Glittering trails of giant snowballs seen in weirdest ring of Saturn

Weird half-mile-sized objects have now been seen punching through what may be Saturn's strangest ring, leaving sparkling trails behind them. And researchers say these findings could shed light on the oddball behavior of that ring.

The Saturnian ring in question is the planet's F ring, the outermost discrete ring of the planet. The F ring is unusually active, with features changing on a timescale as short as a few hours.

"I think the F ring is Saturn's weirdest ring," said researcher Carl Murray at Queen Mary University of London.

Scientists have known that Saturn's moon Prometheus and other relatively large objects can generate channels, ripples and snowballs in the F ring. However, it was uncertain what happened to these snowballs after they were created.

Now, using the Cassini probe to Saturn, Murray and his colleagues find these snowballs can tear through the F ring, leaving behind glittering trails the researchers are calling "mini-jets." Sometimes these snowballs traveled in packs, creating exotic-looking mini-jets resembling the barb of a harpoon. (Here's a NASA video of a close-up view of a mini-jet.)

"These findings show us that the F ring region is like a bustling zoo of objects from a half-mile in size to moons like Prometheus a hundred miles in size, creating a spectacular show," Murray said. "These latest Cassini results go to show how the F ring is even more dynamic than we ever thought."

Murray's group chanced upon a tiny trail in an image from Jan. 30, 2009, and tracked it over eight hours. The footage confirmed the snowball originated in the F ring. They next went back through the Cassini image catalog to see if the phenomenon was frequent.

"The F ring has a circumference of 550,000 miles, and these mini-jets are so tiny they took quite a bit of time and serendipity to find," said Nick Attree, a Cassini imaging associate at Queen Mary. "We combed through 20,000 images and were delighted to find 500 examples of these rogues during just the seven years Cassini has been at Saturn."

These snows apparently collide with the F ring at gentle speeds of about 4 miles per hour. These collisions drag twinkling ice particles out of the F ring with them, leaving a trail typically 20 to 110 miles long. The scientists presented their findings April 24 at the European Geosciences Union meeting in Vienna, Austria.

These findings are not only an extra piece of the complex puzzle that is the F ring, but they could help shed light on dusty rings in general, including the one around the sun that Earth and the other planets were once born from, said Linda Spilker, Cassini project scientist based at NASA's Jet Propulsion Laboratory. "We can't wait to see what else Cassini will show us in Saturn's rings," she added.