How Saturn got its rings: a ‘recent’ smash between icy moons
For most of its history, more than four billion years, Saturn hung naked in the heavens without its famous rings.
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, for 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.
Two moons that once circled the planet met their demise in a spectacular crash, scattering icy debris that still circles Saturn in the bright disk visible today, according to their study.
Jupiter, Uranus and Neptune all have faint rings around them, but these are dwarfed in size and splendour by those that orbit Saturn, the gas giant and second largest planet in the solar system. Although they are less than 100 metres thick in some places, the complex set of banded rings is made of water ice and so is highly reflective in the sunlight, making it clearly visible from Earth.
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 very little dust on their surface, suggesting that they were created relatively recently in astronomical terms.
Using the Cosma supercomputer, researchers at Durham and Glasgow universities worked with NASA to simulate more than 200 collisions between two icy moons to model how the debris from these collisions could 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 due to 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 disk 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 last few hundred million years. They found that these moons would have been similar in size to two of Saturn’s extant moons: Dione, which measures around 700 miles in diameter, and Rhea, which is 950 miles wide.
Dr Luis Teodoro, of the University of Glasgow, 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.”
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