In the long human effort to understand where we come from, Japan is preparing to reach across the solar system and bring back a piece of another world's moon. On October 19th, the MMX spacecraft will depart Tanegashima Space Center bound for Phobos, one of Mars's two small and poorly understood satellites, with the aim of returning a sample to Earth by 2031. The mission carries a question as old as planetary science itself: are these moons born of Mars, or wanderers captured from the outer solar system? The answer, encoded in a few grams of ancient rock, could quietly rewrite our understanding