Sun and its planets. Artwork of the nine planets of the solar system and the Sun (across bottom). The size of the Sun and planets is to scale. Four small, rocky planets (lower left) are in the inner solar system (right-left): Mercury, Venus, Earth and Mars. Four large, gas giant planets are in the outer solar system (bottom-top): Jupiter, Saturn, Uranus and Neptune. Finally, Pluto (top left) is a small planet of rock and ice. Planetary rings and moons, a solar flare and a comet, are also shown. The Sun, a star in the Milky Way (partially seen in the background), contains 99.9% of the mass of the solar system.