Queen Mary scientists working with images from NASA’s Cassini spacecraft have discovered strange half-mile-sized objects punching through parts of Saturn’s F ring, leaving glittering trails behind them. These trails in the rings, which scientists are calling ‘mini-jets’, fill in a missing link in our understanding of the curious behaviour of the F ring. The results were presented April 24 at the European Geosciences Union meeting in Vienna, Austria.
Scientists have known that relatively large objects like the moon Prometheus (as long as 92 miles across) can create channels, ripples and snowballs in the F ring. But until recently they didn’t know what happened to these snowballs after they were created.
Now Professor Carl Murray, Nick Attree, Nick Cooper and Gareth Williams from Queen Mary’s Astronomy Unit have found evidence that some of the smaller snowballs survive, and their differing orbits mean they go on to strike through the F ring on their own.
Professor Murray’s group happened to see a tiny trail in an image from 30 January 2009 and tracked it over eight hours. The long footage confirmed the small object originated in the F ring, so they went back through the Cassini image catalogue to see if the phenomenon was frequent.
“The F ring has a circumference of 550,000miles (881,000kilometers) 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.”
The small objects appear to collide with the F ring at gentle speeds — something on the order of about 4 mph (2 meters per second). The collisions drag glittering ice particles out of the F ring with them, leaving a trail 20 to 110 miles (40 to 180 kilometers) long.
Professor Murray commented: “I think the F ring is Saturn’s weirdest ring, and these latest Cassini results go to show how the F ring is even more dynamic than we ever thought. These findings show us that the F ring region is like a bustling zoo of objects from a half mile to moons like Prometheus a hundred miles in size, creating a spectacular show,” he added.
In some cases, the objects travelled in packs, creating mini-jets that looked quite exotic, like the barb of a harpoon. Other new images show grand views of the entire F ring, showing the swirls and eddies that ripple around the ring from all the different kinds of objects moving through and around it.
Linda Spilker, Cassini project scientist based at NASA’s Jet Propulsion Laboratory, commented: “Beyond just showing us the strange beauty of the F ring, Cassini’s studies of this ring help us understand the activity that occurs when solar systems evolve out of dusty disks that are similar to, but obviously much grander than, the disk we see around Saturn. We can’t wait to see what else Cassini will show us in Saturn’s rings.”
The Science and Technology Facilities Council is the UK sponsor of astronomy.