The Moon is Earth's most reliable companion in space, orbiting our world for about 4.5 billion years—almost as long as our planet has existed. But new analysis of crystals from the Moon's surface shows that the satellite may be much older than previously thought.

The Moon is thought to have formed when the first Earth collided with a Mars-sized protoplanet, an event dated to about 4.35 billion years ago based on rocks on the lunar surface. Pinning down the timeline of the Moon's evolution doesn't just tell us the history of that rocky globe—it helps planetary scientists understand the evolution of our world and the larger solar system.

Now, a group of researchers posits that while estimates for the Moon range between 4.35 billion and 4.51 billion years old, the younger date indicates a remelting event distinct from the "original crystallization of the lunar magma ocean," they wrote in. a paper PUBLISHED now on NATURE.

The abundance of 4.35 billion-year-old rocks on the surface suggests to the team that this is due to a massive melting event, and the true age of the Moon is somewhat older. The researchers deduced an older age from zircon crystals from the lunar surface, obtained by the Apollo missions. Although the rest of the lunar surface underwent remelt, some of the crystals near the surface did not, thus keeping a truer record of the Moon's age.

The team says the Moon is hardly older than 4.53 billion years old, "the earliest time at which core formation could have stopped." The earliest time the Moon was formed, researchers say, was about 180 million years before the last water heating event on the satellite. In other words, if the lunar surface we know and love is mostly the result of a melting event, and the Moon is older than commonly thought, it isn't. superlative older than thought.

In the paper, the team says that "current models do not support the idea of ​​impacts being responsible for the reset event," although the jury remains out on what could have caused such widespread lunar melting. face The researchers say that the remelting may be “driven by the Moon's orbital evolution”—in other words, the stress of the Moon's gravitational pull on bodies like Earth and the Sun.

Earlier this year, research PUBLISHED on Nature Geoscience concluded that the Moon must have turned on itself within a few million years of its formation. The new paper further complicates the origin story of our long-time companion in solar orbit.

We still have it still a long way off with space exploration, although the Artemis program—that will return humans to the Moon for the first time in decades—will be an important step in understanding the origins of our rocky satellite.