Saturn`s moon Tethys in color shows weird features

This color mosaic of Saturn`s icy moon Tethys shows a range of features and color variations on the moon's trailing hemisphere. The mosaic, whose image data were taken a few months ago, was compiled by our planetology research group at Freie Universität Berlin and recently published in a press release of the NASA/JPL-Photojournal.


Color mosaic of Saturn`s moon Tethys
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Quite obvious at global scale is the yellowish color of the surface to the left, compared to the whitish color near the center and to the right. The probable reason for this are small icy dust grains which were ejected from the Saturnian moon Enceladus and which preferentially hit the leading side of Tethys, coloring it white.

Linear, reddish deposits of the Moon’s surface

The real surprise were linear, reddish arc-shaped deposits which popped out clearly in the images. A few of them were seen faintly in observations made earlier in the Cassini mission, but the color images of this recent observation are the first to show large northern areas of Tethys under the illumination and viewing conditions necessary to see the red deposits clearly.

The origin of the features and their reddish color is unknown. The red deposits appear to be geologically young because they cut across older features like impact craters.

This observation triggered a late re-design of Cassinis future observation plans. In mid-November, Cassini will now observe again such a red deposit from a distance of less than 10,000 km.


Tethys in front of the Planet

The icy moon seems to be tiny compared to the huge Saturn. In this image the lamellar shadow-strips of ring-system are visible on the northern hemisphere of the planet. In the southern polar region, clouds are visible. (Image from 10th June 2005 with the wide angle camera of the ISS experiment (ISS-WAC), shot from a distance of roughly 1.4 million km).

With a diameter of 1,062 km, Tethys is the fifth-largest moon of Saturn. Its low density suggests that the moon is primarily composed of water ice. The surface is heavily cratered, in some areas more than in others. The most prominent surface features are the Odysseus impact basin, measuring 445 km in diameter (nearly half of the moon´s diameter) and the Ithaca Chasma graben system, showing a width of 65 to 100 km and depth up to 5 km, covering large parts of Tethys. Tethys was already discovered in 1684 by the French astronomer Jean-Dominique Cassini and named after the Titaness Tethys from the Greek mythology.



In this image a section of a b/w mosaic is visible; with 100 m/px one of the best resolved visualisation of the Moon’s surface. Typical landforms of the moon´s surface like old and young impact craters, as well as diagonal graben are visible (images from the flyby from April 2012, obtained with the narrow angle camera (ISS-NAC), distance to Tethys 17.000 km).

Image processing

The image data were acquired on April 11, 2015 during sequence S88 with the Imaging Science-Subsystem (ISS) on board the Cassini spacecraft. Because the moon's surface is fairly uniform in natural colors, clear, green, infrared and ultraviolet spectral filters were combined to make the view of subtle color differences across Tethys surface visible to the human eye.

The systematic processing of the data and the production of the image products shown here were carried out by staff members of the Planetary Sciences and Remote Sensing Group of the Freie Universität Berlin. This mosaic is an orthographic projection constructed from 52 Cassini images, which were obtained at a distance of approximately 33,000 miles (53,000 km) from Tethys. Resolution is about 1,000 feet (300 m) per pixel.


Image Credit

NASA/JPL-Caltech/Space Science Institute/FU Berlin



The international Cassini-Huygens mission is a joint project of NASA, ESA and ASI, the Italian Space Agency aimed at the exploration of the Saturnian system. The Cassini spacecraft explores the planet and its moons since its arrival in Saturn´s orbit 2004. Huygens, the landing capsule built by ESA, has been the first European contribution to a space mission to the Outer Solar System. The Jet Propulsion Laboratory (JPL) at the California Institute of Technology in Pasadena manages the mission for NASA's Science Mission Directorate. 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.

Further information about the Cassini-Huygens Mission can be found on our webpages, on the webpages of NASA and and on the homepage of the Cassini Imaging Team