Asteroid 2016 HO3

Asteroid 2016 HO3 - Earth's Constant Companion
NASA Jet Propulsion Laboratory
Summary from View From The Porch:

Gaia has a pet rock.

It's not a moon, because it orbits the sun, not the earth. Well, sort of. Its orbit around the sun kind of oscillates around the earth, hence its name: Kamo'oalewa, which is apparently Hawaiian for something along the lines of 'oscillating celestial object'.

There are questions about its origin, whether it's a rogue asteroid that's been swept up in our gravitational orbit or what. The current prevalent theory is that it's an actual chunk of the moon knocked loose in a giant cosmic fender bender, and is following us through space like the celestial equivalent of those busted turn signal lenses you see lying on the pavement in busy intersections.

In order to settle the mystery, and because it would be a baller accomplishment that would be a feather in their space program's cap, China is planning on sending a probe to retrieve samples from it for study.