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Comets gave rings their ripples

Ripples in the rings of Saturn and Jupiter are the consequence of collisions with cometary fragments, according to two papers.

Matthew Hedman at Cornell University in Ithaca, New York, and his colleagues spotted the ripple in one of Saturn's rings while analysing images taken by the Cassini spacecraft in 2009. Because a ripple's wavelength is related to how long ago it was created, the researchers calculated that this ripple began in 1983. They say that debris from a colliding comet crashed into particles in the ring, causing it to tilt and wobble.

Another group that included Hedman and was led by Mark Showalter at the SETI Institute in Mountain View, California, found two sets of ripples in images of Jupiter's rings taken by the Galileo and New Horizons spacecraft. The team reports that Jupiter's rings were hit by debris from two comets, the first of which struck in 1990 and the second in 1994. The authors associated this latter hit with a known Jupiter strike by the Shoemaker–Levy 9 comet in July 1994.

Monitoring the rings' wobble may help astronomers to map the internal structure of the planets' cores.

Science doi:10.1126/science.1202238 (2011); Science doi:10.1126/science.1202241 (2011)

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Comets gave rings their ripples. Nature 472, 8–9 (2011).

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