Oh My, Saturn Is Losing Its Rings!

Saturn’s ring particles are following the planet’s magnetic field straight into its atmosphere. At the rate the material is draining away, the rings may only be around for another 100 million years — a very short time compared to the 4.5-billion-year age of the solar system. NASA’s Goddard Space Flight Center/David Ladd

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.

Saturn’s rings are composed mostly of water ice mixed with a trace of rocky material. Each chunk orbits the planet as it were a separate tiny moon. NASA

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.

Bathed in ultraviolet light from the sun and zapped by meteoroid impacts, tiny particles blasted by the impacts become electrically charged and track toward the planet along its magnetic field as “ring rain.” NASA

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.

Artist’s view of ring particles spiraling down Saturn’s invisible magnetic field lines (similar to those in a bar magnet) into the upper atmosphere. NASA

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.

An artist’s impression of how Saturn may look in the next hundred million years. The innermost rings disappear as they rain onto the planet first, very slowly followed by the outer rings. NASA/Cassini/James O’Donoghue

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.

Temporary beauty? This image was made as the Cassini spacecraft scanned across Saturn and its rings on April 25, 2016. NASA/JPL-Caltech/Space Science Institute

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!

6 Responses

  1. Edward M. Boll

    With Wirtanen now in the morning, it has solar system company in the east. This morning as I got up early for work, I saw how empty the sky would have been without planets.I looked at Venus, then Mercury. Then I did a double take.What I saw looked like a double Mercury. Was I seeing things? I even kidded myself that I had seen a super nova. Then, getting more awake it came to me. The star below Mercury was a reutnkng morning Jupiter.

  2. Edward M. Boll

    Another question. Has Wirtanen achieved for us it’s full glory now, not considering moonlight. As it’s altitude increases night after night so should it’s hours of visibility as it slowly fades.

    1. astrobob

      Yes, it should begin to fade now since it’s both past perihelion and moving away from the Earth. I’m hoping for a possible appearance of a visible tail as our perspective on the comet changes.

  3. Troy

    I wonder if the partial rings of Neptune (actually regions of more concentrated ring material) are the remnants of a more grander ring system that has underwent decay.

    1. astrobob

      Hi Troy,
      Could be — I wondered the same. Maybe a future study will reveal particles there draining into the planet’s field.

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