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Saturn’s icy moon Tethys features unexplained arc-shaped, reddish streaks

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Latest set of images captured by NASA’s Cassini mission have provided with clear view of unexplained arc-shaped, reddish streaks on the surface of Saturn’s icy moon Tethys, which though were visible earlier were not clear enough.

The enhanced-colour images of Tethys show that the red arcs across the surface of the moon are narrow, curved lines, and are among the most unusual colour features to be revealed by Cassini’s cameras. Images were taken using clear, green, infrared and ultraviolet spectral filters and were then combined to create the enhanced-colour views, which highlight subtle color differences across the icy moon’s surface at wavelengths not visible to human eyes.

The arcs have become visible as the Saturn system moved into its northern hemisphere summer over the past few years illuminating the northern latitudes providing the most clear view.

This enhanced-color mosaic of Saturn's icy moon Tethys shows a range of features on the moon's trailing hemisphere. Tethys is tidally locked to Saturn, so the trailing hemisphere is the side of the moon that always faces opposite its direction of motion as it orbits the planet. Credits: NASA/JPL-Caltech/Space Science Institute

This enhanced-color mosaic of Saturn’s icy moon Tethys shows a range of features on the moon’s trailing hemisphere. Tethys is tidally locked to Saturn, so the trailing hemisphere is the side of the moon that always faces opposite its direction of motion as it orbits the planet.
Credits: NASA/JPL-Caltech/Space Science Institute

“The red arcs really popped out when we saw the new images,” said Cassini participating scientist Paul Schenk of the Lunar and Planetary Institute in Houston. “It’s surprising how extensive these features are.”

Cassini mission scientists are still not clear about the origins of the features and their reddish colour. One of the possibility that the scientists are looking at is that the reddish material is exposed ice with chemical impurities, or the result of outgassing from inside Tethys.

Another theory is that these arcs could also be associated with features like fractures that are below the resolution of the available images.

Except for a few small craters on Saturn’s moon Dione, reddish-tinted features are rare on other moons of Saturn. Many reddish features do occur, however, on the geologically young surface of Jupiter’s moon Europa.

“The red arcs must be geologically young because they cut across older features like impact craters, but we don’t know their age in years.” said Paul Helfenstein, a Cassini imaging scientist at Cornell University, Ithaca, New York, who helped plan the observations. “If the stain is only a thin, colored veneer on the icy soil, exposure to the space environment at Tethys’ surface might erase them on relatively short time scales.”

The Cassini team is currently planning follow-up observations of the features, at higher resolution, later this year.

“After 11 years in orbit, Cassini continues to make surprising discoveries,” said Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California. “We are planning an even closer look at one of the Tethys red arcs in November to see if we can tease out the source and composition of these unusual markings.”

This enhanced-color mosaic of Tethys shows terrain slightly farther to the southwest than images taken a couple of hours earlier. A version with standard image processing is available, along with a strongly enhanced version. Credits: NASA/JPL-Caltech/Space Science Institute

This enhanced-color mosaic of Tethys shows terrain slightly farther to the southwest than images taken a couple of hours earlier. A version with standard image processing is available, along with a strongly enhanced version.
Credits: NASA/JPL-Caltech/Space Science Institute