A discarded piece of human ambition — a spent Falcon 9 rocket stage the size of a school bus — will complete its unintended journey Wednesday morning, striking the lunar surface at 5,400 miles per hour after drifting uncontrolled for over a year. The collision, expected to carve a 60-foot crater into Einstein crater on the moon's western edge, harms no one on Earth, yet it quietly asks a question humanity has long deferred: what responsibility do we bear for the debris we scatter across the heavens? In the growing age of lunar exploration, this unplanned impact arrives as both an accidental ex