Structure of the Moon

It may be fanciful to think that the Moon is made of cheese, or that there is a man in the Moon, but how did we work out what the Moon is made from?

Working out the structure of the Moon

During the Apollo missions, many geological experiments were carried out to try and work out the Moon's structure. The experiments studied the seismic activity or 'moonquakes'. 

The seismic waves generated by these quakes change as they move through different materials. The experiments analysed the changes to these waves to work out which parts of the Moon were solid or not.

Internal structure

Like the terrestrial or rocky planets Venus, Mercury, Earth and Mars, the Moon is made up of concentric layers formed by the melting and separation of magma

There is a solid outer crust about 65km deep, below which is a silicate mantle about 1,000km thick. At the centre there is a metallic core with a radius of about 500km. 

The core is not magnetic, suggesting that unlike the Earth's core, the centre of the Moon is solid and has no convection.

Surface of the Moon, photographed by Apollo 8 astronauts © NASA

Surface of the Moon, photographed by Apollo 8 astronauts © NASA

Surface

If you look closely at the Moon's surface you can see that it has light and dark patches. If you look even closer, perhaps through binoculars or a telescope, you can make out that the dark patches look smooth and the light patches are pitted with craters. 

The dark areas are called maria, the Latin for sea. They are mainly made of basalt and were formed billions of years ago when lava flowed over the surface. 

The light areas are highlands or tarrae, made from a mineral rich in calcium and aluminium. They are much older than the maria and bear the scars of numerous asteroid impacts.

Cartoon image of lab coats with T.rex name label

Our fossil insect collection includes Rhyniognatha hirsti, the world's oldest fossil insect, dating back some 400 million years.