How did the moon form?

by | Jun 23, 2017


How Did the Moon Form? The predominant theory is that a Mars-sized planet struck the Earth when it was around 100 million years old (which is when the Earth was still very young and likely still molten).

The name given to this planet that struck Earth is Theia. The theory (called the “giant impact theory”) proposes that Theia struck the Earth and debris from the collision formed our Moon. Evidence for this is the fact that the Earth and the Moon have different compositions so that the prior theory that the Earth and Moon condensed from the same nebula was rendered unlikely.

This collision with Theia is also what set the Earth spinning as it does, and gives Earth its tilt and wobble. The giant impact theory seems likely based on computer simulations and the differences in make-up between the Earth and the Moon, but there is no definitive evidence.

In the past year there has been a new theory proposed – a multiple impact theory. This theory is similar to the giant impact theory but instead of a single big impact, it theorizes that around 20 smaller impacts over time created the rocks and debris that formed the moon.


This graphic above illustrates how the moon may have formed after multiple collisions on Earth. Moon- to Mars-sized impactors strike the Earth and leave a disk of debris orbiting the planet. The debris forms “moonlets” and migrate farther away from the Earth due to a tidal interaction, but eventually settle at a distance known as the Hill radius. Here, the moonlets merge to eventually form the moon.

1 Comment

  1. In relation to the moon and one of your earlier ifod’s.

    First total solar eclipse over the entire US in 99 years is happening Aug 21st.


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