Near-Earth asteroid may be a fragment of the moon

In an extraordinary revelation, researchers from the University of Arizona have shed light on how a fragment of the moon could have transitioned to becoming a near-Earth asteroid. 

The study is focused on the asteroid Kamo`oalewa, which was proposed by a UArizona team in 2021 to be a fragment of the moon. 

Now, after two years, another research group at the same university has provided further insight, suggesting a unique trajectory that could have made such a transformation possible.

Lunar fragments 

Study senior author Professor Renu Malhotra noted that so far, only distant asteroids from beyond the orbit of Mars have been considered a source of near-Earth asteroids. “We are now establishing that the moon is a more likely source of Kamo`oalewa.”

This raises intriguing prospects of the presence of many undiscovered lunar fragments within the near-Earth asteroid population. 

Unique characteristics

The researchers were particularly interested in two unique aspects of Kamo’oalewa. First, it is designated as Earth’s quasi-satellite. This term is reserved for asteroids that have orbits resembling Earth’s so closely that they give the illusion of orbiting the Earth, even though their actual path is around the sun. 

The other peculiar aspect of Kamo`oalewa is its longevity, said Jose Daniel Castro-Cisneros, the study’s lead author and a graduate student in the Department of Physics. 

Unlike other celestial objects that occupy Earth-like orbits temporarily, Kamooalewa is expected to remain Earth’s companion for millions of years. 

Meteoroid impact

Interestingly, a 2021 study had already hinted at Kamo`oalewa’s lunar origins. The asteroid’s spectrum was distinctly different from other near-Earth asteroids but closely mirrored that of the moon. This led to the theory that a meteoroid impact might have ejected this fragment from the lunar surface.

Earth-like orbits 

In the current study, the researchers set out to investigate the feasibility of a lunar fragment adopting a quasi-satellite orbit. The challenge is that moon fragments capable of escaping the gravitational pull of both Earth and the moon usually don’t end up in Earth-like orbits. 

However, using precise numerical simulations which accounted for gravitational impacts from all planets, the team found that certain lunar fragments can land in such orbits. Kamo`oalewa might just be one of these fragments, a result of a lunar impact occurring in the last few million years.

Throughout its history, the moon has been bombarded by asteroids, which is evident in the numerous impact craters preserved on its surface, explained Malhotra. Impacts cause lunar material to be ejected from the moon’s surface, but most of that material usually falls back on the moon, she said.

Study implications 

According to the researchers, the study’s findings could help understand more about near-Earth asteroids, which are considered a hazard to Earth. Malhotra noted that more detailed studies of Kamo`oalewa and determining this asteroid’s origin in a specific impact crater on the moon will provide useful insights on impact mechanics.

Castro-Cisneros said the team is planning to identify the specific conditions that allowed the orbital pathway of Kamo`oalewa. 

“We looked at Kamo`oalewa’s spectrum only because it was in an unusual orbit,” said Malhotra. “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.”

Video Credit: Jose Daniel Castro-Cisneros/University of Arizona

The study is published in the journal Communications Earth & Environment.

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