Saturn has 62 moons. Of those, 53 have been formally named while nine others are such recent discoveries that they haven't yet received an official name. Titan, the largest of Saturn's moons, is more massive than the planet Mercury and has a nitrogen-rich atmosphere similar to Earth's. Enceladus, another moon, likely has an internal ocean as evidenced by the volcanoes of ice that plume from its surface into space and fall back to the surface as snow. Complex organic molecules have been detected in Enceladus, making it one of the prime candidates for finding extraterrestrial life in our solar system. There may be only nine formally recognized planets in our solar system, but there are 181 moons orbiting those planets, each with their own complexities and unique mysteries.
Saturn's moon Dione is one of those mysteries. Dione is smaller than Earth's moon, and exists in orbital resonance with Enceladus, meaning that it completes one orbit of Saturn for every two completed by Enceladus. This orbital resonance is likely the source of the geologic heat found in Enceladus, which reveals itself in the form of Enceladus's dramatic ice volcanoes. Despite being smaller than Earth's moon, Dione proves that size isn't everything in terms of astronomical weirdness. Data from Cassini shows that, along with an orbital relationship, Dione shares other similarities with Enceladus, most notably the presence of an interior ocean., but Dione isn't simply a twin of Enceladus. According to a new study published in journal Geophysical Research Letters, the small moon has a mystery all its own. Streaking across its surface are bright white stripes unlike anything else seen in the solar system, and so far scientists don't know what they are.
Scientists have ruled out geologic causes for the stripes like tectonic activity. Instead, they say that whatever the stripes are made of, they're likely draped across the surface like snow. What's strange is how they're draped. Other bodies in the solar system, including Saturn's moon Rhea, show bright lines on the surface but none as straight and seemingly intentional as the lines on Dione. The lines are between six and sixty two miles long and three miles wide and perfectly straight. Not only are they perfectly straight, but they run parallel to Dione's equator, a trait that scientists say is very unusual. They are unbroken, which scientists take to mean that they are a relatively new phenomenon and possibly part of an ongoing phenomenon in the Saturn system.
The authors of the study say that the cause of these mysterious lines is likely due to some off world influence:
We explored different ways of forming linear features on planetary surfaces and favor the draping of exogenic material across a planetary surface by encounters with either Saturn's rings, co‐orbital moons, or close flyby of comets. This debris may introduce materials into the Dione system that could contribute to creating a more habitable Dione.
Recently, scientists demonstrated that one of the building blocks of life here on earth was probably formed in space and deposited here on Earth. With a liquid water interior and constant depositing of off-world material on Dione, it seems possible that some strange chemistry could make its way into the underground sea and begin the process of life. Of course, such life would be likely be microscopic and completely outside our ability to study it for many years to come. This does show that, once again, the more we learn about our corner of space, the more mysteries we uncover.