WASHINGTON (AFP) - Saturn's rings are younger than scientists thought and appeared within the last 10 to 100 million years, according to research published on Thursday (Jan 17) based on findings from Nasa's Cassini spacecraft.
The sixth planet from the Sun formed about 4.5 billion years ago, along with the rest of the planets in our solar system, and spent the bulk of its existence without the characteristic rings it is known for today.
Astronomers have long believed the rings could be young, and perhaps formed by collisions between the moons of Saturn or by a comet that shattered in close proximity to the planet.
Some of these answers have come into sharper focus because of Cassini, an unmanned United States-European probe that launched in 1997 and ended in 2017 with a planned death plunge into Saturn's surface.
At the end of its mission, Cassini made 22 orbits, circling between Saturn and its rings, getting closer to them than any spacecraft in history.
By studying how the flight path of Cassini was deflected by the gravity of the rings, scientists were able to deduce the rings' mass and approximate age.
"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 lead author Luciano Iess of Sapienza University of Rome.
Understanding the rings' age and mass is "a fundamental goal of its mission", he added.
A lesser mass indicates younger rings because as they age, the rings would attract more debris and grow heavier.
The rings are made up of 99 per cent ice.
The study did not delve into the question of where the rings came from, but supported theories such as a comet or moon collision.