That the pockmarked face of the Moon was caused by billions of years of collisions is well known, but we are only now able to understand just how big the asteroids hitting our satellite really were.

Researchers Pete Schultz and David Crawford from Brown University have analyzed a famous impact crater within the Mare Imbrium (the Sea of Showers). The latest observation suggests a lower limit for the size of the bolide – a bright meteor – of 250 kilometers (155 miles) in diameter, much larger than previously thought.

The size put it in the class of proto-planetary asteroids, objects large enough to be the likely precursors of planets. Its impact on the Moon has been significant, leaving a 1,250-kilometer-diameter (775 miles) crater.

“We show that Imbrium was likely formed by an absolutely enormous object, large enough to be classified as a protoplanet,” said Pete Schultz, professor of Earth, environmental, and planetary sciences at Brown University, in a statement.

“This is the first estimate for the Imbrium impactor’s size that is based largely on the geological features we see on the Moon.”

The size of the impactor is not the only interesting find in this study, which is published this week in Nature. The researchers were also able to explain the so-called Imbrium Sculpture, a pattern of grooves that extend radially around the crater, as well as a second set of grooves extending from a region to the northwest of the crater center.

“This second set of grooves was a real mystery,” Schultz said. “No one was quite sure where they came from.”

The scientists used virtual and physical models to work out how the second set of grooves formed. They believe chunks from the main object broke apart and hit the Moon before the main body.  

Some of the chunks might even have escaped our satellite’s gravity, and hit the Moon or Earth at a later time. This discovery could significantly expand our understanding of the Late Heavy Bombardment when comets and asteroid were repeatedly hitting the rocky planets of the Solar System.

“The Moon still holds clues that can affect our interpretation of the entire Solar System,” Schultz added. “Its scarred face can tell us quite a lot about what was happening in our neighborhood 3.8 billion years ago.”