1. When the solar system was forming, part of the protoplanetary disk was inside the ice line, and part of the disk was outside the ice line.

1. Define the ice line. How do the materials in the disk change beyond the ice line? (2 point)

1. Which category of planets is found outside the ice line? How do the properties of these planets reflect the location where they formed? (2 points)

1. Which feature of the solar system can be explained if the planets all formed out of a flat, rotating disk? (1 point)

1. Answer each of these questions about what constitutes a planet:

1. What three features are required for an object to be a planet? (1 point)

1. Ganymede is larger than the planet Mercury and orbits Jupiter. Is it a planet? Why or why not? (1 point)

1. What do asteroids and comets have in common? How do they differ? List two similarities and two differences between these groups. (2 points)

1. How can astronomers infer the composition of an exoplanet? (1 point)

1. Name one of the changes made to the nebular hypothesis to account for the properties of exoplanets. What property necessitated this change? (2 points)