A photo taken of an astronaut during the Apollo 16 mission to the Moon in 1972. He is standing close to a crater's edge. His...Read More >>A photo taken of an astronaut during the Apollo 16 mission to the Moon in 1972. He is standing close to a crater's edge. His footprints in the surface regolith will remain for millions of years since there is no wind or erosion to remove them. The Moon is made of rock and metal—just like the Earth and the other rocky planets (Mercury, Venus and Mars). The crust, the Moon’s outer shell, is covered by lunar soil, also called regolith: a blanket of fine rock particles, varying between three and 20 metres (10–65 feet) deep. The footprint of the first person to walk on the Moon, Neil Armstrong, is preserved in regolith. This layer was produced by the pulverizing of the lunar surface rocks by asteroids and meteorites over millions of years. The Moon’s crust itself is about 50 kilometres (30 miles) deep. Its rocks are mostly composed of the elements oxygen and silicon. The crust also contains the metals magnesium, iron, calcium and aluminium.
A view of the Moon’s surfaceA view of the Moon's internal layersScientists can only guess at what the internal composition of the Moon is. Deep inside, the Moon probably has a solid iron core, containing small amounts of sulphur and nickel. This is surrounded by a liquid iron outer core. The inner core makes up only about 20% of the Moon (compared to about 50% of the other rocky planets and moons). Above the core is the largest internal layer, the rocky mantle, which is about 1000 kilometres (600 miles) thick. In the past, magma from this hot, partly molten, mantle would have burst up through the crust in volcanoes. These created the lava plains we see today on the Moon’s surface, known as mare. The lava later cooled and solidified to form solid rock. All the Moon’s volcanoes became extinct.
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The Moon is the second-densest body in the Solar System, beaten only by Jupiter's moon, Io.
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