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We may have located the exact birthplace of a strange asteroid that seems to have originated on the moon.

In 2021, astronomers noticed that asteroid 469219 Kamo鈥榦alewa, which orbits the sun on the same trajectory as Earth, looked unusual. The light bouncing off it appeared strangely red, marking it apart from the thousands of other near-Earth asteroids we know about.

One of the only plausible chemical compositions that could have produced this distinctive colour matches that of some lunar rock samples, hinting that the asteroid originally came from the moon. It would have been launched into space as a result of an earlier asteroid smashing into the surface and forming a crater.

Now, at the University of Arizona and her colleagues have calculated that the source crater needed to produce such an asteroid would probably be between 10 and 20 kilometres wide and would have formed in the past several million years. They say that the most likely crater, according to these requirements, is the Giordano Bruno crater on the moon鈥檚 far side.

鈥淏eing able to connect an asteroid in space with a specific origin means that we can study the impact process in much more detail,鈥� says Malhotra. 鈥淎ll our understanding about how impacts work comes, mainly, from numerical simulations.鈥�

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Malhotra and her team calculated several different scenarios and have multiple lines of evidence, including Kamo鈥榦alewa鈥檚 current orbit and size, that support such a crater producing the asteroid, but it is difficult to be more certain until we sample material from the asteroid itself, she says.

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China plans to return a sample from Kamo鈥榦alewa with its Tianwen-2 mission, scheduled to launch next year.

鈥淚t鈥檚 extremely challenging to link [Kamo鈥榦alewa] to a specific crater,鈥� says , who is also at the University of Arizona but wasn鈥檛 involved in this work. The asteroid appears to have undergone a significant amount of space weathering, involving chemical changes caused by radiation in outer space, which would have taken a long time, possibly longer than the several million years the Giordano Bruno crater has existed, he says.