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Alien worlds have long been a staple of science fiction. But today, thanks to modern astronomical instrumentation and the achievements of many enterprising observational astronomers, the existence of planets outside our solar system – also known as exoplanets – has moved into the realm of science fact. With planet hunters finding ever smaller, more Earth-like worlds, our understanding of the cosmos is forever changed, yet the question of how astronomers make these discoveries often goes unanswered.
How Do You Find an Exoplanet? is an authoritative primer on the four key techniques that today's planet hunters use to detect the feeble signals of planets orbiting distant stars. John Johnson provides you with an insider's perspective on this exciting cutting-edge science, showing how astronomers detect the wobble of stars caused by the gravitational tug of an orbiting planet, the slight diminution of light caused by a planet eclipsing its star, and the bending of space-time by stars and their planets, and how astronomers even directly take pictures of planets next to their bright central stars.
Accessible to anyone with a basic foundation in college-level physics, How Do You Find an Exoplanet? sheds new light on the prospect of finding life outside our solar system, how surprising new observations suggest that we may not fully understand how planets form, and much more.
PREFACE ix
1. Introduction 1
1.1 My Brief History 1
1.2 The Human Activity of Watching the Sky 3
1.3 Asking Why the Planets Move as They Do 8
1.4 Exoplanets and Completing the Copernican Revolution 16
2. Stellar Wobbles 23
2.1 At the Telescope 23
2.2 For Every Action 28
2.3 Eccentric Orbits 39
2.4 Measuring Precise Radial Velocities 45
2.5 Stellar Jitter 49
2.6 Design Considerations for a Doppler Survey 52
2.7 Concluding Remarks 57
3. Seeing the Shadows of Planets 59
3.1 Measuring and Reading Transit Signals 62
3.2 The Importance of a/R 71
3.3 Transit Timing Variations 74
3.4 Measuring the Brightness of a Star 77
3.5 Radial Velocities First, Transits Second 81
3.6 Transit First, Radial Velocities Second 83
3.7 From Close In to Further Out 89
4. Planets Bending Space-Time 90
4.1 The Geometry of Microlensing 94
4.2 The Microlensing Light Curve 103
4.3 The Microlensing Signal of a Planet 106
4.4 Microlensing Surveys 109
5. Directly Imaging Planets 114
5.1 The Problem of Angular Resolution 115
5.2 The Problem of Contrast 122
5.3 The Problem of Chance Alignment 129
5.4 Measuring the Properties of an Imaged Planet 130
6. The Future of Planet Hunting 132
6.1 Placing the Solar System in Context 133
6.2 Learning How Planets Form 138
6.3 Finding Life Outside the Solar System 141
6.4 Giant Planets as the Tip of the Iceberg 144
6.5 The Future of the Doppler Method: Moving to Dedicated Instrumentation 148
6.6 The Future of Transit Surveys 153
6.7 The Future of Microlensing 155
6.8 The Future of Direct Imaging 158
6.9 Concluding Remarks 160
BIBLIOGRAPHY 163
GLOSSARY 171
INDEX 177
John Asher Johnson is professor of astronomy at Harvard University.
"Johnson's enthusiasm for his vibrant field is palpable in this valuable, concise guide for amateur astronomers and anyone else not afraid of a few technicalities."
– Lewis Dartnell, New Scientist
"Johnson [...] takes us on an enjoyable journey to the world of exoplanet hunters [...] An excellent book for anyone interested but also for astronomy students if their curriculum includes one-semester course in exoplanets."
– Read about Science
"This little red book is a thorough yet very understandable introduction to one of the hottest topics in astronomy – planets outside the solar system. Johnson, one of the leading scientists in the field, has created a great primer for undergraduate students wishing to gain enough knowledge to undertake a project or perhaps win an internship in the field."
– Choice
"Johnson has woven the personal side of being a scientist with rigorous intuition about the techniques used to detect exoplanets. We hear the fresh and articulate voice of a young professor who grew into the shoes of a full-fledged scientist. Johnson's experiences and insights will touch the hearts and minds of readers."
– Debra Fischer, Yale University
"With remarkable clarity, Johnson presents a concise yet personable, technical yet accessible must-read for all students and practitioners of exoplanet discovery."
– Sara Seager, Massachusetts Institute of Technology
"How Do You Find an Exoplanet? is well focused on the fundamentals and accessible to a wide range of readers. Johnson is highly respected in the exoplanet community, and here he has emphasized what's important, while minimizing or explaining jargon. I know of no serious competitors to this book."
– Eric B. Ford, Pennsylvania State University
"How Do You Find an Exoplanet? presents an engaging overview of modern exoplanetary detection techniques. John Johnson brings a firsthand narrative to this remarkable scientific detective story, while explaining the technical fine points at an accessible level."
– Greg Laughlin, University of California, Santa Cruz
