The dazzling array of rings around the planet Saturn may have formed relatively recently in the solar system’s history when two icy moons collided and were smashed into millions of fragments, a study suggests.
For most of its history, more than four billion years, Saturn hung naked in the heavens without its famous rings, which formed just a few hundred million years ago, researchers have said.
They say two moons that once circled the planet met their demise in a spectacular crash, scattering icy debris that still circles Saturn in the bright disc visible today.
Jupiter, Uranus and Neptune all have faint rings around them, but they are dwarfed in size and splendour by those that encircle Saturn, a gas giant that is second largest planet in the solar system. Although less than 100 metres thick in some places, the banded ring system is made of water ice and so is highly reflective in the sunlight and clearly visible through a telescope.
The Cassini spacecraft spent 13 years in orbit around Saturn, even diving between the planet and its innermost ring. The probe confirmed that the rings are made of almost pure ice. It also confirmed that the chunks of ice — some as small as grains of sand, others as large as mountains — have accumulated little dust on their surface, suggesting that they were created recently in astronomical terms.
Using Durham University’s Cosma supercomputer, researchers from Durham and Glasgow University worked with Nasa to simulate more than 200 collisions between two icy moons and see how the debris might have been dispersed in orbit around Saturn.
Any debris thrown further away from Saturn, beyond a boundary known as the Roche limit, would probably have clumped together to form new moons. Objects that orbit within the Roche limit, a distance of about two or three times the radius of a planet, will either be torn apart or will remain fragmented, unable to clump together under their own gravity because of the strong gravitational pull of the planet. Any debris from a collision between two moons that was scattered close to Saturn would have formed a disc of icy fragments.
The results, published in the Astrophysical Journal, confirm that a collision of this kind could have formed Saturn’s rings within the past few hundred million years. The two moons involved would have been similar in size to two of Saturn’s extant moons: Dione, about 700 miles in diameter, and Rhea, which is 950 miles wide.
Luis Teodoro, of Glasgow University, said: “The apparent geological youth of Saturn’s rings has been a puzzle since the Voyager probes sent back their first images of the planet. This collaboration has allowed us to examine the possible circumstances of their creation, with fascinating results.”
