NASA
Nasa: What Is a Planet?
This lesson teaches students about the characteristics of planets, comets, asteroids, and trans-Neptunian objects. After learning about these different things, students then are to debate about a new object that is found in space.
California Institute of Technology
Spitzer Science Center: Historias Desde Espacio: Premiacion a Las Planetas
All the planets are competing to see who is the best planet in the Solar System. Read the story in Spanish to learn the results of the pageant. Excellent source of information presented in a fun manner.