The moon is Earth’s most reliable partner in space, orbiting our planet for about 4.5 billion years – almost as long as our planet has existed. But a new analysis of crystals from the moon’s surface indicates that the satellite may be even older than previously thought.
The Moon is believed to have formed when the early Earth collided with a Mars-sized protoplanet, an event that dates back to about 4.35 billion years ago, based on rocks on the Moon’s surface. Determining the chronology of the Moon’s evolution not only gives us the key to the history of this rocky sphere, but also helps planetary scientists understand the evolution of our world and the entire solar system.
The team of researchers argues that while the moon’s age ranges from 4.35 to 4.51 billion years, the younger date indicates a melting event distinct from “the initial crystallization of the lunar magma ocean,” as they write in a paper published today in the journal Nature.
The abundance of 4.35 billion-year-old rocks on the surface suggested to the team that they were formed by a large-scale melting event, and the Moon’s true age is somewhat older. The researchers determined the older age based on zircon crystals from the lunar surface found during the Apollo missions. While the rest of the lunar surface has gone through melting, some crystals near the surface have not, thus preserving a more accurate record of the moon’s age.
The team notes that the moon is almost certainly no older than 4.53 billion years, “the earliest time that core formation could have stopped.” According to the researchers, the earliest time the moon could have formed is approximately 180 million years before the later tidal heating event of the satellite. In other words, if the lunar surface we know and love is largely the result of melting, and the Moon is older than commonly thought, it is not extremely older than thought.
In the paper, the team stated that “current models do not support the idea that collisions are responsible for the reset event,” although the jury remains out on what could have caused such large-scale lunar surface melting. The researchers say that the melting could have been “caused by the moon’s orbital evolution” – in other words, the strain of the moon’s gravitational pull from bodies like the Earth and the Sun.
Earlier this year, a study published in the journal Nature Geoscience concluded that the Moon probably turned inside out several million years before it was formed. The new paper further complicates the origin story of our longtime partner in solar orbit.
We still have a long way to go in space exploration, although the Artemis program, which will return humanity to the moon for the first time in decades, will be an important step in understanding the origins of our rocky satellite.
