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.

The past few years have seen an incredible explosion in our knowledge of the universe. Since its 2009 launch, the Kepler satellite has discovered more than two thousand exoplanets, or planets outside our solar system. More exoplanets are being discovered all the time, and even more remarkable than the sheer number of exoplanets is their variety. In Exoplanets, astronomer Michael Summers and physicist James Trefil explore these remarkable recent discoveries: planets revolving around pulsars, planets made of diamond, planets that are mostly water, and numerous rogue planets wandering through the emptiness of space. This captivating book reveals the latest discoveries and argues that the incredible richness and complexity we are finding necessitates a change in our questions and mental paradigms. In short, we have to change how we think about the universe and our place in it, because it is stranger and more interesting than we could have imagined.

Learn about the planets that exist outside of our solar system, and the actions scientists are taking to learn more about them. --

Come along for the captivating hunt for planets like our own Envisioning Exoplanets traces the journey of astronomers and researchers on their quest to explore the universe for a planet like Earth. Exoplanets--worlds beyond our solar system--were once dismissed as science fiction. But now, with more than 4,000 confirmed exoplanets, countless possibilities exist for what remains to be uncovered in the universe. This book follows the exhilarating progression of exoplanet research from its earliest stages operating on the fringes of scientific research to the newest developments of renowned agencies around the world searching for planets capable of hosting life. Featuring provocative questions about the universe and more than 200 remarkable illustrations from Michael Caroll, Ron Miller, and other key members of the International Association of Astronomical Artists, Envisioning Exoplanets is an intergalactic visual voyage.

In the mid-1990s, astronomers made history when they began to find planets orbiting stars in the Milky Way. More than eight hundred planets have been found since then, yet none of them is anything like Earth and none could support life. Now, armed with more powerful technology, planet hunters are racing to find a true twin of Earth. Science writer Michael Lemonick has unique access to these exoplaneteers, as they call themselves, and Mirror Earth unveils their passionate quest. Unlike competitors in other races, Geoff Marcy, Bill Borucki, David Charbonneau, Sara Seager, and others actually consult and cooperate with one another. But only one will be the first to find Earth's twin. Mirror Earth tells the story of their competition.

The past decade has delivered remarkable discoveries in the study of exoplanets. Hand-in-hand with these advances, a theoretical understanding of the myriad of processes that dictate the formation and evolution of planets has matured, spurred on by the avalanche of unexpected discoveries. Appreciation of the factors that make a planet hospitable to life has grown in sophistication, as has understanding of the context for biosignatures, the remotely detectable aspects of a planet's atmosphere or surface that reveal the presence of life. Exoplanet Science Strategy highlights strategic priorities for large, coordinated efforts that will support the scientific goals of the broad exoplanet science community. This report outlines a strategic plan that will answer lingering questions through a combination of large, ambitious community-supported efforts and support for diverse, creative, community-driven investigator research.

“How do alien, faraway worlds reveal their existence to Earthlings? Let Donald Goldsmith count the ways. As an experienced astronomer and a gifted storyteller, he is the perfect person to chronicle the ongoing hunt for planets of other stars.” —Dava Sobel Astronomers have recently discovered thousands of planets that orbit stars throughout our Milky Way galaxy. With his characteristic wit and style, Donald Goldsmith presents the science of exoplanets and the search for extraterrestrial life in a way that Earthlings with little background in astronomy or astrophysics can understand and enjoy. Much of what has captured the imagination of planetary scientists and the public is the unexpected strangeness of these distant worlds, which bear little resemblance to the planets in our solar system. The sizes, masses, and orbits of exoplanets detected so far raise new questions about how planets form and evolve. Still more tantalizing are the efforts to determine which exoplanets might support life. Astronomers are steadily improving their means of examining these planets’ atmospheres and surfaces, with the help of advanced spacecraft sent into orbits a million miles from Earth. These instruments will provide better observations of planetary systems in orbit around the dim red stars that throng the Milky Way. Previously spurned as too faint to support life, these cool stars turn out to possess myriad planets nestled close enough to maintain Earthlike temperatures. The quest to find other worlds brims with possibility. Exoplanets shows how astronomers have broadened our planetary horizons, and suggests what may come next, including the ultimate discovery: life beyond our home planet.

Do you wonder if humans are the only beings who wonder if they are alone in the universe? Our sun is a star. In the night sky are all kinds of stars, and orbiting those stars are planets like the ones in our own solar system. Could those planets have life like we do on Earth? Planet Earth is not too big, not too small, not too hot, and not too cold. It’s just right. Our very own Goldilocks planet . . . . Follow a young girl as she explores these questions in this gorgeous book about the wondrous search for another Goldilocks planet.

Solar System Planets and Exoplanets provides a current viewpoint of planetary systems. The solar system’s planets and exoplanets are addressed in an overview manner, and specific space probe data are used to provide a current state of knowledge of Venus and Mars. Recent Mars data and associated observations are addressed in several chapters. Of particular interest are data that suggest the possibility that life could have existed on the planet’s surface during its past when Mars’ atmosphere was wetter and denser. The search for life on Mars is one of the main objectives of space missions, and it is an ongoing theme of this book. Key to the existence of life is the evolution of the radiation output of the Sun that is discussed and projected into the future. Space probe data related to the Asteroid Belt is also presented. Technological advances in terms of operating aircraft on Mars and propulsion systems provide useful commentary regarding future innovations that will enhance upcoming space missions and the search for life.

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