Thérèse Encrenaz

In this third corrected and revised edition students and lecturers in astronomy and planetary science as well as planet observers will find a mine of up-to-date information on the solar system and its interaction with the interplanetary medium, its various objects, comparative planetology, discussion of questions for further research and future space exploration.

Exoplanet, extrasolar planet, exoEarth, exojupiter: neologisms still absent from many dictionaries. These terms are, however, current among astronomers, and are heard in their answers to a question already two millennia old: are there planets like ours elsewhere in the Universe? Greek atomists such as Epicurus were convinced of the existence of an infinite number of solar systems like our own, but it was only in 1995 that a real answer began to emerge. An extrasolar planet had been detected... a planet orbiting another star... a star like the Sun. So, the solar system was not unique! By mid- 2006 more than 200 giant exoplanets had been discovered. At this rate of discovery it seems that Earth-like planets may be found within a decade. The discovery of exoplanets held some surprises, in that they exhibited very different characteristics from what might have been expected. Although most of them are gas giants of masses comparable to Jupiter's mass, as a result of the rather insensitive nature of current detection methods, why are they from ten to fifty times closer to their stars than is Jupiter? How were these 'hot Jupiters' formed? Another surprise about exoplanets is that many of them have very elliptical orbits, while the planets of the solar system have much more circular orbits.

In this third corrected and revised edition students and lecturers in astronomy and planetary science as well as planet observers will find a mine of up-to-date information on the solar system and its interaction with the interplanetary medium, its various objects, comparative planetology, discussion of questions for further research and future space exploration.

The Earth is the only planet in the Solar System where liquid water is present on the surface, a condition that seems necessary for the development of life. Its sisters Venus and Mars are extremely different. Why did these three planets, born under fairly comparable conditions, evolve to the conditions we observe today? Understanding the physical or chemical factors that are at the origin of such divergent evolutions is a first step in an approach to the problem of the origin of life on Earth.This question takes on a new dimension with the discovery of thousands of planets around the stars of our Galaxy, some of which could resemble the Earth. Could they be home to life? With their discovery, the question "Are we alone in the Universe?" is no longer limited to our Solar System, and the field of possibilities opens up to infinity. It is now possible to approach the problem from a scientific perspective and not only from a philosophical one, as was the case in the past.The enthusiasm of the public for the subject sometimes results in sensational and premature announcements. This book reminds us that there is still a long way to go before we can detect life outside the Earth.

More than 4300 planets around nearby stars Who could have imagined this extraordinary harvest only thirty years ago? As the vast majority of stars are 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 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.

What is a planet? The answer may seem obvious; still, the definition of a planet has continuously evolved over the centuries, and their number has changed following successive discoveries. In 2006, the decision endorsed by the International Astronomical Union to remove Pluto from the list of planets has well illustrated the difficulty associated with their definition. The recent discovery of hundreds of exoplanets around nearby stars of our Galaxy opens a new and spectacular dimension to astrophysics. We presently know very little about the physical nature of exoplanets. In contrast, our knowledge on solar system planets has made huge progress over the past decades, thanks, especially, to space planetary exploration. The purpose of this book is first to characterize what planets are, in their global properties and in their diversity. Then, this knowledge is used to try to imagine the physical nature of exoplanets, starting from the few parameters we know about them. Throughout, we keep in mind the ultimate question of the search for possible extraterrestrial life: Could life exist or have existed in the solar system and beyond?Thérèse Encrenaz is Emeritus Senior Scientist at the Centre National de la Recherche Scientifique. She works at the Observatoire de Paris, at the Laboratoire d'Etudes Spatiales et d'Instrumentation en Astrophysique (LESIA). She is a specialist of the study of planetary atmospheres, and has been involved in several space missions.

What is life and where can it exist? What searches are being made to identify conditions for life on other worlds? If extraterrestrial inhabited worlds are found, how can we explore them? In this book, two leading astrophysicists provide an engaging account of where we stand in our quest for habitable environments, in the Solar System and beyond. Starting from basic concepts, the narrative builds scientifically, including more in-depth material as boxed additions to the main text. The authors recount fascinating recent discoveries from space missions and observations using ground-based telescopes, of possible life-related artefacts in Martian meteorites, extrasolar planets, and subsurface oceans on Europa, Titan and Enceladus. They also provide a forward look to future missions. This is an exciting, informative read for anyone interested in the search for habitable and inhabited planets, and an excellent primer for students in astrobiology, habitability, planetary science and astronomy.

Over the past ten years, the discovery of extrasolar planets has opened a new field of astronomy, and this area of research is rapidly growing, from both the observational and theoretical point of view. The presence of many giant exoplanets in the close vicinity of their star shows that these newly discovered planetary systems are very different from the solar system. New theoretical models are being developed in order to understand their formation scenarios, and new observational methods are being implemented to increase the sensitivity of exoplanet detections. In the present book, the authors address the question of planetary systems from all aspects. Starting from the facts (the detection of more than 300 extraterrestrial planets), they first describe the various methods used for these discoveries and propose a synthetic analysis of their global properties. They then consider the observations of young stars and circumstellar disks and address the case of the solar system as a specific example, different from the newly discovered systems. Then the study of planetary systems and of exoplanets is presented from a more theoretical point of view. The book ends with an outlook to future astronomical projects, and a description of the search for life on exoplanets. This book addresses students and researchers who wish to better understand this newly expanding field of research.

Over the past ten years, the discovery of extrasolar planets has opened a new field of astronomy, and this area of research is rapidly growing, from both the observational and theoretical point of view. The presence of many giant exoplanets in the close vicinity of their star shows that these newly discovered planetary systems are very different from the solar system. New theoretical models are being developed in order to understand their formation scenarios, and new observational methods are being implemented to increase the sensitivity of exoplanet detections. In the present book, the authors address the question of planetary systems from all aspects. Starting from the facts (the detection of more than 300 extraterrestrial planets), they first describe the various methods used for these discoveries and propose a synthetic analysis of their global properties. They then consider the observations of young stars and circumstellar disks and address the case of the solar system as a specific example, different from the newly discovered systems. Then the study of planetary systems and of exoplanets is presented from a more theoretical point of view. The book ends with an outlook to future astronomical projects, and a description of the search for life on exoplanets. This book addresses students and researchers who wish to better understand this newly expanding field of research.

In Searching for Water in the Solar System, Thérèse Encrenaz takes the reader on a journey through the Universe in search of water. She begins by introducing the most well-known of molecule H2O, its physical and chemical characteristics and its cosmic Formation and abundance. She examines the methods by which the presence of water is detected, both within the solar system and beyond. One by one she visits a diversity of locations in the cosmos, from the nearest planets to the furthest galaxies, where water has been discovered. In the formation of the solar system, she explains how the water molecule played a major part, with the so-called ‘ice frontier’ determining the natures of the terrestrial and giant planets. The book explores the presence of water in the various bodies of the Solar System: in the giant planets, with their rings and systems of satellites, in comets, asteroids and in the terrestrial planets. By tracing the history of water in the atmospheres of Mars, Venus and the Earth, the author explains how small differences in temperatures, causing water to exist in different states on different planets – vapour on Venus, liquid on Earth and solid ice on Mars – have led to a great divergence in the evolutions of the three planets. The story of water on Mars, an aspect of great topical interest, offers an insight into the possibility (still only a theory) that there was once life on that planet. The book concludes by looking at the important role played by water in studies of habitable exoplanets.

This book provides a comprehensive overview of our current knowledge of comets. It presents a fascinating survey of the study of comets throughout history, from antiquity to the present day, and includes the most recent discoveries on the exceptional comets Hale-Bopp and Hyakutake. The authors discuss the role of comets in the formation of our Solar System and describe the links between comets, asteroids and the recently discovered Kuiper-belt objects. The book also includes new insights into the composition and nature of cometary nuclei, with results from the most up-to-date observation techniques. Written in a clear and lively style, and beautifully illustrated, this book will appeal to anyone interested in comets and astronomy, professionals and amateurs alike. It will be of particular interest to students and researchers in astronomy, astrophysics and planetary science, as well as general readers with a good background in physics.