Earth Acquiring the Moon
Country: United States
Date: Fall 2009
What is the leading theory on how the Earth acquired the moon?
Although the capture of the Moon was a popular theory in the 20th century, the current
scientific consensus is the "Giant Impact" theory, which states that an object about the
size of Mars (unknown but called "Theia") impacted the Earth around 4.5 Billion years ago.
At first there would have been a ring of debris around the Earth, but over time the debris
gathered through mutual gravitation to form the Moon. The initial impact is also thought
to have established the roughly 24-hr day, and most of the Earth's tilt. There are some
murky aspects to the impact theory, but compared to all others it is the best supported
A few good simulations of the impact can be found on Youtube...
Update: June 2012