CICLOPS: Cassini Imaging Central Laboratory for OPerationS

Sister moons
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Sister moons
PIA 06629

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  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 (1,123 kilometers, 698 miles across). The double-pronged feature Carthage Linea points toward the crater Turnus at the 9 o'clock position near the terminator, and Palatine Linea runs toward the moon's bottom limb near the 5 o'clock position.

In contrast, the surface of Tethys (1,062 kilometers, 660 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 narrow angle camera on March 7, 2005, from 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.

[Caption updated on October 4, 2005.]

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 Cassini-Huygens mission for NASA's Science Mission Directorate, Washington, D.C. The imaging team consists of scientists from the US, England, France, and Germany. The imaging operations center and team lead (Dr. C. Porco) are based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission, visit and the Cassini imaging team home page,

Credit: NASA/JPL/Space Science Institute
Released: April 18, 2005 (PIA 06629)
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