Astronomers have long believed that Saturn’s unique rings formed at the same time as the planet about 4.5 billion years ago in the early days of our Solar System. That hypothesis received a serious challenge from a 2019 analysis of data collected by NASA’s Cassini spacecraft, which suggested that the rings were 10 million to 100 million years ago — a blink of an eye. in the eye of cosmic time scales. Now, a new analysis of data on how much dust has accumulated in the rings confirms that controversial finding, according to a new paper published in the journal Science Advances.
“In a way, we got closure on a question that started with James Clerk Maxwell,” said co-author Sascha Kempf, an astronomer at the University of Colorado, Boulder. In 1610, Galileo Galilei was the first to observe the rings. , although his telescope was too crude to recognize these as actual rings. He described them as “Saturn’s ears” as they look like two small planets on either side of Saturn. Galileo was amazed when the “ears” disappeared in 1612 as they passed Earth through the ring plane, even more so when they were seen again the following year.
Christopher Wren suspected that Saturn had a ring in 1657, although Christiaan Huygens beat him to publication, suggesting that the ring was separated from the planet in his 1659 treatise. Saturnium system, who also noted his discovery of Saturn’s moon, Titan. Robert Hooke noticed the shadows of the rings. By 1675, Giovanni Cassini had figured out that the ring was a series of small rings with gaps between them. More than a century ago, Pierre-Simon Laplace mathematically demonstrated that any solid ring would be unstable. Maxwell determined that the “ring” must contain many small particles, all independently orbiting Saturn, confirmed by observations in 1859. Now we know that the particles are almost entirely ice water.
The Space Age made it possible to send probes to explore our Solar System, and Pioneer 11, Voyager 1, and Voyager 2 all sent more detailed images of the ringed planet. Then in 1997, NASA launched the Cassini orbiter, a joint venture with the European Space Agency to explore Saturn, its moons, and its ring system. Cassini spent 13 years orbiting the gas giant doing just that, providing stunning images of unprecedented resolution, as well as a host of scientific insights—including evidence that the so-called “ring rain” falling on the planet can cause the rings to gradually disappear. in less than 100 million years.
Among the instruments aboard Cassini is the Cosmic Dust Analyzer, whose data show that the rings are slowly but steadily contaminated with a mixture of rocky dust and other organic compounds—mostly from micrometeoroids in the Kuiper Belt. “Think of the rings like the carpet in your house,” says Kempf. “If there is a clean carpet laid, you have to wait. The dust will settle on your carpet. The same is true for the rings. ” That is important because an argument for a young age is that the water ice in Saturn’s rings is too bright and pure for structures believed to be 4.5 billion years old. Accumulated layers of dust should darken them even more.
During the spectacular “Grand Finale” in 2017, Cassini performed 22 dives between Saturn and its rings, enabling scientists to determine the mass of both before the spacecraft fell into its fiery orbit. death in the atmosphere of the gas giant. That Cassini data is what Luciano Iell of the Sapienza University of Rome and his co-authors relied on for their 2019 paper because they allowed to determine the amount of soot in the rings, the rate of its fall , and the age of the dust. . They concluded that the rings were no more than 100 million years old, emerging at a time when dinosaurs still roamed the Earth—a vivid detail that launched a thousand headlines and helped the idea gain traction. a fortress in the popular imagination. They also found that Saturn’s B Ring is too large to melt the inflowing dust, which would explain the relative purity of the ice particles.
Those results were met with skepticism by some, due to many uncertainties. Among the skeptics is Aurelien Crida, a planetary scientist at the Cote d’Azur Observatory, who published a rebuttal to Iell and so on. later that year in Nature Astronomy. To explain the lack of dust build-up in the rings, Crida suggested that a kind of “scrubber” on the planet prefers to remove the dust from the rings through ring rain. Cassini’s data show that this rain contains only 24 percent ice, compared to the rings themselves, which are 95 percent ice. Crida found a possible candidate for this scrubbing mechanism in a 2017 paper by Kempf’s group (published in the same special issue of Science), which noted the presence of nanograins that coalesce from the primary rings flowing through Saturn.