Beneath the frozen shell of Enceladus, one of Saturn's quieter moons, an ocean stirs—one that may hold the conditions life requires to begin. Over years of patient measurement, NASA's Cassini spacecraft gathered chemical evidence from plumes erupting into space: salt from dissolved rock, hydrogen from hydrothermal vents, and phosphorus in concentrations that dwarf Earth's own seas. No organism has been found, but the ingredients are present, and the question of whether life needs only the right chemistry—or something more—remains one of the deepest the human mind can ask.