Several scientific moon origin theories exist. Each tries to explain how the earth’s moon was created. Today, the Theia impact theory is the most accepted. However, other popular explanations are the capture and planet co-formation theories.
Moon Origin Theories
Theia Impact Theory
During the birth of the solar system, a number of planets were formed. The planets were created from a giant cloud of dust and gas. One of these was a planet named Theia. This planet was about the size of Mars. Theia collided with the earth not long after it had been created.
The collision caused parts of the crust of both planets to be thrown into space. Over time, gravity pulled these fragments to the Earth and Theia. The mixture of fragments became part of the Earth and Theia. Theia became Earth’s moon. Since both bodies joined with the same pool of fragments the earth and the moon are similar chemically.
Another version of this theory suggests that the earth was struck by many objects. The collisions created many fragments orbiting the earth. Over time, these fragments merged into ‘moonlets’. And, eventually the moonlets merged into the moon.
Capture Hypothesis
The capture hypothesis starts off much like the impact hypothesis. The Earth and a smaller planet were created from a giant cloud of dust and gas. However, as the smaller planet approached the earth a collision did not occur.
The earth’s gravity simply captured the smaller planet. The smaller planet began to orbit as the earth’s moon. However, if this hypothesis was correct, the moon and the earth should have very different compositions. Both the moon and earth are similar in composition.
Co-formation Theory
A third theory suggests that the earth and the moon actually formed together as a double system. The moon was not created through impact or capture. Instead, the theory claims that the two planetary bodies were born together at the same time.
Reflections
Vocabulary
- crust
- hypothesis
- theory
Notes
- The Theia impact theory suggests that the moon is the result of a collision of two planets.
- An alternate hypothesis is that the moon was captured by the Earth’s gravity.
- A third hypothesis states that the moon and Earth were created together at the same time.
