New research suggests that we might have missed something very important in our understanding of how the Moon formed.
Despite its importance and relative proximity, scientists are still not sure how the Moon actually formed in the first place. But one of the leading theories suggests that there was a giant impact between the Earth and a Mars-sized object known as “Theia”, which tore off a huge chunk that somehow left behind the Moon.
Now, researchers have simulated that collision in new ways – and found that we might have missed an important part of the puzzle. That new discovery could change how we understand the formation of the Moon and give us a better sense of when it might actually have happened, say the researchers behind it.
Previously, researchers had thought that the geologic properties of the Earth and Theia were relatively unimportant, and they had largely ignored the strength of the materials colliding because it was irrelevant given the intense energy involved.
In the new research however, scientists revisited the collision and used new simulations that allowed them to incorporate the geologic strength of the objects and the ways that it might vary depending on how hot they were. And those simulations suggested that the strength and temperature of the colliding objects “actually matters quite a bit”, said Adeene Denton, a scientist at the Southwest Research Institute who led the work.
The nature of the collision would depend significantly on the temperature of the bodies as they collided, they found, since hotter bodies are weaker than cold ones. Depending on that temperature and the material strength, some collisions led to a fully intact Moon just hours after the collision, and others led to a disc of material around the Earth that would eventually go on to form a Moon over time.
“Depending on how hot the Earth and Theia are prior to the collision, the impact can destroy Theia and produce this massive disk of debris that eventually forms the Moon,” Dr Denton said. “But when I used the same parameters as original impact modelling — down to the equal temperature structures inside both bodies — within around five hours, an intact Moon emerged.”
Previous simulations have shown a quickly formed, intact Moon. But the new research is the first to suggest that the strength of the objects and their temperature is central to whether and how that actually happened.
“These surprising and exciting new results imply a potential connection between the physical properties of the Moon today, including perhaps its volatile content, and the thermal state of the Earth and Theia at the time of the giant impact,” said Robin Canup, the scientist who helped develop the theory of a big crash that led to the Moon with a paper in 2001, and did not contribute to the new research. “This in turn might help scientists better constrain when the Moon-forming event occurred.”
It still remains unclear why exactly the Moon and the Earth are so similar. But one suggestion is that both Theia and Earth were originally formed in a close environment, whereas Mars came about further away.
“Because Earth and Mars formed in the same neighborhood of the solar system, they are like siblings,” Dr Denton said. “The Moon and Earth are more like fraternal twins.”
The work is reported in a new paper, ‘Collisional Capture of an Intact Moon Depends on Strength’, published in the Astrophysical Journal Letters.
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