Discover what dwarf planet Pluto can tell us about the architecture of the solar system in this video from NOVA: Chasing Pluto. According to scientific theory, our solar system started out as a swirling cloud of gas and dust. As material began to clump together, larger and larger bodies formed. The largest of the planets are the gas giants Jupiter and Saturn. At the other end of the size spectrum are Pluto and the other dwarf planets—celestial objects that somehow stopped growing. Dwarf planets are the most common type of planet in the solar system. Some scientists believe they may contain key ingredients for life: water, energy, and organic matter.