Lunar Oddities and The Origin of the Moon 6.4 Lunar Oddities and The Origin of the Moon

Lunar Oddities There are two things that make our Moon unique among moons: First - Our Moon orbits at 5° from the plane of the Earth’s Orbit, and not in the plane of the equator. Most moons orbit right along the equator of their parent planet.

Earth’s Moon is also quite large when compared to Earth, at about 1/81st of Earth’s mass. Most moons are about 1/1000th of the mass of the planet they orbit. For example, this is Io against Jupiter’s surface.

Origin Hypotheses Before Apollo 11 brought back lunar rocks from its surface, scientists developed three hypotheses to explain the Moon’s origin. They planned to use the rocks to prove one of these hyotheses as correct...

Hypothesis #1 The Moon is a smaller planet captured by Earth’s gravity, so… the rocks should be unlike Earth rocks. Conclusion: the lunar rocks are too similar in composition to Earth’s rocks, so this hypothesis is wrong.

Hypothesis #2 Earth and the Moon formed as “twin” planets formed at the same time, so…the rocks should be similar to Earth’s. Conclusion: The lunar rocks are not identical in composition to Earth rocks, to this hypothesis is wrong as well.

Hypothesis #3 The Moon began as a bulge that spun off the Earth, so…Earth and Moon rocks should be almost identical. Conclusion: Again,the lunar rocks are not identical in composition to Earth rocks, to this hypothesis is wrong as well.

Lunar Rocks Catch Scientists by Surprise! The composition of the Apollo 11 lunar rocks was a complete surprise, and did not match any of the current hypotheses. A new one was needed.

Here are the Rock Facts... The collection of lunar rocks were composed of many high-melt temperature materials, but very few of low-melt temperature.

The high-melt temperature materials perfectly matched Earth rock. Scientists concluded that the material for the Moon must have come from Earth, and then been heated to a very high temperature before cooling.

The “Violent Birth” Hypothesis Our current idea on how the Moon was formed is called The Violent Birth Hypothesis: A Mars-sized planet struck the Earth in its early history, when the Earth was still molten.

Heat from the collision melted part of the Earth Heat from the collision melted part of the Earth. Material was ejected; some of it formed the Moon.

The low-temperature melting materials vaporized during the collision, leaving the high-temperature melting materials to gradually cool into our Moon. This explains both its orbital AND the compositional oddities.

This also predicted a small metallic core for the Moon…which was confirmed.