There are actually thousands more planets in the solar system than you probably know, orbiting the sun beyond Neptune. One such so-called dwarf planet is Quaoar, merely 690 miles wide (less than half the size of Pluto), and 44 times farther from the sun than Earth (it takes 288 years to complete one orbit). According to a new paper published Wednesday in Nature, it turns out Quaoar even has a ring around it like Saturn or Jupiter. That would be pretty delightful news if scientists knew why—Quaoar’s ring orbits the planet from an extreme distance where it should theoretically be impossible to exist. The ring is supposed to be a complete moon, instead of a stream of much smaller rocks in a ring-like structure. The team behind the discovery, made thanks to a European space telescope called CHEOPS, thinks that perhaps freezing temperatures may have prevented the rocks from coming together into a moon, and instead they dispersed into a ring. But no one is sure. The existence of the ring is already one of astronomy’s most perplexing mysteries of the year so far.