Courtesy of NASA/JPL/University of Colorado
An ultraviolet view of Saturn’s A ring, colored by NASA. The red Cassini Division (left) is about the width of the United States.
The Cassini spacecraft is off to a blazing start. During its first day in orbit around Saturn, the probe’s ultraviolet camera beamed back colorful images that are already expanding our understanding of the planet’s majestic rings. UV snapshots highlight fine variations in the rings, explains Jeff Cuzzi, a planetary scientist at NASA’s Ames Research Center and a member of the Cassini science team. Because humans cannot perceive ultraviolet radiation, NASA researchers use artificial colors to illustrate what Cassini’s cameras saw. “The subtle shades of blue and green will tell us about a combination of grain size and particle composition,” Cuzzi says. Red indicates areas where the rings are nearly empty or where ring particles are particularly small—places where ultraviolet radiation from interstellar hydrogen shines through. Turquoise denotes the presence of water ice, confirming that the outer rings have significant ice reserves.
While scientists await more compositional information, Cassini’s observations are also yielding fresh insight into the rings’ fantastically complex construction. Fine-scale structures, roughly 650 feet wide, appear in certain places but not in others, for mysterious reasons. “Another surprise is that the moon Prometheus seems to be disturbing the F ring more than we had suspected,” says Cuzzi. The gravity of Prometheus and of other small satellites was once presumed to help hold Saturn’s rings together, not disrupt them. Researchers now suspect the orbit of this moon may be more chaotic than they previously thought.
Cuzzi stresses that the real work of Cassini’s four-year mission hasn’t even begun: “We will search for small moons in empty gaps, attempt to detect tiny meteoroids crashing into the rings, conduct dozens of stellar and radio occultations, and perform more sensitive compositional studies.” There will also be true-color close-ups of the rings for those who want to see what the planet would look like to a visitor with a set of human eyes. The first of these provided a revelation of another kind: a vista of muted yellows, grays, and mauves that is unique in the solar system.