Differences between the near and far sides of the Moon could be the result of a collision between the Moon and a “Trojan” companion that occurred billions of years ago. That is the conclusion of geophysicists in the US and Switzerland who have done computer simulations on how the Moon would be affected by such a massive impact.
Ever since the Luna 3 space mission ventured behind the Moon in 1959, we have known that the nearside and farside of the Moon are different. The nearside (which always faces the Earth) is dominated by relatively smooth basalt plains called “maria”, while the farside is mountainous and deeply pitted with craters. The two sides are also believed to be different beneath the surface, with the nearside crust appearing much thinner than the crust on the farside.
Scientists have several theories for why the two sides are so different. These include tidal heating of the Moon by the Earth’s gravitational field or a piling up of debris from the huge impact crater at the Moon’s south pole.