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 Chapter 8 By reading this chapter, you will learn

What triggered the formation of the solar system? Go to: youtube, search for “Birth of the Solar System” from NationalGeographicNationalGeographic ( YndGc&feature=related) YndGc&feature=related Take notes on how the solar system formed.

Formation of the solar system

The abundances of the chemical elements are the result of cosmic processes The vast majority of the atoms in the universe are hydrogen and helium atoms produced in the Big Bang

Where did all the heavier elements come from?

1.Nuclear fusion is a process by which (a)the nuclei of lighter elements combine together into heavier elements. (b)grains of dust and ice collide and stick together to form the nuclei (inner cores) of planetesimals. (c)the nuclei of heavier elements split apart into lighter elements. 2.The two most common substances in the Universe are (a)hydrogen and helium. (b)hydrogen and nitrogen. (c)carbon and oxygen. 3.The fact that all the planets orbit the Sun in the same direction is strong evidence that a) the solar system formed from a rotating cloud of gas that collapsed. b) the planets were formed elsewhere in the Galaxy and were later captured by the Sun. c) after the planets formed, collisions between them eventually caused them all to move in the same direction. d) None of the above. We do not have any idea yet how our solar system may have formed. Click on “enter” to review your answers 1, a, 2. a, 3. a

The interstellar medium is a tenuous collection of gas and dust that pervades the spaces between the stars Nebulosity

The abundances of radioactive elements reveal the solar system’s age Each type of radioactive nucleus decays at its own characteristic rate, called its half-life, which can be measured in the laboratory This is the key to a technique called radioactive age dating, which is used to determine the ages of rocks The oldest rocks found anywhere in the solar system are meteorites, the bits of meteoroids that survive passing through the Earth’s atmosphere and land on our planet’s surface Radioactive age-dating of meteorites, reveals that they are all nearly the same age, about 4.56 billion years old

The Sun and planets formed from a solar nebula Nebular 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 age-dating) The chemical composition; by mass, 98% H & He and 2% heavier elements ( where did these heavier element come from?) The nebula flattened into a disk: Accretion disk The Sun formed by gravitational contraction of the center of the nebula -> Protosun. After about 10 8 years, T protosun > 10 million : started H fusion, became “Sun”.

The planets formed by the accretion of planetesmals and the accumulation of gases in the solar nebula

Formation of the solar system 1.Planetesimals collide and stick together to form protoplanets because a) of their mutually attractive gravitation. b) they are weakly charged and can attract each other. c) chemical bonds hold them together if they happen to collide. d) Both b and c 2.The terrestrial planets formed close to the Sun because a) this was where most of the silicates in the solar nebula were located. b) silicates could only condense close to the Sun. c) it was too hot for the large protoplanets forming here to capture any significant amounts of hydrogen or helium. d) there was no hydrogen or helium in the inner solar nebula where these planets formed. 3.The Jovian planets formed in the outer solar system far from the Sun because a) this was where most of the hydrogen and helium in the solar nebula was located. b) there were no silicates in the outer solar system.c) it was cool enough for the protoplanets forming here to capture significant amounts of hydrogen or helium. d) there was no hydrogen or helium in the inner solar nebula to form Jovian planets. Click on “enter” to review your answers 1, a, 2. c, 3. c

Astronomers have discovered planets orbiting other stars Geoff Marcy is using the 10-meter Keck telescope in Hawaii to measure the Doppler effect in stars that wobble because of planets orbiting around them So far, he and other teams have found more than 300 extrasolar planets

Extrasolar Planets Most of the extrasolar planets discovered to date are quite massive and have orbits that are very different from planets in our solar system

Extra solar planet question: Extrasolar planets are not seen directly. An observation that has been used to indirectly show they exist is a) the regular back and forth movement of the position of spectral lines of the parent stars. b) the change in luminosity of the parent star when a planet moves in front of it.c) detection of methane, which can only exist in planetary atmospheres. d) detection of faint oxygen lines which can only exist in planetary atmospheres. Click on “enter” to review your answers a

Future plans The Keck Interferometer combines the light of the world's largest optical telescopes to measure the emission from dust orbiting nearby stars and to directly detect and characterize hot gas giant planets in other solar systems. SIM PlanetQuest (in the next decade) will measure the distances and positions of stars several hundred times more accurately than any previous observations. SIM's precision will allow us to determine the distances to stars throughout the galaxy and to detect evidence of planets just slightly larger than Earth. The two Terrestrial Planet Finder obs will be detecting and characterizing Earth-like up to 45 lys away. Atmospheric signatures (such as H 2 O, CO 2, and O 3 ) of habitable or even inhabited planets. asa.gov/missions/mis sions_index.cfm