SAN DIEGO, April 21 (UPI) -- Prisms left on the moon by U.S. astronauts 40 years ago aren't reflecting as much light as they previously did and scientists suspect dust is the reason.
The study, led by University of California-San Diego Associate Professor Tom Murphy, shows light reflected by the prisms is fainter than expected and mysteriously dims even more during a full moon.
"Near full moon, the strength of the returning light decreases by a factor of 10," said Murphy, who leads the effort to precisely measure the distance from Earth to the moon by timing the reflections of pulses of laser light. "Something happens on the surface of the moon to destroy the performance of the reflectors at full moon."
Although the scientists say they only expect to recapture one in 100 million billion particles of light, or photons, their instrument detects merely a tenth as much light most nights. And when the moon is full the results are 10 times worse.
The researchers said they are now attempting to determine the source of the dust, which might come from micrometeorites that constantly strike the moon's surface.
The study that included scientists from the University of Washington, the Massachusetts Institute of Technology, Humboldt State University, the Apache Point Observatory and Harvard University is to appear in a forthcoming issue of the journal Icarus.