Saturn’s rings form a giant dusty doughnut encircling the planet

Motes of dust from Rings of Saturn They appear to float much further above and below the planet than scientists thought possible, suggesting that the rings are more like a giant dusty donut.

The underlying structure of Saturn's rings is extremely thin, extending outward for tens of thousands of kilometers but vertically for only 10 meters, creating spectacular appearance as seen from Earth. However, there are some variations in this shape, such as the plumper outer E ring, powered by Saturn's moon Enceladus, which ejects ice from its underwater ocean.

Now, Frank Postberg of the Free University of Berlin and his colleagues analyzed data from NASA's Cassini spacecraft during 20 orbits in 2017, the final year of the mission, when it took an extremely steep path through the rings, starting at distances three times the radius of Saturn above the planet and ending at similar distances below.

The Cassini spectrometer, the Cosmic Dust Analyzer, detected hundreds of tiny rocky particles at the top of Cassini's trajectory that had a chemical composition similar to grains found in the main ring, with low iron content. “This is a really special spectral type that we will never see again anywhere in the Saturn system,” Postberg says.

“There are many more objects close to the ring plane, but it is still surprising that we see these ring particles so high, both above and below the ring plane,” he says.

To rise so high, more than 100,000 kilometers from the main ring, Postberg and his team calculated that the particles would need speeds of more than 25 kilometers per second to escape Saturn's gravity and magnetic forces.

It's unclear what process could give them that speed, Postberg says. The simplest explanation is that tiny meteorites crash into the rings and scatter particles, but this does not produce shrapnel fast enough.

However, micrometeorites colliding with Saturn's rings can create temperatures high enough to vaporize the rock, according to a recent study that found Saturn's rings are much older. than previously thought. Postberg and his colleagues suggest that this vaporized rock could be ejected from the rings at much greater speeds than shrapnel and then condense at distances far from the planet.

Surprising to find dust so far from the main ring, says Frank Spahn from the University of Potsdam in Germany, who was not involved in the study. That's because particles in Saturn's main ring are small, meaning they collide infrequently, and they're sticky, so collisions tend to be more like snowballs hitting each other than billiard balls, he says.

Micrometeorite impacts occur throughout the solar system, so the same could happen on other ringed planets such as Uranus. “If you hit icy rings at high speed, the process could be universal. You might expect similar dust halos above and below other rings,” Postberg says.

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