NASA's Cassini spacecraft has provided new images of Saturn's moons Tethys and Hyperion, showing features not seen before.
Last weekend, Cassini flew closer than ever before to each of them.
Tethys has a scarred, ancient surface, an icy landscape with steep cliffs and craters.
A giant rift called Ithaca Chasma cuts across the disk of Tethys. Much of the topography in this region, including that of Ithaca Chasma, has been thoroughly hammered by impacts. This appearance suggests that the event that created Ithaca Chasma happened very long ago.
A new image of the Tethys' south polar region shows a region not photographed during the Voyager era.
Astronomers described Hyperion as spongy-looking with dark-floored craters that speckle its surface. Scientists don't know what the dark material is.
In addition, the new images suggest the possibility that Hyperion's crater walls have experienced multiple episodes of landslides. Such "downslope" movement is evident in the filling of craters with debris and the near elimination of many craters along the steeper slopes.
Answers to these questions may help solve the mystery of why this object has evolved different surface forms from other moons of Saturn, scientists with Space Science Institute in Boulder, Colorado said in a statement today.
Cassini flew by Hyperion at a distance of 310 miles (500 kilometers). Hyperion is 163 miles (266 kilometers) wide. It has an irregular shape, and spins in a chaotic rotation. Much of its interior is empty space; it's like a pile of rubble, scientists say.
Cassini was within 930 miles (1,500 kilometers) of Tethys, a moon that is 665 miles (1,071 kilometers in diameter.