Shop Windows to the Universe

Become a nitrogen atom in the nitrogen cycle in our Traveling Nitrogen Classroom Activity Kit/Game. See all our games, activity kits and classroom activities.
This is an illustration of the Chicxulub impact.
Click on image for full size
NASA/JPL

The Collisional Ejection Theory

Currently, the theory that best explains all the evidence is the collisional ejection theory. This theory holds that the Moon formed from debris ejected from the Earth when a large object (possibly as large as Mars) crashed into the Earth. Simulations of this scenario show that energy from such a collision produces a stream of vaporized rock from the impact. The Moon forms from this cooled material.

This theory explains many of the known properties of the Moon's orbit and composition. The ejected material would have coalesced in or near the ecliptic plane, putting the Moon into an orbit much like the one it has. The Moon, which is believed to have a small iron core, could have retained this core through the collision. Volatile elements would have been vaporized during the impact. Also, this collision could have tipped the Earth's axis, causing the seasons we now know.

The problem with this theory is that it does not seem very likely, although objections to the theory based on considerations of the angular momentum between the two objects have been resolved in recent computer models.

Shop Windows to the Universe Science Store!

Learn about Earth and space science, and have fun while doing it! The games section of our online store includes a climate change card game and the Traveling Nitrogen game!

Windows to the Universe Community

News

Opportunities

You might also be interested in:

Traveling Nitrogen Classroom Activity Kit

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more

Element (Chemical Element)

An element (also called a "chemical element") is a substance made up entirely of atoms having the same atomic number; that is, all of the atoms have the same number of protons. Hydrogen, helium, oxygen,...more

Charon - largest moon of Pluto

Charon is by far the largest of Pluto's // Call the moon count function defined in the document head print_moon_count('pluto'); known moons. Charon was discovered by the American astronomer James Christy...more

The Co-Formation Theory

The co-formation theory explains the origin of the moon as an object which formed out of the primitive solar nebula at the same time and roughly the same place as the Earth. As shown in this picture, while...more

The Lunar Atmosphere

In decades past it was accepted that moons such as the Earth's moon or the moons of Jupiter were airless bodies with no atmosphere whatsoever. Now, however, measurements have shown that most of these moons...more

The Moon's Magnetosphere

Unlike the Earth, which has a protective shield around it called the magnetosphere, the surface of the moon is not protected from the solar wind. This picture shows the magnetosphere surrounding the Earth,...more

Full Moon Names

You may have heard people refer to a Full Moon in the autumn as the "Harvest Moon" or the "Hunter's Moon". Native Americans in the eastern and northern parts of North America had special names for the...more

Altocumulus

Altocumulus clouds (weather symbol - Ac), are made primarily of liquid water and have a thickness of 1 km. They are part of the Middle Cloud group (2000-7000m up). They are grayish-white with one part...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part by the National Science Foundation and NASA, our Founding Partners (the American Geophysical Union and American Geosciences Institute) as well as through Institutional, Contributing, and Affiliate Partners, individual memberships and generous donors. Thank you for your support! NASA AGU AGI NSF