The Exoplanet Handbook Michael Perryman Frontmatter More Information

Cambridge University Press 978-1-108-41977-2 — The Exoplanet Handbook Michael Perryman Frontmatter More Information

The Exoplanet Handbook

Second Edition

With the discovery of planets beyond our solar system 25 years ago, exoplanet research has expanded dramatically, with new state-of-the-art ground-based and space-based missions dedicated to their discovery and characterisation. With more than 3500 exoplanets now known, the complexity of the discovery techniques, observations, and physical characterisation has grown substantially. This handbook ties all these avenues of research together across a broad range of exoplanet science. Planet formation, exoplanet interiors and atmospheres, and habitability are discussed, providing in-depth coverage of our knowledge to date. Comprehensively updated from the first edition, this book includes instrumental and observational developments, in-depth treatment of the new Kepler mission results and hot Jupiter atmospheric studies, and major updates on models of exoplanet formation. With extensive references to the research literature and appendices covering all individual exoplanet discoveries, it is a valuable reference to this exciting field for both incoming and established researchers.

During a 30-year career with the European Space Agency (ESA), Michael Perryman was the scientific leader of the Hipparcos astrometry mission, 1981–97, also serving as project manager for its operational phase, 1989–93. With Lennart Lindegren, he was the co-originator of the Gaia astrometry mission, a project expected to make important contributions to exoplanet science in the coming years. He was ESA’s project scientist for Gaia from its earliest concepts in 1995 until the Critical Design Review in 2008, establishing the payload concept, technical feasibility, operational and data analysis principles, and its organisational structure, and coordinating its scientific case. He was Professor of Astron- omy at Leiden University between 1993 and 2009, and Bohdan Paczynski´ Visiting Professor at Princeton University in 2013.

Praise for the First Edition

‘The Exoplanet Handbook by Michael Perryman is an exhaustive reference for the techniques, facts and theory of exoplanet science. An excellent and objective resource for novice and expert alike, this compendium is destined for the libraries of all serious students of the art.’ Adam Burrows, Princeton University

‘Perryman’s book is truly a major achievement: it is an astonishingly complete overview of everything we know about exoplanets. The Exoplanet Handbook will serve as the seminal reference in this field for many years. I would (and will) strongly encourage any graduate students interested in doing serious research in exoplanets to buy a copy of this book.’ B. Scott Gaudi, The Ohio State University

‘Michael Perryman’s new book provides not only a thorough discussion of what we have learnt about extrasolar planets since the first discoveries over 15 years ago, but also a clear and comprehensive review of the wide range of observational and theoretical techniques that have been employed to find and characterise them. This volume is a must-have for serious researchers in the field, and will be an invaluable reference for many years to come.’ I. Neill Reid, Space Telescope Science Institute

‘...more technically detailed and comprehensive than many of the rival texts. ...it is an ideal companion for a Ph.D. student in the field, as well as an excellent reference for the experienced researcher ...this is also an excellent, detailed textbook suitable for a specialist undergraduate or postgraduate lecture course.’ The Observatory

‘If I were allowed access to only one book on the subject of extra-solar planets, Michael Perryman’s The Exoplanet Handbook is a contender that would be very hard to beat. The book documents the whirlwind development of this newly- emergent and energetic new field of science ...It is also a compendium of essential physical concepts, useful formulae and computational strategies for analysis of the various types of astronomical data used to discover and characterise exoplanets.’ Andrew Collier Cameron, University of St Andrews

‘This remarkable compilation brings together observations and theoretical explorations of a rapidly growing astronomical field. Literally every possible observational method is explained and recent results given ...While the number of known exoplanets changes weekly, the methods through which we discover and characterise these do not. Highly recommended.’ George F. Benedict, University of Texas, Austin

‘The Exoplanet Handbook provides a very valuable integration of all aspects of the fascinating and interdisciplinary world of exoplanet science. It combines in a coherent context the presentation of the observational techniques, covering recent highlights and future prospects, with the description of the vast range of intertwining phenomena and processes that shape the paths of planet formation, evolution and structure ...The Handbook is an invaluable resource for professional planetary scientists and academic teachers, for both practising astronomers and motivated amateurs, and for advanced undergraduate and graduate students.’ Vittorio Vanzani, Padua University

‘This Handbook is a true encyclopedic reference on exoplanets. Perryman’s new book is a comprehensive review on major programs and results obtained in the last decade in this exciting new domain of astrophysics and as such it is a priceless resource for experts. The detailed descriptions of the foundations of the main observations techniques and key theoretical aspects make it a perfect book for any student wishing to have a comprehensive introduction to exoplanet research. This volume is likely to become an important reference in the field.’ Didier Queloz, Geneva Observatory

‘The Exoplanet Handbook by Michael Perryman is impressive; the content is of high level and very accurate. He has suc- ceeded in providing an exhaustive and up-to-date review of this mature and rich field. The Handbook will surely help Ph.D. students and professional astronomers who want to learn about this field. It will even be useful to experts who want to check details on some specific aspects, either about exoplanets themselves, detection methods, or instrumentation.’ Jean Schneider, CNRS/LUTH, Paris Observatory

‘...Michael Perryman ...has written an excellent, startlingly complete snapshot of the current state of knowledge regard- ing extrasolar planets ...Like any good encyclopedia, The Exoplanet Handbook has as its major strength its reference list, which cites more than 4000 papers. The list provides a near-complete snapshot of all the research that has taken place in the field in the past two decades. Furthermore, the references are deftly integrated into the text, which makes this volume an excellent point of departure for any researcher seeking to chart a new course of exoplanetary investigation.’ Gregory Laughlin, Physics Today

The Exoplanet Handbook

Second Edition

Michael Perryman

Max–Planck–Institut für Astronomie, Heidelberg Zentrum für Astronomie der Universität Heidelberg University College Dublin

University Printing House, Cambridge CB2 8BS, United Kingdom

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Cambridge University Press is part of the University of Cambridge. It furthers the University’s mission by disseminating knowledge in the pursuit of education, learning, and research at the highest international levels of excellence.

www.cambridge.org Information on this title: www.cambridge.org/9781108419772 DOI: 10.1017/9781108304160

c Michael Perryman 2011, 2014, 2018 This publication is in copyright. Subject to statutory exception and to the provisions of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press.

First published 2011 First paperback edition 2014 Second edition 2018

Printed in the United Kingdom by TJ International Ltd. Padstow Cornwall A catalogue record for this publication is available from the British Library.

Library of Congress Cataloging-in-Publication Data Names: Perryman, M. A. C., author. Title: The exoplanet handbook / Michael Perryman (University College Dublin). Description: Second edition. | Cambridge ; New York : Cambridge University Press, [2018] | Includes bibliographical references and indexes. Identifiers: LCCN 2018028046 | ISBN 9781108419772 (Hardback : alk. paper) Subjects: LCSH: Extrasolar planets. Classification: LCC QB820 .P47 2018 | DDC 523.2/4–dc23 LC record available at https://lccn.loc.gov/2018028046 ISBN 978-1-108-41977-2 Hardback

Additional resources for this publication at www.cambridge.org/exoplanethandbook Cambridge University Press has no responsibility for the persistence or accuracy of URLs for external or third-party Internet websites referred to in this publication and does not guarantee that any content on such websites is, or will remain, accurate or appropriate.

Contents

Preface to the Second Edition xix

1 Introduction 1 1.1 The challenge 1 1.2 Discovery status 1 1.3 Outline of the treatment 2 1.3.1 Observational techniques 2 1.3.2 Host star properties and brown dwarfs 4 1.3.3 Theoretical considerations 4 1.3.4 Solar system 5 1.3.5 Appendixes 5 1.3.6 Hyperlinks and online resources 5 1.4 Astronomical terms and units 5 1.5 Deﬁnition of a planet 8 1.6 Planet categories 9 1.6.1 Classiﬁcation by size or mass 9 1.6.2 Giant planets 9 1.6.3 Earths and super-Earths 13 1.7 On-line reference compilations 14 1.8 Future developments 15

2 Radial velocities 17 2.1 Orbits and orbit fitting 17 2.1.1 Description of orbits 17 2.1.2 Orbits from radial velocities 20 2.1.3 Single planet fitting 21 2.1.4 Multiple planet fitting 22 2.1.5 Bayesian methods 23 2.1.6 Algorithmic implementation 24 2.1.7 Detectability and selection effects 26 2.1.8 Scheduling 26 2.2 Measurement principles 28 2.2.1 Doppler shifts 28 2.2.2 Spectral resolution 28 2.2.3 Cross-correlation spectroscopy 28 2.2.4 Determination of barycentric velocities 29 2.3 Wavelength calibration 31 2.3.1 Telluric lines 31 2.3.2 Gas cells 31 2.3.3 Emission lamps 32

2.3.4 Infrared calibration 32 2.3.5 Laser frequency combs 32 2.3.6 Fabry–Pérot étalons 33 2.3.7 Radial velocity standards 33 2.3.8 Fiber coupling 34 2.4 Accuracy limits and error sources 34 2.4.1 Photon noise 35 2.4.2 Detection versus signal-to-noise 35 2.4.3 Exposure metering 35 2.4.4 Instrument errors 35 2.4.5 Stellar activity 36 2.4.6 Excluding other sources of periodicity 38 2.4.7 Bisector analysis 39 2.5 Higher-order radial velocity effects 40 2.5.1 Gravitational redshift variations 40 2.5.2 Zeeman effect 40 2.5.3 Planet-induced tides 41 2.5.4 Planet radial velocity signals 41 2.5.5 Determination of inclination 44 2.6 Radial velocity instruments 45 2.6.1 Overview 45 2.6.2 State-of-the-art in échelle spectroscopy 45 2.6.3 Other optical spectrographs 47 2.6.4 Infrared spectrographs 47 2.6.5 Optical–infrared spectrographs 48 2.6.6 Future instrument plans 49 2.6.7 Externally dispersed interferometry 49 2.6.8 Absolute accelerometry 50 2.7 Introduction to the radial velocity results 50 2.7.1 The ﬁrst radial velocity exoplanets 50 2.7.2 Example radial velocity curves 51 2.7.3 Present radial velocity census 51 2.7.4 Reviews 53 2.7.5 On-line compilations 53 2.8 Surveys according to stellar type 53 2.8.1 Main sequence stars 53 2.8.2 Early-type dwarfs 54 2.8.3 Evolved stars: subgiants and giants 56 2.8.4 M dwarfs 57 2.9 Surveys according to other criteria 59 2.9.1 Nearby stars and volume-limited samples 59 2.9.2 Speciﬁc nearby stars 59 2.9.3 Solar twins and Jupiter analogues 59 2.9.4 Effects of metallicity 60 2.9.5 Open clusters 61 2.9.6 Young stars and associations 61 2.9.7 Follow-up of transit candidates 61 2.10 Masses and orbits 62 2.10.1 Mass distribution 62 2.10.2 Mass of host star 62 2.10.3 Period distribution 62 2.10.4 Eccentricities 63 2.10.5 Brown dwarf desert 64 2.11 Results according to planet type 66 2.11.1 Low-mass planets 66

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2.11.2 Super-Earths and Neptunes 66 2.11.3 High-mass planets 66 2.11.4 Hot Jupiters 67 2.12 Multi-planet systems 67 2.12.1 General considerations 67 2.12.2 Architectures and classiﬁcation 68 2.12.3 Systems with three or more giant planets 68 2.12.4 Systems in mean motion resonance 71 2.12.5 Interacting two-planet systems 77 2.12.6 Non-interacting two-planet systems 77 2.12.7 Super-Earth systems 77 2.13 Binary and multiple stars 78 2.13.1 Present inventory 79 2.13.2 Speciﬁc examples 80

3 Astrometry 81 3.1 Introduction 81 3.2 Astrometric accuracy from ground 82 3.2.1 Single aperture 82 3.2.2 Interferometry 83 3.3 Microarcsec astrometry 84 3.3.1 Light deﬂection 84 3.3.2 Aberration 85 3.3.3 Source motion 85 3.3.4 Astrophysical limits 85 3.4 Modeling planetary systems 86 3.4.1 Proper motion and parallax 86 3.4.2 Multiple planets 86 3.4.3 Keplerian elements 87 3.4.4 Mass and orbit inclination 88 3.4.5 Planet–planet interactions 88 3.4.6 Wavelength dependence 89 3.4.7 Coordinate transformations 89 3.5 Astrometric searches from the ground 90 3.5.1 Single mirror 90 3.5.2 Discoveries and candidates 91 3.5.3 Optical interferometry 91 3.6 Astrometry from space: principles 91 3.7 Astrometry from space: HST 92 3.8 Astrometry from space: Hipparcos 93 3.9 Astrometry from space: Gaia 95 3.9.1 Principles 95 3.9.2 Expected astrometric planet yield 96 3.9.3 Transiting planets from Gaia astrometry 99 3.9.4 Data releases 99 3.10 Other space astrometry projects 99 3.10.1 Proposed space missions 99 3.10.2 Projects no longer under consideration 100 3.11 Radio and sub-mm astrometry 100 3.11.1 Astrometry at radio wavelengths 100 3.11.2 Astrometry at mm/sub-mm wavelengths 101

4 Timing 103 4.1 Candidates and time scales 103 4.2 Pulsars 103

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4.2.1 Characteristics 103 4.2.2 Individual pulsars 105 4.2.3 Other considerations 109 4.3 Pulsating stars 110 4.3.1 Context 110 4.3.2 White dwarfs 110 4.3.3 Rapidly pulsating subdwarfs 111 4.4 Eclipsing binaries 112 4.4.1 Context 112 4.4.2 Candidate systems 113 4.4.3 Complicating factors 113 4.4.4 Individual systems 114 4.5 Transit timing variations 117

5 Microlensing 119 5.1 Introduction 119 5.2 Principles 120 5.2.1 Light bending 120 5.2.2 Magnification 122 5.2.3 Optical depth and event rate 123 5.3 Light curves 124 5.3.1 Single lens characterisation 124 5.3.2 Binary lens characterisation 124 5.3.3 Multiple point mass lenses 125 5.3.4 Critical curves, caustics, and cusps 126 5.3.5 Binary lens caustics 126 5.3.6 Magnification maps 127 5.3.7 High-magnification events 128 5.3.8 Short-duration events 129 5.3.9 Repeating events 129 5.3.10 Binary lens, binary source 129 5.3.11 Free-floating objects 129 5.3.12 Planets orbiting a binary system 130 5.4 Light curve modeling 130 5.4.1 Ray shooting 130 5.4.2 Model fitting 131 5.4.3 Lens–source transverse motion 131 5.5 Higher-order effects 131 5.5.1 Blending 131 5.5.2 Finite source size 131 5.5.3 Limb darkening of the source 132 5.5.4 Orbital motion 132 5.5.5 Parallax and lens mass 133 5.5.6 High-resolution imaging 135 5.6 Potentially observable effects 135 5.6.1 Structure in the lens 135 5.6.2 Structure in the source 136 5.6.3 Physical effects 136 5.6.4 Transiting planets 137 5.6.5 Specific targets 137 5.7 Solar system lensing 137 5.8 Astrometric microlensing 138 5.9 Observations 139 5.9.1 Ground-based: first generation (pre–2010) 139 5.9.2 Ground-based: second generation (post–2010) 141

5.9.3 Ground-based: other 142 5.9.4 Space-based: ongoing 143 5.9.5 Space-based: future 143 5.10 Results 143 5.10.1 Individual objects 143 5.10.2 Statistical results 144 5.10.3 Limitations and strengths 151

6 Transits 153 6.1 Introduction 153 6.2 Transit searches: wide angle 155 6.3 Transit searches: specific targets 157 6.3.1 Radial velocity discoveries 157 6.3.2 Open and globular clusters 158 6.3.3 Circumbinary planets 159 6.3.4 Specific spectral types 160 6.3.5 Solar system transit observations 161 6.4 Surveys from the ground 162 6.4.1 HAT/HATNet 162 6.4.2 WASP/SuperWASP 164 6.4.3 Other searches reporting detected planets 165 6.4.4 Other ground-based surveys 169 6.5 Searches from space: CoRoT 171 6.6 Searches from space: Kepler 174 6.6.1 Instrument details 174 6.6.2 Target stars and accuracies 175 6.6.3 K2 mission extension 176 6.6.4 Future follow-up for Kepler and K2 177 6.6.5 Synopsis of results 178 6.6.6 Contributions to other fields 178 6.7 Other planet discoveries from space 178 6.8 Future observations from space 178 6.8.1 Approved surveys: dedicated 180 6.8.2 Approved surveys: by-products 180 6.8.3 Future follow-up from space: approved 181 6.8.4 Future follow-up from space: candidates 182 6.9 Follow-up observations from the ground 182 6.9.1 Transit photometry 182 6.9.2 High time resolution 182 6.9.3 Interferometric observations 183 6.9.4 Follow-up from ground: networks 183 6.10 Follow-up observations from space 184 6.10.1 EPOXI–EPOCh 184 6.10.2 Hubble Space Telescope 184 6.10.3 Hipparcos 185 6.10.4 MOST 186 6.10.5 Spitzer Space Telescope 186 6.10.6 Others 187 6.11 Accuracy: photometric and timing 187 6.11.1 Stellar activity 187 6.11.2 Photometry from the ground 188 6.11.3 Defocused transits 189 6.11.4 Beam-shaping diffusers 189 6.11.5 Conjugate-plane photometry 189 6.11.6 Timing accuracy 189

6.12 Transit detection and light curve analysis 190 6.12.1 Detrending 190 6.12.2 Transit detection 190 6.12.3 Kepler special cases 191 6.12.4 Light curve fitting 195 6.12.5 Candidate confirmation 196 6.13 Transit light curves 199 6.13.1 Principal transit observables 199 6.13.2 Geometric formulation 200 6.13.3 Light curve fitting 202 6.13.4 Biases 202 6.13.5 Circular orbits 202 6.13.6 Eccentric orbits 203 6.13.7 Physical quantities 205 6.13.8 Doppler variability 206 6.13.9 Secondary eclipse 207 6.13.10 Planet mass determination 207 6.13.11 Asterodensity profiling 207 6.14 Higher-order photometric effects 210 6.14.1 Limb darkening 211 6.14.2 Star spots 211 6.14.3 Stellar rotation and gravity darkening 215 6.14.4 Binary planets 216 6.14.5 Exoplanetary rings 217 6.14.6 Debris and transition disks 218 6.14.7 Planetary oblateness due to rotation 219 6.14.8 Atmospheric and topographic features 221 6.14.9 Night-side emission 221 6.14.10 Early ultraviolet ingress and bow shocks 221 6.14.11 Refraction and stellar mirages 222 6.14.12 Microlensing amplification 223 6.14.13 Variability-induced motion 223 6.14.14 Grazing transits 223 6.14.15 Hill sphere transits 224 6.14.16 Planet–planet eclipses 225 6.14.17 Tidal effects 226 6.14.18 Planetary prolateness under tidal locking 226 6.14.19 Tidally-induced gravity darkening 229 6.14.20 Tidally-excited stellar oscillations 230 6.14.21 Tidal disruption 230 6.14.22 Disintegrating planets and dusty tails 231 6.14.23 Artificial bodies and other civilisations 233 6.14.24 Transits across white dwarfs 233 6.15 Orbital phase curves 233 6.15.1 Reflected light 234 6.15.2 Glint 237 6.15.3 Beaming, ellipsoidal, and reflection effects 238 6.15.4 Doppler beaming 238 6.15.5 Ellipsoidal variations 239 6.15.6 Collective modeling 240 6.15.7 Atmospheric effects 242 6.15.8 Spin–orbit tomography 242 6.15.9 Multi-planet systems 243 6.15.10 Algorithmic implementation 243 6.16 Transits at other wavelengths 243

6.16.1 X-ray 243 6.16.2 Sub-mm and radio 244 6.17 Polarisation 244 6.17.1 Transit effects 244 6.17.2 Scattered light 246 6.18 Rossiter–McLaughlin effect 248 6.18.1 Context 248 6.18.2 Formalism 248 6.18.3 Higher-order effects 250 6.18.4 Transit of Venus 251 6.18.5 Rossiter–McLaughlin at secondary eclipse 251 6.18.6 Line-profile (Doppler) tomography 251 6.18.7 Results 252 6.18.8 Implications for migration models 255 6.19 Secular timing effects 256 6.19.1 Parallax and space motion 256 6.19.2 Distant stellar or planetary companions 257 6.19.3 General relativistic effects 257 6.19.4 Apsidal precession 257 6.19.5 Nodal precession 259 6.19.6 Tidal decay 260 6.19.7 Other time-dependent effects 260 6.19.8 Transitional transits 261 6.20 Transit timing variations 262 6.20.1 General considerations 262 6.20.2 Classification of configurations 263 6.20.3 Other treatments of perturbed systems 265 6.20.4 Orbits and masses 266 6.20.5 Observations from the ground 269 6.20.6 Contributions from Kepler 269 6.20.7 Non-transiting planets 272 6.20.8 Absence of transit timing variations 272 6.20.9 Effect on transit search algorithms 272 6.20.10 Transit duration variations 272 6.21 Trojans 273 6.21.1 Detection from transit timing variations 274 6.21.2 Detection from photometric signatures 274 6.22 Exomoons 275 6.22.1 Detection methods 276 6.22.2 Photo-dynamical treatment 279 6.22.3 Sense of orbital motion 280 6.22.4 Other considerations 281 6.22.5 Searches and candidates 281 6.23 Exocomets 282 6.24 Transit and eclipse spectroscopy 283 6.24.1 Principles 283 6.24.2 Equilibrium temperature and albedo 285 6.24.3 Observations 287 6.25 Range of properties of transiting planets 287 6.26 Kepler distributions and occurrence rates 288 6.26.1 Size and period distributions 288 6.26.2 Eccentricities 289 6.26.3 Occurrence rates 289 6.27 Mass, radius, and composition 291 6.27.1 Small-radii Kepler planets 294

xii

6.27.2 Low-mass gaseous Kepler planets 296 6.27.3 Mass and radius estimation 297 6.27.4 Minimum densities from the Roche radius 298 6.27.5 Effects of photoevaporation 298 6.28 Transiting hot Jupiters 299 6.28.1 Introduction 299 6.28.2 Secondary eclipses 300 6.28.3 Albedos 301 6.28.4 Anomalous (inﬂated) radii 302 6.28.5 Companion planets 304 6.28.6 Stellar companions 305 6.28.7 Satellites 305 6.28.8 Stellar activity and planet surface gravity 305 6.28.9 Other properties 306 6.29 Host stars 307 6.29.1 Stellar radii 307 6.29.2 Stellar densities 307 6.29.3 Metallicity dependence 308 6.29.4 Mass dependence 308 6.29.5 Rotation and gyrochronology 309 6.29.6 Stellar obliquities 311 6.29.7 Asteroseismology 311 6.29.8 Stellar binarity/multiplicity 313 6.30 Multiple planet systems 313 6.30.1 Overview of Kepler results 313 6.30.2 Hill stability 315 6.30.3 Dynamical stability 316 6.30.4 Resonances in the Kepler systems 318 6.30.5 Mutual inclinations of multi-planet systems 322 6.30.6 The Kepler dichotomy 324 6.31 Circumbinary planets 325

7 Imaging 329 7.1 Introduction 329 7.2 Active optics 331 7.3 Atmospheric effects 331 7.3.1 Adaptive optics 331 7.3.2 Speckle and lucky imaging 332 7.4 Coronagraphic masks 333 7.4.1 Introduction 333 7.4.2 Classiﬁcation of concepts 334 7.4.3 Discovery space 338 7.4.4 Other considerations 338 7.4.5 Speckle noise 339 7.5 Other considerations 341 7.5.1 Integral ﬁeld spectroscopy 341 7.5.2 Astrometric orbits 341 7.5.3 Exozodiacal dust 342 7.6 Ground-based imaging instruments 342 7.6.1 First-generation instruments 343 7.6.2 Second-generation instruments 343 7.6.3 Extremely large telescopes 345 7.6.4 Imaging from the Antarctic 347 7.6.5 Interferometry 348 7.7 Space-based imaging instruments 349

xiii

7.7.1 Existing space telescopes 349 7.7.2 Future space telescopes 350 7.7.3 Concepts for future space imaging missions 350 7.8 Other imaging concepts 353 7.8.1 Medium-term prospects 353 7.8.2 Future prospects: resolved imaging 354 7.8.3 Planetary radar 355 7.8.4 Gravitational wave signatures 356 7.8.5 Sub-diffraction limit imaging 356 7.8.6 Desirable innovations 357 7.9 Searches and surveys 357 7.9.1 Searches with ﬁrst-generation instruments 358 7.9.2 Searches with second-generation instruments 359 7.9.3 Searches around exoplanet host stars 360 7.9.4 Searches around binary stars 361 7.10 Discoveries 361 7.10.1 Planets around nearby stars 363 7.10.2 Planets within debris disks 364 7.10.3 Disks with spiral arms 367 7.11 Miscellaneous signatures 368 7.11.1 Planetary and protoplanet collisions 368 7.11.2 Accretion onto the central star 368 7.12 Imaging at other wavelengths 370 7.12.1 X-ray and radio wavelengths 370 7.12.2 Sub-mm and mm wavelengths 370

8 Host stars 373 8.1 Knowledge from astrometry 373 8.1.1 Hipparcos distances and proper motions 373 8.1.2 Gaia 373 8.1.3 Nearby star census 374 8.2 Physical properties 376 8.2.1 Absolute magnitude 376 8.2.2 Effective temperature 377 8.2.3 Parameters from spectroscopy 377 8.2.4 Stellar diameters 378 8.2.5 Masses and radii 378 8.2.6 Stellar ages 379 8.3 Stellar rotation 381 8.3.1 Diagnostics of rotation 382 8.3.2 Obliquities 384 8.3.3 Differential rotation 385 8.3.4 Angular momentum 386 8.3.5 Magnetic ﬁelds 387 8.4 Element abundances 388 8.4.1 Metallicity 388 8.4.2 Occurrence versus metallicity 389 8.4.3 Origin of the metallicity difference 392 8.4.4 Refractory and volatile elements 396 8.4.5 The r- and s-process elements 399 8.4.6 The alpha elements 399 8.4.7 Lithium 400 8.4.8 Beryllium 403 8.5 Occurrence versus stellar type 403 8.5.1 M dwarfs 404

xiv

8.5.2 Solar twins, analogues, and siblings 405 8.5.3 Other stellar classes 406 8.6 Asteroseismology 406 8.6.1 Principles 406 8.6.2 Application to CoRoT and Kepler targets 409 8.6.3 Application to exoplanet host stars 409 8.6.4 Planet and exoplanet seismology 411 8.7 Stellar variability 411 8.8 Stellar multiplicity 412 8.9 White dwarfs 412 8.9.1 Survival considerations 412 8.9.2 Imaging 414 8.9.3 Dust disks 415 8.9.4 Elemental pollution 416 8.9.5 Evidence for differentiation 419 8.10 Star–planet interactions 420 8.10.1 Overview of the various interactions 420 8.10.2 Magnetic and chromospheric activity 420 8.10.3 Stellar winds 422 8.10.4 X-ray emission 422 8.10.5 Radio emission 424 8.10.6 Flares, super-ﬂares and CMEs 427 8.10.7 Energetic neutral atoms 428

9 Brown dwarfs and free-floating planets 429 9.1 Introduction 429 9.1.1 The role of fusion 429 9.2 Discoveries and observations 431 9.2.1 The first brown dwarfs 431 9.2.2 Brown dwarf surveys 431 9.2.3 Future surveys 433 9.2.4 Young clusters and star forming regions 434 9.2.5 Other brown dwarf discoveries 434 9.3 Follow-up observations 434 9.3.1 Observations from the ground 434 9.3.2 Observations from space 434 9.4 Current census 435 9.5 Classification 435 9.6 Physical properties 438 9.6.1 Luminosity and age 438 9.6.2 Radius 438 9.6.3 Temperature 439 9.6.4 Magnetic field 439 9.6.5 Variability, rotation, and condensate clouds 439 9.6.6 X-ray and radio emission 440 9.6.7 Occurrence as binary companions 441 9.7 Formation of brown dwarfs 441 9.8 Disks, outflows, and planets 442 9.8.1 Disks around brown dwarfs 442 9.8.2 Jets and outflows 444 9.8.3 Planets around brown dwarfs 445 9.8.4 Disk/planet formation around brown dwarfs 445 9.9 Free-floating objects 446 9.9.1 By-products of regular star formation 446 9.9.2 Ejected planets and nomads 447

10 Formation and evolution 449 10.1 Context and present paradigm 449 10.1.1 Historical background 449 10.1.2 Present paradigm 450 10.2 Star formation 451 10.2.1 Molecular clouds 451 10.2.2 Protostars and protostellar collapse 452 10.2.3 Young stellar objects 453 10.3 Protoplanetary disks 454 10.3.1 Minimum-mass solar nebula 455 10.3.2 Disk viscosity and turbulence 456 10.3.3 Radial drift 457 10.3.4 Magnetorotational instability 459 10.3.5 Trapping and particle concentration 460 10.3.6 Disk dispersal and photoevaporation 462 10.3.7 Observational constraints 463 10.3.8 Transition disks 464 10.4 Terrestrial planet formation 467 10.4.1 Stages in formation 467 10.4.2 Dust to rocks: sub-micron to 10 m 468 10.4.3 Rocks to planetesimals: 10 m to 10 km 470 10.4.4 Pebbles as primary building blocks 471 10.4.5 Planetesimal coagulation 473 10.4.6 Final configuration 476 10.4.7 Size, shape, and internal structure 477 10.5 Giant planet formation 479 10.5.1 Core accretion 479 10.5.2 Gravitational disk instability 487 10.5.3 Comparison of the two mechanisms 490 10.6 Debris disks 491 10.6.1 Discovery 492 10.6.2 Occurrence 493 10.6.3 Dust modeling 495 10.6.4 Other manifestations 497 10.7 Formation of specific planet classes 498 10.7.1 Hot Jupiters 498 10.7.2 Hot Neptunes to Earths 499 10.7.3 Super-Earths 500 10.7.4 Planetary satellites (exomoons) 504 10.8 Resonances 504 10.8.1 Mean motion resonance 504 10.8.2 Resonance trapping and migration 507 10.8.3 Specific resonances 508 10.9 Long-term stability 509 10.9.1 Secular theory 510 10.9.2 Stability 511 10.9.3 Dynamical packing 514 10.9.4 Chaotic orbits 514 10.10 Orbital migration 517 10.10.1 Evidence for migration 517 10.10.2 Gas disk migration 517 10.10.3 Planetesimal disk migration 523 10.10.4 Planet–planet scattering 525 10.10.5 External gravitational perturbations 526 10.10.6 Lidov–Kozai oscillations 527

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10.10.7 Origin of large stellar obliquities 531 10.11 Tidal effects 531 10.11.1 Relevance of tides 531 10.11.2 Tidal amplitudes 532 10.11.3 Tidal dynamics 533 10.11.4 Tidal equilibrium and Darwin stability 538 10.11.5 Synchronous and non-synchronous rotation 540 10.11.6 Equilibrium tides and dynamical tides 541 10.11.7 Non-linear tides 542 10.11.8 Spin-up of host stars 542 10.11.9 Tidal heating 543 10.11.10 Multi-planet systems 544 10.11.11 Other considerations 545 10.12 Planets in multiple star systems 546 10.12.1 Binary and multiple stars 547 10.12.2 Planet conﬁgurations and stability 548 10.12.3 Planet formation in multiple star systems 550 10.12.4 Discoveries 551 10.12.5 Individual systems 552 10.12.6 Occurrence rates 552 10.12.7 Other insights 552 10.13 Population synthesis 554 10.13.1 Objectives 554 10.13.2 Observational constraints 554 10.13.3 Monte Carlo models 555

11 Interiors and atmospheres 559 11.1 Introduction 559 11.2 Planet constituents 560 11.2.1 Gas, rock, and ice 560 11.2.2 Composition and condensation 561 11.2.3 The snow line 564 11.3 Planet interiors 565 11.3.1 Equations of state 566 11.3.2 Hydrogen and water 567 11.3.3 Structural models 569 11.3.4 Model predictions 572 11.3.5 Terrestrial planets 573 11.3.6 Analytical model for rocky interiors 574 11.3.7 Lava planets 575 11.3.8 Ocean planets 576 11.4 Planet atmospheres 577 11.4.1 Atmospheres of gas giants 578 11.4.2 General circulation models 592 11.4.3 Atmospheres of terrestrial planets 596 11.4.4 Atmospheres of ejected planets 599 11.4.5 Atmospheric erosion 599 11.5 Mass–radius relation 602 11.5.1 General features 602 11.5.2 Terrestrial planets and super-Earths 603 11.5.3 Giant planets 604 11.5.4 Mass–density relation 604 11.5.5 Diagnostics from rotation 605 11.6 Transit and eclipse spectra 605 11.6.1 Data ﬁtting 606

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11.6.2 Results 607 11.6.3 Atmospheric insights from phase curves 614 11.6.4 Future prospects 617 11.7 Habitability 618 11.7.1 Habitable zone 619 11.7.2 Tidal heating 626 11.7.3 Habitability criteria 627 11.7.4 Earth-like planets in the habitable zone 632 11.8 Life 635 11.8.1 Deﬁnition 635 11.8.2 Abiogenesis 635 11.8.3 Development of life on Earth 636 11.8.4 Extraterrestrial life 638 11.8.5 Spectroscopic indicators 638 11.8.6 Search for intelligent life 643 11.8.7 Fermi paradox 648

12 The solar system 649 12.1 The Sun 649 12.1.1 A prototype for exoplanet host stars 649 12.1.2 Birth in a cluster 650 12.1.3 Solar nebula abundances 651 12.1.4 Age and early chronology 652 12.1.5 Solar obliquity 653 12.1.6 Dynamical aspects 654 12.1.7 Irradiance and other considerations 656 12.2 Planets 657 12.2.1 The terrestrial planets 657 12.2.2 The solar system giants 658 12.3 Earth–Moon system 662 12.3.1 Early chronology 662 12.3.2 Earth’s core 663 12.3.3 The Moon 664 12.3.4 The origin of water on Earth 667 12.3.5 Plate tectonics 668 12.3.6 Volcanism and large igneous provinces 670 12.3.7 Impact events 671 12.3.8 Atmosphere of the Earth 672 12.3.9 Disruptive events on Earth 675 12.4 Orbits 675 12.4.1 Ephemerides 675 12.4.2 Orbits and angular momentum 677 12.4.3 Resonances 677 12.4.4 Orbit stability and chaos 677 12.4.5 Planet rotation 679 12.4.6 Planet obliquities 680 12.5 Minor bodies in the solar system 681 12.5.1 Dwarf planets 682 12.5.2 Planetesimals and protoplanets 682 12.5.3 Exchange of impact ejecta 683 12.5.4 Asteroids 683 12.5.5 Trans-Neptunian objects 684 12.5.6 The Kuiper belt 684 12.5.7 Comets 685 12.5.8 Sedna, Planet X and Planet Nine 686

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12.5.9 Retrograde orbits 687 12.5.10 Planetary satellites 687 12.5.11 Trojans 689 12.5.12 Planetary rings 690 12.5.13 Zodiacal dust 691 12.5.14 Interstellar vagabonds 692 12.6 Disk depletion, truncation, and migration 693 12.6.1 Sweeping secular resonances 693 12.6.2 The case for migration 695 12.6.3 The Nice model 695 12.6.4 The Grand Tack model 697 12.6.5 Gas and planetesimal migration 700

Appendix A Numerical quantities 701 Appendix B Notation and acronyms 705 Appendix C Radial velocity exoplanets 713 Appendix D Transiting exoplanets 727 Appendix E Lensing exoplanets 759 Appendix F Imaging exoplanets 761 References 765 Subject index 933 Object index 947

Preface to the Second Edition

Almost 20 years ago, with the subject still in its in- Publication of this second edition coincides with a mi- fancy, and the number of known exoplanets at just 34, I nor respite in the flow of transformational observations prepared a 60-page review of exoplanet research (Perry- which marked the Kepler results, and the start of the man, 2000). The first edition of the Exoplanet Hand- second-generation imaging programmes. Significant book, published in early 2011, grew out of this: a book- new insights will be seen again in 2018–20 with the ob- length review to the end of 2010, when the number of servational advances that will come with the second known planets was just over 500. The aim of both was to data release from Gaia (DR2), and the launches of the collect in one place a synthesis of the knowledge of the Transiting Exoplanet Survey Satellite (TESS), CHEOPS, many areas of exoplanet research. and the James Webb Space Telescope (JWST). Since then progress has continued to flourish. The To emphasise the self-evident, this is primarily a review number of known exoplanets now exceeds 3500, and the of the status of the field. In places, I have used author- research literature stands at more than 17 000 refereed itative text more-or-less directly from the works refer- papers. My goal in this second edition remains the same: enced, implicitly credited to the source. In a work of to collect in one place, and in unified form, an overall such extent, I inevitably cover many topics in which I perspective of the many areas of ongoing research, and have no specific expertise. My hope is that the benefits to provide a synthesis of the developments, discoveries, of a broad, up-to-date, uniform treatment, outweigh any and associated physical phenomena, with pointers to imperfections and errors that will exist as a result. the more detailed literature. It offers a framework for un- A specific challenge faced in this compilation is the derstanding the wider and more definitive research liter- organisation of material, which is now so deeply inter- ature, through to the end of 2017. connected, and which contributes to its fascination. I Amongst many revisions, and a few minor suppres- made an early decision to maintain the chapter organ- sions, there are extensive additions: I have included isation used for the first edition: it probably remains the numerous advances in radial velocity, microlensing, as logical as any, despite the material related to transits imaging (notably SPHERE, GPI, and ALMA), and tran- now being substantially more extensive than any oth- sit instruments. The latter includes the important and ers. Bibliographic appendixes collect detailed results growing class of bright star transiting systems from for each system, and are intended to permit a rapid HATNet, SuperWASP, and others, as well as the trans- overview of which systems have been found, assess their formational results from the Kepler mission. I have also scientific interest to date, allow the chronology of un- added more on progress in quantifying habitability and derstanding for each to be traced, and permit a direct the search for life, and associated considerations such (hyperlinked) access to the relevant ADS and NASA Exo- as the anthropic principle, SETI and the Fermi paradox, planet Archive entries. and many related aspects of solar system research. The partitioning of topics is, as in any library cata- Much progress has also been made on the theoretical loguing system, non-trivial. As just one of countless ex- side. Amongst these are advances in the understand- amples, while it might well be convenient to find all ma- ing of possible formation pathways via the hypothesised terial on ‘hot Jupiters’ in one section, this obviously can- mechanism of pebble accretion; of the formation and not be done without the consequences of dividing up dynamical state of multi-planet systems especially in material on obliquities, Lidov–Kozai migration, forma- connection with resonance capture; of numerous appli- tion, spectroscopy, and so on. cations of tidal theory; of the widespread application of Another challenge was how to handle the references, atmospheric general circulation models (originally de- and what to include. While the subject is developing veloped for understanding the climate of the Earth and so rapidly, I considered that the source of material cited the other solar system planets); and of the development should be retained, in part for verification, in part to give of migration models for the early solar system with their due credit, but more crucially as the entry points for fur- considerable explanatory and predictive content. ther research. Considering and dismissing various alter-

natives (such as retaining only the most frequently-cited Various people have kindly responded to my spe- references, omitting titles, or only making them avail- cific questions, and here I am grateful to Adam Burrows, able online), does result in an extensive bibliography. Ludmila Carone, Andrew Collier Cameron, Jeff Cough- It has the same reference/text ratio as the first edition, lin, Jos de Bruijne, Laurance Doyle, Dainis Dravins, with its merits and with its disadvantages. Jonathan Fortney, Joel Hartman, Réné Heller, Brian Jack- son, Anders Johansen, Hubert Klahr, Heather Knutson, I have attempted to make the references to, and statistics Lennart Lindegren, Abel Méndez, Jerry Orosz, Joshua of, exoplanet discoveries, and the associated literature, Pepper, Don Pollacco, Saul Rappaport, Tom Ruen, Birger as complete as feasible through to the end of 2017. The Schmitz, Alberto Sesana, John Southworth, Jason Wang, fact that some publications were only in preprint form and Peter Wheatley. at that time, combined with a limited attempt to track Again, I am most grateful to all authors who agreed some new studies after that cutoff, leads to some publi- to the use of their figures for this work, which are so in- cations dated 2018. valuable for illustrating the various results. Their names Amongst the uncountable gaps in current knowledge, a are acknowledged in the figure captions. few are perhaps notable. From the observational side, I am grateful to Simon Mitton, who encouraged the no definitive exomoons, planetary rings, or co-orbiting publication of the first edition, and to Lorraine Hanlon planets have yet been found. The detailed form of the for the valuable support of University College Dublin. exoplanet distribution function remains poorly known. I also thank Neil Thomas (University of Florida), and There is no evidence for life, in any form, beyond Earth. Vittorio Vanzani (University of Padua) who communi- From the theoretical side, many details of planet for- cated errors in the first edition. mation remain uncertain, as does the fraction of gas gi- The NASA Astrophysics Data System (ADS), com- ants formed by core accretion or gravitational instabil- bined with on-line journal access, has been indispens- ity. There is no widely embraced paradigm for the for- able for a literature survey on this scale. LATEX, TeXShop, mation, halting, or inflated radii of hot Jupiters, for the and BibDesk were key to its practical development. formation of super-Earths, or for the Kepler ‘dichotomy’. Various online resources, notably the NASA Exoplanet Within the solar system, open questions include the Archive and the Extrasolar Planets Encyclopaedia, have source of the transient heating of the early solar neb- been invaluable. ula, the origin of the solar obliquity, the size (or even As for the first edition, I thank Vince Higgs and col- presence) of Jupiter’s solid core, and to what extent gas leagues at Cambridge University Press, including for this and planetesimal migration have influenced its present edition Esther Miguéliz Obanos, for their highly con- architecture. More definitive answers to some of these structive and efficient support. questions may, perhaps, accompany the third edition. Finally, I owe a considerable debt of gratitude to my I owe a number of people my sincere thanks for their wife Julia. Her support, enthusiasm and indeed her in- assistance. I am pleased to thank the Directors of the terest has been of immense help. Kiepenheuer Institute for Solar Physics (Freiburg), Oskar The electronic pdf version includes hyperlinked navi- von der Lühe and Svetlana Berdyugina, for a period as gation via the Table of Contents, via the Index, as well visiting fellow in 2016, when the major parts of Chap- as through cross-referenced sections, figures, and equa- ters 6–7 were completed. tions. References and Appendixes are hyperlinked as be- I am grateful to the Director of the Instituto de As- low, with the References including links both to the rele- trofísíca de Andalucía (IAA), José Vílchez, and to Pedro vant ADS pages, and back-referencing to the cited pages. Amado González, for a visit to Granada in early 2017, A number of files are made available at the location when Chapters 10–12 were largely completed. www.cambridge.org/exoplanethandbook. A pdf ver- I thank Dr Joan Megson and John Gray for the use sion of the References includes hyperlinks to the rele- of their retreat in Assynt, which allowed me to complete vant ADS pages. Appendixes with planet listings (Ap- some other sections, and to compile the appendixes, pendixes C–F) are hyperlinked at the host star level to with the minimum of distraction. the NASA Exoplanet Archive, with each citation also hy- As for the first edition, I express my particular grat- perlinked to the relevant ADS page. Some figures are itude to Joachim Wambsganss, director of the Zentrum also made available at the same location. für Astronomie der Universität Heidelberg (ZAH/ARI), Notification of errors, major or minor, or significant and to Thomas Henning and Hans-Walter Rix, directors omissions or misrepresentations, will be greatly appre- of the Max–Planck–Institut für Astronomie, Heidelberg, ciated ([email protected]), and will be main- for their invitation to spend a period in Heidelberg to tained at the same www location. prepare the first edition in 2010, and for very kindly host- ing a further period in Heidelberg in early 2018 to finalise Michael Perryman this second edition. Heidelberg, April 2018