The Origin and Evolution of the Solar System

Author: M. M. Woolfson

Published in: Institute of Physics Publishing

ISBN: 0-7503-0458-8

File Type: pdf

File Size:  6 MB

Language: English


Since the time of Newton the basic structure of the solar system and the laws that govern the motions of the bodies within it have been well understood. One central body, the Sun, containing most of the mass of the system has a family of attendant planets in more-or-less circular orbits about it. In their turn some of the planets have accompanying satellites, including the Earth with its single satellite, the Moon. With improvements in telescope technology, and more recently through space research, knowledge of the solar system has grown apace. Since the time of Newton three planets have been discovered and also many additional satellites. A myriad of smaller bodies, asteroids and comets, has been discovered and a vast reservoir of comets, the Oort cloud, stretching out half way towards the nearest star has been inferred. Spacecraft reaching out into the solar system have revealed in great detail the structures of all the types of bodies it contains—the gas giants, terrestrial planets, comets, asteroids and satellites, both with and without atmospheres. At the same time observations of other stars have revealed the existence of planetary-mass companions for some of them.

This suggests that theories must address the origin of planetary systems in general and not just the solar system. Observations of young stars have shown that many are accompanied by a dusty disk and it is tempting to associate these disks with planet formation. In attempting to find a plausible theory the theorist has available not only all the observations to which previous reference has been made above but also a knowledge of the basic laws of physics, particularly those relating to conservation. It turns out that finding a theory consistent with both observation of the spins and orbits of solar system bodies and conservation of angular momentum is difficult, and has proved to be an unresolved problem for some current theories. In this respect it can be said that for some theories the post-Newtonian knowledge is irrelevant since an explanation of the origin of even the basic simple system, as known to Newton, has not been found.

The Origin and Evolution of the Solar Syste book describes the four major theories that have been under development during the last two or three decades: the Proto-planet Theory, the Capture Theory, the Modern Laplacian Theory and the Solar Nebula theory, and gives the main theoretical basis for each of them. Also discussed, but not so fully, is the Accretion Theory, an older model of solar-system formation with some positive features. These theories are examined in detail to determine the extent to which they provide a plausible mechanism for the origin of the solar system and their strengths and weaknesses are analysed. The only theory to essay a complete picture of the origin and evolution of the solar system is the Capture Theory developed by the author and colleagues since the early 1960s. This explains the basic structure of the solar system in terms of well-understood mechanisms that have a finite probability of having occurred. The way in which planets form, and the way that their orbits originate and evolve according to the Capture Theory, suggests the occurrence of a major catastrophic event in the early solar system.
This event was a direct collision between two early planets, in terms of which virtually all other features of the solar system, many apparently disparate, can be explained. As new knowledge about the solar system has emerged so it has lent further support to this hypothesis.

There is a tendency in areas of science like cosmogony for a ‘democratic principle’ to operate whereby the theory that has the greatest effort devoted to it becomes accepted, without question and examination, by many people working in scientific areas peripheral to the subject. These individuals, highly respected in their own fields, swell the numbers of the apparently-expert adherents and, by a positive feedback mechanism, they enhance the credibility of the current paradigm—which is the Solar Nebula Theory in this case. Science writers and those producing radio and television programmes, accepting the verdict of the majority, produce verbal and visual descriptions of an evolving nebula that, if they were to illustrate any scientific principle at all, would be illustrating the invalid principle of the conservation of angular velocity. In scientific television programs material is seen spiralling inwards to join a central condensation having jettisoned its angular momentum in some mysterious fashion on the way in. Computer graphics are not constrained by the petty requirements of science !The ‘democratic principle’ is not necessarily a sound way to determine the plausibility of a scientific theory and there are many examples in the history of science that tell us so. The geocentric theory of the solar system, the phlogiston  theory of burning and the concept of chemical alchemy were all ideas that persisted for long periods with the overwhelming support of the scientific community of the time.

The aim of this book has been to present the underlying science as simply as possible without trivializing or distorting it in any way. None of the important science is difficult—indeed most of it should be accessible to a final-year pupil at school. It is hoped that this book will enable those both inside and outside the community of cosmogonists to use their own judgement to assess the plausibility, or otherwise, of the theories described. For those wishing to delve more deeply into the subject many references are provided. I must give special thanks to my friend and colleague, Dr John Dormand, for help and very useful discussions during the writing of this book. Gratitude is also due to Dr Robert Hutchison for providing illustrations of meteorites.
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