Just 385 years after Galileo discovered the mysterious rings around Saturn, Cornell astronomers are making discoveries of their own. Using the Hubble Space Telescope, from which these photos were taken Nov. 21, 1995, Philip D. Nicholson, professor of astronomy, and graduate student Colleen McGhee took advantage of an unusual geometry to learn more about Saturn's outer rings and some of the planet's 21 moons. With an edge-on view of the rings, called a "ring plane crossing," the astronomers could see faint objects that normally would be lost in the glare of the rings. In these photo pairs, some of the moons are seen in orbit. The Hubble Space Telescope snapped these five pairs of images while the Earth was just above the ring plane and the sun was below it. The telescope captured a pair of images every 97 minutes as it circled the Earth. Moving out from Saturn, the visible rings are: the broad C Ring, the Cassini Division and the narrow F Ring -- usually not visible from Earth. A surprising find: Prometheus, the closest moon to Saturn, has rounded the F Ring's tip in the second pair of images and is approaching the planet. But that is nowhere near where it was predicted to be based on previous observations. Nicholson and McGhee investigated at least five possible causes for this but discarded all of them. Bottom line: "We don't know what could have caused Prometheus' orbit to have changed so much," McGhee said.
Other ring photos by Nicholson are available from the Hubble web site.