At the cold edge of our solar system, a world long assumed to be inert has offered a quiet correction to human assumptions. New analysis of images captured by NASA's New Horizons spacecraft suggests that liquid nitrogen may have flowed across Pluto's surface within the last million years — a geological heartbeat, by cosmic measure. The discovery, rooted in dark markings on the vast Sputnik Planitia glacier, invites us to reconsider what it means for a world to be alive, and how far the restlessness of matter extends into the dark.