In response to the hypothesis, Crida co-authored a commentary for Nature Astronomy, published in September, that presented a litany of uncertainties. The dinosaurian age of the rings is an eye-catching claim, said Crida, but it circumvents an uncomfortable reality: Too many uncertainties exist to permit any firm estimate of the age of the rings. Despite Cassini’s heroics, “we’re not really far ahead of where we were almost 40 years ago,” back when the Voyager probes first took a good look at Saturn, said Luke Dones, a planetary scientist at the Southwest Research Institute in Boulder, Colorado.

Proponents of the younger age stand by their work. “Every new exciting result gets challenged,” said Burkhard Militzer, a planetary scientist at the University of California, Berkeley and a co-author of the Science paper. “It’s the natural way to proceed.”

The debate is about more than the narrow question of the rings’ age. The age of Saturn’s rings will influence how we understand many of Saturn’s moons, including the potentially life-supporting world Enceladus, with its frozen ocean. And it will also push us closer to answering the ultimate question about Saturn’s rings, one that humans have wondered about since Galileo first marveled at them over 400 years ago: Where did they come from in the first place?

Age From a Scale

We know the age of the Earth because we can use the decay of radioactive matter in rocks to work out how old they are. Planetary geologists have done the same for rocks from the moon and Mars.

Saturn’s rings, predominantly composed of ice fragments with trace amounts of rocky matter, don’t lend themselves to this kind of analysis, said Matthew Hedman, a planetary scientist at the University of Idaho. That means age estimates have to be based on circumstantial evidence.

That evidence, in part, comes from dust. Think of the icy rings as resembling a field of snow: After a pristine start, soot from afar gradually pollutes it. In order to estimate the age of the snow, scientists have to measure the rate at which soot is falling, as well as the total amount of soot already there.

Cassini did the first part with its Cosmic Dust Analyzer, which found that Saturn’s rings are being steadily polluted by darker material — a mixture of rocky dust and organic compounds. Most of this material is being delivered by micrometeoroids from the Kuiper belt, a distant source of icy objects beyond the orbit of Neptune. The spacecraft also found that the sooty material currently makes up about 1% of Saturn’s icy rings.

To uncover the total mass of cosmic soot in the rings, researchers then had to weigh the rings themselves. Thankfully, Cassini’s Grand Finale created just such an opportunity. As the spacecraft swooped through the rings, it precisely measured the net gravitational pull at every point. Since gravity fields are dependent on an object’s mass, this feat allowed scientists to directly weigh the entire ring system.