The moon may be much older than previously thought, according to a new study.
Planetary scientists believe the moon's surface may have "remelted" around 4.35 billion years ago, masking much older lunar features beneath.
The moon is thought to have formed when Earth collided with a Mars-sized protoplanet, a rock in the early stages of becoming a planet. That collision was the last giant impact in our planet's history.
Scientists estimated the date of the collision by dating moon rock samples.
Those samples were assumed to have crystallised from the moon's ancient magma ocean that existed after the impact. They placed the moon's age at approximately 4.35 billion years old.
However, in a study published in Nature, Professor Francis Nimmo from the University of California Santa Cruz and his colleagues argue the moon may be much older.
According to their modelling, the moon went through a period of heating and cooling where its surface remelted.
This would mean the rock samples could be from a much earlier period but their "remelted" surfaces are hiding older features.
By studying thermal models and craters on the moon and the age of certain minerals, Prof Nimmo and the team now suggest the moon could be up to 4.51 billion years old, more than one and a half million years older than previously thought.
Their research could also explain why there are fewer craters on the moon's surface than might be expected after it was bombarded about 4 billion years ago by asteroids.
According to the study, the craters would have been erased when the moon heated up.
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There's huge interest in the moon at the moment, as nations race to its south pole where it is believed there may be water.
NASA plans on building bases on the moon's south pole to help humans get to Mars, although it recently delayed its Artemis launch that would have sent a crew looping around the moon next year.