Earth always has more moons than you think

The solar system has some exciting local news: A mysterious space rock, about the size of a building, is coasting alongside Earth on its journey around the sun. Unbeknownst to astronomers until this summer, the object has been shadowing the planet for decades, in a celestial configuration that makes it a "quasi-moon."

When Ben Sharkey , an astronomer at the University of Maryland, first heard about PN7, as scientists now call it, their first thought was: "Oh cool, another one." That's because PN7 is just the latest find in what is a perpetual parade of tiny, moon-ish objects in Earth's vicinity.

Our planet has other quasi-moons like PN7; these orbit the sun, but their looping path through space —sometimes gliding ahead of Earth, other times drifting behind it—make them appear as if