In 1983, an unseen comet struck the rings of Saturn. Almost a decade later, a comet collided with Jupiter. These events tilted and left residual ripple patterns in the rings of both planets, according to a pair of papers in Science that piece together a planetary puzzle.
Published online at ScienceExpress, the studies indicate that a planet’s rings can act like a giant record, preserving the effect of every passing comet. Studying the subtle spiral patterns these comets leave behind allows scientists to play back the history of impacts years and even decades later.
The findings may also provide a new way of studying comet populations in the outer solar system. By looking at changes in planetary rings, scientists may be able to figure out how often comets and other small objects encounter planets, and thus determine how many of these small objects exist in the outer solar system.
“Not only do the rings preserve records of events that happened decades ago, but it’s also remarkable that such large areas of the rings were disturbed so recently,” said Matthew Hedman, lead author of the Saturn study and astronomer at Cornell University.
This series of images shows how a vertical corrugation can be produced from an initially inclined ring, as in the case of the Saturn and Jupiter rings.The top image shows a simple inclined ring, while the lower two images show the same ring at two later times, where the ring particles' wobbling orbits have sheared this inclined sheet into an increasingly tightly-wound spiral corrugation. [Image courtesy of Science/AAAS]
Hedman continued: “It will be interesting to see whether these ring-tilting events can help constrain how much cometary debris is wandering around the outer solar system.”
Analyzing images of Jupiter’s rings observed in 1996 and 2000 by the Galileo spacecraft, and again in 2007 by the Horizon spacecraft, lead author Mark Showalter of the SETI institute and colleagues noticed unusual ripple patterns undulating like a tin roof in the rings of the planet.
Around the same time, Hedman and colleagues discovered similar ripple patterns in the rings of Saturn, from images taken by the Cassini spacecraft in 2009. The teams measured the properties of the ripples and compared them to calculations of how such structures should evolve over time.
Their analysis proved that the rippled rings of Saturn and Jupiter were caused by comets that plowed into the rings of the planets. The resulting debris from the smashes knocked the rings of both planets slightly off balance.
The researchers were able to pinpoint the exact years both events occurred. They show that Saturn’s ring ripples were likely generated by a comet collision in 1983, while Jupiter’s ring ripples occurred after the impact of Comet Shoemaker-Levy 9 in the summer of 1994.
“The Saturn images reveal how the ripples evolve, but not their cause. The Jupiter data prove that comets are the triggers,” said Showalter.