Theories of Formation
for the Moon
http://csep10.phys.utk.edu/astr161/lect/moon/moon_formation.html
Five Serious Theories
Five serious theories have been proposed for the formation of the Moon (not counting the
one involving green cheese): Read each, write down what kind of data would help support
each theory. Using the info on the back page, see which theories you can rule out, based on
the data. Write this down also under the explanations below. Then, research (on-line or
textbook) what the currently supported theory is today and write down what supports that
theory at the bottom of this page.
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 Sunorbiting 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/Giant Impactor 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.
http://www.windows2universe.org/earth/moon/formation_evidence.html
Evidence about the Formation of the Moon
Any successful theory must account for everything we know about the Moon now. Those things
include
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the moon seems to be made of the same material as the Earth's upper mantle.
the Moon has little or no iron in it, and is composed of material unlike the composition of
the Earth as a whole.
the moon is rounded in shape, like the other planets and not like an asteriod or comet
the moon orbits in the same direction as the Earth
the Moon is located in the same plane as the Earth (the ecliptic plane)
theory suggests that the Moon seems to have drifted away from the Earth over the
length of geologic history.
o this means that the Moon was once much closer to the Earth
o this means that the Moon was once bigger in the sky and much brighter than at
present