Neptune's largest moon, Triton, orbits the opposite direction of all other moons in our solar system, and no one is sure why. No, Triton is not a "Death Star... read more
The leading hypothesis is that Triton was part of a binary Kuiper belt object, most likely the larger one. When the binary object passed by Neptune closely, gravitational interactions between the three bodies led to the smaller body of the binary gained velocity and was ejected, while Triton lost velocity and remained stuck in an orbit around Neptune. read more