What Is the Impact Theory for the Moon?

What Is the Giant Impact Theory?

• The Giant Impact Theory or Ejected Ring Theory is the idea that the moon and earth were created at the same time, soon after the solar system itself was created. Scientists think a small planet, about the size of Mars, collided with earth, and heated matter from the outer layers of both planets was released and orbited the earth. This orbiting ring of matter merged together into a mass and formed what we know as the moon.

Giant Impact Theory Evidence

• Earth and the moon have oxygen isotopes that are alike, which scientists suggest is because they were the same distance from the sun when they were both formed. We also know that the moon is made mostly of low-volatility rock that was excessively heated. This collision could account for the excessive heating that has been proven through analyzation of lunar rock samples. Scientists have also theorized that a massive planet collision did occur at that time lending credence to the Giant Impact Theory.

Support for the Giant Impact Theory

• The Giant Impact Theory was introduced in the mid-1970s but was not universally accepted until a 1984 conference where scientists came to a near unanimous conclusion that the Giant Impact Theory was indeed the most likely scenario given the information available. The Giant Impact Theory was the first model suggested that explained the similarities in characteristics between the composition of earth and the moon without drastically changing previously accepted explanations of how these two planets were created.

Previously Accepted Models

• The Giant Impact Theory replaced two previously accepted models that explained how the moon was created. The first theorized that the planet and earth collided with twice the momentum than the Giant Impact Theory proposed. If the momentum was twice as fast, the earth would have then had to undergo a second impact to change the earth's rotation to something similar to today. The second suggests that the earth was larger when the planet hit it but that would have caused the moon to have more iron than it does. Scientists know the moon does not have an iron rich core such as the earth does.