Meteorites reveal new age for moon

After analysing shock signatures found in stony meteorites that came from the main asteroid belt, a NASA-funded research team has estimated the moon's age as slightly less than 4.5 billion years.

The moon-forming giant impact was the inner solar system's biggest and most recent known collision. Its timing, however, is still uncertain.

"This research is helping to refine our time scales for 'what happened when' on other worlds in the solar system," said Bill Bottke of the Southwest Research Institute (SwRI) in San Antonio, Texas.

The team used numerical simulations to show that the giant impact likely created a disk near the Earth that eventually coalesced to form the moon, while ejecting huge amounts of debris completely out of the Earth-moon system.

The fate of that material has been a mystery.

However, it is plausible that some of it would have blasted other ancient inner-solar-system worlds such as asteroids, leaving behind telltale signs of impact-heating shock on their surfaces.

Subsequent, less violent collisions between asteroids have since ejected some shocked remnants back to the Earth in the form of fist-sized meteorites.

"By determining the age of the shock signatures on those meteorites, we were able to infer that their origin likely corresponds to the time of the giant impact, and, therefore, to the age of the Moon," Bottke added.

Once the team concluded that pieces of the moon-forming impact hit main belt asteroids and made ancient impact age signatures in meteorites, they set out to deduce both the timing and the relative magnitude of the bombardment.

The team found that the moon was formed about 4.47 billion years ago.

The paper appeared in the journal Science.