As new major discoveries keep coming in, our view of the solar system is undergoing radical changes. At first we simply divided the solar system into the four inner small planets(Mercury, Venus, Earth and Mars), and the four outer giants(Jupiter, Saturn, Uranus, and Neptune), but Pluto, Eris, and other similar objects are changing all this. A new class of planets -the mini planets, are presumably the true occupants of the outermost solar system.
The inner solar system still remains basically the same with Mercury, Venus, Earth, and Mars as its principle occupants. The inner asteroid belt, with mini-planet Ceres as its leader, separates the inner planets from the four middle giants -Jupiter, Saturn, Uranus, and Neptune. Between Saturn and Uranus is the planetoid Chiron(tiny white dot), which may be the actual mid-point(numerically) of our solar system, separating the traditional visible(to the naked eye) half of our solar system from the modern invisible half.
The outermost solar system, which begins with the Kuiper asteroid belt, is a strange place indeed, with what appears to be a number of planets even smaller than those of the innermost solar system. Pluto and Eris are practically twins in the 1400 to 1500 mile diameter range. In the vicinity of Pluto are somewhat smaller objects like Quaoar, Varuna, Orcus, Ixion, Haumea, and Makemake. All of these objects straddle the Kuiper Belt or outer asteroid zone which is some 30 to 50 AU from the Sun.
Where the Kuiper belt ends there is a strange void followed by a relatively new and unexplored area of space leading to the Oort cloud. One of the recently discovered objects in this space is Sedna, which is smaller than Pluto and anywhere from 2 to 25 times its distance from the Sun. Sedna may be part of a whole new group of bodies or somehow tied in with the most distant and mysterious object in our solar system -a brown dwarf or binary companion to our Sun.