Why Saturn's Rings Disappear Twice | A Journey to Saturn

Are Saturn's rings disappearing? In November twenty twenty-five, from Earth, they very nearly did. You know this planet. Everyone does — it is the one that looks like a drawing. But the rings you picture are a temporary thing, twice over: once by a trick of angles that fooled Galileo, and once for real. Tonight we go there, and we count what is left. This is Saturn as NASA's Cassini spacecraft saw it in twenty sixteen, near the end of thirteen years in orbit. Saturn's main ring system is about two hundred and eighty thousand kilometres across, yet typically only about ten metres thick. Laid beside Earth, the rings would stretch three-quarters of the way to the Moon — and in most places be no thicker than a house. Saturn is the sixth planet from the Sun and the farthest planet known since antiquity — the farthest easily seen with the unaided eye. Search for Saturn in Universe Finder, then fly to it. The map places the planets in a symbolic cluster around the Sun, with the catalogue's stars beyond them — a way to find your bearings, not a model of the planets' true scale. Saturn orbits about one point four billion kilometres from the Sun — nine and a half times Earth's distance — where sunlight takes eighty minutes to arrive. The first vanishing is a trick of angles. Saturn's axis is tilted almost twenty-seven degrees — a little more than Earth's twenty-three — so over its twenty-nine-year orbit the rings tip toward us, then away. These Hubble photographs, taken from nineteen ninety-six to two thousand, show the rings opening up year by year. About every fifteen years Earth passes through the ring plane; the rings turn exactly edge-on and, from Earth, all but vanish. Think of a sheet of paper: turn it edge-on and it is a line; thin it to the proportions of Saturn's rings and the line is gone. Galileo saw it first: in sixteen ten Saturn seemed to have two companions; by the autumn of sixteen twelve they were gone, and he never solved the puzzle. The truth waited for Christiaan Huygens and a better telescope, in sixteen fifty-five — thirteen years after Galileo's death. Hubble photographed the rings edge-on on the twenty-second of May, nineteen ninety-five — a planet with a hairline. It happened again in twenty twenty-five: the exact crossing, in March, was hidden in the Sun's glare, and around the twenty-third of November the rings were a near-edge-on hairline from Earth. The second vanishing is real. Saturn's gravity and magnetic field pull charged icy grains out of the rings and down into the planet as 'ring rain' — observations imply a rate that could fill an Olympic swimming pool about every half hour. Ring rain alone would empty the rings in about three hundred million years; if the extra material Cassini saw falling in near the equator kept falling at that rate, they would be gone in under a hundred million. Cassini's final measurements weighed the rings at about forty percent of the moon Mimas — so light and so clean that one reading puts their age at only ten to a hundred million years, though newer models allow rings far older that simply stay clean. If that young reading is right, the first dinosaurs — two hundred and thirty million years ago — may have looked up at a Saturn with no rings at all. If so, we are alive in a brief window when Saturn wears its rings. Go and look while they last. Saturn is the farthest planet you can easily see with your own eyes: a bright, steady, yellowish point in the night sky. Every number in this film is measured or labelled as an estimate, and every image carries its credit. The sources are in the description. Where should we fly next — Jupiter, or the Ring Nebula? Tell us below. Fly. Explore. Discover. UniverseFinder.com.