Nearby asteroid's birthplace traced to specific crater on the Moon

Many asteroids can be traced back to their parent body – the planet or moon they broke off from. But for the first time, scientists now claim to have traced the origins of an asteroid back to the specific crater it was birthed from.

Craters are not only the scars that asteroid impacts leave on planets or moons, but they can be the birthplace of new asteroids too. If something hits hard enough, fragments of rock can be ejected into space, where they can drift around as new asteroids for untold millennia until they crash into something else, potentially starting the process over again.

Scientists can often tell which parent body any given asteroid originated from, by analyzing the rocks’ composition, reflectiveness, and other signatures. But they usually can’t figure out exactly where on those worlds they came from – until now.

Measuring between about 46 and 58 m (150 and 190 ft) wide, Kamo’oalewa is an asteroid that was discovered in 2016 as a “quasi-satellite” of Earth. That means this strange little space rock technically orbits the Sun, but Earth’s gravity has enough of an influence on it that it never gets too far away from us. In 2021, a follow-up study found that it’s probably a piece of the Moon, based on its reflectivity and orbit.

Now, an international team of scientists has tracked its home even more precisely. Impact and dynamical modeling revealed that to launch a chunk of rock the size of Kamo’oalewa away from the Moon, it would take an impact from an asteroid of at least 1 km (0.6 miles) wide. That in turn would leave a crater larger than 20 km (12.4 miles) in diameter. It also would have had to have been relatively recent – meaning the last few million years – for Kamo’oalewa to still be hanging around.

The team scanned the thousands of craters littering the lunar surface, and found only one that matches the age and size – Giordano Bruno. Named after a 16th-century Italian intellectual whose cosmological views were so ahead of his time that he was burned at the stake for heresy, this crater is located on the far side of the Moon, measures 22 km (14 miles) wide, and has been dated to just 4 million years old.

Kamo’oalewa probably wasn’t the only fragment launched that day – the team estimates that over a thousand pieces of debris measuring dozens of meters wide would have escaped into space.

“While most of that debris would have impacted the Earth as lunar meteorites over the course of less than a million years, a few lucky objects can survive in heliocentric orbits as near-Earth asteroids, yet to be discovered or identified,” said Yifei Jiao, lead author of the study.

We may get a closer look at Kamo’oalewa in the near future. China has selected the little asteroid as the target for its upcoming mission Tianwen-2, which will collect samples and return them to Earth for study. If it is indeed from the Moon, then it should have originated much deeper than any lunar samples collected by previous missions.

“It will be different in important ways from any of the specimens we have so far – one of those connecting pieces that help you solve the puzzle,” said Erik Asphaug, co-author of the study.

The research was published in the journal Nature Astronomy.

Source: University of Arizona