After the landing of the Apollo 11—40 years ago today—there were five other U.S. moon landings, all within a short span of time. The last was Apollo 17, in December of 1972. Since then, Americans have set their sights on other objectives in space, like the creation of space stations, powerful telescopes, and unmanned robots on far-off Mars. Professor Jack Burns at the University of Colorado’s Center for Astrophysics and Space Astronomy often listens to people claim that the moon has already been explored, so why would resources be used for it again? “That’s like saying after Lewis and Clark returned from exploring the Louisiana Purchase that we really don’t need to go any farther west,” he tells The Denver Post.

NASA spends more money on research at CU than at any other university in the world, helping to launch projects such as the Kepler spacecraft last spring, which is on a mission to find other solar systems that could contain planets like Earth. But the moon might yet hold secrets in Earth’s own backyard, and NASA created the Lunar Science Institute last year to prepare for a return. “When it comes to learning how the Earth evolved, most of that record has been wiped out. But on the moon, it is still embedded and almost virtually intact,” Burns says. Meanwhile, Captain Bruce McCandless, a space shuttle astronaut, recalls how he was the voice inside Neil Armstrong’s ear when Armstrong set foot on the moon, as 5 News First in Colorado Springs reports: “I’m certain at the time that none of us appreciated the magnitude of what they were doing, not even the Apollo crew themselves.” Want more? NASA’s homepage is dedicated to the Apollo anniversary, and features a treasure trove of photo galleries, videos, and more, including restored footage of the moon landing.