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Planets have excited the minds of man since prehistory. In our own time planetary science has become a rapidly developing area of astronomical research, as the instruments carried by spacecraft have vastly increased our knowledge of planetary surfaces and interiors. the rocky planets of the inner solar system bear countless craters, scars of their encounters with innumerable meteorites, although the active surface of the earth has contrived to erase these features from our own planet. The outer giants, particularly Jupiter, have vigorous atmospheres, while Io, a satellite of Jupiter, has sulphur volcanoes. In this book Alan Cook explains how the mechanical properties of the planets are determined, how planetary materials behave at high pressure, and how celestial mechanics and the quantum physics of highly condensed matter may be combined to determine the general constitution of the planets.
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Cambridge Planetary Science Series Editors: W.I.Axford, G.E.Hunt, T.O. Mutch
Interiors of the planets
A. H. COOK Jacksonian Professor of Natural Philosophy, University of Cambridge
Interiors of the planets
CAMBRIDGE UNIVERSITY PRESS Cambridge London
New York
Melbourne
Sydney
New Rochelle
CAMBRIDGE UNIVERSITY PRESS Cambridge, New York, Melbourne, Madrid, Cape Town, Singapore, Sao Paulo, Delhi Cambridge University Press The Edinburgh Building, Cambridge CB2 8RU, UK Published in the United States of America by Cambridge University Press, New York www.cambridge.org Information on this title: www.cambridge.org/9780521106016 © Cambridge University Press 1980 This publication is in copyright. Subject to statutory exception and to the provisions of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press. First published 1980 This digitally printed version 2009 A catalogue record for this publication is available from the British Library ISBN 978-0-521-23214-2 hardback ISBN 978-0-521-10601-6 paperback
FOR ISABELL
The works of the Lord are great, sought out of all them that take pleasure therein.' From Psalm 111; carved over the entrance to the Cavendish Laboratory
CONTENTS
1 2 3 4 5 6 7 8 9 10
Foreword Note on the expression of planetary masses Introduction The internal structure of the Earth Methods for the determination of the dynamical properties of planets Equations of state of terrestrial materials The Moon Mars, Venus and Mercury High pressure metals Jupiter and Saturn, Uranus and Neptune Departures from the hydrostatic state Conclusion Appendix 1 Limits and conditions on planetary models Appendix 2 Combination of effects of small departures from a uniform distribution of density Appendix 3 The physical librations of the Moon References Index
ix xi 1 16
51 88 132 171 199 237 273 302 309 318 319 324 343
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FOREWORD
The planets, which have always been objects of wonder and curiosity to those with the opportunity or need to lift their eyes to the heavens, now in our times shine with new and strange lights revealed to us by the far seeing instruments carried upon space craft. The Moon, Mars, Venus and Mercury all bear on their surfaces the crater scars of innumerable meteorites that have fallen upon them from the beginning of the solar system. The Earth alone has an active surface that has obliterated those scars. Thefluidsurface of Jupiter is in constant and vigorous motion, driven by heatflowingout from the interior or, it may be, brought to it by the ultra-violet radiation from the Sun or by the solar wind. The Medicean satellites of Jupiter now'present to us strange and individual faces: would Galileo who first saw the mountains on the Moon or the spots on the Sun have been s