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Chapter 7 - The Nature of Exoplanetary Systems
- Edited by David A. Rothery, The Open University, Milton Keynes, Iain Gilmour, The Open University, Milton Keynes, Mark A. Sephton, Imperial College London
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- Book:
- An Introduction to Astrobiology
- Published online:
- 12 April 2019
- Print publication:
- 01 March 2018, pp 243-274
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Chapter 8 - How to Find Life on Exoplanets
- Edited by David A. Rothery, The Open University, Milton Keynes, Iain Gilmour, The Open University, Milton Keynes, Mark A. Sephton, Imperial College London
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- Book:
- An Introduction to Astrobiology
- Published online:
- 12 April 2019
- Print publication:
- 01 March 2018, pp 275-300
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Summary
In Chapter 7 we were essentially concerned with the first three factors in the Drake equation that were introduced in Section 6.1.1, namely, the rate R at which suitable stars are formed, the probability pp of planets forming around a suitable star, and nE the average number of suitable planets in a habitable zone. We now move on to consider how we could determine the next factor, pl, the probability of life app earing on a suitable planet in a habitable zone.
In this chapter we concentrate on the detection of life that is based on complex carbon compounds and liquid water, i.e. carbon-liquid water life. We thus concentrate on life that resembles life on Earth. In doing so we do not assume that alien life is based on the same carbon molecules as terrestrial life. It might use mirror image isomers of some molecules used by terrestrial life, a carbon compound other than DNA to carry genetic information, or carbon compounds other than proteins to carry out the various functions performed by proteins in terrestrial life. But it is still carbon-liquid water life. Only in Chapter 9 will we free ourselves of this selfimposed (but reasonable) carbon-liquid water restriction. There, in the search for extraterrestrial intelligence (SETI) we will search for evidence of technological civilization regardless of the chemical basis of the life-forms.
In searching for signs of carbon-liquid water life, we are at least looking for something that we know to be possible. Another justification stems from fundamental chemistry. No element other than carbon has anywhere near the same facility to form compounds of sufficient complexity, diversity and versatility to supp ort the many processes of life (Section 1.1.2). Few liquids app roach water in its ability to act as both a solvent and a reactant. Ammonia is a possible alternative to water at low temperatures (at a pressure of 1 bar it is liquid from 195 K to 240 K), but it is pure speculation whether a low-temperature form of life could use ammonia in place of water. A third justification is that we know how to detect evidence of carbon-liquid water life. Apart from SETI, we have a poorer idea of how to detect life that has an entirely different chemical basis from ours, particularly as we are restricted to detection from afar.
Contributors
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- By Mitchell Aboulafia, Frederick Adams, Marilyn McCord Adams, Robert M. Adams, Laird Addis, James W. Allard, David Allison, William P. Alston, Karl Ameriks, C. Anthony Anderson, David Leech Anderson, Lanier Anderson, Roger Ariew, David Armstrong, Denis G. Arnold, E. J. Ashworth, Margaret Atherton, Robin Attfield, Bruce Aune, Edward Wilson Averill, Jody Azzouni, Kent Bach, Andrew Bailey, Lynne Rudder Baker, Thomas R. Baldwin, Jon Barwise, George Bealer, William Bechtel, Lawrence C. Becker, Mark A. Bedau, Ernst Behler, José A. Benardete, Ermanno Bencivenga, Jan Berg, Michael Bergmann, Robert L. Bernasconi, Sven Bernecker, Bernard Berofsky, Rod Bertolet, Charles J. Beyer, Christian Beyer, Joseph Bien, Joseph Bien, Peg Birmingham, Ivan Boh, James Bohman, Daniel Bonevac, Laurence BonJour, William J. Bouwsma, Raymond D. Bradley, Myles Brand, Richard B. Brandt, Michael E. Bratman, Stephen E. Braude, Daniel Breazeale, Angela Breitenbach, Jason Bridges, David O. Brink, Gordon G. Brittan, Justin Broackes, Dan W. Brock, Aaron Bronfman, Jeffrey E. Brower, Bartosz Brozek, Anthony Brueckner, Jeffrey Bub, Lara Buchak, Otavio Bueno, Ann E. Bumpus, Robert W. Burch, John Burgess, Arthur W. Burks, Panayot Butchvarov, Robert E. Butts, Marina Bykova, Patrick Byrne, David Carr, Noël Carroll, Edward S. Casey, Victor Caston, Victor Caston, Albert Casullo, Robert L. Causey, Alan K. L. Chan, Ruth Chang, Deen K. Chatterjee, Andrew Chignell, Roderick M. Chisholm, Kelly J. Clark, E. J. Coffman, Robin Collins, Brian P. Copenhaver, John Corcoran, John Cottingham, Roger Crisp, Frederick J. Crosson, Antonio S. Cua, Phillip D. Cummins, Martin Curd, Adam Cureton, Andrew Cutrofello, Stephen Darwall, Paul Sheldon Davies, Wayne A. Davis, Timothy Joseph Day, Claudio de Almeida, Mario De Caro, Mario De Caro, John Deigh, C. F. Delaney, Daniel C. Dennett, Michael R. DePaul, Michael Detlefsen, Daniel Trent Devereux, Philip E. Devine, John M. Dillon, Martin C. Dillon, Robert DiSalle, Mary Domski, Alan Donagan, Paul Draper, Fred Dretske, Mircea Dumitru, Wilhelm Dupré, Gerald Dworkin, John Earman, Ellery Eells, Catherine Z. Elgin, Berent Enç, Ronald P. Endicott, Edward Erwin, John Etchemendy, C. Stephen Evans, Susan L. Feagin, Solomon Feferman, Richard Feldman, Arthur Fine, Maurice A. Finocchiaro, William FitzPatrick, Richard E. Flathman, Gvozden Flego, Richard Foley, Graeme Forbes, Rainer Forst, Malcolm R. Forster, Daniel Fouke, Patrick Francken, Samuel Freeman, Elizabeth Fricker, Miranda Fricker, Michael Friedman, Michael Fuerstein, Richard A. Fumerton, Alan Gabbey, Pieranna Garavaso, Daniel Garber, Jorge L. A. Garcia, Robert K. Garcia, Don Garrett, Philip Gasper, Gerald Gaus, Berys Gaut, Bernard Gert, Roger F. Gibson, Cody Gilmore, Carl Ginet, Alan H. Goldman, Alvin I. Goldman, Alfonso Gömez-Lobo, Lenn E. Goodman, Robert M. Gordon, Stefan Gosepath, Jorge J. E. Gracia, Daniel W. Graham, George A. Graham, Peter J. Graham, Richard E. Grandy, I. Grattan-Guinness, John Greco, Philip T. Grier, Nicholas Griffin, Nicholas Griffin, David A. Griffiths, Paul J. Griffiths, Stephen R. Grimm, Charles L. Griswold, Charles B. Guignon, Pete A. Y. Gunter, Dimitri Gutas, Gary Gutting, Paul Guyer, Kwame Gyekye, Oscar A. Haac, Raul Hakli, Raul Hakli, Michael Hallett, Edward C. Halper, Jean Hampton, R. James Hankinson, K. R. Hanley, Russell Hardin, Robert M. Harnish, William Harper, David Harrah, Kevin Hart, Ali Hasan, William Hasker, John Haugeland, Roger Hausheer, William Heald, Peter Heath, Richard Heck, John F. Heil, Vincent F. Hendricks, Stephen Hetherington, Francis Heylighen, Kathleen Marie Higgins, Risto Hilpinen, Harold T. Hodes, Joshua Hoffman, Alan Holland, Robert L. Holmes, Richard Holton, Brad W. Hooker, Terence E. Horgan, Tamara Horowitz, Paul Horwich, Vittorio Hösle, Paul Hoβfeld, Daniel Howard-Snyder, Frances Howard-Snyder, Anne Hudson, Deal W. Hudson, Carl A. Huffman, David L. Hull, Patricia Huntington, Thomas Hurka, Paul Hurley, Rosalind Hursthouse, Guillermo Hurtado, Ronald E. Hustwit, Sarah Hutton, Jonathan Jenkins Ichikawa, Harry A. Ide, David Ingram, Philip J. Ivanhoe, Alfred L. Ivry, Frank Jackson, Dale Jacquette, Joseph Jedwab, Richard Jeffrey, David Alan Johnson, Edward Johnson, Mark D. Jordan, Richard Joyce, Hwa Yol Jung, Robert Hillary Kane, Tomis Kapitan, Jacquelyn Ann K. Kegley, James A. Keller, Ralph Kennedy, Sergei Khoruzhii, Jaegwon Kim, Yersu Kim, Nathan L. King, Patricia Kitcher, Peter D. Klein, E. D. Klemke, Virginia Klenk, George L. Kline, Christian Klotz, Simo Knuuttila, Joseph J. Kockelmans, Konstantin Kolenda, Sebastian Tomasz Kołodziejczyk, Isaac Kramnick, Richard Kraut, Fred Kroon, Manfred Kuehn, Steven T. Kuhn, Henry E. Kyburg, John Lachs, Jennifer Lackey, Stephen E. Lahey, Andrea Lavazza, Thomas H. Leahey, Joo Heung Lee, Keith Lehrer, Dorothy Leland, Noah M. Lemos, Ernest LePore, Sarah-Jane Leslie, Isaac Levi, Andrew Levine, Alan E. Lewis, Daniel E. Little, Shu-hsien Liu, Shu-hsien Liu, Alan K. L. Chan, Brian Loar, Lawrence B. Lombard, John Longeway, Dominic McIver Lopes, Michael J. Loux, E. J. Lowe, Steven Luper, Eugene C. Luschei, William G. Lycan, David Lyons, David Macarthur, Danielle Macbeth, Scott MacDonald, Jacob L. Mackey, Louis H. Mackey, Penelope Mackie, Edward H. Madden, Penelope Maddy, G. B. Madison, Bernd Magnus, Pekka Mäkelä, Rudolf A. Makkreel, David Manley, William E. Mann (W.E.M.), Vladimir Marchenkov, Peter Markie, Jean-Pierre Marquis, Ausonio Marras, Mike W. Martin, A. P. Martinich, William L. McBride, David McCabe, Storrs McCall, Hugh J. McCann, Robert N. McCauley, John J. McDermott, Sarah McGrath, Ralph McInerny, Daniel J. McKaughan, Thomas McKay, Michael McKinsey, Brian P. McLaughlin, Ernan McMullin, Anthonie Meijers, Jack W. Meiland, William Jason Melanson, Alfred R. Mele, Joseph R. Mendola, Christopher Menzel, Michael J. Meyer, Christian B. Miller, David W. Miller, Peter Millican, Robert N. Minor, Phillip Mitsis, James A. Montmarquet, Michael S. Moore, Tim Moore, Benjamin Morison, Donald R. Morrison, Stephen J. Morse, Paul K. Moser, Alexander P. D. Mourelatos, Ian Mueller, James Bernard Murphy, Mark C. Murphy, Steven Nadler, Jan Narveson, Alan Nelson, Jerome Neu, Samuel Newlands, Kai Nielsen, Ilkka Niiniluoto, Carlos G. Noreña, Calvin G. Normore, David Fate Norton, Nikolaj Nottelmann, Donald Nute, David S. Oderberg, Steve Odin, Michael O’Rourke, Willard G. Oxtoby, Heinz Paetzold, George S. Pappas, Anthony J. Parel, Lydia Patton, R. P. Peerenboom, Francis Jeffry Pelletier, Adriaan T. Peperzak, Derk Pereboom, Jaroslav Peregrin, Glen Pettigrove, Philip Pettit, Edmund L. Pincoffs, Andrew Pinsent, Robert B. Pippin, Alvin Plantinga, Louis P. Pojman, Richard H. Popkin, John F. Post, Carl J. Posy, William J. Prior, Richard Purtill, Michael Quante, Philip L. Quinn, Philip L. Quinn, Elizabeth S. Radcliffe, Diana Raffman, Gerard Raulet, Stephen L. Read, Andrews Reath, Andrew Reisner, Nicholas Rescher, Henry S. Richardson, Robert C. Richardson, Thomas Ricketts, Wayne D. Riggs, Mark Roberts, Robert C. Roberts, Luke Robinson, Alexander Rosenberg, Gary Rosenkranz, Bernice Glatzer Rosenthal, Adina L. Roskies, William L. Rowe, T. M. Rudavsky, Michael Ruse, Bruce Russell, Lilly-Marlene Russow, Dan Ryder, R. M. Sainsbury, Joseph Salerno, Nathan Salmon, Wesley C. Salmon, Constantine Sandis, David H. Sanford, Marco Santambrogio, David Sapire, Ruth A. Saunders, Geoffrey Sayre-McCord, Charles Sayward, James P. Scanlan, Richard Schacht, Tamar Schapiro, Frederick F. Schmitt, Jerome B. Schneewind, Calvin O. Schrag, Alan D. Schrift, George F. Schumm, Jean-Loup Seban, David N. Sedley, Kenneth Seeskin, Krister Segerberg, Charlene Haddock Seigfried, Dennis M. Senchuk, James F. Sennett, William Lad Sessions, Stewart Shapiro, Tommie Shelby, Donald W. Sherburne, Christopher Shields, Roger A. Shiner, Sydney Shoemaker, Robert K. Shope, Kwong-loi Shun, Wilfried Sieg, A. John Simmons, Robert L. Simon, Marcus G. Singer, Georgette Sinkler, Walter Sinnott-Armstrong, Matti T. Sintonen, Lawrence Sklar, Brian Skyrms, Robert C. Sleigh, Michael Anthony Slote, Hans Sluga, Barry Smith, Michael Smith, Robin Smith, Robert Sokolowski, Robert C. Solomon, Marta Soniewicka, Philip Soper, Ernest Sosa, Nicholas Southwood, Paul Vincent Spade, T. L. S. Sprigge, Eric O. Springsted, George J. Stack, Rebecca Stangl, Jason Stanley, Florian Steinberger, Sören Stenlund, Christopher Stephens, James P. Sterba, Josef Stern, Matthias Steup, M. A. Stewart, Leopold Stubenberg, Edith Dudley Sulla, Frederick Suppe, Jere Paul Surber, David George Sussman, Sigrún Svavarsdóttir, Zeno G. Swijtink, Richard Swinburne, Charles C. Taliaferro, Robert B. Talisse, John Tasioulas, Paul Teller, Larry S. Temkin, Mark Textor, H. S. Thayer, Peter Thielke, Alan Thomas, Amie L. Thomasson, Katherine Thomson-Jones, Joshua C. Thurow, Vzalerie Tiberius, Terrence N. Tice, Paul Tidman, Mark C. Timmons, William Tolhurst, James E. Tomberlin, Rosemarie Tong, Lawrence Torcello, Kelly Trogdon, J. D. Trout, Robert E. Tully, Raimo Tuomela, John Turri, Martin M. Tweedale, Thomas Uebel, Jennifer Uleman, James Van Cleve, Harry van der Linden, Peter van Inwagen, Bryan W. Van Norden, René van Woudenberg, Donald Phillip Verene, Samantha Vice, Thomas Vinci, Donald Wayne Viney, Barbara Von Eckardt, Peter B. M. Vranas, Steven J. Wagner, William J. Wainwright, Paul E. Walker, Robert E. Wall, Craig Walton, Douglas Walton, Eric Watkins, Richard A. Watson, Michael V. Wedin, Rudolph H. Weingartner, Paul Weirich, Paul J. Weithman, Carl Wellman, Howard Wettstein, Samuel C. Wheeler, Stephen A. White, Jennifer Whiting, Edward R. Wierenga, Michael Williams, Fred Wilson, W. Kent Wilson, Kenneth P. Winkler, John F. Wippel, Jan Woleński, Allan B. Wolter, Nicholas P. Wolterstorff, Rega Wood, W. Jay Wood, Paul Woodruff, Alison Wylie, Gideon Yaffe, Takashi Yagisawa, Yutaka Yamamoto, Keith E. Yandell, Xiaomei Yang, Dean Zimmerman, Günter Zoller, Catherine Zuckert, Michael Zuckert, Jack A. Zupko (J.A.Z.)
- Edited by Robert Audi, University of Notre Dame, Indiana
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- The Cambridge Dictionary of Philosophy
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- 05 August 2015
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- 27 April 2015, pp ix-xxx
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DEVELOPMENT OF A CHEMICAL CONTROL STRATEGY FOR THE PINE FALSE WEBWORM, ACANTHOLYDA ERYTHROCEPHALA (L.) (HYMENOPTERA: PAMPHILIIDAE)
- D. Barry Lyons, Blair V. Helson, Geraldine C. Jones, John W. McFarlane
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- Journal:
- The Canadian Entomologist / Volume 125 / Issue 3 / June 1993
- Published online by Cambridge University Press:
- 31 May 2012, pp. 499-511
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The pine false webworm, Acantholyda erythrocephala (L.) (Hymenoptera: Pamphiliidae), is an introduced sawfly that is becoming increasingly important as a pest of pine plantations in Ontario. Laboratory bioassays of 10 insecticides, applied to excised pine branches containing eggs immediately prior to hatching, indicated that carbaryl and permethrin at low dosages were efficacious in controlling larvae. Neither carbaryl nor permethrin affected egg hatch, and field trials at various dosages indicated that 500 g AI per ha of carbaryl significantly reduced larval numbers and mitigated defoliation of 1-year-old and current-year foliage. Comparisons of single early (during egg hatch), single late (mean instar about 3.8), and combinations of early and late applications of lower concentrations of both chemicals suggested that the late application better reduced webworm populations. All tested application rates of permethrin and carbaryl provided significant foliar protection, particularly to current-year foliage. Dosages as low as 35 g AI per ha of permethrin and 125 g AI per ha of carbaryl in mistblower applications of third- and fourth-instar larvae may provide suitable protection, depending on management objectives. Ground applications using a mistblower resulted in no differences in efficacy on branches from different vertical strata, but reduced efficacy was observed on branches on the sides of the trees opposite where sprays were applied. Spray drift tests with carbaryl at 500 g AI per ha indicated that some population reduction occurred in trees up to two 2.1-m-spaced rows downwind from treated trees. Thus, each row would not need to be sprayed in operational programs.
Contributors
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- By Rose Teteki Abbey, K. C. Abraham, David Tuesday Adamo, LeRoy H. Aden, Efrain Agosto, Victor Aguilan, Gillian T. W. Ahlgren, Charanjit Kaur AjitSingh, Dorothy B E A Akoto, Giuseppe Alberigo, Daniel E. Albrecht, Ruth Albrecht, Daniel O. Aleshire, Urs Altermatt, Anand Amaladass, Michael Amaladoss, James N. Amanze, Lesley G. Anderson, Thomas C. Anderson, Victor Anderson, Hope S. Antone, María Pilar Aquino, Paula Arai, Victorio Araya Guillén, S. Wesley Ariarajah, Ellen T. Armour, Brett Gregory Armstrong, Atsuhiro Asano, Naim Stifan Ateek, Mahmoud Ayoub, John Alembillah Azumah, Mercedes L. García Bachmann, Irena Backus, J. Wayne Baker, Mieke Bal, Lewis V. Baldwin, William Barbieri, António Barbosa da Silva, David Basinger, Bolaji Olukemi Bateye, Oswald Bayer, Daniel H. Bays, Rosalie Beck, Nancy Elizabeth Bedford, Guy-Thomas Bedouelle, Chorbishop Seely Beggiani, Wolfgang Behringer, Christopher M. Bellitto, Byard Bennett, Harold V. Bennett, Teresa Berger, Miguel A. Bernad, Henley Bernard, Alan E. Bernstein, Jon L. Berquist, Johannes Beutler, Ana María Bidegain, Matthew P. Binkewicz, Jennifer Bird, Joseph Blenkinsopp, Dmytro Bondarenko, Paulo Bonfatti, Riet en Pim Bons-Storm, Jessica A. Boon, Marcus J. Borg, Mark Bosco, Peter C. Bouteneff, François Bovon, William D. Bowman, Paul S. Boyer, David Brakke, Richard E. Brantley, Marcus Braybrooke, Ian Breward, Ênio José da Costa Brito, Jewel Spears Brooker, Johannes Brosseder, Nicholas Canfield Read Brown, Robert F. Brown, Pamela K. Brubaker, Walter Brueggemann, Bishop Colin O. Buchanan, Stanley M. Burgess, Amy Nelson Burnett, J. Patout Burns, David B. Burrell, David Buttrick, James P. Byrd, Lavinia Byrne, Gerado Caetano, Marcos Caldas, Alkiviadis Calivas, William J. Callahan, Salvatore Calomino, Euan K. Cameron, William S. Campbell, Marcelo Ayres Camurça, Daniel F. Caner, Paul E. Capetz, Carlos F. Cardoza-Orlandi, Patrick W. Carey, Barbara Carvill, Hal Cauthron, Subhadra Mitra Channa, Mark D. Chapman, James H. Charlesworth, Kenneth R. Chase, Chen Zemin, Luciano Chianeque, Philip Chia Phin Yin, Francisca H. Chimhanda, Daniel Chiquete, John T. Chirban, Soobin Choi, Robert Choquette, Mita Choudhury, Gerald Christianson, John Chryssavgis, Sejong Chun, Esther Chung-Kim, Charles M. A. Clark, Elizabeth A. Clark, Sathianathan Clarke, Fred Cloud, John B. Cobb, W. Owen Cole, John A Coleman, John J. Collins, Sylvia Collins-Mayo, Paul K. Conkin, Beth A. Conklin, Sean Connolly, Demetrios J. Constantelos, Michael A. Conway, Paula M. Cooey, Austin Cooper, Michael L. Cooper-White, Pamela Cooper-White, L. William Countryman, Sérgio Coutinho, Pamela Couture, Shannon Craigo-Snell, James L. Crenshaw, David Crowner, Humberto Horacio Cucchetti, Lawrence S. Cunningham, Elizabeth Mason Currier, Emmanuel Cutrone, Mary L. Daniel, David D. Daniels, Robert Darden, Rolf Darge, Isaiah Dau, Jeffry C. Davis, Jane Dawson, Valentin Dedji, John W. de Gruchy, Paul DeHart, Wendy J. Deichmann Edwards, Miguel A. De La Torre, George E. Demacopoulos, Thomas de Mayo, Leah DeVun, Beatriz de Vasconcellos Dias, Dennis C. Dickerson, John M. Dillon, Luis Miguel Donatello, Igor Dorfmann-Lazarev, Susanna Drake, Jonathan A. Draper, N. Dreher Martin, Otto Dreydoppel, Angelyn Dries, A. J. Droge, Francis X. D'Sa, Marilyn Dunn, Nicole Wilkinson Duran, Rifaat Ebied, Mark J. Edwards, William H. Edwards, Leonard H. Ehrlich, Nancy L. Eiesland, Martin Elbel, J. Harold Ellens, Stephen Ellingson, Marvin M. Ellison, Robert Ellsberg, Jean Bethke Elshtain, Eldon Jay Epp, Peter C. Erb, Tassilo Erhardt, Maria Erling, Noel Leo Erskine, Gillian R. Evans, Virginia Fabella, Michael A. Fahey, Edward Farley, Margaret A. Farley, Wendy Farley, Robert Fastiggi, Seena Fazel, Duncan S. Ferguson, Helwar Figueroa, Paul Corby Finney, Kyriaki Karidoyanes FitzGerald, Thomas E. FitzGerald, John R. Fitzmier, Marie Therese Flanagan, Sabina Flanagan, Claude Flipo, Ronald B. Flowers, Carole Fontaine, David Ford, Mary Ford, Stephanie A. Ford, Jim Forest, William Franke, Robert M. Franklin, Ruth Franzén, Edward H. Friedman, Samuel Frouisou, Lorelei F. Fuchs, Jojo M. Fung, Inger Furseth, Richard R. Gaillardetz, Brandon Gallaher, China Galland, Mark Galli, Ismael García, Tharscisse Gatwa, Jean-Marie Gaudeul, Luis María Gavilanes del Castillo, Pavel L. Gavrilyuk, Volney P. Gay, Metropolitan Athanasios Geevargis, Kondothra M. George, Mary Gerhart, Simon Gikandi, Maurice Gilbert, Michael J. Gillgannon, Verónica Giménez Beliveau, Terryl Givens, Beth Glazier-McDonald, Philip Gleason, Menghun Goh, Brian Golding, Bishop Hilario M. Gomez, Michelle A. Gonzalez, Donald K. Gorrell, Roy Gottfried, Tamara Grdzelidze, Joel B. Green, Niels Henrik Gregersen, Cristina Grenholm, Herbert Griffiths, Eric W. Gritsch, Erich S. Gruen, Christoffer H. Grundmann, Paul H. Gundani, Jon P. Gunnemann, Petre Guran, Vidar L. Haanes, Jeremiah M. Hackett, Getatchew Haile, Douglas John Hall, Nicholas Hammond, Daphne Hampson, Jehu J. Hanciles, Barry Hankins, Jennifer Haraguchi, Stanley S. Harakas, Anthony John Harding, Conrad L. Harkins, J. William Harmless, Marjory Harper, Amir Harrak, Joel F. Harrington, Mark W. Harris, Susan Ashbrook Harvey, Van A. Harvey, R. Chris Hassel, Jione Havea, Daniel Hawk, Diana L. Hayes, Leslie Hayes, Priscilla Hayner, S. Mark Heim, Simo Heininen, Richard P. Heitzenrater, Eila Helander, David Hempton, Scott H. Hendrix, Jan-Olav Henriksen, Gina Hens-Piazza, Carter Heyward, Nicholas J. Higham, David Hilliard, Norman A. Hjelm, Peter C. Hodgson, Arthur Holder, M. Jan Holton, Dwight N. Hopkins, Ronnie Po-chia Hsia, Po-Ho Huang, James Hudnut-Beumler, Jennifer S. Hughes, Leonard M. Hummel, Mary E. Hunt, Laennec Hurbon, Mark Hutchinson, Susan E. Hylen, Mary Beth Ingham, H. Larry Ingle, Dale T. Irvin, Jon Isaak, Paul John Isaak, Ada María Isasi-Díaz, Hans Raun Iversen, Margaret C. Jacob, Arthur James, Maria Jansdotter-Samuelsson, David Jasper, Werner G. Jeanrond, Renée Jeffery, David Lyle Jeffrey, Theodore W. Jennings, David H. Jensen, Robin Margaret Jensen, David Jobling, Dale A. Johnson, Elizabeth A. Johnson, Maxwell E. Johnson, Sarah Johnson, Mark D. Johnston, F. Stanley Jones, James William Jones, John R. Jones, Alissa Jones Nelson, Inge Jonsson, Jan Joosten, Elizabeth Judd, Mulambya Peggy Kabonde, Robert Kaggwa, Sylvester Kahakwa, Isaac Kalimi, Ogbu U. Kalu, Eunice Kamaara, Wayne C. Kannaday, Musimbi Kanyoro, Veli-Matti Kärkkäinen, Frank Kaufmann, Léon Nguapitshi Kayongo, Richard Kearney, Alice A. Keefe, Ralph Keen, Catherine Keller, Anthony J. Kelly, Karen Kennelly, Kathi Lynn Kern, Fergus Kerr, Edward Kessler, George Kilcourse, Heup Young Kim, Kim Sung-Hae, Kim Yong-Bock, Kim Yung Suk, Richard King, Thomas M. King, Robert M. Kingdon, Ross Kinsler, Hans G. Kippenberg, Cheryl A. Kirk-Duggan, Clifton Kirkpatrick, Leonid Kishkovsky, Nadieszda Kizenko, Jeffrey Klaiber, Hans-Josef Klauck, Sidney Knight, Samuel Kobia, Robert Kolb, Karla Ann Koll, Heikki Kotila, Donald Kraybill, Philip D. W. Krey, Yves Krumenacker, Jeffrey Kah-Jin Kuan, Simanga R. Kumalo, Peter Kuzmic, Simon Shui-Man Kwan, Kwok Pui-lan, André LaCocque, Stephen E. Lahey, John Tsz Pang Lai, Emiel Lamberts, Armando Lampe, Craig Lampe, Beverly J. Lanzetta, Eve LaPlante, Lizette Larson-Miller, Ariel Bybee Laughton, Leonard Lawlor, Bentley Layton, Robin A. Leaver, Karen Lebacqz, Archie Chi Chung Lee, Marilyn J. Legge, Hervé LeGrand, D. L. LeMahieu, Raymond Lemieux, Bill J. Leonard, Ellen M. Leonard, Outi Leppä, Jean Lesaulnier, Nantawan Boonprasat Lewis, Henrietta Leyser, Alexei Lidov, Bernard Lightman, Paul Chang-Ha Lim, Carter Lindberg, Mark R. Lindsay, James R. Linville, James C. Livingston, Ann Loades, David Loades, Jean-Claude Loba-Mkole, Lo Lung Kwong, Wati Longchar, Eleazar López, David W. Lotz, Andrew Louth, Robin W. Lovin, William Luis, Frank D. Macchia, Diarmaid N. J. MacCulloch, Kirk R. MacGregor, Marjory A. MacLean, Donald MacLeod, Tomas S. Maddela, Inge Mager, Laurenti Magesa, David G. Maillu, Fortunato Mallimaci, Philip Mamalakis, Kä Mana, Ukachukwu Chris Manus, Herbert Robinson Marbury, Reuel Norman Marigza, Jacqueline Mariña, Antti Marjanen, Luiz C. L. Marques, Madipoane Masenya (ngwan'a Mphahlele), Caleb J. D. Maskell, Steve Mason, Thomas Massaro, Fernando Matamoros Ponce, András Máté-Tóth, Odair Pedroso Mateus, Dinis Matsolo, Fumitaka Matsuoka, John D'Arcy May, Yelena Mazour-Matusevich, Theodore Mbazumutima, John S. McClure, Christian McConnell, Lee Martin McDonald, Gary B. McGee, Thomas McGowan, Alister E. McGrath, Richard J. McGregor, John A. McGuckin, Maud Burnett McInerney, Elsie Anne McKee, Mary B. McKinley, James F. McMillan, Ernan McMullin, Kathleen E. McVey, M. Douglas Meeks, Monica Jyotsna Melanchthon, Ilie Melniciuc-Puica, Everett Mendoza, Raymond A. Mentzer, William W. Menzies, Ina Merdjanova, Franziska Metzger, Constant J. Mews, Marvin Meyer, Carol Meyers, Vasile Mihoc, Gunner Bjerg Mikkelsen, Maria Inêz de Castro Millen, Clyde Lee Miller, Bonnie J. Miller-McLemore, Alexander Mirkovic, Paul Misner, Nozomu Miyahira, R. W. L. Moberly, Gerald Moede, Aloo Osotsi Mojola, Sunanda Mongia, Rebeca Montemayor, James Moore, Roger E. Moore, Craig E. Morrison O.Carm, Jeffry H. Morrison, Keith Morrison, Wilson J. Moses, Tefetso Henry Mothibe, Mokgethi Motlhabi, Fulata Moyo, Henry Mugabe, Jesse Ndwiga Kanyua Mugambi, Peggy Mulambya-Kabonde, Robert Bruce Mullin, Pamela Mullins Reaves, Saskia Murk Jansen, Heleen L. Murre-Van den Berg, Augustine Musopole, Isaac M. T. Mwase, Philomena Mwaura, Cecilia Nahnfeldt, Anne Nasimiyu Wasike, Carmiña Navia Velasco, Thulani Ndlazi, Alexander Negrov, James B. Nelson, David G. Newcombe, Carol Newsom, Helen J. Nicholson, George W. E. Nickelsburg, Tatyana Nikolskaya, Damayanthi M. A. Niles, Bertil Nilsson, Nyambura Njoroge, Fidelis Nkomazana, Mary Beth Norton, Christian Nottmeier, Sonene Nyawo, Anthère Nzabatsinda, Edward T. Oakes, Gerald O'Collins, Daniel O'Connell, David W. Odell-Scott, Mercy Amba Oduyoye, Kathleen O'Grady, Oyeronke Olajubu, Thomas O'Loughlin, Dennis T. Olson, J. Steven O'Malley, Cephas N. Omenyo, Muriel Orevillo-Montenegro, César Augusto Ornellas Ramos, Agbonkhianmeghe E. Orobator, Kenan B. Osborne, Carolyn Osiek, Javier Otaola Montagne, Douglas F. Ottati, Anna May Say Pa, Irina Paert, Jerry G. Pankhurst, Aristotle Papanikolaou, Samuele F. Pardini, Stefano Parenti, Peter Paris, Sung Bae Park, Cristián G. Parker, Raquel Pastor, Joseph Pathrapankal, Daniel Patte, W. Brown Patterson, Clive Pearson, Keith F. Pecklers, Nancy Cardoso Pereira, David Horace Perkins, Pheme Perkins, Edward N. Peters, Rebecca Todd Peters, Bishop Yeznik Petrossian, Raymond Pfister, Peter C. 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Acknowledgements
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1 - The Solar System
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Summary
Though Pluto, and the far-flung depths of the Solar System, is the focus of this book, it is essential that Pluto is placed in the context of the planetary system that it inhabits – our Solar System. In the first place, this is because Pluto is just one of a large and varied number of bodies that orbit the Sun, and cannot be treated as an isolated body in space. Secondly, much of the material in this chapter is needed to support and enhance your understanding of subsequent chapters.
But before we get to the Solar System, I start by examining its cosmic neighbourhood: a vast assemblage of stars called the Galaxy, which we see in the sky as the Milky Way.
A JOURNEY INTO OUR GALAXY
The Sun, which is at the centre of the Solar System, is one of about two hundred thousand million stars that make up the Galaxy. From extensive observations made from Earth it is clear that it has a beautiful form that, face-on, is something like that in Figure 1.1.
The stars, of various kinds, plus tenuous interstellar gas and dust, often woven into stunning forms, are concentrated into a disc highlighted by spiral arms (Figure 1.1). In our Galaxy the disc is about 100 000 light years in diameter (see Box 1.1), and most stars are in a thin sheet about 1000 light years thick – roughly the same ratio of diameter to thickness as a CD. This sheet is called the thin disc.
5 - Surfaces, atmospheres and interiors of Pluto and Charon
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So far, I've said very little about the surfaces and atmospheres of Pluto and its satellites, and for interiors I've given only the mean global densities and a broad indication of global compositions. In this chapter the compositions will be discussed in more detail, and internal models will be introduced.
I start with surfaces and atmospheres, which are clearly of intrinsic interest, but also because they provide clues and constraints about the interiors of Pluto and Charon. Very little is known about Nix and Hydra, therefore almost nothing is said here about these tiny satellites.
In Chapter 6 you will see that what we learn about Pluto and its satellites helps us to learn about other objects in the outer Solar System, notably the Kuiper belt objects.
First, some basic science. How do we obtain information about the surfaces and atmospheres of distant bodies? The answer is through measuring their albedos (reflectivities), which has already been discussed in Section 3.1, and by measuring their electromagnetic reflection and emission spectra.
REFLECTION AND EMISSION SPECTRA
The albedo of a body gives us information averaged over a wide range of wavelengths in solar radiation, particularly visible wavelengths. The reflectance spectrum is the reflectivity versus wavelength, and provides much more detailed information about a body. A reflectance spectrum is obtained with a device called a spectrometer, the essential components of which are illustrated in a simple way in Figure 5.1.
Index
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Preface
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Pluto is a very tiny, distant world. It orbits the Sun beyond the giant planet Neptune, the outermost of the other eight planets in the Solar System. In inward order from Neptune these planets are Uranus, Saturn, Jupiter, Mars, Earth, Venus and Mercury. Pluto has a diameter a little less than one fifth of the diameter of our planet, which itself is a long way from being the largest planet in the Solar System. That title belongs to the giant planet Jupiter, with a diameter just over 11 times that of the Earth.
Why should a book be devoted to such a tiddler among the planets? There are three main reasons. First, the discovery of Pluto in 1930 is a fascinating episode in our quest to discover whether the Solar System beyond Neptune is devoid of planetary bodies. Second, ever since its discovery, controversy has been rampant about what sort of body Pluto is. Is it deserving of the status of planet, or is it too small for that? The classification of Pluto is an excellent example of the role of classification in all branches of science: classification not only comes with great advantages but also with difficulties. Third, Pluto is the closest large member of the Edgeworth-Kuiper belt, a great swarm of small bodies that orbit the Sun beyond Neptune. Though the existence of such a belt had been predicted in the 1940s, it was not until the 1990s that discoveries of other trans-Neptunian bodies were made.
4 - Pluto's family
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As well as Charon, Pluto has two other satellites, both very tiny. Pluto is thus the largest member of a small family. In this chapter the emphasis is on the family as a whole.
The two tiny satellites were discovered in May 2005 by H A Weaver and colleagues, with the Hubble Space Telescope during studies of Pluto in relation to NASA's New Horizons spacecraft, now on its way to Pluto (Chapter 8). The discovery team proposed the Greek names Nyx and Hydra, but as Nyx already appeared in the names of two asteroids, the spelling was changed from the Greek Nyx to the Egyptian Nix. In mythology Nix (Nyx) is the goddess of darkness and light, very appropriate for a satellite orbiting the god of the underworld. Nix is also the mother of Charon – rather a small mother for such a large child! Hydra is a nine-headed serpent, a suitable name for the ninth planet Pluto. In June 2006 the International Astronomical Union approved these names.
Figure 4.1 shows an HST image of Pluto and all three satellites obtained on 15 February 2006. Pluto and Charon are grossly overexposed so that the very faint Nix and Hydra can be imaged. Nix and Hydra are the two dots, Hydra being the further from Pluto.
7 - Is Pluto a planet?
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What an extraordinary question! Mercury, Venus, the Earth, Mars, Jupiter, Saturn, Uranus and Neptune are planets, so why not Pluto? Pluto's planetary status had been questioned by some astronomers from not long after its discovery, on the basis of its small mass and eccentric, inclined orbit. But the crunch came in 2006. It was in that year that, after much debate and several votes, the International Astronomical Union, at its triennial General Assembly in Prague in August, which I attended, classified Pluto as a dwarf planet. This short chapter is devoted to Pluto's classification, which is an ongoing issue. But first let's consider the wider issue of the role of classification in science.
THE ROLE OF CLASSIFICATION IN SCIENCE
In science, classification provides an economy of description, a tool for structuring knowledge, and can also lead to deeper understanding.
A simple example is provided by crystals. All crystals share two attributes that define the class:
the basic unit, be it an atom or a molecule, is arranged in one of a variety of repeating patterns in space
they are solids, i.e. they retain their external form and do not flow like liquids.
The economy of description is that, in place of saying ‘one form of water ice is a solid with its component molecules arranged in a repeating pattern in space’, one just says ‘crystalline water’.
Contents
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List of tables
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2 - The discovery of Uranus, Neptune and Pluto
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Before I tell you the story of Pluto's discovery, it is both instructive and relevant to the discovery of Pluto for you to learn, briefly, about the discovery of Uranus and, in more detail, about the discovery of Neptune. Between them, these three planets were found by strikingly different means.
THE DISCOVERY OF URANUS
Until 1781 just five planets were known: Mercury, Venus, the Earth, Mars, Jupiter and Saturn, all readily visible to the unaided eye. Then, on 26 April of that year a scientific paper was read to the Royal Society that opens as follows.
‘On Tuesday the 13th of March, between ten and eleven in the evening, while I was examining the small stars in the neighbourhood of H Geminorum, I perceived one that appeared visibly larger than the rest: being struck with its uncommon magnitude, I compared it to H Geminorum and the small star in the quartile between Auriga and Gemini, and finding it so much larger than either of them, suspected it to be a comet.’
This is the opening of a paper written by the Germano-British astronomer William Herschel (1738–1822). It was read to the Royal Society by the British physician William Watson (1744–1825). Thus was announced to the world the discovery, not of a comet, but of what was soon shown to be a planet. Its true nature was clear by May 1781 after its large, low eccentricity orbit had been established.
9 - Pluto: gateway to beyond?
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What would it be like to stand on Pluto: what would we see, what would we feel? Would Pluto be useful as a launch pad for spacecraft to go to other Kuiper belt objects, to the Oort cloud and even to the stars?
TO STAND ON PLUTO
The sky
The distances from Pluto to the stars are so very much greater than from Pluto to the Earth, that the same constellations will appear in Pluto's sky as in the Earth's sky, and the same Milky Way, all with the same relative brightnesses. The retrograde rotation of Pluto means that the stars will rise in the West and set in the East. The solar day on Pluto, as on the Earth, is the time between successive noons (at noon the Sun is at its maximum altitude). On Earth this interval is one (solar) day. Pluto's axial rotation period is longer than that of the Earth, and therefore the solar day is longer, 6.387 Earth days. The Sun, planets, and stars thus move considerably more slowly across Pluto's sky than across our skies.
The rotation axis on Earth is directed at a point in the northerly sky near the fairly bright star Polaris (the Pole Star), which is a little under 1° from the exact point around which the sky appears to rotate. On Pluto the corresponding point is about 15° East from the bright star Altair.
6 - The Edgeworth-Kuiper belt
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With the discovery of Pluto, was the Solar System complete? No, far from it!
WHY SEARCH FOR MORE TRANS-NEPTUNIAN OBJECTS?
In 1930, soon after Pluto's discovery, the American astronomer Frederick C Leonard (1896–1960) wondered whether Pluto was the first of many trans-Neptunian objects awaiting discovery, but he does not seem to have acted on his prescient speculation. In July 1943, in the Journal of the British Astronomical Association, the Anglo-Irish polymath Kenneth Essex Edgeworth (1880–1972) stated that beyond Neptune the solar nebula was too thinly dispersed to have made planets, but instead many smaller bodies were present, some of which become comets. He expressed similar views in 1949 in an edition of the Monthly Notices of the Royal Astronomical Society (MNRAS). This was a year before the Dutch astronomer Jan Hendrick Oort (1900–1992) proposed the existence of a distant spherical shell of small icy bodies that enveloped the Solar System and supplied long period comets to its inner regions – the Oort cloud (Section 1.2). Such a cloud is not the belt of trans-Neptunian objects that Edgeworth had proposed; his belt was not so far away and was largely confined to the planes of the planetary orbits.
Whether there was such a belt of trans-Neptunian objects was also considered by the Dutch-American astronomer Gerard Kuiper (1905–1973) in a 1951 edition of the journal Astrophysics, but he concluded that such a belt no longer existed! This was based on the then belief that Pluto was about the mass of the Earth and would thus have scattered the bodies away.
3 - Pluto: a diminishing world
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As soon as Pluto was discovered, astronomers were eager to learn as much as possible about this remote world. What type of body was it that lurked at the outer edge of the Solar System? The most fundamental properties are size and mass. These give the mean density by dividing the mass by the volume; the mean density in turn constrains Pluto's composition.
PLUTO'S SIZE
If Pluto could be seen as a disc then, with its distance known, its size could be estimated from its measured angular diameter, as described in Section 1.6. You might think that with a sufficiently large telescope a disc would have been seen. For telescopes at the Earth's surface this is not the case. There are two reasons for this, given in Box 2.1, reasons that I slightly enlarge upon here.
First, there is the intrinsic limit of the optics (the diffraction limit), the larger the main lens or mirror, and/or the shorter the wavelengths detected, the smaller the fuzzy disc image of a point of light and the better the telescope's resolution. Visible light covers the wavelength range of about 0.38 millionths of a metre (a micrometre), to about 0.75 micrometres. The human eye is most sensitive at about 0.55 micrometres, which we see as green. At this wavelength, a telescope with a perfect main lens or mirror a metre in diameter produces a fuzzy disc such that two points of light separated by about 0.14 arcsec (each imaged as a fuzzy disc), could just be distinguished.
Pluto
- Sentinel of the Outer Solar System
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Orbiting at the edge of the outer Solar System, Pluto is an intriguing object in astronomy. Since the fascinating events surrounding its discovery, it has helped increase our understanding of the origin and evolution of the Solar System, and raised questions about the nature and benefits of scientific classification. This is a timely and exciting account of Pluto and its satellites. The author uses Pluto as a case study to discuss discovery in astronomy, how remote astronomical bodies are investigated, and the role of classification in science by discussing Pluto's recent classification as a dwarf planet. Besides Pluto, the book also explores the rich assortment of bodies that constitute the Edgeworth–Kuiper Belt, of which Pluto is the largest innermost member. Richly illustrated, this text is written for general readers, amateur astronomers and students alike. Boxed text provides more advanced information especially for readers who wish to delve deeper into the subject.
Glossary
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