Solar system planets. Artwork of the eight planets of the solar system arrayed from left to right in their order from the Sun (partly seen 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. In August 2006, Pluto (not shown) became a Dwarf planet. Planetary rings and moons are shown, as well as the asteroid belt (between Mars and Jupiter). Saturn's largest moon is Titan (orange). The four largest Jovian moons, shown here, are Ganymede, Callisto, Europa and Io. The Sun contains 99.9% of the mass of the solar system.