NASA says laser beams reflected between Earth and Moon, could enhance experiments

Dozens of times over the last decade, NASA scientists have launched laser beams at a reflector the size of a paperback novel about 240,000 miles (385,000 kilometers) away from Earth. The US space agency announced Tuesday, in collaboration with their French colleagues, that they received signal back for the first time, an encouraging result that could enhance laser experiments used to study the physics of the universe.

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. Scientists have been using reflectors on the Moon since the Apollo era to learn more about our nearest neighbor.

NASA says 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 have 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 — 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 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 to figure out why some of them are returning only a 10th of the expected signal.

There are five reflecting panels on the Moon. Two were delivered by Apollo 11 and 14 crews in 1969 and 1971, respectively. They are each made of 100 mirrors that scientists call “corner cubes,” as they are corners of a glass cube; the benefit of these mirrors is that they can reflect light back to any direction it comes from. Another panel with 300 corner cubes was dropped off by Apollo 15 astronauts in 1973. Soviet robotic rovers called Lunokhod 1 and 2, which landed in 1970 and 1973, carry two additional reflectors, with 14 mirrors each. Collectively, these reflectors comprise the last working science experiment from the Apollo era.

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What do researchers aim to achieve?

By measuring how long it takes laser light to bounce back — about 2.5 seconds on average  — researchers can calculate the distance between Earth laser stations and Moon reflectors down to less than an inch, or a few millimeters. This is about the thickness of an orange peel.

Magnetic measurements of Moon samples returned by Apollo astronauts revealed something no one had expected given how small the Moon is: our satellite had a magnetic field billions of years ago. Scientists have been trying to figure out what inside the Moon could have generated it.

Laser experiments could help reveal if there’s solid material in the Moon’s core that would’ve helped power the now-extinct magnetic field. But to learn more, scientists first need to know the distance between Earth stations and the Moon reflectors to a higher degree of accuracy than the current few millimeters.

“The precision of this one measurement has the potential to refine our understanding of gravity and the evolution of the solar system,” said a Goddard planetary scientist who helped design LRO’s reflector.

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