ASTRONOMY In 1970, a Russian robotic vehicle called Lunokhod 1 explored the surface of the moon for a few months before suddenly going silent. Many astronomers assumed that the rover had fallen into a crater, but a team led by Arizona State University recently spotted it in images taken by NASA’s Lunar Reconnaissance Orbiter, parked miles from where everyone had been searching.

The rover is more than just space junk. Lunokhod 1 is equipped with a retroreflector—a high-quality mirror that precisely reflects light back. The researchers suspected that the rover’s retroreflector might be covered in moon dust or might be facing away from Earth, but when they aimed a laser beam at the vehicle from the Apache Point Observatory in New Mexico, the beam bounced back.

That’s great news for lunar researchers. Laser measurements from four other reflectors on the moon already allow precision tracking of the moon’s orbital path around the Earth. Astronomers have used that tracking data to investigate the gravitational fields of all the objects in the solar system. The addition of a fifth reflector at a location far from the others now enables astronomers to calculate the moon’s flexure, or “bendiness.” Flexure relates to distribution of mass, so the new information from the fifth mirror will offer clues about the inner composition of the moon, revealing the concentration of solid and liquid material in the lunar core.