Cassini data suggests Saturn's rings are surprisingly young

Pablo Tucker
January 21, 2019

Previous attempts to deduce the gravitational pull of Saturn's rings from Cassini's trajectory didn't match the predictions of planetary models, but researchers realized strong winds originating deep within Saturn's' atmosphere had also influenced the probe's path. Their age was determined by studying doppler-shifted radio signals from the doomed Cassini spacecraft.

Cassini's view of Saturn during its final flyby of the gas giant.

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.

In cosmic terms, Saturn's rings won't last very long, and we may be very lucky to be around at the same time they are. Some believed they formed when the planet did 4.5 billion years ago, using icy debris leftover from the formation of the solar system.


In the next 100 million years, Saturn's rings will completely disappear, and, as revealed by a new Science study, planetary scientists have realized that it acquired its rings only very recently.

The first such opportunity came from Cassini in 2017, when the probe began performing "dives" over the rings, preparing for a heroic death in the atmosphere of Saturn.

The gravitational field measurements were different to what scientists expected. It also indicated that Saturn's atmospheric layers start rotating in sync deeper into the planet compared to Jupiter. But Saturn's precise day length has stumped scientists for decades. 17, 2019, an Italian-led team reported in the journal Science that the planet's primary rings appear to be 10 million to 100 million years old. This means that if humans were alive during the age of the dinosaurs, our instruments would have seen a lonely Saturn, without its signature bands. Saturn, which is mostly made up of hydrogen and helium, has an interesting atmosphere. Made up of heavy elements, the team found that the planet's core is about 15 to 18 Earth masses, or 15 percent of the total mass of the planet.

The fact that the rings of Saturn and other giant planets should gradually fade due to the fact that on the surface of their grains of ice must be deposited tiny particles of dust and organic matter, gradually darkening as a result of its "bombing" of the ultraviolet rays of the Sun. "While, on human timescales, it seems that Saturn will always have its rings, across the lifetime of the solar system, these rings are set to quickly fade into obscurity".


"Particles in the rings feel this oscillation in the gravitational field". Scientists reached this conclusion after seeing that they had a small mass.

"The researchers used waves in the rings to peer into Saturn's interior, and out popped this long-sought, fundamental characteristic of the planet". Or, perhaps one of Saturn's icy moons got whacked by an impact with a large comet.

It's possible the rings originally were denser than they are now and have thinned over time, which would put them more in line with Saturn's age. By knowing the mass of the rings, and how much of that mass is composed of dust (about 1%), the researchers were able to calculate how long it would have taken for the rings to accumulate that much dust.

So, Mankovich and his colleagues studied those observable waves and used them to backtrack inward to the planet itself.


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