What is the Moon made of?

The Moon’s violent history has led to its rather colourful present

Regardless of what Wallace and Gromit may have told their viewers, the Moon is not made of cheese. The fifth largest moon in the Solar System, and our nearest neighbour, is made primarily of rock. Almost similar to Earth, the Moon is also composed of a core, mantle and crust, but its geological activity is extinct now.

The centre of the Moon is an iron-rich core accounting for roughly 20 per cent of its radius. There is a partially molten region surrounding the iron core and then a mantle that stretches between the molten core layer to the crust of the Moon, most likely composed of minerals like olivine and pyroxene.

The crust of the Moon has a thickness ranging from 70 to 150 kilometres, and its composition has been observed to contain oxygen, silicon, magnesium, iron, calcium and aluminium. It also contains relatively small amounts of titanium, uranium, thorium, potassium and hydrogen. All of these elements make up the stunning surface of the Moon that everyone can see from Earth, consisting of dark Maria (Latin for ‘seas’) that were once impact basins filled with lava. The volcanoes spread all over the lunar surface were once active, but now they all lie dormant, having not had an eruption for millions of years. The only refreshment the surface receives is when an asteroid hits it, causing the many impact craters visible from Earth.

NASA’s Galileo spacecraft imaged the Moon’s northern hemisphere using its Solid-State Imaging (SSI) instrument while on its voyage to Jupiter, creating a spectacular image. The SSI was capable of capturing many different images in varying wavelengths ranging from visible to near-infrared light. The different wavelengths correspond to a different colour and composition, meaning the scientists behind the mission could visually distinguish the different compositions on the lunar surface.

Water ice found at lunar poles

From data collected by the Indian Space Research Organisation’s Chandrayaan-1 spacecraft, launched in 2008, scientists have found definitive evidence of water ice located at both poles of the Moon.

Courtesy of NASA’s Moon Mineralogy Mapper (M3) instrument, scientists were able to detect the presence of solid ice. The instrument was able to locate the reflective properties expected from ice and also differentiate between liquid water or vapour and solid ice based on the distinctive way its molecules absorb infrared light.

These sources are located in the shadows of craters near the poles, where temperatures never get above -157 degrees Celsius. This has tantalising implications for any mission back to the Moon, as the water could possibly be used as drinking water or even rocket fuel for future exploration.

Image credit: NASA/JPL

This article was originally published in How It Works issue 118, written by Lee Cavendish

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