The Moon has intrigued people for thousands of years, and in recent centuries, scientists have tried to figure out how and when it formed. One reason for sending astronauts to the Moon was to answer this question. The Moon also helps us understand more distant objects in space. But if we can’t determine the Moon’s exact age, how can we know the age of other things in space?
The Moon is believed to have formed from a collision between Earth and a Mars-sized planet. This event is thought to have happened around 4.35 billion years ago, based on dating rocks brought back from the Moon.
However, some evidence, like the age of certain minerals on the Moon’s surface, suggests the Moon might be about 4.51 billion years old. It means it came to be about 200 million years after the formation of our solar system.
Some scientists are skeptical about the idea of the Moon-forming so late. In the solar system’s early days, debris and planetary bodies collided to form planets. By 200 million years, most of this chaos had settled into larger bodies. Because of this, many scientists who simulate the solar system’s evolution find it unlikely that such a massive collision could have formed the Moon so late in the process.
In a new study, UC Santa Cruz Professor Francis Nimmo and his co-authors suggest a possible explanation for the Moon’s age discrepancy. They propose that around 4.35 billion years ago, the Moon underwent a “remelting” due to Earth’s tidal pull, causing significant geological activity and intense heating. This remelting could have “reset” the age of the lunar rocks, effectively hiding the Moon’s true age, much like a volcanic facelift.
Researchers suggest that a remelting event caused by the Moon’s changing orbit could explain why many lunar rocks, including those collected by the Apollo missions, are around 4.35 billion years old. Instead of these rocks forming during the Moon’s initial solidification, they might have been remelted later. Using modeling, the authors show that tidal heating from Earth’s pull could have been strong enough to trigger this remelting around 4.35 billion years ago, effectively “resetting” the apparent age of the lunar samples.
The research team compares the Moon’s hypothetical remelting event to the volcanic activity on Jupiter’s moon Io, the most volcanically active body in the solar system. Like Io, which experiences tidal forces causing volcanic eruptions, the early Moon may have undergone widespread volcanic activity due to similar tidal heating from Earth.
Study cracked a vital process in Moon rock formation
The researchers also suggest that this remelting could explain why fewer lunar impact basins are from early bombardments than expected, as they would have been erased during the heating event. Based on this idea, the team proposes that the Moon’s formation occurred between 4.43 and 4.53 billion years ago, at the higher end of previous age estimates.
Nimmo said the next research stage will involve more complex simulations that refine our understanding of how tidal heating might have reset the Moon’s geological clock. This and additional lunar samples from future missions should shed more light on the Moon’s true age.
The team is now looking forward to more detailed modeling to explore further the effects of tidal heating on the Moon’s geology.
“As more data becomes available—particularly from ongoing and future lunar missions—the understanding of the Moon’s past will continue to evolve,” Nimmo said. “We hope that our findings will spark further discussion and exploration, ultimately leading to a clearer picture of the Moon’s place in the broader history of our solar system.”
Journal Reference:
- Nimmo, F., Kleine, T. & Morbidelli, A. Tidally driven remelting around 4.35 billion years ago indicates the Moon is old. Nature 636, 598–602 (2024). DOI: 10.1038/s41586-024-08231-0