presence and absence of orbiting material at some ring edges can be as little as 160 feet, or 50 meters, about the length of a typical commercial jetliner, he said.

The stellar occultation process also shows very high-resolution views of several density waves visible in the rings, including a previously unstudied one. Density waves are ripple-like features in the rings caused by the influence of Saturn’s moons. The density waves, which resemble a tightly wound spiral much like the groove in a phonograph record, slowly propagate away from the resonance toward the perturbing moon. The shapes of these wave peaks and troughs help scientists understand whether the ring particles are hard and bouncy, like a golf ball, or soft and less bouncy, like a snowball.

A density wave analysis by scientists involved in NASA’s Voyager 2 mission that visited Saturn in 1981 were used to determine the mass and thickness of the planet’s rings.

posted by: kyawoo at 11:35 | link | comments |
saturn, astronomy

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