Moon formed 4.47 billion years ago, says study

The impact signatures provide insights into the last stages of planet formation in the inner solar system.

The full moon sets behind the Swiss Alps' mountains, in Charrat, Canton of Valais, Switzerland.

The moon may have been created about 4.47 billion years ago, according to a new study of meteorites that provides clues to the giant collision which formed Earth and the lunar body.

A giant impact between a large protoplanet and the proto-Earth formed the Moon. The timing of this giant impact, however, is uncertain, with the ages of the most ancient lunar samples returned by the Apollo astronauts still being debated.

Research indicates numerous kilometre-sized fragments from the giant impact struck main belt asteroids at much higher velocities than typical main belt collisions, heating the surface and leaving behind a permanent record of the impact event.

Collisions on these asteroids in more recent times delivered these shocked remnants to Earth, which scientists have now used to date the age of the moon.

By modelling the evolution of giant impact debris over time and fitting the results to ancient impact heat signatures in stony meteorites, the team was able to infer that the moon formed about 4.47 billion years ago, in agreement with many previous estimates.

The most ancient solar system materials found in meteorites are about 100 million years older than this age. The impact signatures provide insights into the last stages of planet formation.

They can also help researchers deduce the earliest bombardment history of ancient bodies like Vesta, one of the targets of NASA’s Dawn mission.