SS TTHHEELLUUCCEENNTTLLIIBBRRAARRYY OOFF CCIIEENNCCEE AANNDD TT EECCHHNNOOLLOOGGYY Comets and Asteroids by Don Nardo San Diego (cid:127) Detroit (cid:127) New York (cid:127) San Francisco (cid:127) Cleveland (cid:127) New Haven, Conn. (cid:127) Waterville, Maine (cid:127) London (cid:127) Munich Cover: Comet Hyakutake, discovered in 1996, is one of the brightest comets ever discovered, and has a tail more than 300 million miles long. © 2004 by Lucent Books. Lucent Books is an imprint of The Gale Group, Inc., a division of Thomson Learning, Inc. Lucent Books®and Thomson Learning™ are trademarks used herein under license. For more information, contact Lucent Books 27500 Drake Rd. Farmington Hills, MI 48331-3535 Or you can visit our Internet site at http://www.gale.com ALL RIGHTS RESERVED. No part of this work covered by the copyright hereon may be reproduced or used in any form or by any means—graphic, electronic, or mechanical, including photocopying, recording, taping, Web dis- tribution or information storage retrieval systems—without the written permission of the publisher. LIBRARY OF CONGRESS CATALOGING-IN-PUBLICATION DATA Nardo, Don, 1947– Comets and asteroids / by Don Nardo. v. cm. — (The Lucent library of science and technology) Includes bibliographical references. Contents: Comets demystified, asteroids discovered—How asteroids and comets formed—Vital statistics of asteroids and comets—Voyages to the comets and asteroids—How humans will mine asteroids and comets—When comets and asteroids strike earth. ISBN 1-59018-286-3 (hardback : alk. paper) 1. Comets—Juvenile literature. 2. Asteroids—Juvenile literature. [1. Comets. 2. Asteroids.] I. Title. II. Series. QB721.5N37 2004 523.6—dc22 2003016736 Printed in the United States of America Table of Contents Foreword 4 Introduction 7 Mountains in the Sky Chapter 1 15 Comets Demystified, Asteroids Discovered Chapter 2 28 How Asteroids and Comets Formed Chapter 3 41 Vital Statistics of Asteroids and Comets Chapter 4 55 Voyages to the Comets and Asteroids Chapter 5 68 How Humans Will Mine Asteroids and Comets Chapter 6 80 When Comets and Asteroids Strike Earth Notes 94 Glossary 97 For Further Reading 99 Major Works Consulted 101 Additional Works Consulted 103 Index 107 Picture Credits 112 About the Author 112 Foreword “The world has changed far more in the past 100 years than in any other century in history. The reason is not political or economic, but technological—technologies that flowed directly from advances in basic science.” — Stephen Hawking, “A Brief History of Relativity,” Time, 2000 The twentieth-century scientific and technological revolution that British physicist Stephen Hawking describes in the above quote has transformed virtually every aspect of human life at an unprecedented pace. Inventions unimaginable a century ago have not only become commonplace but are now considered neces- sities of daily life. As science historian James Burke writes, “We live surrounded by objects and systems that we take for granted, but which profoundly affect the way we behave, think, work, play, and in general conduct our lives.” For example, in just one hundred years, transporta- tion systems have dramatically changed. In 1900 the first gasoline-powered motorcar had just been intro- duced, and only 144 miles of U.S. roads were hard- surfaced. Horse-drawn trolleys still filled the streets of American cities. The airplane had yet to be invented. Today 217 million vehicles speed along 4 million miles of U.S. roads. Humans have flown to the moon and commercial aircraft are capable of transporting passen- gers across the Atlantic Ocean in less than three hours. The transformation of communications has been just as dramatic. In 1900 most Americans lived and worked on farms without electricity or mail delivery. Few people had ever heard a radio or spoken on a tele- phone. A hundred years later, 98 percent of American 4 Foreword 5 homes have telephones and televisions and more than 50 percent have personal computers. Some families even have more than one television and computer, and cell phones are now commonplace, even among the young. Data beamed from communication satel- lites routinely predict global weather conditions and fiber-optic cable, e-mail, and the Internet have made worldwide telecommunication instantaneous. Perhaps the most striking measure of scientific and technological change can be seen in medicine and pub- lic health. At the beginning of the twentieth century, the average American life span was forty-seven years. By the end of the century the average life span was ap- proaching eighty years, thanks to advances in medicine including the development of vaccines and antibiotics, the discovery of powerful diagnostic tools such as X rays, the life-saving technology of cardiac and neonatal care, and improvements in nutrition and the control of infectious disease. Rapid change is likely to continue throughout the twenty-first century as science reveals more about physical and biological processes such as global warm- ing, viral replication, and electrical conductivity, and as people apply that new knowledge to personal decisions and government policy. Already, for example, an inter- national treaty calls for immediate reductions in indus- trial and automobile emissions in response to studies that show a potentially dangerous rise in global tem- peratures is caused by human activity. Taking an active role in determining the direction of future changes de- pends on education; people must understand the possi- ble uses of scientific research and the effects of the tech- nology that surrounds them. The Lucent Books Library of Science and Technology profiles key innovations and discoveries that have trans- formed the modern world. Each title strives to make a complex scientific discovery, technology, or phenome- non understandable and relevant to the reader. Because scientific discovery is rarely straightforward, each title 6 Comets and Asteroids explains the dead ends, fortunate accidents, and basic scientific methods by which the research into the subject proceeded. And every book examines the practical appli- cations of an invention, branch of science, or scientific principle in industry, public health, and personal life, as well as potential future uses and effects based on ongoing research. Fully documented quotations, annotated bibli- ographies that include both print and electronic sources, glossaries, indexes, and technical illustrations are among the supplemental features designed to point researchers to further exploration of the subject. Introduction Mountains in the Sky If a person goes outside on a clear, moonless night in the countryside, far from city lights, he or she will be treated to a breathtaking sight. Above stretches a velvet black canopy studded with thousands of pin- points of light, some bright and lustrous, others so faint they are barely visible. Most of these, of course, are stars like the Sun, except that they lie much far- ther away than the huge gaseous ball whose light and heat make life on Earth possible. A few of the brighter points of light in the dark canopy are planets in our own solar system, the Sun’s family. But these few easily visible solid bodies, each thousands of miles in diameter, are only the tip of the iceberg, so to speak, of the material making up the solar system. Lurking in the darkness among them, usually invisible to unaided human eyes, are billions of smaller objects. Some are no larger than cars or houses, while others are five, ten, fifty, or a hundred miles across. “Lost amid the stars,” writes noted science historian Curtis Peebles, “there are mountains in the sky. Some are worlds in their own right, others are the irregular splinters of collisions [that happened] ages ago.”1 Those orbiting mountains that are composed mainly of metal and rock are known as asteroids, while those made up mostly of ice and rock are comets. Because of 7 Mountains in the Sky 9 ing stars,” while in ancient Zaire (in Africa), they were “hair stars,” in reference to their hairlike tails. Similarly, the European name—comet—which be- came universally accepted, comes from the ancient Greek word kome, meaning “hair.” Whatever the ancients chose to call comets, nearly all agreed that these objects were omens, or super- natural signs, of one kind or another. The most com- mon view was that they foretold coming disasters or ill fortune. An ancient Chinese document titled Record of the World’s Change states: Comets are vile stars. Every time they appear in the south, something happens to wipe out the old and establish the new. Also, when comets appear, whales die. In Sung . . . times, when a comet ap- peared in the constellation of the Big Dipper, all soldiers died in chaos. . . . When a comet appears in the North Star, the emperor is replaced. If it ap- pears in the end of the Big Dipper, everywhere there are uprisings and war continues for several years. If it appears in the bowl of the Dipper, a prince controls the emperor. Gold and gems be- come worthless. . . . Scoundrels harm nobles. Some leaders appear, causing disturbances. Ministers conspire to rebel against the emperor.2 The other common belief regarding cometary omens was that they signaled the birth, death, or military victories of great kings, generals, and other human leaders. The immortal English playwright William Shakespeare summarized it best in a famous line from his play Julius Caesar: “When beggars die, there are no comets seen; the heavens themselves blaze forth the death of princes.”3 In fact, the pass- ing of the real Julius Caesar, some sixteen centuries before Shakespeare wrote these lines, was said to have been marked by a comet. According to Caesar’s Greek biographer Plutarch: “Of [the] supernatural events [marking Caesar’s death] there was, first, the