What Is the Moon Made Of?

The 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 impact breaking off a piece of Earth when it was 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 probably consists primarily of iron, with some sulfur and nickel.

The core likely is small, accounting for just 1 to 2 percent of the Moon's mass.

The Crust, Mantle, and Core of the Moon

The largest portion of the 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 0.42% chromium, 0.18% titanium, 0.12% manganese, 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 Atmosphere of the Moon

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, carbon dioxide, with trace amounts of oxygen, aluminum, silicon, phosphorus, sodium, and magnesium ions.

Because conditions contrast sharply between day and night, 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.