Physics and Chemistry of the Solar System

John S. Lewis

• Publisher: Academic Press
• Year: 2004
• Print ISBN: 9780124467446
• eBook ISBN: 9780080470122
• Edition: 2
• Topic: Physical Sciences
• Subtopic: Astronomy & Astrophysics

Physics and Chemistry of the Solar System, 2nd Edition, is a comprehensive survey of the planetary physics and physical chemistry of our own solar system. It covers current research in these areas and the planetary sciences that have benefited from both earth-based and spacecraft-based experimentation. These experiments form the basis of this encyclopedic reference, which skillfully fuses synthesis and explanation. Detailed chapters review each of the major planetary bodies as well as asteroids, comets, and other small orbitals. Astronomers, physicists, and planetary scientists can use this state-of-the-art book for both research and teaching. This Second Edition features extensive new material, including expanded treatment of new meteorite classes, spacecraft findings from Mars Pathfinder through Mars Odyssey 2001, recent reflections on brown dwarfs, and descriptions of planned NASA, ESA, and Japanese planetary missions.* New edition features expanded treatment of new meteorite classes, the latest spacecraft findings from Mars, information about 100+ new discoveries of planets and stars, planned lunar and planetary missions, more end-of-chapter exercises, and more* Includes extensive new material and is amply illustrated throughout* Reviews each major planetary body, asteroids, comets, and other small orbitals

I

Introduction

Nature and Scope of the Planetary Sciences

When asked in an interview to give his viewpoint on the frontiers of science, the famous physicist Victor Weisskopf commented that the most exciting prospects fell into two categories, the frontier of size and the frontier of complexity. A host of examples come to mind: cosmology, particle physics, and quantum field theory are clearly examples of the extremes of scale, and clearly among the most exciting frontiers of science. Biology, ecology, and planetary sciences are equally good examples of the frontier of complexity.

When we peruse the essential literature of planetary science, we find that we must, over and over again, come face to face with these same extremes. First, we are concerned with the origin and nuclear and chemical evolution of matter, from its earliest manifestation as elementary particles through the appearance of nuclei, atoms, molecules, minerals, and organic matter. Second, on the cosmic scale, the origin, evolution, and fate of the Universe emerge as themes. Third, we are confronted with the problem of understanding the origin and development of life. In each case, we are brought face to face with the spontaneous rise of extreme complexity out of extreme simplicity, and with the intimate interrelationship of the infinitesimally small and the ultimately large.

Further, our past attempts at addressing these three great problems have shown us that they are remarkably intertwined. The very issue of the origin of life is inextricably tied up with the chemistry of interstellar clouds, the life cycles of stars, the formation of planets, the thermal and outgassing history of planetary bodies, and the involvement of geochemical processes in the origin of organic matter. The connection between life and planetary environments is so fundamental that it has been given institutional recognition: it is not widely known outside the field, but research on the origin of life in the United States is a mandate of the National Aeronautics and Space Administration.

Wherever we begin our scientific pilgrimage throughout the vast range of modern science, we find ourselves forced to adopt ever broader definitions of our field of interest. We must incorporate problems not only on the frontier of complexity, but also from both extreme frontiers of scale. In this way, we are compelled to trespass across many hallowed disciplinary boundaries.

Further, as we seek an evolutionary account of the emergence of complexity from simplicity, we become able to see more clearly the threads that lead from one science to another. It is as if the phenomena of extreme scale in physics existed for the express purpose of providing a rationale for the existence of astronomy.

The other disciplines evolve logically from cosmic events:

The astronomical Universe, through the agency of nuclear reactions inside stars and supernova explosions, populates space with atoms of heavy elements, which are the basis of chemistry.

The course of spontaneous chemical evolution of interstellar matter produces both mineral grains and organic molecules, giving rise to geochemistry and organic chemistry.

Solid particles accrete to form large planetary bodies, and give us geology.

Radioactive elements formed in stellar explosions are incorporated into these planets, giving life to geophysics.

Melting, density-dependent differentiation, and outgassing take place, and atmospheres and oceans appear: petrology, meteorology, and oceanography become possible.

Organic matter is formed, accumulated, concentrated, and processed on planetary surfaces, and biology is born.

Planetary science may then be seen as the bridge between the very simple early Universe and the full complexity of the present Earth. Although it partakes of the excitement of all of these many fields, it belongs to none of them. It is the best example of what an interdisciplinary science should be: it serves as a unifying influence by helping to dissolve artificial disciplinary boundaries, and gives a depth and vibrancy to the treatment of evolutionary issues in nature that transcends the concerns and the competence of any one of the parent sciences. But there is more: planetary science is centrally concerned with the evolutionary process, and hence with people’s intuitive notion of “how things work.” There is as much here to unlearn as there is to learn.

We, at the turn of the millennium, still live under the shadow of the clockwork, mechanistic world view formulated by Sir Isaac Newton in the 17th century. Even the education of scientists is dedicated first and foremost to the inculcation of attitudes and values that are archaic, dating as they do from Newton’s era: viewpoints that must be unlearned after sophomore year. We are first led to expect that the full and precise truth about nature may be extracted by scientific measurements; that the laws of nature are fully knowable from the analysis of experimental results; that it is possible to predict the entire course of future events if, at one moment, we should have sufficiently detailed information about the distribution and motion of matter. Quantum mechanics and relativity are later taught to us as a superstructure on Newtonian physics, not vice versa. We must internally turn our education upside down to accommodate a universe that is fundamentally quantum-mechanical, chaotic, and relativistic, within which our “normal” world is only a special case.

All of these issues come to bear on the central question of the evolution of the cosmos and its constituent parts. Most of us have had a sufficient introduction to equilibrium thermodynamics to know that systems spontaneously relax to highly random, uninteresting states with minimum potential energy and maximum entropy. These are the classical conclusions of J. Willard Gibbs in the 19th century. But very few of us are ever privileged to hear about the development of nonequilibrium thermodynamics in the 20th century, with its treatment of stable dissipative structures, least production of entropy, and systems far removed from thermodynamic equilibrium. Think of it: systems slightly perturbed from equilibrium spontaneously relax to the dullest conceivable state, whereas systems far from equilibrium spontaneously organize themselves into structures optimized for the minimization of disorder and the maximization of information content!

It is no wonder that the whole idea of evolution is so magical and counterintuitive to so many people, and that the critics of science so frequently are able to defend their positions by quoting the science of an earlier century. We often hear expressed the idea that the spontaneous rise of life is as improbable as that a printshop explosion (or an incalculable army of monkeys laboring at typewriters) might accidentally produce an encyclopedia. But have we ever heard that this argument is obsolete nonsense, discredited by the scientific progress of the 20th century? Sadly, there is a gap of a century between the scientific world view taught in our schools and the hard-won insights of researchers on the present forefront of knowledge. The great majority of all people never learn more than the rudiments of Newtonian theory, and hence are left unequipped by their education to deal with popular accounts of modern science, which at every interesting turn is strikingly non-Newtonian. News from the world of science is, quite simply, alien to them. The message of modern science, that the Universe works more like a human being than like a mechanical wind-up toy, is wholly lost to them. Yet it is precisely the fundamental issues of how things work and how we came to be, what we are and what may become of us, that are of greatest human interest. The “modern” artist or writer of the 20th century often asserted modernity by preaching the sterility of the Universe and the alienation of the individual from the world. But this supposed alienation of the individual from the Universe is, to a modern scientist, an obsolete and discredited notion.

The problems of evolutionary change and ultimate origins are not new concerns. Far from being the private domain of modern science, they have long been among the chief philosophical concerns of mankind. Astronomy and astrology were the parents of modern science. The earliest human records attest to mankind’s perpetual fascination with origins:

Who knows for certain and can clearly state

Where this creation was born, and whence it came?

The devas were born after this creation,

So who knows from whence it arose?

No one knows where creation comes from

Or whether it was or was not made: Only He who views it from highest heaven knows; Surely He knows, for who can know if He does not?

Rigveda × 129.6–7

Circa 3000 BC

Such an attitude, reflective of curiosity, inquiry, and suspended belief, is admirably modern. But today, in light of the exploration of the Solar System, we need no longer regard our origins as complete mysteries. We can now use the observational and theoretical tools of modern science to test rival theories for their faithfulness to the way the Universe really is. Some theories, when tested by the scientific method, are found to give inaccurate or even blatantly wrong descriptions of reality and must be abandoned. Other theories seem to be very reliable guides to how nature works and are retained because of their usefulness. When new data arise, theories may need to be modified or abandoned. Scientific theories are not absolute truth and are not dogma: they are our best approximation of truth at the moment. Unlike dogma, scientific theories cannot survive very long without confronting and accommodating the observed facts. The scientific theories of today are secondary to observations in that they are invented—and modified—by human beings in order to explain observed facts. They are the result of an evolutionary process, in which the “most fit” theories (those that best explain our observations) survive. In planetary science, that process has been driven in recent years in part by the discovery and study of several new classes of bodies both within our Solar System and elsewhere. It is the great strength of science (not, as some allege, its weakness) that it adapts, modifies, and overturns its theories to accommodate these new realities. Our plan of study of the Solar System mirrors this reality.

This book will begin with what little we presently know with confidence about the earliest history of the Universe, and trace the evolution of matter and its constructs up to the time of the takeover of regulatory processes on Earth by the biosphere. We introduce the essential contributions of the various sciences in the order in which they were invoked by nature, and build complexity upon complexity stepwise. Otherwise, we might be so overawed by the complexity of Earth, our first view of nature, that we might despair of ever gaining any understanding at all.

This approach should also dispel the notion that we are about to understand everything. It is quite enough to see that there are untold vistas for exploration, and more than enough of the Real to challenge our most brilliant intellects and most penetrating intuitions.

Let us approach the subject matter covered herein with the attitude that there are a number of fundamental principles of nature, of universal scope, that allow and force the evolutionary process. With our senses at the most alert, willing to entertain the possibility of a host of hypotheses, and determined to subject all theories and observations alike to clos...

Table of contents

• Cover image
• Title page
• Table of Contents
• Front Matter
• Copyright page
• Dedication
• Foreword
• Chapter I: Introduction
• Chapter II: Astronomical Perspective
• Chapter III: General Description of the Solar System
• Chapter IV: The Sun and the Solar Nebula
• Chapter V: The Major Planets
• Chapter VI: Pluto and the Icy Satellites of the Outer Planets
• Chapter VII: Comets and Meteors
• Chapter VIII: Meteorites and Asteroids
• Chapter IX: The Airless Rocky Bodies: Io, Phobos, Deimos, the Moon, and Mercury
• Chapter X: The Terrestrial Planets: Mars, Venus, and Earth
• Chapter XI: Planets and Life around Other Stars
• Chapter XII: Future Prospects
• Appendix I: Equilibrium Thermodynamics
• Appendix II: Absorption and Emission of Radiation by Quantum Oscillators
• Appendix III: Exploration of the Solar System
• Appendix IV: Basic Physical Constants*
• Appendix V: Gravity Fields
• Suggested Readings
• Index
• International Geophysics Series