Giant Planets of Our Solar System An Introduction Patrick G. J. Irwin Giant Planets of Our Solar System An Introduction Published in association with PP raxisraxis PP ublishingublishing Chichester, UK Dr Patrick G. J. Irwin Atmospheric, Oceanic, and Planetary Physics Clarendon Laboratory Oxford UK and St Anne’s College Oxford UK SPRINGER–PRAXIS BOOKS IN ASTRONOMY AND PLANETARY SCIENCES SUBJECT ADVISORY EDITORS: Dr Philippe Blondel, C.Geol., F.G.S., Ph.D., M.Sc., Senior Scientist, Department of Physics, University of Bath, Bath, UK; John Mason, M.Sc., B.Sc., Ph.D. ISBN 3-540-31317-6 Springer-Verlag Berlin Heidelberg New York Springer is part of Springer-Science + Business Media ( springeronline.com) Bibliographic information published by Die Deutsche Bibliothek Die Deutsche Bibliothek lists this publication in the Deutsche Nationalbibliografie; detailed bibliographic data are available from the Internet at http://dnb.ddb.de Library of Congress Control Number: 2005938845 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 licences issued by the Copyright Licensing Agency. Enquiries concerning reproduction outside those terms should be sent to the publishers. # Praxis Publishing Ltd, Chichester, UK, 2003 Reprinted with corrections and issued as an abridged paperback, 2006 Printed in Germany The use of general descriptive names, registered names, trademarks, 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. Cover design: Jim Wilkie Project management: Originator Publishing Services, Gt Yarmouth, Norfolk, UK Printed on acid-free paper Contents Preface . xi Acknowledgements xiii Abbreviations . xv List of figures xix List of tables . xxiii List of colour plates . xxv 1 Introduction . 1 1.1 The giant outer planets. . 1 1.2 Observed atmospheres of the giant planets . 5 1.2.1 Jupiter . 5 1.2.2 Saturn . 8 1.2.3 Uranus . 9 1.2.4 Neptune 11 1.3 Satellites of the outer planets 12 1.4 Exploration of the outer planets 13 1.5 Organization of book . . . 14 1.6 References 15 1.7 Bibliography . 15 2 Formation of the giant planets . 17 2.1 Formation of the universe and primordial constituents . 17 2.2 Formation of the stars and evolution of the interstellar medium . 18 2.3 Formation of the protosolar nebula . 21 2.3.1 Collapse of the interstellar cloud . . 21 2.3.2 Formation of circumstellar disc . . . 23 2.4 Formation of the Jovian planets and comets 28 2.4.1 Core accretion model 28 2.4.2 Gravitational instability model 32 2.5 Formation of Jovian satellites . 32 2.6 Bulk composition of the outer planets and isotape ratios. . 33 2.6.1 Constraints on formation: D/H ratio . 33 2.6.2 Constraints on formation: Nitrogen 39 2.7 Interiors of the giant planets 39 2.7.1 Gravitational data 39 2.7.2 Magnetic field data . 42 2.7.3 Internal structure of Jupiter and Saturn . 42 2.7.4 Internal structure of Uranus and Neptune 45 2.8 Migration and extrasolar planets . 47 2.9 References 48 2.10 Bibliography . 51 3 Evolution processes in outer planet atmospheres 53 3.1 Introduction . 53 3.2 Thermal escape . 53 3.2.1 Jeans’ formula 53 3.2.2 Diffusion and limiting flux 55 3.2.3 Hydrodynamic escape . 58 3.3 Impacts with comets and planetesimals . . . 59 3.4 Internal differentiation processes 59 3.4.1 Effective radiating temperature of planets 60 3.5 Evolution of the giant planet atmospheres . 62 3.5.1 Jupiter . 62 3.5.2 Saturn . 63 3.5.3 Uranus and Neptune 64 3.6 References 65 3.7 Bibliography . 65 4 Vertical structure of temperature, composition, and clouds 67 4.1 Pressure and temperature profiles . 67 4.1.1 Pressure 67 4.1.2 Temperature . 68 4.1.3 Secondary effects on temperature/pressure profiles . 73 4.1.4 Temperature/pressure profiles of the outer planets . 76 4.2 Vertical mixing–eddy mixing coefficients. . . 77 4.3 Composition profiles – general considerations . 81 4.3.1 Disequilibrium species . 81 4.3.2 Photolysis . 84 vi Contents 4.3.3 Condensation . . . 89 4.3.4 Extraplanetary sources . 91 4.4 Composition and cloud profiles of the giant planets . 92 4.4.1 Jupiter . 92 4.4.2 Saturn . 103 4.4.3 Uranus . 110 4.4.4 Neptune 116 4.5 References 125 4.6 Bibliography . 131 5 Dynamical processes 133 5.1 Introduction . 133 5.2 Mean circulation of the giant planet atmospheres 133 5.2.1 Equations of motion 135 5.2.2 Mean zonal motions in the giant planet atmospheres . . . 141 5.3 Eddy motion in the giant planet atmospheres . 147 5.3.1 Turbulence in the giant planet atmospheres . 147 5.3.2 Waves in the giant planet atmospheres 151 5.3.3 Vortices in the giant planet atmospheres . 156 5.4 Mean and eddy circulation of the giant planet atmospheres 158 5.4.1 Tropospheric circulation 158 5.4.2 Stratospheric and upper tropospheric circulation 163 5.5 Meteorology of Jupiter . . 164 5.5.1 General circulation and zonal structure 164 5.5.2 Storms and vortices . 169 5.5.3 Waves . 173 5.6 Meteorology of Saturn . . 177 5.6.1 General circulation and zonal structure 177 5.6.2 Storms and vortices . 179 5.6.3 Waves . 180 5.7 Meteorology of Uranus . 183 5.7.1 General circulation and zonal structure 183 5.7.2 Storms and vortices . 184 5.7.3 Waves . 185 5.8 Meteorology of Neptune . 185 5.8.1 General circulation and zonal structure 185 5.8.2 Storms and vortices . 187 5.8.3 Waves . 190 5.9 References 191 5.10 Bibliography . 196 6 Radiative transfer processes in outer planetary atmospheres . 197 6.1 Introduction . 197 6.2 Interaction between electromagnetic radiation and particles 198 6.2.1 Fermi’s golden rule . 198 Contents vii 6.2.2 Electric and magnetic moments . . . 199 6.3 Molecular spectroscopy: vibrational–rotational transitions . 200 6.3.1 Molecular vibrational energy levels . 200 6.3.2 Molecular rotational energy levels . 201 6.3.3 Rotational transitions . 203 6.3.4 Vibration–rotation bands . 204 6.3.5 Inversion bands and inversion-doubling 208 6.3.6 Diatomic homonuclear molecules . . 208 6.3.7 Line-broadening . 209 6.3.8 Giant planet gas transmission spectra . 211 6.4 Radiative transfer in a grey atmosphere . . . 212 6.4.1 Nadir viewing 213 6.4.2 Net flux and disc-averaging 216 6.4.3 Limb-viewing . 218 6.4.4 Radiative balance 220 6.4.5 Local thermodynamic equilibrium . 221 6.4.6 Transmission calculations . 222 6.5 Scattering of light by particles . 225 6.5.1 Rayleigh or dipole scattering . 226 6.5.2 Mie theory 227 6.5.3 Non-spherical particles . 228 6.5.4 Analytical forms of phase functions 229 6.6 Radiative transfer in scattering atmospheres 229 6.6.1 Plane-parallel approximation . 230 6.6.2 Spherical atmospheres and limb-viewing: Monte Carlo simulations 232 6.7 Giant planet spectra 233 6.7.1 General features of giant planet spectra: UV to microwave 233 6.7.2 Near-IR and visible reflectance spectra 234 6.7.3 Thermal-IR spectra . 236 6.7.4 Microwave spectra . 241 6.8 Appendix . 242 6.8.1 Planck function . 242 6.9 References 244 6.10 Bibliography . 245 7 Sources of remotely sensed data on the giant planets . 247 7.1 Introduction . 247 7.2 Measurement of visible, IR, and microwave spectra . 248 7.2.1 Detection of IR radiation . 248 7.2.2 Radiometers/photometers . 249 7.2.3 Grating spectrometers . 250 7.2.4 Michelson interferometers . 251 7.2.5 Detection of microwave radiation. . 254 7.3 Ground-based observations of the giant planets 255 viii Contents 7.3.1 Terrestrial atmospheric absorption . 255 7.3.2 Angular resolution . 257 7.3.3 Brightness . 260 7.4 Ground-based visible/IR observatories 261 7.4.1 European Southern Observatory (ESO) – Very Large Telescope (VLT) . 263 7.4.2 The Mauna Kea observatories 265 7.4.3 Other major observatories . 268 7.5 Airborne visible/IR observations 268 7.5.1 Kuiper Airborne Observatory 269 7.6 Ground-based microwave observatories . 270 7.6.1 The Institut de RadioAstronomie Millime ´ trique (IRAM) 271 7.6.2 Very Large Array (VLA) . 272 7.6.3 Very Large Baseline Array (VLBA) 273 7.6.4 Berkeley Illinois Maryland Association (BIMA) 274 7.6.5 Owens Valley Radio Observatory (OVRO) 274 7.6.6 Nobeyama Millimeter Array (NMA) 275 7.7 Space-based telescopes . . 276 7.7.1 HST . 277 7.7.2 ISO . 279 7.7.3 Submillimeter Wave Astronomy Satellite (SWAS) . 283 7.8 Flyby spacecraft 284 7.8.1 Pioneer . 286 7.8.2 Voyager 288 7.8.3 Ulysses . 292 7.9 Orbiting spacecraft 292 7.9.1 Galileo . 292 7.9.2 Cassini/Huygens . 300 7.10 Retrievals . 303 7.10.1 Exact, least squares, and Backus–Gilbert solution . 306 7.10.2 Linear optimal estimation . 307 7.10.3 Non-linear optimal estimation 309 7.10.4 Joint retrievals . . 309 7.11 References 309 7.12 Bibliography . 310 Index 313 Contents ix