Posted on behalf of Rick Lovett

Mysterious ripples in Jupiter’s rings, first observed when the Galileo spacecraft passed by in 1996, were caused by the impact of Comet Shoemaker-Levy 9 into Jupiter in 1994, scientists reported on 5 October, at the annual meeting of the American Astronomical Society’s Division for Planetary Sciences, in Pasadena, California.

The ripples, generated by the impact of fast-moving dust particles from the fragmented comet [corrected], have evolved over time, progressively winding more and more tightly, like a coiling rope, said Mark Showalter of the SETI Institute, Mountain View, California, and Joseph Burns of Cornell University, Ithaca, New York. By mathematically turning back the clock, the scientists uncovered two sets of ripples, one tracing to 1994, and the other to an unknown event in 1990.

Such ripples have also been discovered in Saturn’s C and D rings, where they appear to reflect an event in 1983 or 1984, the scientists said.

The simple passage of an asteroid, like a giant bullet, couldn’t have produced such widespread disruption, the scientists added. Instead, it required a shotgun blast of smaller particles, such as would be produced by broken-up comet.

“The rings are witness plates for cometary impacts, giving their frequencies and sizes,” Burns added. And, he noted, “The evolution of the corrugations shows how the rings respond to abrupt disturbances, and tell about the planet’s gravity.”

Comets aren’t the only cause of ripples. In the same symposium, Philip Nicholson of Cornell University described a narrow gap in the C ring (see illustration), with a raised edge on one side, and a dipped one on the other, each about 1.5 kilometers tall. “It’s like a snapped-up hat rim, Humphrey Bogart style,” he said. This feature, and adjacent ripples seem to have been set off by a resonance with the gravity of the giant moon Titan. “It’s yanking the ring particles up due to the inclination of its orbit,” he said.

Illustration: Matthew Hedman, Cornell University