Are Saturn’s Rings Really as Young as the Dinosaurs?

The Cassini spacecraft perished in a literal blaze of glory on September 15, 2017, when it ended its 13-year study of Saturn by intentionally plunging into the gas giant’s swirling atmosphere . The crash came after a last few months of furious study, during which Cassini performed the Grand Finale — a sensational, death-defying dance that saw the spacecraft dive between the planet and its rings 22 times.Original story reprinted with permission from Quanta Magazine, an editorially independent publication of the Simons Foundation whose mission is to enhance public understanding of science by covering research develop­ments and trends in mathe­matics and the physical and life sciences.|||As new perspectives often do, this one revealed a surprise. Previously, planetary scientists had assumed that Saturn’s rings were as old as the solar system itself—about 4.5 billion years old. But cosmic clues hidden deep within the rings caused some Cassini scientists to massively revise this figure. The rings aren’t as old as the solar system, they argued in a paper published this summer in the journal Science. They emerged no more than 100 million years ago, back when dinosaurs roamed Earth.
An explosion of media coverage linking the rings to the age of dinosaurs helped to quickly solidify the new findings in the public’s eye. If you enter the search phrase “how old are Saturn’s rings,” Google returns the answer “100.1 million years.”Aurélien Crida, a planetary scientist at the Côte d’Azur Observatory, was incredulous at this definitive declaration. “I was a bit pissed off by how it was assessed, that the rings are young, and it’s over,” he said.He and other skeptics have pointed out that there are a lot of potential problems with the argument, from the physics of the ring pollution to the origins of the rings themselves. “The rings look young, but that doesn’t mean the rings are really young,” said Ryuki Hyodo, a planetary scientist at the Japanese Aerospace Exploration Agency. “There are still some processes that we are not considering.”
The rings were named alphabetically in the order they were discovered. Starting from the innermost ring, the D ring is followed by the C, B, A, F, G and E rings.Video: NASA/JPL-Caltech/Space Science Institute
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.

Illustration: Lucy Reading-Ikkanda/Quanta Magazine, Source: NASA/JPL-Caltech/Space Science Institute; NASA’s Goddard Space Flight Center