📚 Study helper: This page helps you learn and practice for school. Read it, listen to it, and try to name the Moon's layers from the outside in!
The Moon is Earth's only natural satellite.
NASA Space Place says the Moon is a rocky, cratered place.
NASA says the Moon is made of rock and metal.
Like Earth, the Moon has layers inside it.
NASA says the Moon has three main layers.
They are the crust, the mantle, and the core.
On top, the Moon is covered with dust and broken rock.
Let us look at each part, one by one.
Elementary: Rock and Metal, Layer by Layer
The Moon is not soft. It is hard rock, all the way through.
NASA compares the Moon to a chocolate-dipped cherry.
There is a core in the center.
There is a thick mantle around the core.
And there is a thin crust on the outside.
The crust — the thin skin on the outside
The crust is the Moon's outermost layer.
It is thin, like the skin of a fruit.
The crust is made of rock.
NASA says the minerals in the crust are made up of things like oxygen, silicon, magnesium, iron, calcium, and aluminum.
The mantle — the thick rock layer in the middle
Under the crust is the mantle.
NASA says the mantle is the thickest layer of the Moon.
It is mostly solid rock.
The core — the metal ball in the center
Deep in the center is the core.
NASA says the core is mostly iron. Iron is a metal.
The inner part of the core is solid.
The outer part of the core is melted, or molten.
The dusty top — regolith
The very top of the Moon is dusty and rocky.
NASA calls this dusty layer regolith. It is the Moon's soil.
Regolith is made of broken pieces of Moon rock.
Space rocks hit the Moon again and again. The hits break the rock into smaller and smaller pieces.
The pieces can be tiny dust, or big rocks. Some pieces are as big as a house, NASA says.
Light patches and dark patches
Look at the Moon. You can see light areas and dark areas.
The light areas are called the highlands. They are higher ground made of crust rock.
The dark areas are called maria. Maria is a Latin word for seas.
But maria are not seas of water, NASA says. They are wide, flat places where lava filled big craters long ago.
Why are there so many craters?
Craters are dents made when space rocks hit the Moon.
The Moon has almost no air. NASA Space Place says there is no wind or air on the Moon to erase craters.
So the dents stay. The dusty footprints of astronauts who walked on the Moon are still there today.
How do scientists think the Moon formed?
Scientists believe the Moon formed long ago, NASA Space Place says.
Scientists believe Earth and an object about the size of Mars smashed into each other.
The crash sent chunks into space.
Gravity pulled the chunks together, and that made the Moon.
This is what scientists believe happened. It is their best idea from the clues they study.
Middle School: What the Moon Is Made Of, With More Detail
NASA Science puts it this way: according to leading theories about how the Moon formed, much of the stuff that makes up the Moon was once part of Earth.
And like Earth, the Moon consists of three main layers: a crust, a mantle, and a core.
Billions of years ago, the Moon was a molten world, NASA says. As it solidified, the heaviest materials — metals like iron — sank down into the Moon's center, and the lighter materials — lower density rocks — rose towards the surface.
NASA calls the result a structure a bit like a chocolate-dipped cherry: a solid core, a mostly solid and partly liquid mantle, and a thin outer crust.
The core: two sections, mostly iron
NASA says the Moon's core consists of two sections: a solid, mostly iron inner core within a molten outer core.
Though primarily made of iron, the core contains some nickel and sulfur as well.
NASA says the Moon's core extends about 20 percent of the way from the Moon's center to its surface. That is a smaller share than in other well-studied rocky worlds, NASA notes.
NASA Science's Moon Facts page adds measurements: the solid, iron-rich inner core is 149 miles (240 kilometers) in radius, and it is surrounded by a liquid iron shell 56 miles (90 kilometers) thick, with a partially molten layer around the iron core.
The mantle: the thickest layer
The lunar mantle is the thickest layer of the Moon, NASA says.
It is mostly solid, but the zone closest to the lunar core is partly molten. NASA says some moonquakes may originate there.
The mantle is mainly composed of basalt rich in olivine and pyroxene. NASA notes that if you have ever seen peridot, you have seen the gem form of olivine, a mineral named for its green hue.
The Moon Facts page says the mantle is most likely made of minerals like olivine and pyroxene, which are made up of magnesium, iron, silicon, and oxygen atoms.
The crust: thin, and thicker on one side
The crust is the Moon's outermost layer.
NASA says the crust is about 37 miles (60 km) thick on the side farthest from Earth, but only 25 miles (40 km) thick on the near side. NASA calls that difference a scientific puzzle, and says scientists are still trying to find out why the lunar crust is so uneven.
Minerals forming the lunar crust are made up of oxygen, silicon, magnesium, iron, calcium, and aluminum, along with small amounts of titanium, uranium, thorium, potassium, and hydrogen, NASA says.
Highlands and maria: two kinds of crust rock
NASA says the Moon's relatively bright, elevated highlands are rich in elements like calcium and aluminum.
The darker depressions, called maria, have more iron and titanium.
Maria are seas of cooled lava which flooded vast impact basins between 4.2 and 1.2 billion years ago, NASA says. The lunar highlands are older parts of the crust that survived the intense, basin-forming impacts.
Regolith: the broken-rock covering
Lunar regolith is the Moon's soil, NASA says. This dusty, rocky substance is the result of a constant assault on the lunar surface, from meteorites of all sizes to charged particles from the Sun.
The bombardment has broken down the upper layers of the crust, creating a thick layer of loose material that sits on top of the bedrock. Its particles include tiny dust motes, house-sized boulders, and everything in between, NASA says.
The regolith is made up of fractured and broken pieces of lunar rocks, sourced from the highlands, mare basalts, and deeper materials dug up by large impacts — perhaps even from the mantle, NASA says. It also contains pieces of meteorites and debris from throughout the solar system.
Generally, the older the surface, the thicker the regolith, NASA says. The regolith in some parts of the young maria is relatively thin — only a few feet deep — while the older regolith on the lunar highlands can be 66 feet (20 m) deep.
Beneath the lunar regolith is a region called the megaregolith, an upper layer of the crust composed of cracked, shattered bedrock, and massive pieces of impact ejecta, NASA says.
The Moon Facts page describes nearly the entire Moon as covered by a rubble pile of charcoal-gray, powdery dust and rocky debris called the lunar regolith.
How scientists study what the Moon is made of
Besides analyzing pieces of the Moon that Apollo astronauts brought home to Earth, scientists learn about the Moon's composition and structure by studying its light signatures — this is called spectroscopy — along with its rotation, gravitational effects, and moonquakes, NASA says.
Four seismometers deployed on the Moon by NASA astronauts during the Apollo program functioned until 1977, and left behind data that researchers still use today, NASA says.
Scientists also study the Moon's composition using data from orbiting observatories like the current Lunar Reconnaissance Orbiter and the past Gravity Recovery and Interior Laboratory mission, NASA says.
NASA Space Place adds that astronauts collected hundreds of pounds of lunar soil and rock samples, and that the Lunar Reconnaissance Orbiter has been circling the Moon and sending back measurements since 2009.
Formation, in NASA's framing
NASA Space Place says scientists believe the Moon formed early in the solar system's history, after Earth and an object about the size of Mars smashed into each other, and the impact sent chunks of Earth and the impactor into space that were pulled together by gravity, creating the Moon.
The Moon Facts page says the Moon likely formed after a Mars-sized body collided with Earth several billion years ago, and the resulting debris from both Earth and the impactor accumulated to form our natural satellite. The newly formed Moon was in a molten state, NASA says.
NASA also notes that the Moon harbors water ice, with the highest concentrations within darkened craters at the poles, and NASA Space Place says there is frozen water tucked away in craters near the Moon's poles.
Gravity on the surface of the Moon is one-sixth of Earth's, NASA says, and the Moon has almost no atmosphere.
Crust: The crust is the Moon's outermost layer. It is the thin outer layer of rock, like a skin.
Mantle: The mantle is the thick layer of rock under the crust. NASA says it is the thickest layer of the Moon, and it is mostly solid.
Core: The core is the center part of the Moon. NASA says it is mostly iron, a metal, with a solid inner part and a molten outer part.
Molten: Molten means melted. Long ago the Moon was a molten world, and part of its core is still molten today, NASA says.
Regolith: Regolith is the Moon's soil. It is a dusty, rocky layer made of broken pieces of Moon rock, and it sits on top of the crust.
Maria: Maria are the dark, flat areas you can see on the Moon. Maria is a Latin word for seas, but they are not water. They are places where lava filled big craters and then cooled.
Highlands: The highlands are the light, higher areas of the Moon. NASA says they are rich in calcium and aluminum.
Crater: A crater is a dent in the Moon's surface. Craters form when space rocks hit the Moon.
Olivine and pyroxene: These are minerals. NASA says the Moon's mantle is mainly made of rock rich in olivine and pyroxene. Peridot is the gem form of olivine.
📚 Study helper: Great job! Now try this. Say the three layers from the outside in: crust, mantle, core. Then answer this: what is the name of the Moon's dusty soil? Regolith!
NASA Space Place — All About the Moon: https://spaceplace.nasa.gov/all-about-the-moon/en/
NASA Space Place — Why Does the Moon Have Craters?: https://spaceplace.nasa.gov/craters/en/