Every Lost World In Our Solar System Explained In 14 Minutes

Earth's Second Moon The Moon has two faces that do not match. The near side, the one permanently turned toward Earth, is relatively low and flat, covered in the dark volcanic plains that are visible from the ground. The far side is the opposite. It is rugged, heavily cratered, and its crust is dramatically thicker, in places by more than a dozen miles. This mismatch is known as the lunar dichotomy, and its cause has never been fully settled. One explanation, put forward in 2011, is that the Earth once had a second moon. In this model the young Earth possessed two satellites, both formed from the debris of the giant impact that created the Moon in the first place. The larger became the Moon we know. The smaller, roughly a thousand miles across, shared its orbit and sat at one of the gravitationally stable points ahead of or behind it.