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CURRENT NATURAL SCIENCES CURRENT NATURAL The Exoplanet SCIENCES CURRENT NATURAL Revolution James Lequeux, Thérèse Encrenaz The Exoplanet and Fabienne Casoli Revolution ore than 4300 planets around nearby stars! Who could have imagined this extraordinary harvest only thirty years ago? As the vast majority of stars are M surrounded by planets, we can surmise that there must be more than a hundred billion planets in our Galaxy. The Solar system is therefore very far from unique. However, it looks quite different from most of the external systems that we know today, but the variety The Revolution Exoplanet of planetary systems is such that it is difficult to conclude that the Solar System is truly particular. Understanding how diverse planet systems were formed and how they evolved, studying the nature of exoplanets and their atmospheres, are challenges that hundreds of researchers around the world are working on. Does any of these planets harbor life? We do not yet have an answer, but the new means of observation and analysis that astronomers have and will soon have at their disposal are so powerful that they could give a first answer in a few decades, and perhaps even in a few years if we are lucky. This book gives a comprehensive vision of this complex and fascinating area of research, presented in a simple and lively way. James Lequeux is an emeritus astronomer at the Paris Observatory. His domains of expertise are the interstellar matter and the evolution of stars and galaxies. He has directed the Marseilles Observatory. He has written many books on the history of astronomy, and several popular books. Thérèse Encrenaz is an expert in planetary atmosphe res. She has directed the Department of Space Research at the Paris Observatory and was adjunct President of this Observatory. She has written many textbooks and popular books. Casoli Encrenaz, F. T. J. Lequeux, Lequeux, J. Fabienne Casoli is President of the Paris Observatory. Her specialty is radioastronomy. She has James Lequeux, Thérèse Encrenaz been adjunct director of the French National Center for Space Studies and of the National Institute of Sciences of the Universe, and directed the Institute of Space Astronomy in Orsay. and Fabienne Casoli www.edpsciences.org 9 782759 822102 ISBN : 978-2-7598-2210-2 9782759822102_Exoplanet.indd 1 18/06/2020 18:15 CURRENT NATURAL SCIENCES CURRENT NATURAL The Exoplanet Revolution James Lequeux, Thérèse Encrenaz CURRENT NATURAL SCIENCES The Exoplanet and Fabienne Casoli Revolution ore than 4300 planets around nearby stars! Who could have imagined this extraordinary harvest only thirty years ago? As the vast majority of stars are M surrounded by planets, we can surmise that there must be more than a hundred billion planets in our Galaxy. The Solar system is therefore very far from unique. However, it looks quite different from most of the external systems that we know today, but the variety The Revolution Exoplanet of planetary systems is such that it is difficult to conclude that the Solar System is truly particular. Understanding how diverse planet systems were formed and how they evolved, studying the nature of exoplanets and their atmospheres, are challenges that hundreds of researchers around the world are working on. Does any of these planets harbor life? We do not yet have an answer, but the new means of observation and analysis that astronomers have and will soon have at their disposal are so powerful that they could give a first answer in a few decades, and perhaps even in a few years if we are lucky. This book gives a comprehensive vision of this complex and fascinating area of research, presented in a simple and lively way. James Lequeux is an emeritus astronomer at the Paris Observatory. His domains of expertise are the interstellar matter and the evolution of stars and galaxies. He has directed the Marseilles Observatory. He has written many books on the history of astronomy, and several popular books. Thérèse Encrenaz is an expert in planetary atmosphe res. She has directed the Department of Space Research at the Paris Observatory and was adjunct President of this Observatory. She has written many textbooks and popular books. Casoli Encrenaz, F. T. J. Lequeux, Lequeux, J. Fabienne Casoli is President of the Paris Observatory. Her specialty is radioastronomy. She has James Lequeux, Thérèse Encrenaz been adjunct director of the French National Center for Space Studies and of the National Institute of Sciences of the Universe, and directed the Institute of Space Astronomy in Orsay. and Fabienne Casoli www.edpsciences.org 9 782759 822102 ISBN : 978-2-7598-2210-2 9782759822102_Exoplanet.indd 1 18/06/2020 18:15 J. Lequeux, T. Encrenaz and F. Casoli The Exoplanet Revolution CURRENT NATURAL SCIENCES EDP Sciences Cover image: a planet just formed in the disk of gas and dust surrounding the dwarf star PDS 70. In this near-infrared, high-resolution image, the planet is seen as a bright point inside the remains of the disk. The star itself, at the center, is occulted by a mask. © European Southern Observatory, A. Müller et al. Printed in France © 2020, EDP Sciences, 17 avenue du Hoggar, BP 112, Parc d’activités de Courtabœuf, 91944 Les Ulis Cedex A This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, re-use of illustrations, recitation, broad-casting, reproduction on microfilms or in other ways, and storage in data bank. Duplication of this publication or parts thereof is only permitted under the provisions of the French Copyright law of March 11, 1957. Violations fall under the prosecution act of the French Copyright law. ISBN (print): 978-2-7598-2210-2 - ISBN (ebook): 978-2-7598-2211-9 Table of Contents Introduction 1 Chapter 1. The prehistory of exoplanets 5 First ideas and speculations ................................ 5 The evolution of concepts on the formation of the Solar System ...... 8 The discovery of protoplanetary disks ......................... 11 The first attempts to detect exoplanets ........................ 12 Bibliography .......................................... 17 Chapter 2. The first detections 19 An unexpected discovery: planets around a pulsar! ................ 19 1995: The first planet around a star like ours! ................... 21 The success of velocimetry ................................. 27 Bibliography .......................................... 31 Chapter 3. The method of transits 33 What is a planetary transit? ............................... 33 Observations from the Earth ............................... 36 The Space Age ......................................... 37 The CoRoT mission ................................. 37 The Kepler Mission .................................. 38 Primary and Secondary Transits. 40 Transmission spectroscopy (primary transit) ................ 41 Emission spectroscopy (secondary transit) .................. 43 Gravitational transits .................................... 44 Bibliography .......................................... 46 Chapter 4. Detecting and viewing exoplanets 47 Advantages and limitations of indirect methods of detection ......... 47 The transit method .................................. 47 Exoplanets detected as gravitational microlenses ............. 48 Exoplanets detected by velocimetry or astrometry ............ 49 Direct observation: a very difficult problem ..................... 50 Coronography. 51 The black-fringe interferometer ......................... 52 How to obtain perfect images: adaptive optics ............... 53 Combined coronography and adaptive optics. 55 A new track for the future: the search for exoplanets in the radio domain .......................................... 57 Bibliography .......................................... 57 IV The Exoplanet Revolution Chapter 5. The variety of exoplanets 59 The outstanding results of the last twenty years .................. 59 A multitude of exoplanets ............................. 59 Giant exoplanets very close to their stars .................. 59 Orbits of all kinds. 60 Many multiple systems ............................... 61 Planets around double stars. 62 The different classes of exoplanets ........................... 62 Hot and Cold Jupiters. 64 Super-Earths and Neptunes. 67 Earths and Habitable Planets .......................... 70 Bibliography .......................................... 73 Chapter 6. The birth of stars and protoplanetary disks 75 Protostars, jets and disks .................................. 75 The protoplanetary disks .................................. 78 The ice lines in protoplanetary disks .......................... 82 Planet-disk interactions ................................... 84 Bibliography .......................................... 87 Chapter 7. Formation and evolution of planetary systems 89 The formation of planets .................................. 89 The evolution of planetary systems: what does the Solar System teach us?. 92 Why no super-Earths in the Solar System? ..................... 98 Expelled planets, isolated exoplanets ......................... 98 What future for the Solar System? ........................... 100 What consequences for our understanding of exoplanetary systems? .... 102 Bibliography .......................................... 104 Chapter 8. The physical nature of exoplanets 107 The observables ........................................ 107 The first measurements of the atmospheric composition of hot Jupiters .. 111 Possible causes of
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