Apollo 16 Returns: Moon Mission Safely Completed

Apollo 16 splashed down in the Pacific Ocean on April 27, 1972, completing the fifth crewed mission to land on the Moon and the first to explore the lunar highlands. Commander John Young and Lunar Module Pilot Charles Duke spent 71 hours on the surface, conducted three extravehicular activities totaling over 20 hours, drove the Lunar Roving Vehicle for 26.7 kilometers, and collected 95.8 kilograms of lunar samples. Command Module Pilot Ken Mattingly remained in orbit, operating cameras and instruments that mapped the lunar surface in unprecedented detail. The mission nearly ended before it reached the Moon. During the lunar orbit insertion burn, Mattingly reported a malfunction in the backup steering system of the Command Module's engine. Mission Control in Houston spent six hours analyzing the problem, during which time the lunar landing was in jeopardy. Engineers ultimately determined the issue was a minor oscillation that would not affect the engine's primary system, and the landing proceeded. The delay shortened the surface stay but did not eliminate any of the planned geological traverses. Apollo 16's scientific target was the Descartes Highlands, selected because geologists believed the region's bright, hilly terrain was volcanic in origin. The samples Young and Duke collected upended that hypothesis. Rather than volcanic rock, the highlands proved to be composed primarily of breccia, rock shattered and fused by ancient meteorite impacts. The discovery fundamentally changed understanding of the Moon's geological history, demonstrating that impact processes, not volcanism, had shaped most of the lunar surface. Science sometimes advances most when predictions prove wrong. The mission's return was notable for an experiment Mattingly performed during the transearth coast: he conducted a spacewalk to retrieve film cassettes from cameras mounted on the service module, floating outside the spacecraft 200,000 miles from Earth. Young and Duke, meanwhile, conducted cosmic ray and biological experiments inside the command module. Apollo 16 was the penultimate lunar landing mission; only Apollo 17 in December 1972 would follow. Half a century later, the samples collected in the Descartes Highlands continue to yield new scientific insights about the Moon's formation and evolution.