The classic view of our solar system contains eight orderly planets, some with moons in neat orbits – but when we look closer, we discover a bunch of stuff missing from this simple, clockwork model. Wandering worlds that seem out of place, found in the gaps between and beyond the planets, offer clues that our cosmic neighborhood is far more dynamic than we once thought. From the meteorites that impact Earth, to a moon that orbits backwards, to an imposter lurking in the asteroid belt, these wandering worlds are rewriting what we know – and even how we think about – our solar system.