2022 NX1

2022 NX1 is a minimoon that visits more than once.^[1] It was briefly bound to Earth in January 1981 and again in June 2022, each time without finishing a loop around us, and it is predicted to come back in December 2051 and this time complete one.^[1] The guide Minimoons explains the definition and the two kinds.

Found on the way out

It was discovered on 2 July 2022 at the Moonbase South Observatory at Hakos, by the observers Duszanowicz and Camarasa with telescopes of 0.28 to 0.36 m aperture, and the Minor Planet Center designated it 2022 NX1 on 17 July.^[2] By then its closest pass was already behind it: JPL's catalogue puts it 0.0054 au from Earth on 26 June 2022, about 810,000 km, roughly twice the Moon's distance.^[3]

The circular that designated it was unusually cautious. It noted that the object's Earth-like orbit and its evolution over time could point to an artificial origin, something launched from Earth decades ago, or to a piece of rock thrown off the Moon, and that it was being designated anyway in the hope of more observations.^[2] A study published the following month found nothing in its properties or motion incompatible with a natural asteroid, though it was not confirmed natural either.^[1]

Three captures

That study ran the orbit backward and forward. 2022 NX1 was a temporarily captured flyby in January 1981, bound to Earth but gone before completing a revolution, and again in June 2022; JPL lists the earlier pass on 16 January 1981 at 0.0042 au.^[1][3] On 4 December 2051 it returns to 0.0030 au, about 450,000 km, and the study predicts that this time it will be a temporarily captured orbiter, completing at least one loop.^[3][1] A flyby is bound but leaves before one revolution; an orbiter finishes at least one, and the orbiters are about ten times rarer.^[4]

The repeat visits come from its orbit. It follows a horseshoe path at the edge of Earth's co-orbital zone, the region where an object's year almost exactly matches ours, and it belongs to the Arjunas, a loose group of small asteroids on orbits very like Earth's; 1991 VG, another brief minimoon, moves the same way.^[1] Its absolute magnitude of 28.1 makes it brighter, and so probably larger, than 2006 RH120, 2020 CD3 and 1991 VG.^[1]

Where it is now

It is orbiting the Sun slightly outside Earth's path, with a semi-major axis of 1.02 au and a period of 378 days, which is why it drifts back toward us every few decades.^[3] The 2051 visit is the one to watch.^[1] The study also notes that impacts become possible from 2075 on, but that the orbit is not yet known well enough to say more; an object this size would do no harm on the ground, as the guide explains.^[1]