One of the Moon's biggest craters was created by an asteroid more than 250km (150 miles) across, a study suggests. It smashed into the lunar surface about 3.8 billion years ago, forming Mare Imbrium - the feature also known as the right eye of the "Man in the Moon". Scientists say the asteroid was three times bigger than previously estimated and debris from the collision would have rained down on the Earth. The asteroid was so big it could be classified as a protoplanet - a space rock with the potential to become a fully formed world. Lead author Prof...