Field Guide to Meteors and Meteorites PDF
Preview Field Guide to Meteors and Meteorites
Patrick Moore’s Practical Astronomy Series For other titles published in the series, go to www.springer.com click on the series discipline click on the heading “Series” click on the name of the series Field Guide to Meteors and Meteorites O. Richard Norton Lawrence A. Chitwood ISBN 978-1-84800-156-5 e-ISBN 978-1-84800-157-2 DOI: 10.1007/978-1-84800-157-2 British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library Library of Congress Control Number: 2008921357 Patrick Moore’s Practical Astronomy Series ISSM: 1617-7185 © Springer-Verlag London Limited 2008 Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced, stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms of licenses issued by the Copyright Licensing Agency. Enquiries concerning reproduction outside those terms should be sent to the publishers. The use of registered names, trademarks, etc., in this publication does not imply, even in the absence of a specifi c statement, that such names are exempt from the relevant laws and regulations and therefore free for general use. The publisher makes no representation, express or implied, with regard to the accuracy of the information contained in this book and cannot accept any legal responsibility or liability for any errors or omissions that may be made. Cover illustration: Photo of Hammada al Hamra 335 found in Libya in 2004. Courtesy of Dr. Svend Buhl, www.meteorite- recon.com. Printed on acid-free paper 9 8 7 6 5 4 3 2 1 Springer Science + Business Media springer.com To Lawrence A. Chitwood, co-author, colleague and good friend, who died suddenly shortly after this book was completed - His passion for minerals in meteorites, expertise in the use of the petrographic microscope, and remarkable ability to make this complex science understandable contributed greatly to the production of this book. He will be sorely missed. - O. Richard Norton v Preface A Personal Note When I was a 13-year-old kid nearly six decades ago, I discovered the heavens. That discovery changed everything. Finding my way around the night time sky was the first challenge. As I learned the celestial stick figures of Greek and Roman mythology placed there as monuments to ancient gods, they became stationary signposts that allowed me to wander from figure to figure, retracing my steps from celestial pole to celestial equator. I soon learned that hidden within these constellations were objects of great beauty and wonder—star clusters, nebulae, double stars, and galaxies. It wasn’t long before I laid aside the simple star charts that I had carefully cut out from the Long Beach, California Press-Telegram. In their stead, I purchased a book by my namesake, Norton’s Star Atlas. This marvelous book had sky charts showing many more stars than I had learned about from the newspaper maps, stars so faint that I could barely see them with the unaided eye. There were exceptionally bright stars also. Some of them moved among the starry background, usually moving east but occasionally changing direction and moving west for several weeks before stopping and resuming their easterly courses. I learned that these were the planets of the Solar System and the motions they displayed against the stars had perplexed ancient Greek astronomers for centuries. It wasn’t long before I recognized my physical limitations. If I wanted to continue this adventure, I would need a telescope. Back in those days most amateur astronomers made their own telescopes from mirror to mount. (Nowadays, if you have the dollars you can purchase telescopes that match some of the best found in professional observatories.) I made a 4-in. reflecting telescope out of plate glass and pipe fittings. This modest telescope would be my constant companion until I graduated from high school. With it, I could explore the mountains and craters on the Moon, the rings of Saturn, Jupiter and its Moons, the polar caps of Mars, and on and on. No longer this naked eye astronomy. With my telescope, I had reached out to bring the celestial sphere with all of its wonders a bit closer to me. Besides the obvious Solar System objects, there were more subtle things that were a challenge to find and observe. Asteroids! Through my telescope, I could only see the largest and brightest as a yellowish point of light moving among the stars between Mars and Jupiter. And then there was the occasional comet that seemed to defy all the rules, crossing the orbits of the inner planets with total disregard for their stately motions. Comets were fascinating because, unlike the constellations, they could be seen to change from night to night or even hour to hour, leaving vii viii Preface behind a diaphanous tail of gaseous matter and dust. There were some things in the sky that did move quickly—“falling stars.” I remember lying on my back when I was 9 years old watching the Draconid meteor shower of October 9, 1946, and waiting for the stars to fall. I recall staring at a particularly bright star (probably Vega) and anticipating its final fall to Earth. Needless to say, it’s still there among the summer stars. At that early age, I wasn’t aware that falling stars (or shooting stars) were not stars at all, but dust specks from comets descending to Earth. Once I had learned this association several years later, I was primed to ask more pertinent questions. Could any of this comet dust survive passage through Earth’s atmosphere? Might there be comet dust in my mother’s vacuum cleaner? Comet dust particles, now more accurately called interplanetary dust particles (IDPs), have been collected in the stratosphere by sticky-winged high flying aircraft as we will see. Most of the dust particles are too small to produce visible meteors but annual meteor showers show us that larger particles, a millimeter or greater, do exist and do produce meteors, some very bright ones. Can we go further? Is there a connection between IDPs and other objects of subplanetary mass, namely, the asteroids? Occasionally, brilliant fireballs are observed passing through Earth’s atmosphere leaving a trail of gas and dust behind. These have been photographed in flight, and their orbital paths have been extrapolated backward terminating in the asteroid belt. This implies that there are still large chunks of rocky material out there that have left the asteroid belt and are on their way to Earth. Today our museums house thousands of rocky samples of aster- oids that have come to us from space—free of charge. They are relics of the early Solar System. So we have moved from the fixed stars to celestial objects we can actually touch. Even rock samples collected on the Moon during the Apollo missions have their counterparts on Earth. About 50 stones of lunar origin have been found on Earth in the past decade. More discoveries will follow as meteorite hunters (scientists and amateurs) continue to comb the hot and cold deserts of the world to touch what was once beyond their reach. It wasn’t long before I began to realize that the study of the Solar System requires more than simply acquiring beautiful optical images of distant Solar System objects, as wonderful as they are. Over the years, I recognized the need to expand my knowledge of meteorites to include such diverse fields as petrology, optical mineralogy, petrography, and the study of minerals as they per- tain to meteoritics, the science of meteorites. I invited Lawrence A. Chitwood, volcanologist and geologist for the Deschutes National Forest in central Oregon and an expert in igneous petrology and mineralogy, to write this book with me for he has much of the knowledge that is necessary to study meteoritics. (We met not as scientists, but as musicians. We both play the piano and have performed many classical duets together. Curiously, I learned that he also made a telescope when he was a kid and he too spent hours under the sky memorizing the constellations.) The connection has now been made between those tiny specks of dust that flash across the night sky, their asteroidal precursors and meteorites. No longer must amateur astronomers be content with passively observing the heavens. Not only are meteorites fragments of asteroids but some also contain interstellar grains—and we can actually hold them in our hands. These space rocks have made it to Earth by the thousands, even though it took us centuries to come to terms with them, to realize their true nature. They are scattered all over Earth from pole to pole waiting to be discovered. A new world of exploration awaits the backyard scientist. Amateur astrono- mers, in particular, have surveyed the Solar System with their telescopes but their surveys remain incomplete. Now it is time to look down as well as up; to set aside your telescopes, and arm yourselves with metal detectors, magnets, magnifiers, and microscopes and prepare to explore the wonders of the Solar System locked inside these rocks from space for the last 4.56 billion years. Let this book be your guide to the smaller bodies of the Solar System. O. Richard Norton Acknowledgements This book could not have been written without the assistance of many people. Scientists, collec- tors, meteorite dealers and hunters the world over responded enthusiastically to the notion of a field guide and to our requests for images of all types of meteorites. It is not possible to list all of them here, but their names appear in photo captions throughout the book and we are grateful to them all. In some cases, they supplied wonderful images of specimens we never could have acquired ourselves. In other cases, they sent specimens for us to photograph. Special thanks must be given to John Watson, Consultant Publisher in London, whose initial support of this project led to the idea of a Field Guide to Meteors and Meteorites. We must also thank our Editor Harry Blom for insisting that this book would be full color, thereby allowing us to present the many wonderful images of these elusive visitors from space. Christopher Coughlin, Associate Editor, and Joseph Quatela, Production Editor worked to ensure that the book would fulfill its stated purpose and would function as a general introduction to the subject and a field guide to specific meteorite types. Lastly and certainly not least of all we must thank our wives. The book, as often is the case, took longer than expected to write and they were supportive from beginning to end. Karen Chitwood read and reread much of the text and made many helpful suggestions. Dorothy Sigler Norton, a scientific illustrator, contributed most of the diagrams and other illustrations, as well as online research, editing and endless correspondence. ix Contents Preface—A Personal Note .......................................................................................................... vii Acknowledgements .................................................................................................................... ix Introduction ............................................................................................................................... 1 Part I Ancient Fragments of the Solar System 1 Interplanetary Dust and Meteors ....................................................................................... 5 Interplanetary Dust Particles (IDPs) ................................................................................... 6 Lifetime of IDPs ................................................................................................................ 6 The Zodiacal Light ............................................................................................................ 7 Photographing the Zodiacal Light ................................................................................... 8 Collecting IDPs—No Job for an Amateur ....................................................................... 9 Physical Properties of IDPs .............................................................................................. 10 Deep Sea IDPs ................................................................................................................... 11 Collecting IDPs in Space—The Stardust Mission ........................................................... 12 Meteors .................................................................................................................................. 14 Sporadic Meteors .............................................................................................................. 15 Meteor Showers ................................................................................................................ 16 Early Radio Observations of Meteor Showers ................................................................ 18 Meteor Outbursts and Meteor Storms ............................................................................ 19 The Great Leonid Meteor Storms .................................................................................... 20 Techniques of Observing and Photographing Meteors .................................................. 20 References and Useful Web Sites .......................................................................................... 22 2 Meteorites: Fragments of Asteroids ................................................................................... 23 Asteroids in History .............................................................................................................. 23 xi xii Contents Main Asteroid Belt ................................................................................................................ 24 Asteroids and the Titius-Bode Rule ................................................................................. 24 Discovery of the First Asteroids ....................................................................................... 25 Cataloging and Naming New Asteroids .......................................................................... 27 From Asteroid Belt to Earth ............................................................................................. 27 Near-Earth Objects ........................................................................................................... 28 Trojan Asteroids ................................................................................................................ 29 An Important Job for Dedicated Amateur Astronomers................................................ 29 The Five Major NEO Surveys........................................................................................... 30 Comparing Asteroids with Meteorites ............................................................................ 30 4 Vesta ................................................................................................................................ 33 1 Ceres ............................................................................................................................... 34 Asteroid Close Encounters ............................................................................................... 35 253 Mathilde ..................................................................................................................... 36 433 Eros ............................................................................................................................. 36 Hayabusa ........................................................................................................................... 38 The Dawn Mission to 4 Vesta and 1 Ceres ...................................................................... 40 Manned Missions ............................................................................................................. 40 References and Useful Web Sites .......................................................................................... 41 3 Meteoroids to Meteorites: Lessons in Survival ................................................................. 43 Atmospheric Entry ............................................................................................................... 43 Fireballs ............................................................................................................................. 44 Light, Sound and Heat ..................................................................................................... 44 Ablation ............................................................................................................................. 45 Brecciated Meteorites and Multiple Falls ............................................................................ 48 The Strewn Field ................................................................................................................... 52 Meteorite Surface Features ................................................................................................... 53 The Primary Fusion Crust ............................................................................................... 53 The Secondary Fusion Crust ............................................................................................ 58 Angularity of Stones ......................................................................................................... 58 Regmaglypts, Flow Features and Oriented Meteorites ................................................... 58 The Big Ones ......................................................................................................................... 65 Weathering of Meteorites ..................................................................................................... 68 Mechanical Weathering .................................................................................................... 68 Chemical Weathering ....................................................................................................... 68 References and Useful Web Sites .......................................................................................... 70 Magazines .............................................................................................................................. 71 Useful web sites with information ....................................................................................... 71 Part II The Family of Meteorites 4 The Chondrites .................................................................................................................... 75 Primary Minerals in Chondritic Stony Meteorites ................................................................. 76 Olivine ............................................................................................................................... 77 Pyroxenes .......................................................................................................................... 77 Iron-Nickel Minerals ........................................................................................................ 77 Accessory Minerals ............................................................................................................... 78 Troilite ............................................................................................................................... 78 Iron Oxide ......................................................................................................................... 78 Contents xiii Plagioclase Feldspar .......................................................................................................... 78 Elemental Abundances in Chondritic Meteorites ............................................................... 78 Chemical Types of Ordinary Chondrites ............................................................................ 78 Petrographic Types of Ordinary Chondrites ....................................................................... 81 Ordinary Chondrites ............................................................................................................ 84 Enstatite Chondrites ............................................................................................................. 86 R Chondrites ......................................................................................................................... 88 Carbonaceous Chondrites .................................................................................................... 90 A Chondrule Gallery ............................................................................................................ 106 5 Primitive and Differentiated Meteorites: Asteroidal Achondrites .................................. 113 Differentiation ...................................................................................................................... 114 Achondrites ........................................................................................................................... 115 Primitive Achondrites ........................................................................................................... 116 Asteroidal Achondrites ......................................................................................................... 120 6 Differentiated Meteorites: Planetary and Lunar Achondrites ........................................ 135 Martian SNC group .............................................................................................................. 136 ALH 84001 ............................................................................................................................ 142 Lunar Achondrites ................................................................................................................ 144 Useful Web Sites ................................................................................................................... 145 7 Differentiated Meteorites: The Irons ................................................................................. 149 Alloys of Iron-nickel Meteorites .......................................................................................... 149 Chemical Classification of Iron Meteorites ......................................................................... 151 IAB Group ......................................................................................................................... 151 IC Group ........................................................................................................................... 151 IIAB Group ....................................................................................................................... 152 IIC Group .......................................................................................................................... 152 IID Group ......................................................................................................................... 152 IIE Group .......................................................................................................................... 152 IIF Group .......................................................................................................................... 152 IIG Group ......................................................................................................................... 152 IIIAB Group ...................................................................................................................... 153 IIICD Group ..................................................................................................................... 153 IIIE Group ......................................................................................................................... 153 IIIF Group ......................................................................................................................... 153 IVA Group ......................................................................................................................... 153 IVB Group ......................................................................................................................... 154 Ungrouped Irons or IRUNGR ......................................................................................... 154 Hexahedrites ......................................................................................................................... 154 Octahedrites .......................................................................................................................... 156 Ataxites .................................................................................................................................. 162 Silicated Irons ........................................................................................................................ 164 8 Differentiated Meteorites: Stony-Irons ............................................................................. 167 Pallasites ................................................................................................................................ 168 Main Group Pallasites ...................................................................................................... 168 Eagle Station Pallasites ..................................................................................................... 169 The Pyroxene Pallasites .................................................................................................... 169 Mesosiderites ......................................................................................................................... 172
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