Earth has a second moon—a tiny, 'mini-moon'—that orbits our planet.

Moons are prevalent throughout our solar system. Simply put, a moon is a natural satellite caught in a planet's orbit. With that in mind, Earth's second moon, a mini-moon, has been orbiting the planet for several years without detection, according to reports from The Atlantic.

The Minor Planet Center, an international organization dedicated to studying asteroids, comets, and small celestial bodies orbiting planets, recently announced the discovery of Earth's new natural satellite. This object, known as 2020 CD3, is about the size of a small car, and it is the only one of Earth's satellites—aside from the actual Moon—that was not intentionally placed into orbit by humans.

Astronomers believe that 2020 CD3 has been orbiting Earth for at least a year, possibly up to three, before being detected on February 15, 2020. While its exact nature is still uncertain, it's most likely an asteroid that was pulled into Earth's orbit after being deflected by the planet's gravity. There's a less likely chance it could be a fragment of the Moon, ejected into space after a collision.

The Moon's position as Earth's primary satellite remains secure. Mini-moons like this one might appear more often, but they are generally too small to reflect sunlight or be visible to the naked eye, which is why most go unnoticed until they exit Earth's orbit. The gravitational interactions between the Moon, Earth, and Sun create unstable orbits for such tiny bodies, eventually sending them back into space. For example, 2020 CD3 follows an erratic, looping orbit around Earth that lasts about four months, and it could escape Earth's pull as soon as April 2020.

2020 CD3 isn't the only significant object in Earth's orbit. Here are five human-made objects visible from space.