In this movie from NASA’s Cassini spacecraft, the gravitational pull of Saturn’s moon Prometheus creates patterns in Saturn’s F ring. This movie also happens to show a small trail of icy ring particles dragged out when a tiny object punches through the ring.
Prometheus, which averages 53 miles or 86 kilometers across, is the bright body moving up and down in the frame. The delicate strands of the F ring run across the top of the frame. The trail, made of icy particles dragged out of Saturn’s F ring, varies from about 47 miles (75 kilometers) long to 155 miles (250 kilometers) long over the course of the movie.
Scientists think the trails, also called “mini-jets” by Cassini scientists, are created when small objects about half a mile (1 kilometer) in diameter punch through the F ring and drag icy ring particles behind them. The objects creating the trails were likely originally formed by the pull of the moon Prometheus on tiny F ring particles.
As the moon works its way around Saturn, its gravitational attraction sometimes parts channels in the icy particles of Saturn’s F ring and sometimes pushes together sticky snowballs. The moon’s continued progress around Saturn pulls some of the snowballs apart over time and adds material to others. These trails appear to be the telltale signs of surviving, evolved snowballs that strike through the F ring on their own. Scientists have been able to use Cassini images to track the objects and be sure they have different orbits from the F ring. The collisions occur at gentle speeds, on the order of 4 mph (2 meters per second). The F ring is the outermost of Saturn’s main rings, with a radius of about 87,129 miles (140,220 kilometers).