Satellites are also called moons. All the planets except Mercury and Venus have satellites. The four giant planets, Jupiter, Saturn, Uranus, and Neptune, have many moons. At least two asteroids, called Eugenia and Ida, have single satellites.
Satellites vary greatly in size.
A few satellites are larger than Pluto, the smallest planet. Ganymede and Saturn's moon Titan are also bigger than Mercury. A satellite's composition depends on its distance from the sun and its geologic history. The satellites closest to the sun consist of a broad class of rock called silicate. This is the same material that makes up most of Earth's crust.