Evidence that Mars Used to Have a Ring

Mars only has two moons: Phobos and Deimos. They’re strange, for moons, little more than lumpy, potato-shaped chunks of rock. They’re much too small for self-gravitation to have made them round. And one of them, Deimos, has an unusually tilted orbit. What does that slight tilt tell us about Deimos? About Mars? Deimos is the …