Protoplanets are still-growing bodies that may grow into full-sized planets; if growth stops, they may become dwarf planets. Dwarf planets are mature bodies that do not qualify as full planets under International Astronomical Union (IAU) rules.
After a star forms, gas, rock and ice form a rotating disk. Gravity and electrostatic forces pull particles together into planetesimals; collisions and mergers build bodies hundreds of miles across, which are termed protoplanets.
The article lists three requirements for full-planet status: orbiting the Sun, having enough mass to become spherical, and clearing nearby debris. It says Pluto lost its official planet label in 2006 because it does not clear debris from its path.
