LUNAR FORMATION THEORIES

Five serious theories have been proposed for the formation of the Moon (not counting the one involving green cheese):

1. The Fission Theory: The Moon was once part of the Earth and somehow separated from the Earth early in the history of the Solar System. The present Pacific Ocean basin is the most popular site for the part of the Earth from which the Moon came.

2. The Capture Theory: The Moon was formed somewhere else, and was later captured by the gravitational field of the Earth.

3. The Condensation Theory: The Moon and the Earth condensed together from the original nebula that formed the Solar System.

4. The Colliding Planetesimals Theory: The interaction of earth-orbiting and Sun-orbiting planetesimals (very large chunks of rocks like asteroids) early in the history of the Solar System led to their breakup. The Moon condensed from this debris.

5. The Ejected Ring Theory: A planetesimal the size of Mars struck the earth, ejecting large volumes of matter. A disk of orbiting material was formed, and this matter eventually condensed to form the Moon in orbit around the Earth.