Technically, the Earth has a new moon.

It was discovered in February by astronomers Kacper Wierzchos and Teddy Pruyne at the Catalina Sky Survey observatory near Tucson, Ariz., then shown to be on a chaotic orbit around the Earth as the Earth orbits the sun. That makes it a moon, a natural satellite.

“Orbit integrations indicate that this object is temporarily bound to the Earth,” reads a notice from the International Astronomical Union. “Further observations and dynamical studies are strongly encouraged.”

Dramatic as it sounds, this new moon will not change your life. It will not move the ocean tides, as the Moon does. It will not hit your eye like a big pizza pie, not unless you have access to some serious telescopes. No man’s face is in it, and no one will ever step on it. It neither waxes nor wanes, from crescent to full. It will not reliably measure time, as the Moon always has, which lingers linguistically in the derived word “month.” There will be no manic first day of the week named for 2020 CD3, as the new moon is officially known.

The capital-M Moon is special, and it takes a challenger satellite, this grasping little lunar arriviste, to remind us just how special it is.

The Moon is not, like 2020 CD3, some random chunk of rock the size of a small couch, elongated and vaguely triangular, that happened to be captured by Earth’s gravity, out in the vast distance. It is not, like CD3, a “temporarily captured object,” which entered Earth’s orbit during the Trump administration, and has looped us about 50 times, perhaps already for the last time.

The Moon is a near-spherical key to the origin and sustaining of life itself, and a leading figure in mythological imagination since the first person looked up. As Paul Simon sang: “If you want to write a song about the human race, then na na na na na na yeah yeah yeah, write a song about the Moon.”

2020 CD3 came from away, probably from the solar system’s main asteroid belt between Mars and Jupiter, where it had previously been orbiting only the sun at a similar pace to the Earth. That similarity meant it approached Earth slowly enough to be captured.

The Moon was not captured. It was born of the Earth itself

But the Moon was not captured. It was born of the Earth itself, in a collision nearly 5 billion years ago, when a smaller planet called Theia collided with the proto-Earth at a few kilometres per second. They call this the Big Splash, and it knocked Earth’s orbital axis off centre by 23 degrees, which is why we have annual seasons and, for the moment, polar ice caps.

The Moon is also comparatively huge, about a quarter the diameter of Earth. Most moons are many more times smaller than their planets. You could fit 2020 CD3 in a pickup truck.

Also, the Moon is very close, only about 30 Earth diameters away, one of the most intimate lunar orbits. 2020 CD3 has passed by Earth a lot closer than that but only irregularly.

Most moons are at a distance from their planet because they are formed along with the planets, out of a collapsing accretion disk of matter. If they were closer, they would eventually collide. The big moons are round because their own gravity shapes them that way, but there are some smaller irregularly shaped ones.

It is rare for a moon to be captured into a stable planetary orbit. The most recent moonlet captured even into temporary orbit by Earth’s gravity was 2006 RH120, a similar-sized asteroid that was in orbit for a few months ending in June, 2007.