Did you know that the Earth has a second month?

If you ask a kindergarten child, a high school child, a student or a retiree, you will get the same answer to the question How many months does Earth have?

It’s just that the truth is a little different, because there is another moon in orbit around the Earth, which was discovered only in 2016. And according to a new study in Nature, it is possible to finally know how it formed.

The quasi-moon – called Kamo’oalewa, after a Hawaiian word that refers to a moving celestial object – doesn’t have much to know or share about it. Measuring less than 50 m (164 ft) diameter, is even tiny.

It orbits the Earth in a repeated, corkscrew-like trajectory that brings it no less than 40 to 100 times the 384,000 km (239,000 miles) distance of our best-known moon.

Its strange flight path is caused by the competing gravitational attractions of the Earth and the sun, which bend and continuously tighten the moon’s movements, preventing it from reaching a more conventional orbit.

None of this means that Kamo’oalewa must have particularly exotic origins. The solar system is dotted with asteroids, some of which are captured by the gravity of other planets and become more conventional moons – albeit fragmentary.

Others do not orbit other planets as usual, but line up in front of or behind them and walk their orbits around the sun, like flocks of so-called Trojan asteroids that precede and follow Jupiter.

In any case, the star in question was bound to attract attention, because its composition was a stubborn mystery. Asteroids tend to reflect strongly in certain infrared frequencies, but Kamo’oalewa simply does not. It’s weaker somehow – clearly made of different things, which suggests a different origin.

To investigate the mystery, Sharkey, under the guidance of his doctoral advisor, planetary scientist Vishnu Reddy, first used a NASA-led telescope in Hawaii, commonly used to study asteroids in the vicinity of Earth.

But even with the usually reliable instrument, the infrared signature seemed too weak. Instead, they switched to a monocular telescope led by the University of Arizona, which, as Sharkey says, could “collect every last gram of photons from that object.”

This produced better, clearer results, but they were still incomplete. The rock was made of ordinary silicates, like other asteroids, but they were common only in their general composition, not in their infrared signature, which remained stubbornly deactivated.

Finally, the answer was self-evident. If Kamo’oalewa behaved like a kind of quasi-moon, maybe it was a real moon artifact. Earlier in Sharkey’s doctoral program, one of his advisers published a paper on the monthly samples brought back by the Apollo 14 mission in 1971.

When Sharkey compared the data he was getting with his telescope to what previous geologists had discovered in the rock lab, the results matched perfectly. The type of lunar space weathering silicates they undergo when they are still on the moon’s surface explained exactly the differences in infrared reflectivity between ordinary asteroids and Kamo’oalewa.

How Kamo’oalewa shook off our lunar companion is no mystery. The moon has been bombarded by space rocks for billions of years, leading to the evacuation into space of all kinds of lunar debris (of which almost 500 bits have reached the Earth’s surface in the form of meteorites). The tiny natural satellite is such a piece of lunar rubble that has spiraled away from Selena. But instead of landing on Earth or simply collapsing into space, a quasi-satellite was found in itself.

Kamo’oalewa will not stay that long, as its current trajectory is not completely stable. According to estimates by Sharkey and others, the object will remain an earthly companion for only about 300 years – a nothing in cosmic time – after which it will break free of current gravitational chains and spin in a vacuum. Initially part of the Moon, then an Earth companion, he will spend the rest of his long life traveling alone. Who knows, maybe at another point in her existence, she will find a new planet next to which to stay longer.