Saturn's rings are much younger than the planet itself, and likely formed only in the last 100 million years. That's according to a new analysis of observations from NASA's Cassini spacecraft.
Cassini was launched in 1997 and entered the orbit of Saturn in 2004. While the mission is now over, the data collected by the spacecraft is still helping scientists discover new information about the planet, its moons, and other features of the sixth planet in the Solar System, including the age of its rings.
Saturn is believed to have come into existence about 4.5 billion years ago. The conventional belief is that the planet's rings were also formed at the same time as Saturn itself, from icy debris left in orbit around the planet.
However, many researchers increasingly think that the rings are quite young, and were created after the gravitational pull of Saturn tore apart an icy moon or a comet.
While these rings were originally made of bright ice, they were darkened over time by the debris coming from the outer reaches of the Solar System. A few years back, Cassini spacecraft determined that the amount of impurity in Saturn's rings was about one per cent. If scientists could determine the mass of Saturn's rings, they could easily estimate their age by calculating the time taken by the rings to gather enough contaminants to become one per cent impure.
In 2017, when Cassini coasted between Saturn and its rings, its movement was influenced by the gravitational pull of the planet as well as the rings. This enabled the mission team to measure the mass and the gravity of both Saturn and the rings.
The data from Cassini suggested that the rings have a mass of about 15.4 million billion metric tons.
Based on the data, the researchers arrived at the conclusion that Saturn's rings were formed between 10 million and 100 million years ago.
Cassini also revealed many new details about Saturn's internal structure. It observed that jet streams around Saturn's equator extend to a depth of about 9,000 kilometres, rotating massive amounts of mass around the planet. It was also found that Saturn's gravitational field was actually much higher than earlier predicted, and that the field is influenced by how fast Saturn's internal matter spins.
"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 Luciano Iess, of Rome's Sapienza University and lead author of the study.
"And with this work, Cassini fulfils 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 of the study are published in journal Science.
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Saturn's rings only formed in the past 100 million years, suggests analysis of Cassini space probe data
New findings contradict conventional belief that Saturn's rings were formed along with the planet about 4.5 billion years ago