Dione and the Rings
Dione is Saturn’s fourth largest moon, with a diameter of 1,123 kilometers (698 miles). Orbiting outside the ring system of the gas giant, the moon can provide NASA’s Cassini spacecraft with the chance to image it in profile against some stunning backdrops, as is the case here.
Dione is tidally locked with Saturn, so like our own Moon, one side always faces the planet. Cassini (the namesake of Giovanni Cassini, who discovered Dione in 1684) has captured the trailing hemisphere of the moon in this shot. In general, the leading hemisphere of a body should be more heavily cratered, but the trailing hemisphere of Dione features the most heavily cratered areas of the moon, suggesting a major impact that spun Dione around in the recent past. Also evident in this image are some bright wispy lines on the surface, measuring from tens to hundreds of kilometers in length. Cassini images have revealed that these are actually the bright faces of towering cliffs, some of them several hundred meters high. It is theorized that past tectonic activity created these cliffs, exposing water ice that brightly reflects the light from the distant Sun.
Image credit: NASA/JPL-Caltech/Space Science Institute