Where Did the Moon Come From?

Where Did the Moon Come From?

How did our Moon form? Where did it come from? Finally, and perhaps most importantly, what clues does the Moon hold in regard to the formation of our solar system? These are just a few of the questions that both present and past astronomers have struggled to understand throughout the course of human history. This article addresses these questions through an analysis of four theories pertaining to the Moon’s formation. Although these theories remain to be unproven by the scientific community, they offer a unique perspective on our Moon’s formative years that is both plausible and credible given our current understanding of the solar system at large.

Impact Theory of the Moon's Formation

The most prominent theory pertaining to the Moon’s formation is known as the “Impact Theory.” This hypothesis argues that the Moon likely formed from a massive object hitting the Earth during its early years. Scientists believe that the early solar system was full of drifting debris that was left over from the cloud of dust (and gas) that surrounded our early Sun. As a result, scientists believe that an impact between our future Earth and a massive object was not only plausible, but inevitable given the chaotic conditions surrounding our planet at the time.

According to scientists, the object that struck Earth (known as “Theia”) was likely the size of Mars. After colliding with the Earth, the massive collision threw large chunks of Earth’s vaporized crust into space, which then became bound to one another through the effects of gravity. This hypothesis helps to explain why the Moon is composed of lighter elements, as its materials came solely from the Earth’s crust rather than its inner core.

According to this theory, scientists also believe that the core of “Theia” remained largely intact from the impact, and served as the gravitational basis for the crust-like debris to form around its center. Scientific models indicate that the impact between Theia and Earth was nearly 100 million times stronger than the latter event that is believed to have destroyed the dinosaurs.

The impact theory remains full of contradictions and problems, however. If the impact theory was completely true, for example, then-current models suggest that the Moon should be composed of primarily sixty percent of the material that originated from Theia. However, rock samples from the Apollo missions indicate that the Earth and Moon are nearly identical in their composition, differing in composition by only a few parts per million. As a result, researchers in Israel have recently proposed that multiple impacts may have resulted in the formation of the Moon, rather than a single “Giant Impact,” as previously argued.