Every now and again an object from space will pass by Earth and the Moon with just the right direction and speed to go into orbit around us. It’s rare, since usually something coming in from deep space is moving too rapidly to get captured, but if it passes the Moon, say, it can lose a bit of energy and wind up in orbit.

Such is the case for 2025 US6, a small object that approached us early in 2023 and passed Earth in June. It dipped pretty close to us, flew out well past the Moon, then came back for a series of wild movements before going into an elliptical orbit around us. This orbit brought it out as far as the Moon, which made more encounters inevitable, so its orbit is pretty whacky.

Tony Dunn, an amateur astronomer who is quite accomplished in calculating orbits, put up a nifty animation of it on Bluesky:

As you can see it’s currently in an elliptical orbit that is rotating around Earth, then gets a series of higher and higher kicks until it leaves our system in late 2028. It wasn’t discovered until very recently, indicating it’s small (meaning faint). Is it an asteroid?

My friend and colleague Jonathan McDowell, an expert in space missions and orbits, doesn’t think so: 

He thinks it’s likely a Chinese spacecraft called DRO-B, which was a small lunar mission launched in 2024. But wait! That’s after Tony’s animation thinks it came from deep space! How is that possible?

Well, the animation assumes it came from deep space, by taking the current motion and working backwards. By 2024 it was already in Earth orbit, so it’s quite possible it started there, or at least started on Earth and headed for the Moon. 

It and it’s partner spacecraft, DRO-A, were supposed to be sent into a high retrograde lunar orbit, meaning they orbited the Moon “backwards” relative to the Moon’s orbital motion around Earth, and the orbits were highly elliptical. However, the booster for the spacecraft failed to get them out of low-Earth orbit. The Chinese engineers then got to work, and planned an extremely clever and difficult set of maneuvers that allowed the spacecraft to move up their orbits until they could leave Earth and head toward the Moon. The Chinese don’t release much info about their missions, but it’s possible DRO-B then wound up in an orbit that brought it back to Earth.

At the time I wrote this (Monday, Oct. 27) I don’t see 2025 US6 listed at the ESA or JPL sites for asteroids. I’m curious to see if it gets listed there as an asteroid or space junk.

Incidentally, this is not to be confused with a newly discovered small (~20 meter) asteroid called 2025 PN7, which is a quasi-moon of Earth. That means it has an orbit very much like Earth’s, but a bit more elliptical. It orbits the Sun, but from Earth it kinda looks like it orbits us. I’ve written about these guys before. A lot of the time some media, staid as always, posts something like “Earth has a second moon!” but that’s not true in this case. If 2025 US6 does in fact turn out to be an asteroid, it really is a second moon, if only for a few years. 

By the way I was interviewed by a reporter for The Atlantic about PN7, and I’ll link to that when it goes live. And if I hear more about US6 I’ll be sure to update y’all.

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