Whizzing asteroids and comets have battered Earth and all the other solid bodies of our solar system over the eons, but the ethereal rings of the giant planets seemed immune. No longer. In two papers published online today in Science, researchers report that comet impacts in recent decades have left their mark on the rings of both Saturn and Jupiter. In August 2009, the orbiting Cassini spacecraft caught sight of 20-meter-high corrugations rippling across 1500 kilometers of Saturn's inner C ring (regular, narrow bright bands, above), which is only about 10 meters thick. The corrugations turn out to be one continuous wave spiraling outward like the groove in a vinyl LP record. And in 2007, the New Horizons spacecraft on its way to Pluto imaged two wave sets spiraling through each other in the faint, dusty ring of Jupiter. One Jovian wave appears to be still on the move 13 years after fragments from comet Shoemaker-Levy 9 hit the ring on their way to pummeling Jupiter in 1994. But for any impacting object to hit a tenuous ring hard enough to tilt it and set off such reverberations, both teams agree, it would first have to disintegrate into a cloud of fine debris that can hit a broad area of ring. That's just what Jupiter's gravity did to Shoemaker-Levy 9.
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