On the origin of the Moon and findings from the Apollo missions

How the Apollo missions transformed our understanding of the Moon’s origin

This article was originally published on The Planetary Society as a contribution for the Apollo 11 landing anniversary. This is a mirror of the same.

Where did the Moon come from? The origin of our cosmic neighbor is a fundamental question in planetary science. From Galileo’s first telescopic observations of the Moon to humans walking on its surface, our understanding of its origins has come a long way. Yet it is far from complete.

There are multiple hypotheses that have attempted to explain how the Moon came to be. For this article, we’ll focus on the most popular one — The Giant Impact Hypothesis (GIH).

View of the Moon’s north pole seen by the Galileo spacecraft as it flew by on December 7, 1992. Source: NASA Flickr

According to the GIH, 4.5 billion years ago, when the planets had just formed, a titanic collision took place. A young Mars-sized planet (named Theia) collided with the early Earth. The impact ejected a huge amount of material. While some of this material escaped into space, the rest of it stayed in orbit, and consolidated to form the Moon. Here is a simple diagram illustrating the same.