The rings of Saturn appeared very recently, about 10 to 100 million years ago, say researchers in a study published Thursday in the journal Science, based on the final observations of the probe Cassini. This period roughly corresponds to the era of dinosaurs on Earth, which disappeared 65 million years ago.
Saturn, the sixth planet from the Sun, was formed four and a half billion years ago, at the beginning of the solar system, and therefore lived for most of its existence without its rings.
Planetologists had many clues to the relatively young age of the rings, perhaps formed by moon collisions of Saturn, or by the bursting of a comet that would have come too close to the planet. But their exact age had remained one of the great enigmas of the solar system.
The European-American Cassini spacecraft, launched in 1997 and bowed out in 2017, retrieved data to calculate this age. At the end of her mission, Cassini made 22 orbits, passing between Saturn and her rings and approaching them as never before, before deliberately disintegrating in the atmosphere of the planet, after it had run out of fuel.
Its instruments allowed the scientists of the mission to measure the gravitational forces exerted respectively by the rings and by the planet during these dives, and to infer the mass of the rings. This mass, combined with other data, then led to an estimate of age.
“Only by getting closer to Saturn in Cassini’s final orbits have we been able to collect data at the origin of these new discoveries,” said the lead author of the study, Luciano Iess, from the Italian University of Sapienza in Rome.
“With these works, Cassini fulfills the fundamental purpose of its mission: not only to determine the mass of the rings, but to use this information to refine the models and determine the age of the rings”.
As NASA explains, the smaller the mass, the younger the rings, because as they get older, the rings attract debris and become heavier.
The rings consist of 99% ice. The study does not answer the question of their origin, but reinforces the theories of a comet or collision of icy moons.