Dusty lunar mirrors impact relativity tests

APS Meeting - New Scientist : Several times a month, teams of astronomers from three observatories blast the Moon with pulses of light from a powerful laser and wait for the reflections from a network of mirrors placed on the lunar surface by the Apollo missions, as well as two Soviet Lunokhod landers.By timing the light’s round trip, they can pinpoint the distance to the Moon with an accuracy of around a millimeter—a measurement so precise that it has the potential to reveal problems with general relativity.But now Tom Murphy from the University of California, San Diego , thinks the mirrors have become coated in Moon dust. “The lunar reflectors are not as good as they used to be by a factor of 10,” he says.