Sister Moons

Cassini offers this lovely comparison between two of Saturn's satellites, Dione and Tethys,
which are similar in size but have very different surfaces.

Extensive systems of bright fractures carve the surface of Dione (1,118 kilometers, or 695 miles
across). The double-pronged feature Carthage Linea points toward the crater Turnus at the nine
o'clock position near the terminator, and Palatine Linea runs toward the moon's bottom limb near
the five o'clock position.

In contrast, the surface of Tethys (1,071 kilometers, or 665 miles across) appears brighter and
more heavily cratered. The large crater Penelope is near the eastern limb. The huge rift zone
Ithaca Chasma, which is 3 to 5 kilometers (2 to 3 miles) deep and extends for about 2,000
kilometers (1,200 miles) from north to south across Tethys, is hidden in shadow just beyond the
terminator. For comparison, the Grand Canyon in Arizona is about 1.5 kilometers (1 mile) deep,
and about 450 kilometers (280 miles) long.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on March
7, 2005, at a distance of approximately 1.5 million kilometers (908,000 miles) from Tethys and
1.6 million kilometers (994,000 miles) from Dione. The image scale is 9 kilometers (6 miles) per
pixel on Tethys, and 10 kilometers (6 miles) per pixel on Dione.

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 team is based at the Space Science Institute,
Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . For
additional images visit the Cassini imaging team homepage http://ciclops.org .

Credit: NASA/JPL/Space Science Institute