Asteroid near Earth is actually a chunk of the Moon, scientists say

Andrew Griffin
Friday 12 November 2021 05:42

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A near-Earth asteroid known as Kamo`oalewa might be made of a stray chunk of the Moon, scientists have said.

Kamo`oalewa is one of a mysterious and little-understood set of objects called quasi-satellites. It is an asteroid that orbits around the Sun but remains close to the Earth.

As with all objects of that type, Kamo`oalewa is difficult to observe. Though it is relatively close to the Earth – it comes as close as 9 million mile away – it is also very faint, about 4 million times darker than the faintest star humans can see in the sky.

Indeed, Kamo`oalewa can only be seen for a few weeks, every April. And its small size means that scientists can only track it with one of the largest telescopes on Earth.

When it was passing by, however, scientists did manage to examine the patterns in the light that came back from Kamo`oalewa. And what they found suggests that it might have a very familiar origin.

The spectrum of light that came back from the asteroid matched up with rocks that were brought back from the Moon by Nasa’s Apollo missions. As such, it may have originated from the Moon.

Scientists don’t know how it might have broken off from the Moon. That is partly because Kamo`oalewa would be alone as an asteroid with lunar origins, and there is simply nothing else for scientists to compare it with.

Another clue the object’s origins is the way the asteroid moves around in space. Its orbit around the Sun is very similar to the Earth’s – but with a slight tilt.

That is not like other near-Earth asteroids. But it might be expected of an object that came from the Moon.

“It is very unlikely that a garden-variety near-Earth asteroid would spontaneously move into a quasi-satellite orbit like Kamo`oalewa’s,” said Renu Malhotra, a co-author on the study, in a statement. “It will not remain in this particular orbit for very long, only about 300 years in the future, and we estimate that it arrived in this orbit about 500 years ago.”

A paper describing the research, ‘Lunar-like silicate material forms the Earth quasi-satellite (469219) 2016 HO3 Kamoʻoalewa’, is published in Nature’s Communications Earth & Environment.

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