A recently released picture of the F Ring around Saturn shows it being obliterated on a certain portion by the passing of the tiny moon Prometheus through it. The image was snapped by the NASA/ESA Cassini spacecraft on August 21. The probe, which has been orbiting the gas giant for many years, took advantage of its distant vantage point to image the interesting effects that the diminutive moon had on one of Saturn's most interesting rings. Its main trait is that it changes its appearance on a timescale of hours, which makes it the most active structure of this type in the solar system.

It is also the outermost discrete ring circling the gas giant, and, as such, it is heavily influenced by the two moons flanking it, Prometheus and Pandora. The ring itself is composed of a central line and a spiral strand waving around the former. The first moon has the most dramatic influence on the structure of the ring. As it moves within it, it tends to basically “steal” matter from it, carving channels into the small formation, which is only a few hundred kilometers wide. It was known before that the Prometheus had the power to create kinks and knots in the F Ring, but the extent of this influence was not accurately assessed until the new Cassini observations.

“The moon and the ring have eccentric, offset orbits, so Prometheus dips in and out of the F ring as it travels around Saturn. Its gravitational force drags the dust-sized particles at the edge of the F ring along for the ride,” a press release on the official news blog of the NASA Jet Propulsion Laboratory (JPL) says. The institution is involved in controlling Cassini. It is located on campus at the California Institute of Technology (Caltech), in Pasadena, California.

“The ability of the potato-shaped Prometheus […] was first theorized in the late 1990s and finally imaged by Cassini in 2004. But because these so-called 'streamer-channels' have constantly shifted as Prometheus and the F ring have moved, the F ring has never looked the same twice. The gravitational pull of other moons on other rings has created waves in the edges, but nothing quite as extreme as the streamer-channels of Prometheus,” the release adds. Most likely, the cause for these events is the fact that the moon orbits around Saturn at a higher speed than the ring does.

Cassini is currently halfway through its extended mission period, which ends in 2010. It was launched in 1997 and managed to reach an orbit around Saturn in 2004. It has been sending large amounts of valuable scientific data ever since, and chances are that the mission will get another extension beyond next year. Enceladus is a very small moon, with a diameter of just 310 miles, or about 500 kilometers.