Saturn Spent Billions of Years Without Its Rings

Gwen Vasquez
January 21, 2019

Estimates of the age of Saturn's rings vary widely. Their age was determined by studying doppler-shifted radio signals from the doomed Cassini spacecraft.

After analyzing the final set of orbits in September 2017, however, the extent to which Cassini's trajectory was deflected initially didn't make sense.

From Cassini's super-close vantage point, immersed in Saturn's gravity field, the spacecraft relayed measurements that led the team to another surprising discovery.

The masses of Saturn's fainter D, F, G and E rings are considered negligible, the researchers wrote. This is much younger than Saturn, which formed about 4.5 billion years ago. He said there is a flux of "contaminant particles" present around Saturn that is sprayed onto the rings at a constant rate.

Saturn's rings are much younger than the planet itself, and likely formed only in the last 100 million years.

In the final phase of NASA's Cassini mission, the spacecraft dived between Saturn and its innermost ring, at altitudes 1,616-2,423 miles (2,600-3,900 km) above the cloud tops. 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.

Scientists had previously relied on density waves, or ripples, through the rings caused by the motion of the 62 moons in Saturn orbit to estimate ring mass. So the planet could've existed without its rings for an extremely long time - up to 4,490,000,000 years. According to the new data, the core features a mass of roughly 15 to 18 Earth masses.

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The outcome of this jet, the origin of which is now uncertain, is that by speeding up the rotation of the outer 15% of the planet, it increases the centrifugal force, resulting in part of the outer atmosphere uplifting slightly, affecting the planet's gravitational pull. "This is to say that to my very great amazement Saturn was seen to me to be not a single star, but three together, which nearly touch each other".

The length of a day on each of our solar system's planets ranges from a mere 10 hours on Jupiter, all the way up to 5,832 hours on Venus.

In addition to revealing the age of Saturn's rings, the gravity measurements taken during Cassini's close passes allowed the team to uncover more information about the planet's gaseous interior structure. Scientists reached this conclusion after seeing that they had a small mass.

Iess was especially excited by the measurements of the planet itself, which revealed that its gravitational field differed from initial expectations. Low on fuel, it plunged into the atmosphere of Saturn, to avoid crashing onto the planet's moons.

"I think it is incredibly telling that we have now seen several separate results, using very different techniques, that have all independently suggested a surprisingly short age for Saturn's rings", says Tom Stallard of the University of Leicester and a co-author of the Icarus paper. "It was easier to believe that it formed at the same time as Saturn and its satellites did", Nicholson says. But because the rings have some gravitational pull, Cassini deviated a bit from that path, and scientists can work backwards from that to figure out the mass of the rings.

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.

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