Most of the planets in the universe orbit a star. They are part of a system of planets, similar to our own solar system. But a few planets drift alone in the cosmos. For whatever reason, be it a near collision or slow gravitational perturbations that destabilize its orbit, these planets are cast out of their star system and sent adrift. These rogue planets are notoriously challenging to find, but as we start to discover them we're finding they are a bit more common than we'd thought. Now a new study posits a reason why.