Starship Asterisk*

This photograph shows the Laser Ranging Facility at the Geophysical and Astronomical Observatory at NASA's Goddard Space Flight Center in Greenbelt, Md. The observatory helps NASA keep track of orbiting satellites. Credit: NASA

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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. They announced today, 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. 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. ...

• Earth, Planets and Space 72:113 (06 Aug 2020) DOI: 10.1186/s40623-020-01243-w