To keep Saturn’s A ring contained, its moons stand united

Saturn’s moon Janus

Cassini maintains its reputation for surprises right to the end. It’s the ‘moon resonances’ that maintain ring stability, but with a new twist.

For three decades, astronomers thought that only Saturn’s moon Janus confined the planet’s A ring – the largest and farthest of the visible rings.

But after poring over NASA’s Cassini mission data, Cornell astronomers now conclude that the teamwork of seven moons keeps this ring corralled, as Phys.org explains.

Without forces to hold the A ring in check, the ring would keep spreading out and ultimately disappear.

“Casini 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 Radwan Tajeddine, a research associate in astronomy and lead author of the new research.

“What Confines the Rings of Saturn?” is planned for publication Oct. 18 in the Astrophysical Journal. Tajeddine also will present this research in a poster at the American Astronomical Society’s Division of Planetary Science meeting Oct. 17 in Provo, Utah.

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.

Cassini, which crashed into Saturn Sept. 15 at the mission’s end, provided valuable data and detailed images of the planet’s rings. The A ring looks similar to a vinyl record; it has “density waves” that resemble a record’s grooves that are created by what astronomers call moon resonances.

These resonance markers enabled scientists to deduce that the moons’ gravitational influence help to slow and reduce the spreading ring’s momentum.

Continued here.