Learning Goals

Studying this chapter will enable you to

	Summarize the major planetary features that a theory of solar-system origins must explain.
	Outline the process by which planets form as natural by-products of star formation, and explain how that process accounts for the overall properties of our solar system.
	Describe how comets and asteroids formed, and explain their role in determining planetary properties.
	Discuss the role of collisions in determining specific characteristics of the solar system.
	Outline the properties of known extrasolar planets, and explain how they differ from planets in the solar system.
	Discuss how observations of extrasolar planets challenge current theories of solar-system formation.