Universe Eighth Edition Universe Roger A. Freedman William J. Kaufmann III CHAPTER 8 Comparative Planetology II The Origin of Our Solar System CHAPTER 8 Comparative Planetology II The Origin of Our Solar System

HW – Chapter 8 Online Quiz due Monday 10/11

8-1 The key characteristics of the solar system that must be explained by any theory of its origins 8-2 How the abundances of chemical elements in the solar system and beyond explain the sizes of the planets 8-3 How we can determine the age of the solar system by measuring abundances of radioactive elements 8-4 Why scientists think the Sun and planets all formed from a cloud called the solar nebula 8-5 How the solar nebula model explains the formation of the terrestrial planets 8-6 Two competing models for the origin of the Jovian planets 8-7 How astronomers test the solar nebula model by observing planets around other stars By reading this chapter, you will learn

A.Overestimate of the true age B. Underestimate of the true age

Key Ideas Models of Solar System Formation: The most successful model of the origin of the solar system is called the nebular hypothesis. According to this hypothesis, the solar system formed from a cloud of interstellar material called the solar nebula. Models of Solar System Formation: The most successful model of the origin of the solar system is called the nebular hypothesis. According to this hypothesis, the solar system formed from a cloud of interstellar material called the solar nebula. This occurred 4.56 billion years ago (as determined by radioactive dating). This occurred 4.56 billion years ago (as determined by radioactive dating).

Key Ideas The Solar Nebula and Its Evolution: The chemical composition of the solar nebula, by mass, was 98% hydrogen and helium (elements that formed shortly after the beginning of the universe) and 2% heavier elements (produced much later in the centers of stars, and cast into space when the stars died). The Solar Nebula and Its Evolution: The chemical composition of the solar nebula, by mass, was 98% hydrogen and helium (elements that formed shortly after the beginning of the universe) and 2% heavier elements (produced much later in the centers of stars, and cast into space when the stars died). The heavier elements were in the form of ice and dust particles. The heavier elements were in the form of ice and dust particles.

Key Ideas Formation of the Planets and Sun: The terrestrial planets, the Jovian planets, and the Sun followed different pathways to formation. Formation of the Planets and Sun: The terrestrial planets, the Jovian planets, and the Sun followed different pathways to formation. The four terrestrial planets formed through the accretion of dust particles into planetesimals, then into larger protoplanets. The four terrestrial planets formed through the accretion of dust particles into planetesimals, then into larger protoplanets. In the core accretion model, the four Jovian planets began as rocky protoplanetary cores, similar in character to the terrestrial planets. Gas then accreted onto these cores in a runaway fashion. In the core accretion model, the four Jovian planets began as rocky protoplanetary cores, similar in character to the terrestrial planets. Gas then accreted onto these cores in a runaway fashion.

Key Ideas In the alternative disk instability model, the Jovian planets formed directly from the gases of the solar nebula. In this model the cores formed from planetesimals falling into the planets. The Sun formed by gravitational contraction of the center of the nebula. After about 108 years, temperatures at the protosun’s center became high enough to ignite nuclear reactions that convert hydrogen into helium, thus forming a true star.

Key Ideas Extrasolar Planets: Astronomers have discovered planets orbiting other stars. Extrasolar Planets: Astronomers have discovered planets orbiting other stars. Most of these planets are detected by the “wobble” of the stars around which they orbit. Most of these planets are detected by the “wobble” of the stars around which they orbit. A small but growing number of extrasolar planets have been discovered by the transit method, by microlensing, and direct imaging. A small but growing number of extrasolar planets have been discovered by the transit method, by microlensing, and direct imaging. Most of the extrasolar planets discovered to date are quite massive and have orbits that are very different from planets in our solar system. Most of the extrasolar planets discovered to date are quite massive and have orbits that are very different from planets in our solar system.