Sun and its planets. Artwork of the nine planets of the solar system arrayed from left to right in their order from the Sun (at left). The size of the Sun and planets is to scale. The four small, rocky planets of the inner solar system are Mercury, Venus, Earth and Mars. The four large, gas giant planets of the outer solar system are Jupiter, Saturn, Uranus and Neptune. Finally, Pluto is a small planet of rock and ice. Planetary rings and moons, solar flares and the asteroid belt (between Mars and Jupiter), are also shown. The Sun contains 99.9% of the mass of the solar system.