Although Tethys and Janus both orbit Saturn and are both made of more or less the same materials, they are very different worlds. Their contrasts are related, in large part, to their sizes.
Tethys (1,062 kilometres or 660 miles across) is large enough to be spherical and to have varied geology, like chasms and smooth plains, along with some puzzling arc-shaped features. Much smaller Janus (179 kilometres or 111 miles across) is irregularly shaped and has (so far) shown few signs of geologic activity apart from impact craters.
This view looks toward the sunlit side of the rings from about 1 degree above the ring plane. The image was taken in visible light with the Cassini spacecraft wide-angle camera on 23 November 2015.
The view was acquired at a distance of approximately 44,000 kilometres (28,000 miles) from Tethys and at a Sun-Tethys-spacecraft, or phase, angle of 54 degrees. Image scale is 3 kilometres (1.8 miles) per pixel.
The Cassini mission is a cooperative project of NASA, ESA and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colorado.