This asteroid is a piece of the Moon. How did it come to be?

In 2021, a near-Earth asteroid named Kamo`oalewa was discovered to be a hunk of the Moon, and now new research has finally put forward a theory linked to its unusual orbit which suggests how it might have been created.

“Several hypotheses have been proposed for the origin of Kamo‘oalewa,” the researchers write in their new paper.

“The focus of the present work is to examine the hypothesis that Kamo‘oalewa originated as lunar ejecta. We approach this by numerically simulating test particles launched from the Moon’s surface and following their subsequent orbital evolution.”

It’s important to note that Kamo`oalewa is not a regular, olympic-swimming-pool-sized asteroid. It orbits the Sun, although it sticks so close to Earth it looks like it orbits the Earth. This is called an Earth quasi-satellite.

It’s also not as fickle as some other asteroids. Modelling has suggested that the asteroid will remain in this same position for millions of years, while most objects in this sort of orbit remain for only a few decades.

“We looked at Kamo`oalewa’s spectrum only because it was in an unusual orbit,” said Professor Renu Malhotra, a planetary scientist at the University of Arizona.

“If it had been a typical near-Earth asteroid, no one would have thought to find its spectrum and we wouldn’t have known Kamo`oalewa could be a lunar fragment.”

The new research has been published in Communications Earth & Environment.  

This new study has looked at how feasible it was that a piece of Moon could end up in this weird orbit. The team simulated Moon explosions, and forecast the orbit of the resulting debris.

“As these ejecta escape the Earth-Moon environment, they face a dynamical barrier for entry into Earth’s co-orbital space,” the researchers wrote.

“However, a small fraction of launch conditions yields outcomes that are compatible with Kamo‘oalewa’s orbit.” While rarely are things sure in science, this does give a way for the asteroid to have ended up in its current position. More research will need to be done to check that this was indeed what happened. The researchers are also investigating the age of Kamo‘oalewa.

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