After poring over NASA‘s Cassini mission data, astronomers have determined that it takes the teamwork of seven moons to keep Saturn’s A ring – the largest and farthest of the visible rings – contained. Without forces to hold the A ring in check, the ring would keep spreading out and ultimately disappear.
For three decades, astronomers thought that only Saturn’s moon Janus confined the planet’s A ring. “Cassini provided detail on the mass of Saturn’s moons and the physical characteristics of the rings. So mathematically speaking, we concluded that the moon Janus alone cannot keep the rings from spreading out,” said the lead author of the new research Radwan Tajeddine from Cornell University in New York.
The scientists discovered that confinement of the A ring is shared among the moons Pan, Atlas, Prometheus, Pandora, Epimetheus, Mimas and Janus.
“All of these moons work as a group to contain the ring. Together they are strong. United they stand,” said Tajeddine. Gravitational pushes by these moons slow the ring down and pull momentum from it, according to the findings presented at the at the American Astronomical Society’s Division of Planetary Science meeting in Provo, Utah.
Cassini, which crashed into Saturn on September 15 at the mission’s end, provided valuable data and detailed images of the planet’s rings. “This was exactly the sort of information we had hoped the Cassini mission would provide, and by doing so it has allowed us to solve this puzzle,” said Joe Burns, Professor at Cornell University.
Scientists are still not sure how the rings formed, but the mechanism of their confinement is finally understood, Tajeddine said. “That’s the novelty of this idea. No one imagined that the rings were held by shared responsibility,” he said. “The density waves created by moons are beautiful to look at, but they actually participate in confining the ring,” Tajeddine said.