The minimoons next door

Astronomers haven't had much more luck finding minimoons in orbit, either. So far, scientists have just spotted one while it was still circling Earth. Starting in 2006, a tiny asteroid called 2006 RH120 stuck around for about 11 months before leaving the Earth-moon system.

However, researchers expect they'll find more of these temporary moons in the coming years. The upcoming Large Synoptic Survey Telescope (LSST) will create regular maps of the night sky, turning up faint and transient events in its surveys.

Though rare, minimoons are so appealing to researchers because they are the closest space rocks to Earth.

“Minimoons are really awesome because they are the most accessible object to get to from Earth in the solar system,” Shober said. This means it will take less energy or fuel to reach these objects than it would for other space rocks — whether for sample return missions, tests of asteroid redirection technologies or resource mining.