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How did the Moon get cratered on the Earth-facing side?

John Corfield, by E-mail

its far side, but there are still many craters on the near side, despite the fact that it’s tidally locked so it always points towards Earth and thus should be shielded from impacts. But the Earth is far from being a perfect shield. If you use an orange to represent the Earth, the Moon would be a large grape, orbiting at a distance of over 2m. That still leaves plenty of room for a rogue asteroid to sneak around to the near side.

Secondly, the Moon hasn’t always been so tightly aligned with the Earth. Until about two billion years ago, the axial tilt on the Moon was quite unstable and may have reached angles as high as 77° to the plane of the Earth’s solar orbit. Before that, when the Moon was first formed by material ejected from Earth’s impact with another Mars-sized planet, it might well have had other orbital irregularities. These would have exposed what is now the Earth-facing side to the rest of the Solar System, until tidal forces between the Earth and the Moon synchronised the Moon’s rotation with its orbit around Earth.

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