How Saturn's rings and inner moons were formed

According to a new study, Saturn's rings and inner moons were formed after the collision of a large satellite with the planet.

Saturn's rings are at present 90 to 95 percent water ice. Previous studies suggest that the rings formed when a small satellite was disrupted by an impacting comet.

"This scenario would have likely resulted in rings that were a mixture of rock and ice, rather than the ice-rich rings we see today," said Dr. Robin M. Canup, associate vice president of the SwRI Planetary Science Directorate in Boulder.

But the new study links the formation of the rings to the formation of Saturn's satellites.

Previous studies suggest that that multiple Titan-sized satellites originally formed at Saturn, but as their orbits spiralled into the planet, they were lost.

As they neared Saturn, the heat would cause its ice to melt and its rock to sink to its center. Such a satellite crosses the region of the current B ring, planetary tidal forces strip material from its outer icy layers, while its rocky core remains intact and eventually collides with the planet.

This produces an initial ice ring that is much more massive than Saturn's current rings.

"The new model proposes that the rings are primordial, formed from the same events that left Titan as Saturn's sole large satellite, " said Canup.

"The implication is that the rings and the Saturnian moons interior to and including Tethys share a coupled origin, and are the last remnants of a lost companion satellite to Titan."

During its extended mission, the Cassini spacecraft will measure the rings' current mass and will indirectly measure the pollution rate of the rings.