The term EARTH'S SATELLITE can be solved by the 4-letter word MOON. The MOON is Earth's only natural satellite and the fifth largest in the Solar System. It is the largest natural satellite of a planet in the Solar System relative to the size of its primary, having a quarter the diameter of Earth and 1/81 its mass. The MOON orbits Earth at an average lunar distance of 384, 400 km (238, 900 mi), or 1.28 light-seconds.