Saturn’s rings may be no more than 400 million years old

The earliest trilobites may have evolved before Saturn donned its icy hoops

An image of Saturn and its rings.

Saturn’s icy, ethereal rings cast a shadow on the planet in this picture captured by NASA’s now-defunct Cassini spacecraft.

JPL-Caltech/NASA, Space Science Institute

Saturn’s rings might have formed while trilobites scuttled about on Earth. Space dust has been accumulating on the icy halos for no more than 400 million years, researchers report in the May 12 Science Advances.

The 4.5-billion-year-old planet appears to have acquired its iconic ornamentation relatively recently, says physicist Sascha Kempf of the University of Colorado Boulder. “We’re quite lucky to see a ring in the first place.”

The rings of Saturn are made of countless icy particles, which become covered with dust as tiny meteoroids strike them. These dustings darken the rings’ complexion, like mud sullies snow on roads in winter.

This cosmic staining was key to the new analysis, as was the now-defunct Cassini spacecraft’s Cosmic Dust Analyzer. From 2004 to 2017, the instrument caught dust-sized micrometeoroids moving around Saturn, measuring their velocity, mass, charge and composition.

Kempf and colleagues identified about 160 particles — out of millions — that could have hailed from beyond the Saturn system. The researchers estimated the rate at which the incoming dust accumulates on Saturn’s rings, and calculated how long it would have taken to darken the rings to their observed color. The planet’s hoops might have materialized more than 100 million years after trilobites — mysterious, extinct invertebrates — appeared on Earth, the team found (SN: 8/30/19).

The age of the rings has been debated for decades (SN: 10/20/16). Even after the new study, there’s still disagreement.

If the rings are somehow losing dust over time, they could be ancient, says planetary scientist Aurélien Crida of Université Côte d’Azur in Nice, France, who was not involved in the study. “Possibly as old as Saturn.”

It seems clear that the rings have been exposed to micrometeoroid impacts for at least a hundred million years, Crida says. But simulations of the rings’ formation from the gravitational shredding of an early moon suggest their size is consistent with an age of billions of years, he says. And researchers have reported silicate grains falling from the rings into Saturn’s atmosphere (SN: 10/4/18). Some unidentified process might be cleaning the rings of the micrometeoroid dust, making them appear younger than they are, Crida says.

Alternatively, the previously reported falling dust might come from meteoroid impacts that shatter ring ice, Kempf says.

Experiments that smash micrometeoroids into ice particles could help resolve the discrepancy, Crida says. For now, the debate over the age of the rings lives on.

Nikk Ogasa is a staff writer who focuses on the physical sciences for Science News. He has a master's degree in geology from McGill University, and a master's degree in science communication from the University of California, Santa Cruz.

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