In the year, 1959, when the first images from the Soviet Luna 3 spacecraft were returned to Earth, since then the scientists have deliberated about the differences between two halves of the moon.
The side which is farther and cannot be seen by us has mountains, valleys and highlands. The visible side is much more flat with huge seas of basalt which create the darker areas. The Man in the Moon is created in theses darker areas.
In science, this is referred to as "Lunar Farside Highlands Problem" and a paper published in the edition of Astrophysical Journal Letters suggests an answer to the puzzle. Jason Wright, assistant professor of astrophysics at Penn State University and his colleagues Steinn Sigurdsson, professor of astrophysics and Arpita Roy, graduate student in astronomy and astrophysics, are of the opinion that the variance dates back to the creation of the Moon.
The Giant Impact Hypothesis proposes that the Moon was made just after the Earth. It is thought that a crash, or at least a sideways blow, with an object of Mars size flung debris from the Earth and the other object called Theia into space. The moon is believed to have formed from this material.
Post event the Moon became tidally locked with the Earth, which specifies that the side facing us is always facing us and it does not rotate away. The effect would have produced intense heat and it is probable that the Earth and Moon stayed molten for some time after the event. As the moon is smaller it would have cooled more quickly than the Earth. The side of the moon facing the Earth, which was 10 to 20 times closer at the time, would have absorbed extra heat from the Earth. This irregular cooling would have caused different concentrations of elements on the two sides of the Moon.
Even though the Giant Impact Hypothesis hasn't been confirmed yet, the study by the German researchers of Moon rocks has added credibility to it.