It has always been puzzling why the Moon's face directed towards Earth and the one we never see are so totally different. One is mostly flat with craters while the other is mountainous. A new study published from research by USA and UK astronomers now proposes an answer. Early in its evolution-- maybe 4 billion years ago when the Moon was still forming from a collision between the Earth and a Mars size planet --a second, smaller rocky mass came together in a slow-motion splat to form the ...