NASA baffled by red ‘graffiti’ on Saturn’s moon Tethys

New imagery from the Cassini spacecraft shows unexplained arc-shaped, reddish streaks on the surface of Saturn’s icy moon Tethys.

The enhanced-colour images were taken using clear, green, infrared and ultraviolet spectral filters then combined. This highlights subtle colour differences across the icy moon’s surface at wavelengths not visible to human eyes.

“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.”  

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

Possibilities being studied include ideas that the reddish material is exposed ice with chemical impurities, or the result of outgassing from inside Tethys. They could also be associated with features like fractures that are below the resolution of the available images.

“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.

“If the stain is only a thin, coloured 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.

Red graffiti2
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.
NASA/JPL-Caltech/Space Science Institute

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