The man in the moon has a black eye and now we know how he got it. A giant dark area – right eye of the Man in the Moon – was created when a massive asteroid more than 240km (150 miles) in diameter crashed into the moon about 3.8 billion years ago.
Researchers in the US know this after experiments using a powerful cannon that can fire projectiles at incredible speeds of 7km/sec (about 26,000km/h) to simulate planetary impacts on a small scale.
Pete Schultz, Professor of Earth, environmental and planetary sciences at Brown University, and his collaborators were trying to understand the impact that produced the Imbrium Basin – an area about 750 miles across that can be seen from Earth as a dark patch.
They used the Vertical Gun Range at the Nasa Ames Research Center. Its centrepiece is a 4.5m (14ft) cannon capable of firing projectiles at extremely high velocity.
An impact chamber and high-speed imaging systems allows the recording and analysis of impacts in detail. The instrument was set up in 1966 to support the Apollo missions and remains in use.
Enormous
The experiments reveal that a massive object shattered on impact. Based on the results, the asteroid was estimated to be some 150 miles across. “We show that Imbrium was likely formed by an absolutely enormous object, large enough to be classified as a protoplanet,” said Prof Schultz. He also pointed out that this size estimate was based on geological features, a series of grooves that surround the basin which were cut by the asteroid on impact.
The groove pattern was a mystery that had not been explained by previous theories . “No one was sure where they came from,” he said.
Prof Schultz and his collaborators then applied the same methods to analyse other impacts on the surface of the moon and other planets. This produced similar results.
He now believes that our area of the solar system was bombarded with extremely large objects about four billion years ago. His work is published on Wednesday in the journal Nature.
These impacts helped to sculpt the surface of our neighbouring planets and may have contributed chemical material, changing the composition of the native soil and rock.
The research shows how much can be learned by looking up at the moon. “The moon still holds clues that can affect our interpretation of the entire solar system,” said Prof Schultz. “Its scarred face can tell us quite a lot about what was happening in our neighbourhood 3.8 billion years ago.”
Vanesa Martinez is on placement at The Irish Times under the BSA/SFI media fellowship programme