Earth’s “half moon” was likely ejected away from the actual moon relatively recently in the solar system’s history, according to a new study.
Kamo’oalewa, a near-Earth object (NEO) 131 to 328 feet wide (40 to 100 meters), was recovered from an asteroid impact between 1 million and 10 million years ago; According to the study, the mile-wide (22 kilometers) Giordano Bruno crater.
Kamoʻoalewa, or officially “469219 Kamoʻoalewa,” was discovered in 2016 by the Pan-STARRS 1 asteroid survey telescope in Haleakalā, Hawaii, as part of NASA’s planetary defense effort to discover space rocks likely to impact our planet. .
Kamo’oalewa, Hawaiian for “oscillating celestial body”, It was later discovered to orbit the Sun in synchronization with the Earth, spinning extremely fast for an asteroid. These surprising features led scientists to investigate the origins of the half-moon. Studies conducted in 2021 revealed that Kamo’oalewa’s composition is similar to rocks derived from the moon, indicating its lunar origin. The question was: Where exactly did the Moon come from?
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“Our key findings are that, unlike the majority of asteroids belonging to the NEO population, Kamo’oaelewa originates from the moon and not from the asteroid belt,” said Center National de la Recherche Scientifique team member and senior investigator Patrick Michel. France’s state research agency CNRS told Space.com.
“Like the detectives, we used all known information about this Kamo’oalewa and the lunar surface to derive a scenario for the origin of this object, starting with the impact that created the Giordano Bruno crater,” Michel said.
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Working like crime scene investigators, the team connected Kamo’oalewa to the Giordano Bruno crater. They used a computer model to mimic the type of impact that could create this moon-like space rock.
This meant taking into account things like the size and velocity distributions of the resulting eruptions and their dynamic evolution. This reconstruction showed that some ejecta would eventually enter orbital 1:1 resonance with the Earth, having the same dynamical properties as Kamo’oalewa.
“Our results show us that, if our scenario is correct, Kamo’oalewa is very likely to be a piece of the lunar surface where we can directly correlate with a known crater,” Michel said.
“Usually the best we can do is determine the source region in the asteroid belt by knowing the current orbit of an NEO. In such predictions a region is often very large, such as the inner or outer asteroid belt.” Additional. “Here we identified a very specific body and location from which this object came, which is very exciting.”
Michel explained that Kamo’oalewa’s orbit is not stable, which led the team to attribute it to a crater that is not very old, probably between 1 million and 10 million years old.
“So we also needed the crater not to be too large so that a solid piece the size of Kamo’oaelewa could be produced,” he continued. “The best candidate was Giordano Bruno, who fit both restrictions.”
The team’s impact modeling also gave them an idea of the size of the space projectile that would create the roughly 14-mile-wide lunar crater and its moon-like jet. They estimated that the asteroid that hit the moon would have needed to be about 1 mile (1.6 kilometers) wide to create the Giordano Bruno crater and liberate Kamo’oalewa.
If an asteroid this size were to hit Earth, it would release approximately the same amount of energy as the explosion of a million-megaton bomb.
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The findings also have implications for our understanding of the NEO population around Earth; It implies that a larger proportion of these objects than suspected may have resulted from impacts on the moon or other solar system bodies.
“Although the majority of NEOs originate from the main asteroid belt between Mars and Jupiter, a small portion may originate from the moon or elsewhere,” Michel said. “When something unusual happens and the origin of the Moon seems possible, we now know that we can check whether a fragment from the Moon will lead to the orbit of the object in question, and close the loop by identifying the crater from which it likely came.”
Michel added that the discovery that Giordano Bruno crater and NEO Kamo’oalewa are likely connected is a stark reminder that impacts of massive space rocks occurred even during this later, calmer period of the solar system’s 4.6 billion-year history.
This underscores the importance of planetary defense projects such as NASA’s recent Double Asteroid Redirection Test (DART), which examined the effectiveness of diverting an asteroid on a collision course with Earth.
“The impacts occur in the interior of the solar system, but while the traces are erased on Earth, they are not erased on the Moon. Our natural satellite therefore contains a record of the impact history around the Earth over the last 4 billion years,” Michel said. said. . “That’s why some of us are extremely interested in planetary defense, the NASA DART mission that performed the first asteroid deflection test, and the European Space Agency Hera mission, on which I served as principal investigator for detail.”
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Michel admits that the team’s results are only temporary. Therefore, although they suggest a strong connection between Kamo’oalewa and the moon, further research on the asteroid will be required to confirm this connection.
“The next most exciting work on Kamo’oalewa will be presented by the Chinese Tiawen-2 mission, which should be launched in 2025 to sample the asteroid’s surface and send the samples to Earth for laboratory analysis,” he said. “This is a very challenging task because no one has ever visited such a small object that spins around in just 28 minutes.
“Analysis of the samples will tell us for the first time what happened.” [are] “The physical and thermodynamic state of a fragment of this size removed from the lunar surface by an impact, which is something we cannot determine in our impact model.”
The team’s research was published Friday, April 19, in the journal Nature Astronomy.