This crater could be the place where Earth’s ‘second moon’ broke off the first: ScienceAlert

You may never be able to go home again, as the old saying goes, but for a piece of rock that shares Earth’s orbit around the sun, you might finally know where it is.

The origin of the asteroid Kamo’oalewa, discovered in 2016, is a mystery, but astronomers think it is part of the moon. A new analysis has even identified the crater from which it may have been carved out.

Using numerical simulations, a team led by astronomer Yifei Jiao of Tsinghua University in China determined the properties of the crater that most likely spawned the asteroid, and found a real one that matches those properties: the Giordano Bruno crater at the other side of the earth. the moon.

“We investigated the processes of impact-induced lunar fragments migrating into Earth’s co-orbital space and presented support for the possible origin of Kamo’oalewa from the formation of the Giordano Bruno crater a few million years ago,” the researchers write in their article.

“This would directly connect a specific asteroid in space to its source crater on the moon, and suggests the existence of more small asteroids composed of lunar material yet to be discovered in near-Earth space.”

Earth, compared to most planets in the solar system, is relatively light in terms of the moon. Although a giant as far as moons go, the only natural satellite sharing our orbital space seems rather lonely.

That said, it’s surprisingly difficult to see things in space, even when they’re close, and we tend to overlook the extra “minimoons” hanging around our environment.

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Kamo’oalewa is a kind of example for the shadow family of our planet. It has been hanging around for at least centuries, sharing Earth’s proximity to the Sun. And its distance from Earth varies considerably, meaning it would be particularly elusive.

Ultimately, of course, we found it, and it was a bit of a puzzle. But last year scientists published a pre-print article with a very plausible explanation.

The way Kamo’oalewa reflects light, and its color, is very similar to that of the moon’s surface and not at all like other asteroids near Earth. Combined with a close study of its orbital properties, they concluded that the strange rock was once part of the moon.

Jiao and colleagues have now taken the analysis a step further, using the asteroid’s physical and orbital properties and lunar impact models to figure out where on earth it came from.

For example, since Kamo’oalewa has a fairly fast rotation, it must be a pretty sturdy clump. Otherwise it would fly apart in a haze of fragments. Because it is a monolith, it is reasonable to assume that it was excavated as a single piece, rather than as a solidified pile of loose debris ejected on impact.

Working backwards involves an impact that leaves a crater larger than about 10 to 20 kilometers (6 to 12 miles).

Near-Earth asteroids typically don’t stay near Earth for more than about 100 million years, meaning Kamo’oalewa must be younger than this. An impact of the magnitude needed to rip out the asteroid would also produce debris, which is expected to stick around for about 10 million years. Since we found no such debris, this implies that Kamo’oalewa is between 10 and 100 million years old.

There are not many craters on the moon that meet the size requirement and are also younger than 100 million years old. There are several dozen candidates, but the Giordano Bruno crater, 22 kilometers across and less than 10 million years old, is the best of them, the researchers found.

“It is clear that the largest, youngest craters are more likely sources, because they produce more escaping fragments that still remain in space or in the co-orbital region of Earth,” they write. “And indeed, Giordano Bruno is the only possible source crater that meets the criterion.”

The pyroxene composition around the crater walls and rim is similar to the composition of Kamo’oalewa, and up to 400 fragments the size of Kamo’oalewa are believed to have been ejected from the site following the impact of an asteroid only 1.66 kilometers in diameter.

Simulations suggest that most of these fragments will be ejected from Earth’s co-orbital space ten million years after impact, but it is absolutely possible that rare exceptions may persist and end up in an orbit similar to that from Kamo’oalewa.

The evidence is far from conclusive, but we’ll find out soon. We have lunar meteorites here on Earth that have been associated with the Giordano Bruno crater.

And China’s National Space Administration plans next year to launch Tianwen-2, an asteroid sampling mission that will explore Kamo’oalewa, retrieve a sample and deliver it here for Earth scientists to study. Perhaps even future missions could discover what happened to the rest of the rocks that flew into space with Kamo’oalewa.

The research was published in Nature.