Astronomers’ Universe Series editor Martin Beech, Campion College, The University of Regina, Regina, Saskatchewan, Canada More information about this series at http://www.springer.com/series/6960 Steven J. Dick Classifying the Cosmos How We Can Make Sense of the Celestial Landscape Steven J. Dick Ashburn, VA, USA ISSN 1614-659X ISSN 2197-6651 (electronic) Astronomers' Universe ISBN 978-3-030-10379-8 ISBN 978-3-030-10380-4 (eBook) https://doi.org/10.1007/978-3-030-10380-4 Library of Congress Control Number: 2019930431 © Springer Nature Switzerland AG 2019 This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, express or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Cover caption: © Mark Garlick / Science Photo Library This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland What’s so amazing That keeps us stargazing? And what do we think we might see? – Kermit the Frog, “Rainbow Connection” To the Past James E. Dick & Elizabeth Grieshaber Dick The Present Terry, Gregory & Jenna, Anthony & Elizabeth, Mary Lou, Karen, Chris & Mark And the Future Adeline, Benjamin, John, James, Daniel The Hubble Ultra Deep Field, released in 2014 with its visible, near-infrared, and ultraviolet components, contains more than 10,000 galaxies stretching back in time almost to the Big Bang. It covers an area of the Southern Hemisphere sky equivalent to looking through a straw. How to understand these objects, and indeed all the objects in the universe? Classification is always the first step. Credit: NASA, ESA, H. Teplitz and M. Rafelski (IPAC/Caltech), A. Koekemoer (STScI), R. Windhorst (Arizona State University), and Z. Levay (STScI) Acknowledgments The development of the Three Kingdom system for astronomy has had a long gestation. I began work on the idea shortly after finishing The Biological Universe in 1995, the kind of release from a 15-year project that urges the mind in new directions. I had attended numerous meetings of the American Astronomical Soci- ety and the International Astronomical Union (IAU), where a zoo of increasingly exotic astronomical objects was revealed and elab- orated. What eventually became what I dub here the “3K” system was my personal search for order amidst this profusion of objects. At the same time, the “Three Domain” system of biologist Carl Woese was much in the news, uprooting previously cherished ideas in biological classification. Despite criticism of his system, biolo- gists seemed to have a better handle on their objects of study than astronomers, and seemed to take comprehensive classification systems more seriously than their astronomical counterparts, who have historically had only piecemeal systems. The heated contro- versy over the planetary status of Pluto, in which I participated and voted on at the IAU in Prague in summer 2006, highlighted this deficiency in astronomy, as does the continual discovery of new exoplanets and other exotic objects. I first broached the subject of a comprehensive classifica- tion system for astronomy publicly in broad outline in my Dibner Library Lecture, “Extraterrestrial Life and Our World View at the Turn of the Millennium,” delivered at the Smithsonian Institu- tion on May 2, 2000. It was elaborated in more detail in my LeRoy E. Doggett Prize Lecture at the winter meeting of the American Astronomical Society in Washington, D.C. in January 2006. And it was discussed in one chapter of my book Discovery and Classifica- xii Acknowledgments tion in Astronomy: Controversy and Consensus (Cambridge Uni- versity Press, 2013). My duties as NASA Chief Historian prevented the further development and publication of the system until now, and I am thankful to Springer for publishing it with so many illus- trations. Particular thanks to Maury Solomon, Hannah Kaufman, and Sharmila Sasikumar at Springer. I am indebted to the fabulous and essential Smithsonian Astrophysical Observatory/NASA Astrophysics Data System (http://adswww.harvard.edu/) as the major source for much of the literature used and cited in the notes. The reader can access most of that literature by accessing that web site and entering author and date. I have also found very useful the following compilations and commentaries: Marcia Bartusiak, ed., Archives of the Universe: A Treasury of Astronomy’s Historic Works of Discovery (New York: Pantheon Books, 2004); Kenneth Lang and Owen Gingerich, eds., A Source Book in Astronomy and Astrophysics, 1900-1975, (Cam- bridge, MA.: Harvard University Press, 1979); and Helmut Abt, ed., American Astronomical Society Centennial Issue: Selected Fundamental Papers Published This Century in the Astronomi- cal Journal and the Astrophysical Journal, Astrophysical Journal, 525 (1999). The Journal for the History of Astronomy, edited for 40 years by Michael Hoskin at Churchill Cambridge, College, and now by James Evans, is a vast treasure trove of information that I have also used extensively, as is the Journal of Astronomical His- tory and Heritage, edited by Wayne Orchiston. Both are available via ADS. For the latest astronomy news I have found very use- ful the Nova research highlights of the American Astronomical Society at https://aasnova.org, as well as the websites of particular observatories such as Hubble, Spitzer, Chandra and ground-­based observatories such as ALMA and the European Southern Observa- tory. The Mikulski Archive for Space Telescopes (https://archive. stsci.edu/), located at the Space Telescope Science Institute, is another great resource. In addition to primary and secondary literature, I have not hesitated to make cautious use of press releases, which often con- tain revealing quotations from discoverers not present in their technical publications. I have occasionally made use of newspa- per reports, which often pinpoint the date the discovery was made public, although, as I am at pains to say in my previous book, “dis- covery” itself is an extended process. For illustrations, and much more, my debt to NASA and worldwide astronomical observato- Acknowledgments xiii ries will be evident. NASA’s Planetary Data System (https://pds. nasa.gov/) is an almost inexhaustible source of imagery. My thanks as well to the unparalleled astronomy treasures of the US Naval Observatory in Washington, D.C, and its ever-help- ful Librarians over a period of many years: Brenda Corbin, Sally Bosken, and Gregory Shelton. My employment as an astronomer and historian there, only steps from its world-class library, kept me immersed in the astronomical literature for almost a quar- ter century. Last but not least, my thanks to those astronomers and historians who read all or part of the manuscript. Though ­inevitably opinions will vary on some of the classifications in this volume, any final faults are my own. My hope is that the book is useful to those trying to make sense of the ever-changing celestial landscape, and that it spurs provocative discussion about discov- ery, interpretation and classification. This book may be considered a companion to my book Dis- covery and Classification in Astronomy, published by Cambridge University Press in 2013, where the Three Kingdom system was first published in full as an Appendix and briefly discussed in a section of Chapter 8. I have on occasion used passages from that volume in this book when appropriate for describing the history of discovery of particular objects, and have given the proper cita- tion for readers who may wish to consult the earlier book for the broader context. Ashburn, VA Steven J. Dick January, 2019 Contents Introduction to Astronomy’s Three Kingdoms ���������������������� xix Part I The Kingdom of the Planets 1. The Protoplanetary Family ������������������������������������������������� 7 Class P 1: Protoplanetary Disk ������������������������������������������� 7 2. The Planet Family ��������������������������������������������������������������� 13 Class P 2: Terrestrial (Rocky) ��������������������������������������������� 13 Class P 3: Gas Giant ����������������������������������������������������������� 21 Class P 4: Ice Giant ������������������������������������������������������������� 28 Class P 5: Pulsar Planet ������������������������������������������������������� 32 3. The Circumplanetary Family ��������������������������������������������� 37 Class P 6: Satellite ���������������������������������������������������������������