skip navigation
Saturn from Cassini Astronomy 161:
An Introduction to Solar System Astronomy
Prof. Richard Pogge, MTWThF 2:30

Lecture 30:
The Moon

Key Ideas:

Surface of the Moon: Interior of the Moon The Origin of the Moon

The Neighbor Moon

After the Earth, the Moon is the best known body in the Solar System:

Lunar Terrain

Maria (seas)


Moon Rocks

Our most detailed knowledge of the Moon comes from ~382 kg of rocks and regolith samples returned by 9 space missions:

United States:

Soviet Union:

The results from these studies are summarized below.


Regolith (literally "blanket rock") is the layer of dust and fragmented rock produced by meteor impacts that covers the uppermost surfaces of most moons, planets and asteroids in the inner Solar System.

Lunar Regolith:

Lunar History

The surface of the Moon was entirely shaped by meteor impacts and their effects:




Youngest terrain on the Moon.

Maria are flows of magma from deep fractures in the crust:


Oldest terrain on the Moon.

Unusual mineral content of highland breccias:

The Lunar Interior



Core: None or very small

Is there a Lunar Core?

Moon has no global magnetic field now, so no molten core like the Earth.

Did the Moon have a core in the past?


The Moon may have had a molten core and magnetic field 3.6-3.8 Gyr ago, but it no longer has one.

Origin of the Moon

Any theory for the origin of the Moon must explain these facts: At least 4 basic formation models have been proposed. All of these are testable with observations.

Theories of Moon Formation




Giant Impact: (favored theory)

The impact theory is currently favored.

The impact theory has many strong points in its favor:

There are still lingering questions, but it does the best so far at explaining the observed properties of the Moon.

Return to [ Unit 5 Index | Astronomy 161 Main Page ]
Updated: 2007 November 1
Copyright Richard W. Pogge, All Rights Reserved.