This enhanced-color mosaic of Tethys shows a range of features including mysterious arc-shaped streaks.

The red ‘arcs’ are narrow, curved lines on Tethys’ surface. They are among the most unusual color features on Saturn’s moons to be revealed by the NASA/ESA Cassini spacecraft.

Images taken using clear, green, IR and UV spectral filters were combined to create this enhanced-color mosaic, which highlights subtle color differences across the moon’s surface at wavelengths not visible to human eyes.

The origin of the features and their reddish color is a mystery to scientists with the Cassini mission.

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

Possibilities being studied include ideas that the reddish material is exposed ice with chemical impurities, or the result of outgassing from inside the icy moon.

They 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 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 Cassini imaging scientist Dr Paul Helfenstein of Cornell University in Ithaca, NY.

“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,” he said.