The Moon formed in just five hours: scientists discover how it happened
Perhaps one of the most dramatic events in the history of our solar system happened much faster than previously thought. According to a new study, the Moon could have formed almost entirely within just five hours following a massive collision approximately 4.5 billion years ago.
Perhaps one of the most dramatic events in the history of our solar system happened much faster than previously thought. According to a new study, the Moon could have formed almost entirely within just five hours following a massive collision approximately 4.5 billion years ago.
For decades, the accepted explanation was that an ancient body similar in size to Mars, called Theia, collided with the young Earth. The impact ejected huge amounts of molten rock into space, creating a disk of debris around the Earth. According to the classic scenario, this material gradually coalesced until the Moon was formed.
However, researchers from the Southwest Research Institute and the University of Arizona are now proposing a different possibility: under certain conditions, the collision itself could have produced an almost complete Moon within a few hours.
The decisive factor: temperature and physical strength
The researchers discovered that the decisive factor might be the temperature and physical strength of the Earth and Theia before the collision. In previous models, the two bodies were treated almost like giant liquids, assuming that the immense energy of the collision would break them apart regardless, erasing the importance of their geological structure.
But when the researchers included the strength of the rocks and their temperature in the calculations, the results changed significantly.
"Depending on how hot the Earth and Theia were before the collision, the impact could destroy Theia and create a huge disk of debris that would eventually become the Moon," explained Dr. Adin Denton, who led the study.
However, when she used the same basic conditions as previous models but gave both bodies a similar internal structure and temperature, something completely different happened. "Within about five hours, a whole Moon appeared," she said.
The explanation is that hotter bodies are physically weaker and therefore tend to break apart more easily. Cooler and stronger bodies can survive a larger portion of the collision's force and do not necessarily have to disintegrate completely into a cloud of debris.
A new understanding of the ancient process
The idea that the Moon could have formed within hours is not entirely new. A prominent 2022 study already presented models in which the Moon formed almost immediately after the collision. The innovation in the current study is the understanding that the temperature and strength of the two colliding bodies may dramatically change the result, determining whether a Moon forms almost immediately or as a disk of material that builds up later.
According to the researchers, the new scenario may help explain some properties of the Moon that do not fit easily into the traditional model, including its chemical composition and the amount of volatile materials remaining. Dr. Robin Canup, who has previously studied the formation of the Moon, said the results might even help scientists narrow down the time range in which the ancient collision occurred.
The connection between Earth, the Moon, and Theia
One of the big open questions is why the Earth and the Moon are so similar in composition. If a large part of the Moon formed from material that came from Theia, one would expect it to be more different from the Earth. One possibility is that Theia and the Earth formed from the beginning in the same area of the ancient solar system.
Denton compared it to a family. According to her, the Earth and Mars are like "brothers" that formed in the same neighborhood of the solar system, but the Earth and the Moon are more like "fraternal twins." While the study does not prove this is exactly how the Moon formed, it adds an intriguing possibility: instead of being built over a long period from a cloud of debris, the Moon we see every night may have been born almost all at once—in less than a day.
