Astronomers have always wondered whether Saturn’s rings have been around a long, long time or whether they were acquired much more recently. We now have an answer. New NASA research confirms that Saturn is rapidly losing material from its iconic rings as a dusty rain of ice particles pulled in by the planet’s gravity and funneled along its magnetic field straight down into the upper atmosphere.
“We estimate that this ‘ring rain’ drains an amount of water products that could fill an Olympic-sized swimming pool from Saturn’s rings in half an hour,” said James O’Donoghue of NASA’s Goddard Space Flight Center. O’Donoghue is the lead author of a new study on ring rain in the publication Icarus.
Combining information from the Voyager 1 and 2 Saturn flybys back in the early 1980s with more recent data from the NASA’s highly-successful Cassini mission, which measured “ring rain” rates, the rings have less than 100 million years left to survive. And based on the rate of infall, the rings are surprisingly young, possibly no older than 100 million years.
If you could go back in time and find a safe spot to set up a telescope between the velociraptors and brontosauruses, you’d have likely stared at a ringless Saturn. That means we’re seeing the rings today smack in the middle of their lifetime. It makes you wonder if the paltry ring systems presently visible around Jupiter, Uranus and Neptune were once as grand as Saturn’s is today.
Saturn’s rings are mostly made of chunks of water ice ranging in size from microscopic dust grains to boulders several yards (meters) across. Saturn’s gravity wants to draw in all this icy flotsam and jetsam, but their orbital speeds keeps the chunks where they’re at. Meanwhile, other forces are at work. Tiny ring particles can become electrically charged by ultraviolet light in sunlight, while bombardment by dust-sized micrometeorites creates puffs of similarly charged particles on impact. Once the particles have an electric charge, they can feel the pull of Saturn’s magnetic field and are drawn in by the pull of the planet’s gravity.
Between micrometeorite munching and UV light, the rings are being slowly eroded and siphoned into the planet’s upper atmosphere similar to how particles arriving in the solar wind are directed along Earth’s invisible magnetic field lines into the ionosphere, where they slam into atoms and spark auroras. At Saturn, once the ring particles arrive in the atmosphere they vaporize and react with other molecules that when energized by sunlight create glowing bands of infrared light that were detected by the dual 10-meter telescopes at the Keck Observatory in Hawaii. Infrared is a form of light we feel as heat.
Various theories have been proposed for the rings’ origin. If the planet got them later in life, they could have formed when small, icy moons in orbit around Saturn collided, perhaps prompted by a gravitational shove from a passing asteroid or comet. Another theory suggests that a comet or asteroid may have struck one of the planet’s moons, the debris spreading into the rings.
The first signs of ring rain appeared in Voyager 2 data in 1981 when scientists found weird variations in Saturn’s electrically-charge upper atmosphere, changes in the density of the rings and three dark bands encircling the planet at mid-northern latitudes. When the bands were later linked to the shape of Saturn’s gigantic magnetic field, another researcher proposed that electrically charged particles from the rings were flowing down the invisible field lines and dumping water (ice) into the planet’s atmosphere. The water washed away the haze, making it appear dark in reflected sunlight. Add in what we’ve learned recently from Cassini and the Keck observations, we finally have a finger on the pulse of the rings’ dissolution.
The team would like to see how the ring rain changes with the seasons on Saturn. Like the Earth, the tip of Saturn’s axis gives the planet seasons, with the rings exposed to varying amounts of sunlight during its 29.5-year orbit. Since ultraviolet light from the Sun charges the ice grains and makes them respond to Saturn’s magnetic field, varying exposure to sunlight should change the quantity of ring rain.
So, it looks like just 100 million years left? Better start counting ’em!