Scientists propose that the moon may have formed in a mere five hours following a cataclysmic collision between the early Earth and a Mars-sized planet named Theia, according to a new study. This theory challenges the long-held view that the moon gradually coalesced from debris over many years.
Researchers from the Southwest Research Institute and the University of Arizona utilized advanced computer simulations to explore various impact scenarios. Their findings suggest that under certain conditions, a largely intact moon could have rapidly emerged from the aftermath of the collision. A key factor identified in these simulations is the temperature of the colliding bodies.
"Depending on how hot the Earth and Theia are prior to the collision, an impact can destroy Theia and produce this massive disk of debris that eventually forms the moon," said Dr. Adeene Denton. "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."
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The study, published in Astrophysical Journal Letters, highlights the critical role of the geological properties of the colliding worlds, which were previously often treated as fluid-like. By incorporating the strength of planetary materials and their temperatures, the simulations revealed significantly different outcomes.
"Hotter planets are weaker and more easily torn apart," the researchers stated. "However cooler worlds are stronger and more likely to survive the impact in one piece."
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These findings could offer explanations for some of the moon's enigmatic characteristics, such as its composition and the presence of volatile materials. Dr. Robin Canup, who conducted earlier research on lunar origins, noted the potential connection between the moon's current physical properties and the thermal state of Earth and Theia at the time of impact.
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The shared compositional makeup of Earth and the moon remains a subject of scientific inquiry. One hypothesis suggests that Theia and early Earth originated from the same region of the protoplanetary disk. In contrast, Mars, which formed further away, exhibits distinct compositional differences.
"Because Earth and Mars formed in the same neighbourhood of the solar system, they are like siblings," Dr. Denton explained. "The moon and Earth are like fraternal twins."
In recent lunar history, an out-of-control SpaceX rocket stage impacted the moon in February 2022, creating a visible crater approximately 60 feet wide. The rocket stage, weighing 9,920 pounds, struck the lunar surface at approximately 5,400 miles per hour.