Nasa will celebrate a remarkable anniversary this month. Fifty years ago the last astronauts to visit the moon returned to Earth, leaving behind the final tell-tale signs that our species had once visited another world. For three days in December 1972, Apollo 17 crewmen Gene Cernan and Harrison “Jack” Schmitt explored the moon’s Taurus-Littrow valley, travelling over 30km in their lunar rover while collecting more than 100kg of rocks for return to Earth.
Then, on 14 December, geologist Schmitt returned to the mission’s lunar lander while Cernan gave a brief speech that was broadcast to Earth. “We shall return, with peace and hope for all mankind,” he pledged. Then Cernan closed the spaceship’s hatch, placed his hand on the yellow ignition button and uttered the last words that
