The rings of Saturn may have formed much later than the planet itself, according to a new analysis of gravity science data from NASA's Cassini spacecraft.
The findings, led by scientists from Rome's Sapienza University, indicate that Saturn's rings formed between 10 million and 100 million years ago. From our planet's perspective, that means Saturn's rings may have formed during the age of dinosaurs.
Saturn formed 4.5 billion years ago, in the early years of our solar system. There have been clues that its ring system is a young upstart that attached to Saturn years afterward. But how long afterward?
To figure out the age of the rings, scientists needed to measure the mass of the rings, or how much material they hold.
Researchers had the remote-sensing measurements from Cassini and both of NASA's Voyager spacecraft in the early 1980s. Then came Cassini's unprecedented, up-close data from its final orbits in 2017. As the spacecraft was running out of fuel, it performed 22 dives between the planet and the rings.
The dives allowed the spacecraft to act as a probe, falling into Saturn's gravity field, where it could feel the tug of the planet and the rings.
Radio signals sent to Cassini from the antennas of NASA's Deep Space Network and the European Space Agency relayed the spacecraft's velocity and acceleration.
Once scientists knew how much gravity was pulling on Cassini, causing it to accelerate - down to a fraction of a millimeter per second - they could determine how massive the planet is and how massive the rings are.
"Only by getting so close to Saturn in Cassini's final orbits were we able to gather the measurements to make the new discoveries," said Cassini radio science team member and lead author Luciano Iess, of Sapienza University of Rome.
"And with this work, Cassini fulfills a fundamental goal of its mission: not only to determine the mass of the rings, but to use the information to refine models and determine the age of the rings."
The findings were published in the journal Science.
The new evidence of young rings lends credence to theories that they formed from a comet that wandered too close and was torn apart by Saturn's gravity -- or by an event that broke up an earlier generation of icy moons.