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Published in 2010 by Britannica Educational Publishing (a trademark of Encyclopædia Britannica, Inc.) in association with Rosen Educational Services, LLC 29 East 21st Street, New York, NY 10010. Copyright © 2010 Encyclopædia Britannica, Inc. Britannica, Encyclopædia Britannica, and the Thistle logo are registered trademarks of Encyclopædia Britannica, Inc. All rights reserved. Rosen Educational Services materials copyright © 2010 Rosen Educational Services, LLC. All rights reserved. Distributed exclusively by Rosen Educational Services. For a listing of additional Britannica Educational Publishing titles, call toll free (800) 237-9932. First Edition Britannica Educational Publishing Michael I. Levy: Executive Editor Marilyn L. Barton: Senior Coordinator, Production Control Steven Bosco: Director, Editorial Technologies Lisa S. Braucher: Senior Producer and Data Editor Yvette Charboneau: Senior Copy Editor Kathy Nakamura: Manager, Media Acquisition Erik Gregersen: Associate Editor, Astronomy and Space Exploration Rosen Educational Services Jeanne Nagle: Senior Editor Nelson Sá: Art Director Nicole Russo: Designer Introduction by Greg Roza Library of Congress Cataloging-in-Publication Data Outer solar system: Jupiter, Saturn, Uranus, Neptune, and the dwarf planets / edited by Erik Gregersen.—1st ed. p. cm.—(An explorer’s guide to the universe) “In association with Britannica Educational Publishing, Rosen Educational Services.” Includes index. ISBN 978-1-61530-051-8 (eBook) 1. Solar system—Popular system. 2. Sattelites—Popular system. 3. Kuiper Belt—Popular system. I. Gregersen, Erik. QB501.2.O98 2010 523.2—dc22 2009036104 On the cover: A highly visible ring system differentiates Saturn from the other planets of the outer solar system–Jupiter, Neptune, Uranus–and the dwarf planet Pluto. Cover photo: © www.istockphoto.com/sololos
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CONTENTS Introduction 10 Chapter 1: Asteroids 19 Major Milestones in Asteroid Research 20 Bode’s Law 21 Later Advances in Asteroid Studies 22 Geography of the Asteroid Belt 22 Names and Orbits of Asteroids 23 Distribution and Kirkwood Gaps 23 Near-Earth Asteroids 25 Main-Belt Asteroid Families 27 Hungarias and Outer-Belt Asteroids 28 Trojan Asteroids 29 Asteroids in Unusual Orbits 30 The Difference Between Asteroids and Comets 30 Measuring Asteroids 31 Size and Albedo 31 Classification of Asteroids 33 Rotation and Shape 33 Mass and Density 35 Composition 36 Asteroid Taxonomic Classes 37 Spacecraft Exploration 38 Origin and Evolution of the Asteroids 41 Notable Asteroids 42 Ceres 42 Eros 44 Geographos 45 Hermes 45 Icarus 46 Pallas 46 Vesta 46 Chapter 2: Meteors and Meteorites 48 Basic Features of Meteors 49 Meteor Showers 51 Meteorites: Surviving Atmospheric Entry 53 Measurement of Meteoroid Orbits 57 Reservoirs of Meteoroids in Space 58 Directing Meteoroids to Earth 59
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Meteorites 61 Recovery of Meteorites 62 Types of Meteorites 63 Chondrites 64 Achondrites 68 Iron Meteorites 70 Stony Iron Meteorites 71 Association of Meteorites with Asteroids 72 The Ages of Meteorites and Their Components 73 Cosmic-Ray Exposure Ages of Meteorites 76 Meteorites and the Formation of the Early Solar System 77 Meteorite Craters 80 The Impact-Cratering Process 82 Variations in Craters Across the Solar System 84 Meteorite Craters as Measures of Geologic Activity 85 Meteoritics 86 Notable Meteorites 87 Allende Meteorite 87 Ensisheim Meteorite 87 Murchison Meteorite 87 Orgueil Meteorite 88 Chapter 3: Jupiter 89 Basic Astronomical Data 90 Planetary Data for Jupiter 91 The Atmosphere 92 Nature of the Great Red Spot 93 Cloud Composition 94 Atmospheric Characteristics 95 Atmospheric Abundances for Jupiter 96 Temperature and Pressure 98 Other Likely Atmospheric Constituents 99 Collision with a Comet and an Asteroid 99 Radio Emission 101
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The Magnetic F