Some Aspects Of The Dynamical History Of The Earth Moon System

The age-old question of how our home planet and its satellite originated has in recent times undergone a minor revolution. The emergence of the "giant impact theory" as the most successful model for the origin of the Moon has been difficult to reconcile with some aspects of the Earth, and the development of an integrated model for the origin of the Earth-Moon system has been difficult for this reason. However, recent technical advances in experimental and isotopic work, together with intensified interest in the modeling of planetary dynamics, have produced a wealth of new results requiring a rethinking of models for the origin of the Earth and Moon. This book is intended to serve as a resource for those scientists working closely in this field, while at the same time it provides enough balance and depth to offer an introduction for students or technically minded general readers. Its thirty chapters address isotopic and chemical constraints on accretion, the dynamics of terrestrial planet formation, the impact-triggered formation of the Earth-Moon system, differentiation of the Earth and Moon, the origin of terrestrial volatiles, and conditions on the young Earth and Moon. Covering such subjects as the history and origin of the Moon's orbit, water on the Earth, and the implications of Earth-Moon interactions for terrestrial climate and life, the book constitutes a state-of-the-art overview of the most recent investigations in the field. Although many advances have been made in our ability to evaluate competing models of the formation of the Earth-Moon system, there are still many gaps in our understanding. This book makes great strides toward closing those gaps by highlighting the extensive progress that has been made and pointing toward future research.

Since the beginning of civilization, the origins of the Earth and Moon have been the subjects of continuing interest, speculation, and enquiry. These are also among the most challenging of all scientific problems. They are, perhaps to a unique degree, interdisciplinary, having attracted the attention of philosophers, astronomers, mathematicians, geologists, chemists, and physicists. A large and diverse literature has developed, far beyond the capacity of individuals to assimilate adequately. Consequently, most of those who attempt to present review-syntheses in the area tend to reflect the perspectives of their own particular disciplines. The present author's approach is that of a geochemist, strongly influenced by the basic phil osophy of Harold Urey. Whereas most astronomical phenomena are controlled by gravitational and magnetic fields, and by nuclear interactions, Urey (1952) emphasized that the formation of the solar system occurred in a pressure-temperature regime wherein the chemical properties of matter were at least as important as those of gravitational and magnetic fields. This was the principal theme of his 1952 book, "The Planets," which revolutionized our approach to this subject. In many subsequent papers, Urey strongly emphasized the importance of meteorites in providing critical evidence of chemical conditions in the primordial solar nebula, and of the chemical fractionation processes which occurred during formation of the terrestrial planets. This approach has been followed by most subsequent geochemists and cosmochemists.

The Earth-Moon neighborhood is the scene of a large variety of applications that concern asteroids, lunar exploration and space debris in Earth orbit. In particular, recent efforts by the scientific community have focused on the possibility of extending the human operations beyond the radiation belts; of exploiting in-situ resources, either on the lunar surface or on asteroids retrieved to the vicinity of the Earth; and of mitigating the space debris concern by taking advantage of the lunar perturbation. The characteristic dynamics in the cislunar space represents an opportunity for the mission designer, but also a challenge in terms of theoretical understanding and operational control. This Research Topic covers the Earth-Moon dynamics in its complexity and allure, considering the most relevant aspects for both natural and artificial objects, in order to get a new comprehension of the dynamics at stake along with the operational procedures that can handle it.

P. Brosche The development of the ideas and observational techniques related to the subject of our meeting "Tidal friction and the Earth's rotation", Bielefeld, September 1977 is one of the most fascinating books - not merely chapters! - of the modern history of science. Its genealogical tree is as intricate as that of mankind itself: There are dead ends and superfluous re-discoveries. Due to these circumstances and to the pure extent of the topic, it is impossible to give more than a few highlights here. The first relevant observational fact was discovered by the famous English astronomer E. Halley in 1695 (Berry, 1961). He simply could not arrive at an agreement between ancient and recent eclipses using a constant mean angular motion of the Moon. Instead, he had to introƯ duce an empirical acceleration term in the mean motion. Known as the "secular acceleration", it has ever since been a most challenging subƯ ject of celestial mechanics and a main branch of the genealogical tree already mentioned. In 1754, completely independently and almost certainly in ignorance of those specialists' activities, the German philosopher Kant established the idea of tidal friction as a decelerating mechanism for the rotation of the Earth (Felber, 1974). Although he made some errors in his rough computations, the majority of the constitutive elements of his concept have survived to the present day (Brosche, 1977).

The origin of the Moon remains an unsolved problem of the planetary science. Researchers engaged in celestial dynamics, geophysics, and geochemistry are still discussing various models of creation of our closest cosmic neighbour. The most popular scenario, the impact hypothesis involving a collision early in the Earth's history, has been substantially challenged by the new data. The birth and development of a planet-moon system always plays a role in the formation of an entire planetary system around our Sun or around another star. This way, the story of our Moon acquires broader ramifications for one of the hottest topics of the modern scholarship. All this has motivated the authors of this book to consider a new concept and to compare the currently discussed theories, analyzing their advantages and shortcomings in explaining the experimental data.

Where did we come from? Before there was life there had to be something to live on - a planet, a solar system. During the past 200 years, astronomers and geologists have developed and tested several different theories about the origin of the solar system and the nature of the Earth. Together, the three volumes that make up A History of Modern Planetary Physics present a survey of these theories. The early twentieth century saw the replacement of the Nebular Hypothesis with the Chamberlain-Moulton theory that the solar system resulted from the encounter of the Sun with a passing star. Fruitful Encounters follows the eventual refutation of the encounter theory and the subsequent revival of a modernised Nebular Hypothesis. Professor Brush also discusses the role of findings from the Apollo space programme, especially the analysis of lunar samples, culminating in the establishment, in the 1980s, of the 'giant impact' theory of the Moon's origin.

This book is devoted to the problems that occur when attempting to understand and construct a concise representation of the original conditions, composition and dynamics of the evolution of the Earth-Moon system in the form in which it is seen today. This volume will perhaps contribute to a better understanding of what is necessary to research the dynamics of the Solar system.

On January 20-21, 1964, the Institute for Space Studies of the Goddard Space Flight Center, National Aeronautics and Space Administration, was host to an international group of astronomers, physicists, and Earth scientists, gathered to discuss the Earth-Moon system. This was the sixth in a continuing series of interdisciplinary meetings on topics in space physics held at the Institute. The conference was organ ized by G.J.F. MacDonald, of the University of California at Los Angeles, and by R.H. Dicke, of Princeton University. The working title of the conference was "The Dynamics of the Earth-Moon System," and indeed much of the contents of this proceedings volume is concerned with dynamical problems, but the conference dealt with many other topics concerning the Earth-Moon system, and hence we have adopted the shorter title for this volume. The conference proceedings have been somewhat rear·· ranged from the order in which the papers were actually presented. In doing this the editors are exercising hindsight to bring together closely related discussions. The first paper, by D. Brouwer, discusses the motions and moments of inertia of the Moon and their relation to the lunar figure and composition. From this discussion it emerges there remain many uncertainties in the motion of the Moon associated with the lunar composition and the distribution of its mass.