As a rule, you can safely assume that moons and asteroids will all orbit in the same direction. If they didn't, interactions with their host would likely send them flying off course. However, it's now clear that there are exceptions to this rule: researchers have discovered that an asteroid is crossing Jupiter in the opposite direction of all planets in the Solar System. These backwards-orbiting rocks are rare anywhere in the system (they represent just 0.01 percent of known asteroids), but this is the very first time one has been caught doing so in tandem with a planet. How is it sticking around, then?