© NASAA close-up photograph of the laser reflecting panel deployed by Apollo 14 astronauts on the Moon in 1971.
The reflector NASA scientists aimed for is mounted on the Lunar Reconnaissance Orbiter (LRO), a spacecraft that has been studying the Moon from its orbit since 2009. One reason engineers placed the reflector on LRO was so it could serve as a pristine target to help test the reflecting power of panels left on the Moon's surface about 50 years ago. These older reflectors are returning a weak signal, which is making it harder to use them for science.
Scientists have been using reflectors on the Moon since the Apollo era to learn more about our nearest neighbor. It's a fairly straightforward experiment: Aim a beam of light at the reflector and clock the amount of time it takes for the light to come back. Decades of making this one measurement has led to major discoveries.
One of the biggest revelations is that the Earth and Moon are slowly drifting apart at the rate that fingernails grow, or 1.5 inches (3.8 centimeters) per year. This widening gap is the result of gravitational interactions between the two bodies.
"Now that we've been collecting data for 50 years, we can see trends that we wouldn't have been able to see otherwise," said Erwan Mazarico, a planetary scientist from NASA's Goddard Space Flight Center in Greenbelt, Maryland who coordinated the LRO experiment that was described on August 7 in the journal Earth, Planets and Space.
"Laser-ranging science is a long game," Mazarico said.
But if scientists are to continue using the surface panels far into the future, they need figure out why some of them are returning only a 10th of the expected signal.
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