The Moon may have formed just hours after the giant impact


A puzzle of planetary proportions

The team modeled the Theia-Earth collision about 400 times, using smoothed particle hydrodynamics in their numerical simulations. This method, commonly deployed for giant impact simulations, allows scientists to model particles under the influence of both gravity and pressure. Previously, hundreds of thousands to millions of particles were used to simulate the formation of the Moon. But these new simulations used up to one hundred million particles, making them one of the most detailed to date.

The extra computing power showed that at lower resolutions, researchers miss crucial behaviors that occur in such collisions. “We went into this project not knowing exactly what the results of these high-resolution simulations would be,” Kegerreis said. “So in addition to the big reveal that standard resolutions can give you misleading answers, it was very exciting that the new results could include an orbiting satellite resembling the Moon.”

In their direct training simulations, the team was able to produce a Moon with a wide orbit and an interior that is not completely melted. Together, these attributes could help explain the Moon’s inclined orbit and relatively thin crust.

As intriguing as they are, simulations are still unable to explain everything we know about the Moon. Namely, the new simulations were able to form a Moon made up of 60% Earth material. But that’s still not enough to explain the extreme isotopic similarities between Earth and the Moon.

“Even a cluster with 60% protoEarth material, with the rest of Theia, should still produce a much larger Earth-Moon isotope difference than what we see,” said Robin Canup, assistant vice president of the Science and Technology Division. space engineering from SwRI. , Told Astronomy.

And while the paper suggests that material from Theia and Earth may not have completely mixed in the rapidly forming Moon, creating a gradient of Earth-like material closer to the surface, Canup says that it’s not very likely. “For any part of the Moon that forms intact, there is no possibility of mixing between protolunar and post-impact Earth material to remove such compositional differences.”


Looking forward

Determining the specifics of the Moon’s formation will require further analysis of lunar rocks excavated from unexplored regions of the Moon – which NASA’s upcoming Artemis missions hope to help. Scientists are also looking to collect samples from below the Moon’s surface. Combined with simulations like these, researchers hope to be able to solve the mystery of exactly how the Moon formed around nascent Earth around 4.5 billion years ago.

And, as a bonus, learning more about our celestial partner will also reveal more about Earth itself.

“The more we learn about the birth of the Moon, the more we discover about the evolution of our own Earth,” said Vincent Eke, a researcher at Durham University and co-author of the new study. “Their histories are intertwined – and could find an echo in the histories of other planets altered by similar or very different collisions.”

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