SATURN'S rings were the victim of a hit-and-run – and the culprits may be centaurs, strange objects that are part icy comet, part rocky asteroid.
In earlier work with images from the Cassini spacecraft, Matthew Hedman, now at the University of Idaho, noticed that two of the planet's rings sported alternating bright and dark bands. He argued they were low hills and valleys caused by a small comet that had smacked into the rings. The features could be seen getting smaller over time, suggesting the impact occurred in 1983.
Now, he and colleagues have found that the collision shoved the ring particles side to side as well as up and down. That let them work out the angle of the incoming object – nearly perpendicular to the ring plane.
Using data from the Minor Planet Center, they found two objects with the right orbit to be the perpetrators of the collision. Both were centaurs, travelling on unstable orbits in the outer solar system (Icarus, in press ).
The rings may not settle down any time soon, Hedman adds. There is evidence that similar patterns in other rings are hundreds of years old.
This article appeared in print under the headline "Centaurs galloped into Saturn's rings"
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