Scientists are baffled after sighting several large, reddish arcs across the surface of one of Saturn's moons. The markings on Tethys are a few miles wide and several hundred miles long, per NASA's Jet Propulsion Laboratory. The images were taken by the Cassini-Huygens spacecraft, and while photos it took in 2004 hint at the red features, they "really popped" in images sent this April, per Cassini scientist Paul Schenk. The photo is a color-enhanced one, and the result of bringing together images "taken using clear, green, infrared, and ultraviolet spectral filters," reports Phys.org. Saturn has a 29-year orbit, and as the planet gradually moved into its northern hemisphere summer in recent years, "northern latitudes have become increasingly well illuminated," per NASA.
Little is known about the origin, age, and composition of the markings, although researchers have their hypotheses. The red hue could be "exposed ice with chemical impurities, or the result of outgassing from inside Tethys," NASA explains. "The red arcs must be geologically young because they cut across older features like impact craters," adds Cassini imaging scientist Paul Helfenstein. The next six months will see Cassini get a last look at the moons Enceladus and Dione, according to Discovery News, which notes the spacecraft will take a "suicidal plunge" on Sept. 15, 2017. NASA will also take higher resolution photos of Tethys' markings later this year to further study the unusual arcs. (Scientists recently discovered surprises in Saturn's outer ring.)