How Do You Solve a Moon Mystery? Fire a Laser at It

The moon is drifting away. Every year, it gets about an inch and a half farther from us. Hundreds of millions of years from now, our companion in the sky will be distant enough that there will be no more total solar eclipses.For decades, scientists have measured the moon's retreat by firing a laser at light-reflecting panels, known as retroreflectors, that were left on the lunar surface, and then timing the light's round trip. But the moon's five retroreflectors are old, and they're now much...