The moon may be much older than we thought

Further analysis of lunar rocks and modeling will help scientists to better understand the moon and its history

The moon may be much older than previously believed.

Scientists are challenging prior conceptions about its formation some 4.35 billion years ago in a new “idea paper.”

The Earth and its moon are believed to have originated from similar materials: the resulting debris from a massive impact when one large object was struck by another, according to Nasa. The moon’s formation was believed to be approximately 200 million years after that of our solar system. But, that’s a long time, some see the idea of the collision forming the moon this late as improbable, and it doesn’t account for the ages of some zircon minerals on its surface.

A possible answer is that the moon underwent a “remelting,” resetting the age of the lunar rocks, according to three international scientists.

“We predict that there shouldn’t be any lunar rocks that are older than 4.35 billion years because they should have experienced the same resetting,” UC Santa Cruz Professor Francis Nimmo said in a statement. “Because this heating event was global, you shouldn’t find rocks anywhere on the moon that are significantly older than that.”

An artist's impression shows what the moon may have looked like during intense volcanic activity. This ‘remelting’ could be an explanation for when and how the moon formed, scientists said this week (Credit: Alexey Chizhik/Max Planck Institute for Solar System Research)

Nimmo’s “idea paper” was published Wednesday in the journal Nature.

The remelting, it says, was due to the tidal pull of the Earth, causing heating and geological upheaval. In a process known as “tidal heating,” the gravitational forces between two celestial bodies cause internal friction, resulting in the warming. They said this was likely more pronounced in the moon’s early history, citing modeling that showed its orbit would have been unstable during periods in its early years. The instability would cause it to experience tidal forces from the Earth.

There are parallels between this event and current volcanic activity on Jupiter’s moon Io, which is driven by similar tidal forces.

The remelting of the moon would also explain why there are fewer lunar impact basins from early hits than might be expected, they said.

A lunar zircon grain is seen under a microscope. The mineral crystals were used in previous research estimating that the moon was tens of millions of years older than previously believed (Jennika Greer)

The paper comes after 2023 research estimating that the moon was 40 million years older than previously thought. The Northwestern University study analyzed zircon crystals gathered by the Apollo 17 astronauts in 1972.

The next research will work to understand how tidal heating could reset the age of the moon. They noted that lunar samples from China’s Chang’e 6 mission will help to provide invaluable data, and that more detailed modeling is necessary.

“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.”