Solar system. Artwork of the nine planets orbiting the Sun (far left). The orbits of the planets and their moons are shown as blue lines. Distances and sizes are not to scale. Four small, rocky planets make up the inner solar system. They are, across bottom from left to right: Mercury, Venus, Earth and Mars. Earth's Moon and the small moons of Mars (Deimos, outer; Phobos, inner) are seen. Four gas giant planets in the outer solar system (right to left, across top) are: Jupiter, Saturn, Uranus and Neptune. Also seen are: the eccentric orbit of the planet Pluto, the asteroid belt (between Mars and Jupiter), a solar flare, and the Milky Way galaxy.