The solar system consists of the sun and objects that orbit around it. The sun is at the center and is a star. There are nine planets including Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. The inner planets are closest to the sun and include Mercury, Venus, Earth and Mars. Earth is unique among inner planets as it has water and oxygen in its atmosphere to support life. The outer planets are farther from the sun and made of gases, including Jupiter, Saturn, Uranus and Neptune. Pluto is smaller than other outer planets. Asteroids and comets also orbit the sun.