As NASA's Cassini spacecraft continues its looping orbit around Saturn's moons, astronomers are receiving a flood of new, close-up shots of the ringed planet's satellites. In mid-January Cassini captured images of two of Saturn's closest and most intriguing neighbors: Mimas and Enceladus.
Mimas, made famous by its eerie similarity to the Death Star from Star Wars, is seen against a beautiful blue Saturn in this image shot from 1.4 million kilometers (870,000 miles) away. Sunlight passing sideways through Saturn's atmosphere is scattered at shorter wavelengths, giving the planet's northernmost latitudes their bluish hue. (The same effect makes the sky blue here on Earth.) The dark lines on the planet are shadows cast by Saturn's rings.
Looking much closer (213,000 km), Mimas's famous crater, Herschel, peers into Cassini's camera like a cyclops. When seen face on, the amazing size of the 130-km wide crater — roughly one-third the size of the moon itself — becomes clear. Since Voyager took the first close-up images of Mimas more than two decades ago, scientists have questioned how the moon stayed intact despite having been hit with by something so large. Astronomers believe that the moon is extremely ice-rich, and it was most likely the durability of the ice that allowed the mid-size body to survive the incredible impact.
Another moon known to be ice-rich is Enceladus. The image below, shot from 367,000 km, is a tantalizing tease to astronomers; Cassini will make a super-close (500 km) flyby of the moon on March 9th. Here we see strange swirling wrinkles on Enceladus. The frozen moon appears incredibly bright — nearly all of the light it receives is reflected by the surface ices — and its surface looks amazingly fresh. There are several rifts and faults, but very few craters on Enceladus, suggesting a surface that was tectonically and perhaps volcanically active in recent geologic times.
As Cassini continues to weave around Saturn's moons, expect to see more images like these in the coming weeks and months. You can keep tabs on the mission at the Jet Propulsion Laboratory Web site, where raw images are posted often. News and science results will appear on this site as events unfold.