October 15, 2007
The cold, cratered landscape of Saturn's moon Tethys shines in stark relief in this crescent view.
Aside from its obvious aesthetic beauty, this particular Cassini mosaic was obtained mainly to understand important details about how the surface of Tethys (1,071 kilometers, or 665 miles across) reflects light at high phase angles (the sun-Tethys-spacecraft viewing angle). The beautiful interplay of light with surface topographic features is an important factor in this regard. The surface is heavily cratered, and at this oblique angle the craters give the surface a highly scalloped appearance.
Unlike some high-resolution crescent views of Saturn's moons, this image truly gives Tethys the appearance of being composed of ice and frost. There appear to be numerous sun glints sparkling across the surface. Some of these might be specular (or mirror-like) reflections off of exposed walls of solid ice inside craters, or they might be uniformly large, frosty or icy-particle covered facets of topography that are so oriented as to give exceptionally bright but diffuse reflections.
The shadows cast by most craters in the scene are not dark, but rather, they are illuminated by light bouncing off of their sunlit walls and those of other craters. This light, which has been scattered multiple times, makes visible some details along the shadowed walls and floors of craters that would not otherwise be visible in this viewing geometry.
This mosaic was assembled from four clear filter, narrow-angle camera images, with low resolution, wide-angle camera data filling a small gap in coverage. The view is an orthographic projection and has a resolution of 211 meters (692 feet) per pixel. An orthographic view is most like the view seen by a distant observer looking through a telescope. North is up.
The view was obtained by the Cassini spacecraft on June 29, 2007, from a distance of approximately 38,000 kilometers (24,000 miles) and at a Sun-Tethys-spacecraft, or phase, angle of 152 degrees.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency 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, D.C. 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, Colo.
Credit: NASA/JPL/Space Science Institute