Since several decades, comets have been considered as key witnesses of solar system formation. Their nature has been explored using the modern arsenal of Earth- and space-based observations, and they hold a central place as dynamical arbiters of the planetary system in the new paradigm of solar system evolution known as the Nice Model. Thus, they have the potential to test the various ideas, using the detailed data recently gathered by the ESA/Rosetta mission. This requires an understanding of their origin and evolution, which form the subject of the present book. All the relevant issues are covered, describing both the background and the current frontiers of research.

Comets are small bodies, but of great cosmic relevance. Given its pristine nature, they may preserve valuable and unique information on thechemical and physical processes that took place in theearly solar system, and that may be occurring in the formation of other planetary systems. They might have even played a very important role in the origin of life on Earth. Beyond that, since ancient times comets have inspired awe, superstition, and also curiosity anddebate. Their sudden apparitions challenged the long-held view of the immutability of the heavens, which triggered a long debate on whether comets had a heavenly or terrestrial nature. Therefore, comets have a prominent role in the history of scienti?cthought, that goes back to the most ancient civilizations. The last apparition of comet Halley in 1986 was a landmark since it arouse a great expectation in the scienti?c community and in the public at large. For the ?rst time, a ?otilla of spacecrafts visited a comet. Agreat number of popular and technical books were written on Halley, and comets in general, around the mid-eighties. The interest in comets never subsided after Halley’s passage which is re?ected in the large volume of printed material on these bodies. I have taken the challenge to write a new book on comets that summarizes most of the recent advances on thesubject, including my own workdeveloped during the last 25 years.

Over forty authorities present sections on the nucleus, dust, coma, and tails of comets, along with sections on their origin, and relationships to other solar system bodies. . . . An excellent book.ÑSpace News "The volume is highly recommended to all interested in comets and the Solar System."ÑJournal of the British Astronomical Association "A good representation of the studies that are currently being done on comets, and it is an extremely good source of information on a wide variety of topics."ÑInternational Comet Quarterly "Extremely well-written and informative. . . . A must for library collections."ÑThe Observatory

What are these graceful visitors to our skies? We now know that they bring both life and death and teach us about our origins. Comet begins with a breathtaking journey through space astride a comet. Pulitzer Prize-winning astronomer Carl Sagan, author of Cosmos and Contact, and writer Ann Druyan explore the origin, nature, and future of comets, and the exotic myths and portents attached to them. The authors show how comets have spurred some of the great discoveries in the history of science and raise intriguing questions about these brilliant visitors from the interstellar dark. Were the fates of the dinosaurs and the origins of humans tied to the wanderings of a comet? Are comets the building blocks from which worlds are formed? Lavishly illustrated with photographs and specially commissioned full-color paintings, Comet is an enthralling adventure, indispensable for anyone who has ever gazed up at the heavens and wondered why. Praise for Comet "Simply the best." —The Times of London "Fascinating, evocative, inspiring." —The Washington Post "Comet humanizes science. A beautiful, interesting book." —United Press International "Masterful . . . science, poetry, and imagination." —The Atlanta Journal & Constitution

Tom Van Flandern's book adds a new dimension to cosmology--not only does it present a novel approach to timeless issues, it stands up to the closest scientific scrutiny. Even the most respected scientists today will readily admit that the Big Bang Theory is full of holes. But it takes a new look, like Dark Matter, Missing Planets, and New Comets, to explain not only why the theory is wrong but what to substitute in its place. If you are curious about such things as the nature of matter and the origin of the solar system, but feel inadequately equipped to grasp what modern science has to say about such things, read this book. You will not get the all too common condescending attempt to water down the `mysteries' of modern science into a form intelligible to little non scientist you, but rather a straightforward new theory, logically derived in front of your eyes, which challenges the roots of many of today's complex accepted paradigms, yet whose essence is simple enough to be thoroughly communicated to the intelligent layman without "losing it in the translation."

Although the Earth was formed, together with the other planets, at the birth of the solar system, geological activity has since erased all but a hint of the processes that accompanied its formation. If we wish to explore the processes that occurred in the earliest solar system, and the nature of the environment in which they took place, we must turn to the record contained in more primitive material. Many meteorites appear to satisfy that criterion, and much effort has been applied during the past twenty years or so in identifying those meteorites, or their constituents, that have retained a reliable record of the early solar system. This book provides a synthesis of what has been learned so far about the earliest stages of solar system history through the study of meteorites, and what, given our current level of understanding, remains to be learned. Contents 1. Introduction 2. Source Regions 3. Secondary Processing 4. Irradiation Effects 5. Solar System Chronology 6. Chondrites and the Early Solar System 7. Elemental Composition of Chondrites 8. Magnetic Fields in the Early Solar System 9. Chondrules10. Primitive Material Surviving in chondrites11. Micrometeorites12. Inhomogencity of the Nebula13. Survival of Presolar Material in Meteorites14. Nucleosynthesis15. Nucleocosmochronology16. Summary