In this lesson, we leave the comfortable confines of the inner solar system and venture out beyond Mars and the asteroid belt. The asteroid belt is the demarcation line that separates the terrestrial planets from the solar system’s most massive planets. These are the Jovian giants with their beautiful ring systems and their numerous moons. There is no discernable surface for any of the Jovian planets. Even the existence of a solid core does not indicate that there is a “surface” to stand on. The question here then becomes why such a difference between the inner rocky planets and the outer gas giants? Why is it that the gas giants have such large atmospheres while the inner planets like Earth do not? What do the interiors of Jupiter and Saturn look like for example? How do astronomers learn about planetary interiors? Include in your analysis differences in atmospheric composition, mass, density, number of moons, existence of ring systems and the mechanisms that lead to these differences.