Luna may have had a more complicated birth than we thought
Nesa/noaa
Multiple impacts on Earth could better explain the origins of our Moon than a single giant impact 4.5 billion years ago, and could help solve one of its greatest mysteries.
Consolidation origin of our moon it was hard. The main idea is that it was formed in the early stages of the history of the solar system after the collision of the Earth with a giant Mars-sized object known as Theiawhich may have arisen closer to the sun than where our planet is located. The impact would have thrown debris into space that would have eventually coalesced into the large natural satellite we see today, at a time when the material around the Sun was more mixed up and impacts were common.
But the Earth and Moon are remarkably similar in composition, which makes this model a little tricky since the Moon would have retained more material from Theia than from Earth. “This is a big problem for the canonical model,” says Philip Carter at the University of Bristol, UK.
Instead, Carter and his colleagues suggest that a chain of impacts on Earth over several million years might better explain why the Earth and Moon are so similar in composition. They show that three or more large impacts with our planet in the early solar system, involving objects ranging in size from the current Moon to almost the size of Mars, could explain the origin of the Moon we see today.
In this scenario, each collision will result in a small moon or satellite appearing in Earth's orbit. Over thousands of years, these moons gradually came together under the influence of their gravity, forming one large object. “They will attract and collide with each other,” Carter says. “It’s very unlikely that you’ll end up with a stable system with multiple large moons.”
Previous models also pointed to the origin of the Moon from multiple impacts, but they required much more hits on Earth up to 20 compared to this latest model. “After three impacts, we put enough mass into orbit to form a full moon,” Carter says.
Robert Citron of the Southwest Research Institute in Colorado say fewer impacts “may be better” because the more impacts the model has, the more likely it is that existing moons will be thrown out of Earth's orbit, preventing the moon from forming. However, using more collisions results in a closer compositional similarity between the Earth and the Moon, which better explains what we see today. “When you have multiple hits, you average out more of those hitters,” Citron says.
Finding out how the Moon formed is important because the Earth-Moon system is unusual. “This is such a unique satellite,” Citron says. “It is very large compared to Earth, whereas the Martian moons are very small compared to Mars, and the gas giant moons are very small compared to these planets.”
Carter said more complex modeling is needed to determine which idea is correct, including the severity of the impacts on Earth and the amount of material ejected into space. “It’s still very difficult to actually calculate everything in detail,” he says. “Personally, I prefer this multiple exposure model to the canonical single exposure model.”
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