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For decades, scientists have been trying to understand why the near side of the Moon - the one visible from Earth - is flat and cratered while the rarely-seen far side is heavily cratered and has mountain ranges higher than 3,000m.

This disparity - termed the lunar dichotomy - has already attempted to be explained through a number of different theories, but the latest theory is a bit different. It suggests that when our Moon was created from debris emanating from a 'global-impact' between Earth and a Mars-sized planet, a smaller lunar body was also formed. This smaller lunar body, after initially becoming 'stuck' in a gravitational "tug-of-war" between Earth and the Moon, eventually broke free and collided (at a relatively slow velocity of less than 3km per second) with our Moon.

At this stage, our Moon would have still been forming and cooling, and would have had a 'magma ocean' with a thin crust on top. As a result, when the smaller lunar body crashed into it, it would have forced a build-up of material on the lunar crust and also pushed the underlying magma to the near side of the Moon; producing the topographic differences observed on the Moon today - observations which have been further backed up by NASA's Lunar Prospector spacecraft.

The researchers hope that their theory will be supported by NASA's current Lunar Reconnaissance Orbiter's mission to provide a model of the detailed internal structure of the Moon; they will also hope to look at the findings from high resolution gravity mapping project to be carried out next year by the Gravity Recovery and Interior Laboratory (GRAIL) mission.

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This news story originally appeared on the BBC News website