The Moon is the fifth-largest natural satellite in the solar system and the largest relative to its host planet. It is believed to have formed about 4.5 billion years ago from debris left over after a Mars-sized body collided with Earth. The Moon’s surface is geologically diverse, with large impact basins, craters, mountains, and volcanic plains. It has no atmosphere, magnetic field, or liquid water, but scientists have detected some water ice in shadowed craters near the lunar poles. The Moon’s gravitational pull creates tides in Earth’s oceans and affects our planet’s rotation and axial tilt. It is also an important object for scientific study and has been visited by humans on six Apollo missions.