What Is the Moon Made Of?

No, it's not cheese

The moon
Mark Sutton / EyeEm / Getty Images

The Earth's moon is similar to the Earth in that it has a crust, mantle, and core. The composition of the two bodies is similar, which is part of why scientists think the moon may have formed from a large meteor impact breaking off a piece of the Earth while it was still forming. Scientists have samples from the surface, or crust, of the moon, but the composition of the inner layers is a mystery. Based on what we know about how planets and moons form, the core of the moon is believed to be at least partly molten and likely consists primarily of iron, with some sulfur and nickel. The core is likely small, accounting for just 1-2% of the moon's mass.

Crust, Mantle, and Core

The largest portion of the Earth's moon is the mantle. This is the layer between the crust (the part we see) and the inner core. The lunar mantle is believed to consist of olivine, orthopyroxene, and clinopyroxene. The composition of the mantle is similar to that of the Earth, but the moon may contain a higher percentage of iron.

Scientists have samples of the lunar crust and take measurements of properties of the moon's surface. The crust consists of 43% oxygen, 20% silicon, 19% magnesium, 10% iron, 3% calcium, 3% aluminum, and trace amounts of other elements, including chromium (0.42%), titanium (0.18%), manganese (0.12%), and smaller amounts of uranium, thorium, potassium, hydrogen, and other elements. These elements form a concrete-like coating called regolith. Two types of moon rocks have been collected from the regolith: mafic plutonic and maria basalt. Both are types of igneous rocks, which formed from cooling lava.

The Moon's Atmosphere

Although it is very thin, the moon does have an atmosphere. The composition is not well known, but it is estimated to consist of helium, neon, hydrogen (H2), argon, neon, methane, ammonia, and carbon dioxide, with trace amounts of oxygen, aluminum, silicon, phosphorus, sodium, and magnesium ions. Because conditions contrast sharply depending on the hour, the composition during the day may be somewhat different from the atmosphere at night. Even though the moon has an atmosphere, it is too thin to breathe and includes compounds you wouldn't want in your lungs.

Learn More

If you're interested in learning more about the moon and its composition, NASA's moon fact sheet is a great starting point. You may also be curious about how the moon smells (no, not like cheese) and the difference between the composition of the Earth and its moon. From here, notice the difference between the composition of the Earth's crust and the compounds found in the atmosphere.