The event was captured while Cassini was filming Saturn's moon Prometheus approaching the ring. The moon, which orbits just inside the F-ring, following an elliptical path, brushes up against it every 17 years. During its approach, it's thought to create a ripple in the icy ring's geometry which causes snowball-like pieces to break off. These icy fragments are then thought to quickly crash back into it causing a sparkling mini-jet.
Based on the video, researchers were able to calculate the orbital direction and speed of the snowballs. Results indicate that they followed a very similar orbit to Prometheus and hit at a slow speed of about one meter per second. This points to the culprit being small snowballs created during the moon's previous approach, which survived and went on to strike through the F-ring itself.
"We had seen these mini-jets right from day one but, like most things with the F-ring, it's trying to understand what you're seeing," says Carl Murray, a Cassini imaging team member based at University of London in the UK. The group has found 500 such mini-jets after looking through 25 images of the F-ring. They now plan to examine them more closely to see if they fit the same description as the one caught on film.
If you enjoyed this post, check out a slideshow of Cassini's best images or see moon shadows on Saturn's rings.