Britannica Educational Publishing 
Nature of Planets, Dwarf Planets, and Space Objects [PDF ebook] 

Peering through a telescope, you are likely to encounter a host of celestial bodies-anything from another planet to a comet-speckling the night sky. Careful observation has shown that while each object follows a unique orbit or trajectory, these entities also share numerous qualities and together provide critical information about space and the universe as a whole. This engaging volume surveys the characteristics of the diverse objects that make up the solar system as well as their distinguishing features.