The night sides of Saturn and Tethys are dark places indeed. This image from NASA's Cassini spacecraft shows shadows are darker areas than sunlit areas, and in space, with no air to scatter the light, shadows can appear almost totally black.
This enhanced-color mosaic of Saturn's icy moon Tethys shows a range of features on the moon's trailing hemisphere. This image from NASA's Cassini spacecraft was constructed from 52 images from its narrow-angle camera on April 11, 2015.
In this image from NASA's Cassini spacecraft, two large craters on Tethys, near the line where day fades to night, almost resemble two giant eyes observing Saturn. Tethys is significantly closer to the camera, while the planet is in the background.
Like most moons in the solar system, Tethys is covered by impact craters. Some craters bear witness to incredibly violent events, such as the crater Odysseus (seen here at the right of this image from NASA's Cassini spacecraft).
NASA's Cassini orbiter shows that Tethys appears to be peeking out from behind Rhea, watching the watcher. Scientists believe that Tethys' surprisingly high albedo is due to the water ice jets emerging from its neighbor, Enceladus.
The moons visible in this image from NASA's Cassini spacecraft, Pandora and Atlas, are quite small by astronomical standards, but the rings are also enormous. From one side of the planet to the other, the A ring stretches over 170,000 miles (270,000 km).
NASA's Cassini spacecraft captures a rare family photo of three of Saturn's moons that couldn't be more different from each other. Shown here are Tethys (center), Hyperion (upper left), and Prometheus (lower left).
Seen by NASA's Cassini spacecraft, Tethys, like many moons in the solar system, keeps one face pointed towards the planet around which it orbits. Tethys' anti-Saturn face is seen here, fully illuminated, basking in sunlight.
Tethys' trailing side shows two terrains that tell a story of a rough past. To the north (up, in image) is older, rougher terrain, while to the south is new material dubbed 'smooth plains' by scientists. This image was taken by NASA's Cassini spacecraft.
NASA's Cassini spacecraft captured this image of Tethys, telling the story of a violent history marked by impacts. Seen here are the craters Melanthius (near the center), Dolius (above Melanthius), and Penelope (upper left almost over the limb).
Although Mimas holds the unofficial designation of 'Death Star moon,' Tethys is seen here also vaguely resembling the space station from Star Wars. Apparently, Tethys doesn't want Mimas to have all the fun!
NASA's Cassini spacecraft takes a close look at a row of craters on Saturn's moon Tethys during the spacecraft's April 14, 2012, flyby of the moon. Three large craters are visible along the terminator between day and night on Tethys.
Saturn's moon Tethys orbits in front of the wide shadows cast by the rings onto the planet for this view from NASA's Cassini spacecraft. Tethys appears just below the rings near the center of the image.
Saturn's moon Tethys shows off its tortured surface in this image from NASA's Cassini spacecraft. At top left of image is huge Odysseus Crater. At bottom right is Ithaca Chasma, a series of scarps that runs north-south across the moon.