If you have clear skies this evening, look up and you will see the Moon—a solitary Moon, the same one that has lit Earth's skies for billions of years, circling our planet with clocklike precision. Look up with the vision of the Catalina Sky Survey, though, and you will see something entirely different.
The space around us is less like clockwork than it is like the ebb and flow of ocean currents, as small asteroids wander our part of the solar system in ever-shifting paths. They wander in response to the pressure of sunlight and to subtle gravitational perturbations: sometimes drifting close to Earth, occasionally making an impact, and every once in a while becoming trapped by our planet's gravity.
When option #3 happens, Earth gets a temporary new moon, a mini-me companion to the big one that we simply call "the Moon." That's what happened about three years ago, when Earth acquired its current minimoon, the object currently known as 2020 CD3.
