Comets In The Post Halley Era

In Part Based on Reviews Presented at the 121st Colloquium of the International Astronomical Union, held in Bamberg, Germany, April 24-28, 1989

Comets are always very impressive phenomena. Their appearances at regular, but mostly irregular, times excite people who see them. Astronomers have the obvious advantage of being able to see more of comets, and to study them. Their enthusiasm is reflected in the 50 papers in this book, written by more than 90 experts. The reviews in this book clearly describe a landmark in the history of cometary studies. Knowledge gathered up to and including Comet Halley are presented in two volumes. The first volume is about general aspects of observing and studying comets, where they originate and how their evolution develops. The second volume goes into the details of what a comet is: the nucleus, the coma, cometary dust, plasmas and magnetic fields. The book ends with a reflection by Fred Whipple about Comets in the Post-Halley Era. The book discusses all aspects of comets and is therefore suitable for use in graduate level courses. All astronomers and geophysicists interested in comets will find very useful and well-presented information in this book.

Comets are always very impressive phenomena. Their appearances at regular, but mostly irregular, times excite people who see them. Astronomers have the obvious advantage of being able to see more of comets, and to study them. Their enthusiasm is reflected in the 50 papers in this book, written by more than 90 experts. The reviews in this book clearly describe a landmark in the history of cometary studies. Knowledge gathered up to and including Comet Halley are presented in two volumes. The first volume is about general aspects of observing and studying comets, where they originate and how their evolution develops. The second volume goes into the details of what a comet is: the nucleus, the coma, cometary dust, plasmas and magnetic fields. The book ends with a reflection by Fred Whipple about Comets in the Post-Halley Era. The book discusses all aspects of comets and is therefore suitable for use in graduate level courses. All astronomers and geophysicists interested in comets will find very useful and well-presented information in this book.

In 1993, the U.S. Department of Defense declassified information dealing with frequent explosions in the upper atmosphere caused by meteoric impact. It is estimated that impacts have occurred of a magnitude equivalent to the atomic bomb detonated at Hiroshima. Not all such space voyagers meet their end in the atmosphere, however; huge craters attest to the bombardment of earth over millions of years, and a major impact may have resulted in the extinction of dinosaurs. An impact in Siberia near the beginning of this century proves that such events are not confined to geologic time. Hazards Due to Comets and Asteroids marks a significant step in the attempt to come to grips with the threats posed by such phenomena. It brings together more than one hundred scientists from around the world, who draw on observational and theoretical research to focus on the technical problems related to all aspects of dealing with these hazards: searching for and identifying hazardous comets and asteroids; describing their statistics and characteristics; intercepting and altering the orbits of dangerous objects; and applying existent technologies—rocket boosters, rendezvous and soft-landing techniques, instrumentation—to such missions. The book considers defensive options for diverting or disrupting an approaching body, including solar sails, kinetic-energy impacts, nuclear explosives, robotic mass drivers, and various propulsion systems. A cataclysmic impact posing a threat to life on Earth is a possibility that tomorrow's technology is capable of averting. This book examines in depth the reality of the threat and proposes practical measures that can be initiated now should we ever need to deal with it.

Since 1967. the most prominent events of a General Assembly of the International Astronomical Union are published in a separate volume. The Highlights of Astronomy (volume 9) report on the major scientific presentations made at the XXIst General Assembly July 23-August 1. 1991. Buenos Aires. Argentina. The present volume contains the texts of the three invited Di scourses and of the papers presented duri ng seven Joi nt Discussion Meetings and eight Joint Commission Meetings. The invited Discourses were arranged by the IAU Executive Committee and the Joint Discourses and Commission Meetings by the respective chairpersons. The overall responsability of the General Assembly was carried out by the IAU General Secretary (19B8-1991). Dr. D. McNally. I am indebted to the authors of the invited Di scourses. to the organi zers and editors of the scientific sessions for having provided me with all the material for publication in due time. I want to particularly acknowledge the case with which Dr. J.H. Hughes. who unfortunately died a few days ago from cancer. prepared and checked unti 1 the 1 ast few weeks the report on the new IAU Reference System. This report itself concludes long and difficult discussions among IAU members that he led in a wise and clear sighted manner.

THE MEETING The IAU Symposium 160 ASTEROIDS COMETS METEORS 1999 has been held at Villa Carlotta in Belgirate, on the shore of Lago Maggiore (Italy), from June 14 to June 18, 1993. It has been organized by the Astronomical Observatory of Torino and by the Lunar and Planetary Institute of Houston. It has been a very large meeting, with 323 registered participants from 38 countries. The scientific program included 29 invited reviews, 106 oral communications, and 215 posters. The subjects covered included all the aspects of the studies of the minor bodies of the solar system, including asteroids, comets, meteors, meteorites, interplanetary dust, with special focus on the interrelationships between these. The meeting was structured as follows. 5 morning plenary sessions have been devoted to invited reviews on: (1) search programs (2) populations of small bodies (3) dynamics (4) physical observations and modelling (5) origin and evolution. Two afternoon plenary sessions have been devoted to space missions to small bodies and to interrelationships between the different populations. The afternoon parallel sessions have been devoted to: dynamics of comets; Toutatis, Ida, Gaspra; physical processes in cometary comae and tails; meteorites; the cosmogonic message from cometary nuclei; physics of asteroids; the interplanetary dust complex; comet nuclei; meteors; composition and material properties of comets; dynamics of asteroids.

The IAU symposium No. 150 "Astrochemistry of Cosmic Phenomena" was held at the beautiful and scenic town of Campos do Jordao, Sao Paulo, Brazil from August 5 to 9, 1991, and was attended by 111 registered participants with 17 accompanied guests from 19 countries. The symposium had a wide ranging discussion of the chemistry of astronomical environments with an emphasis on the description of molecular processes that critically influence the nature and evolution of astronomical objects and the identification of specific observations that directly address significant astronomical questions. The subject areas of the symposium included atomic and molecular processes at low and high temperatures and photon interactions, the chemical structure of molecular clouds in the Milky Way and in external galaxies, the chemistry of outflows and their interactions with the interstellar medium, the chemical connections between the interstellar medium and the solar system and pregalactic chemistry. The scientific programme comprised of review talks and con tributed papers, with a general introduction by Professor A. Dalgarno and a final overview of the whole symposium by Professor D. A. Williams. Financial supports from the Sao Paulo State Foundation Support (FAPESP), Brazilian National Research Council(CNPq), Finance Company of Studies and Projects (FINEP), Institute of Astronomy and Geophysics of University of Sao Paulo (IAG-USP) and Inter national Astronomical Union (IAU) are greatfully acknowledged. I am greatly indebted to Professor A.

Minor bodies in the Solar System, though representing only a small fraction of the mass in the Solar System, may well play a fundamental role in terrestrial evolution. This book contains investigations of the dynamics and physics of comets, asteroids and meteor streams, and the rather controversial topic of periodic phenomena in the Solar System as signified by geological records, together with several associated developments in celestial dynamics. All these problems are interwoven. This book makes a contribution towards unravelling the nature of the interactions between the Earth and its celestial environment.