Asteroids                 Comets                 Dwarf planet                 Earth                Jupiter                  Mars

      Mercury                 Moon                    Neptune                         Planets            Planisphere         Pluto

       Rockets                    Satellites              Saturn                            Spaceship       Spacestation       Stars

       Spacesuit                 Sun                        Telescope                     Uranus             Venus

In the inner Solar System, we find the “Inner Planets” – Mercury, Venus, Earth, and Mars – which are so named because they orbit closest to the Sun. In addition to their proximity, these planets have a number of key differences that set them apart from planets elsewhere in the Solar System.

For starters, the inner planets are rocky and terrestrial, composed mostly of silicates and metals, whereas the outer planets are gas giants. The inner planets are also much more closely spaced than their outer Solar System counterparts. In fact, the radius of the entire region is less than the distance between the orbits of Jupiter and Saturn.