1. Venus and Earth are about the same size and mass, yet carbon dioxide is a major constituent of the atmosphere of Venus, while oxygen is much more abundant in the Earth's atmosphere. Explain why the atmospheres are so different.
2. Explain why there are two general families of planets, rocky terrestrial and gaseous jovian.
3. The first planets discovered since ancient times were Uranus and Neptune. Compare how they were discovered.
4. What knowledge do comets and asteroids provide to studies of the origin of the solar system?