What Is The Moon Made Of?
QUICK ANSWER
The Moon is made mostly of silicate rocks. It has a small iron-rich core, a rocky mantle, and a crust of basalt and feldspar. The surface is covered in fine dust called regolith, made of ground-up rock from meteorite impacts. There's also water ice in permanently shadowed polar craters.
The Moon is a rocky body, not unlike a small version of Earth without the active geology. It has a layered structure with a small core, rocky mantle, and thin crust. The surface is covered in a layer of fine, ground-up rock called regolith, kicked up by billions of years of meteorite impacts. And no, it's not made of cheese.
What are the Moon's main layers?
Three main layers: crust, mantle, and core. According to NASA, the Moon's crust is about 30 to 70 miles thick (thicker on the far side than the near side), made primarily of basalt and feldspar. Below that, the mantle is mostly silicate rock similar to Earth's mantle, but cooler and less active. At the center is a small core, partly molten, with a solid inner core of iron and a fluid outer core of iron and other elements. The core is unusually small for a body the Moon's size.
What's on the Moon's surface?
Mostly rock and a layer of dust called regolith. The surface includes two main types of terrain: the bright highlands (heavily cratered ancient crust) and the dark maria (smoother basaltic plains that filled ancient impact basins with lava). The regolith covering most of the surface is a fine, powdery layer of ground-up rock created by billions of years of meteorite and micrometeorite impacts. Apollo astronauts noted that the regolith stuck to everything and was abrasive, with a faint gunpowder-like smell when brought into the lunar module.
Is there water on the Moon?
Yes, surprisingly. NASA's LCROSS mission in 2009 confirmed water ice in permanently shadowed craters near the lunar south pole. More recent missions have detected water in various forms across the lunar surface, including molecular water bound to soil grains in sunlit areas. The total amount is small compared to Earth's water, but it's significant for future lunar exploration: water ice can be melted for drinking water, broken into hydrogen and oxygen for rocket fuel, or otherwise used to support a long-term human presence on the Moon.
Why is the Moon's iron core so small?
Because of how the Moon formed. The leading giant-impact theory suggests the Moon formed from material blasted out of Earth's outer layers, which had less iron than the deeper interior. The Moon ended up with much less iron than Earth. The Moon's core is only about 1 to 2 percent of its mass, compared to about 32 percent for Earth. This composition difference is one of the strongest pieces of evidence for the giant impact origin of the Moon.
The Moon is made mostly of silicate rocks, with a thin crust, thick rocky mantle, and surprisingly small iron core. The surface is covered in regolith, a fine dust of ground-up rock from billions of years of impacts. Water ice exists in permanently shadowed craters near the poles, which may prove valuable for future lunar bases. The Moon's composition tells us a lot about its violent origin from material blasted off the early Earth.
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