The Moon in the Post-Apollo Era

232 Pages·1974·10.94 MB·English

by  Zdeněk Kopal (auth.)

THE MOON IN THE POST-APOLLO ERA
GEOPHYSICS AND
ASTROPHYSICS MONOGRAPHS
AN INTERNATIONAL SERIES OF FUNDAMENTAL TEXTBOOKS
Editor
B. M. MCCORMAC, Lockheed Palo Alto Research Laboratory, Palo Alto, Calif., U.S.A.
Editorial Board
R. GRANT ATHA Y, High Altitude Observatory, Boulder, Colo., U.S.A.
P. J. COLEMAN, JR., University o/California, Los Angeles, Calif., U.S.A.
D. M. HUNTEN, Kitt Peak National Observatory, Tucson, Ariz., U.S.A.
C. DE JAGER, The Astronomical Institute at Utrecht, Holland
J. KLECZEK, Czechoslovak Academy 0/ Sciences, OndTejov, Czechoslovakia
R. LiisT, Institutfor Extraterrestrische Physik, Garching-Miinchen, F.R.G.
R. E. MUNN, Meteorological Serviceo/Canada, Toronto, Ont., Canada
z. SVESTKA, American Science and Engineering, Cambridge, Mass., U.S.A.
G. WEILL, Institut d'Astrophysique, Paris, France
VOLUME 7
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A
THE MOON
IN THE
POST-APOLLO ERA
by
ZDENEK KOPAL
University of Manchester, England
D. REIDEL PUBLISHING COMPANY
DORDRECHT-HOLLAND / BOSTON-U.S.A.
Library of Congress Cataloging in Publication Data
Kopal, Zdenek, 1914-
The Moon in the post-Apollo era.
(Geophysics and astrophysics monographs; v. 7)
Includes bibliographies and index.
1. Moon I. Title. II. Series.
QB581.K595 559.9'1 74-26877
ISBN -13 :978-90-277-0278-4 e-ISBN -13 :978-94-010-2101-2
DOl: 10.1007/978-94-010-2101-2
Published by D. Reidel Publishing Company,
P.O. Box 17, Dordrecht, Holland
Sold and distributed in the U.S.A., Canada, and Mexico
by D. Reidel Publishing Company, Inc.
306 Dartmouth Street, Boston,
Mass. 02116, U.S.A.
All Rights Reserved
Copyright © 1974 by D. Reidel Publishing Company, Dordrecht, Holland
No part of this book may be reproduced in any form, by print, photoprint, microfilm,
or any other means, without written permission from the publisher
TABLE OF CONTENTS
PREFACE VII
Chapter 1 Exploration of the Moon by Spacecraft 1
Chapter 2 Manned Exploration: Apollo (1969-1972) 52
Chapter 3 Basic Facts: Distance, Size and Mass 77
Chapter 4 Shape and Gravitational Field of the Moon 82
Chapter 5 Internal Structure of the Moon 96
Chapter 6 Morphology of Lunar Formations 111
Chapter 7 Surface Structure and Chemical Composition 143
Chapter 8 Stratigraphy and Chronology of the Lunar Surface 171
Chapter 9 Lunar Exosphere 185
Chapter 10 Origin and Evolution of the Moon 197
NAME INDEX 221
PREFACE
The aim of the present book will be to summarize the results of the space exploration
of the Moon in the past fifteen years - culminating in the manned Apollo missions of
1969-1972 - on the background of our previous acquaintance with our satellite made
in the past by astronomical observations at a distance.
Astronomy is one of the oldest branches of science conceived by the inquisitive
human mind; though until quite recently it had been debarred from the status of a
genuine experimental science by the remoteness of the objects of its study. With the
sole exception of meteoritic matter which occasionally finds its way into our labora
tories, all celestial bodies could be investigated only at a distance: namely, from the
effects of attraction exerted by their mass, or from the ciphered messages of their light
carried by nimble-footed photons across the intervening gaps of space.
A dramatic emergence oflong-range spacecraft - capable of carrying men with their
instruments not only outside the confines of our atmosphere, but to the actual surface
of our nearest celestial neighbour - has since 1957 thoroughly changed this time
honoured picture. In particular (as we shall detail in Chapter 1 of this book) space
astronomy ofthe Moon is barely 15 years old. But relative infant as it is by age, it has
already provided us with such a tremendous amount of new and previously inacces
sible scientific data as to virtually revolutionalize our subject. The aim of this book
will be to provide their digest which could be read with understanding - and, I hope,
interest - on the part of the more general reader.
It is not for the first time that the present writer addressed himself to this topic in
recent years. In particular, his Introduction to the Study of the Moon (D. Reidel Publ.
Company, Dordrecht, 1966) went through the press when the first Surveyor landed
on the Moon, and is now out of date as well as out of print. Its second edition of 1969
(hereafter referred to as the Moon II) is, however, still available, and contains much
astronomical background information which need not be repeated in this book. On
the other hand, only most cursory results of the first Apollo landing could have been
mentioned in its text at page-proof stage; and in this respect its contents are likewise
out of date. To make good this shortcoming, in the present volume attention will be
focussed primarily on the results of the lunar manned missions completed between
1969-1972. This is the first book in which this will be done; and our aim will be to
incorporate these results with all our previous knowledge into a coherent picture of
astronomy, physics, chemistry as well as geology or mineralogy of our only natural
satellite.
At first sight, the difficulties inherent in such a task appear formidable. Where so
VIII PREFACE
many perplexing questions from different scientific disciplines are to be brought into
the common focus, no single expert can speak ex cathedra to all. Brash young
Alexanders of the past are known to have tackled some of our knottiest problems by
brutal force. The present writer cannot - alas - compete in such gymnastics, if alone
because of advancing years; and cannot, likewise, embark on a synthesis of relevant
facts and reasonable theories otherwise than by availing himself - at least partly - of
second-hand knowledge.
To amass this knowledge proves by itself a matter of some difficulty. The volume
of new data acquired in the field oflunar research since 1969 is simply tremendous -
seldom in the annals of science do we encounter a comparable 'explosion of informa
tion'. To give some examples, the published Proceedings of the four annual Houston
Lunar Science Conferences, alone exceeded 10000 printed pages of original contribu
tions; and the Moon journal published since 1969 over 4000 pages of additional
literature. To integrate all this information into a single coherent picture constitutes
a task which will take many years for its accomplishment. The present little book
constitutes the first limited attempt at such an integration - made by an astronomer
for whom the Moon is only a part of the solar system. It iS,moreover, almost inevitable
that not all workers in other fields concerned with lunar studies will agree with the
choice of the facts presented in a volume of this size, let alone with their interpreta
tion. But this is only natural; and the whole book was indeed written to this end; for
it is only by sustained efforts to gauge the full meaning of all new information which
was so suddenly thrust upon us that its implications, not only for the Moon and its
past, but also for the origin of the entire solar system can eventually be caught in our
grasp.
CHAPTER 1
EXPLORATION OF THE MOON BY SPACECRAFT
If under the term of 'space astronomy' we understand investigations which must be
carried out above the main mass of the terrestrial atmosphere, then space astronomy
of the Moon is barely 15 years old. Before giving a brief account of its development
and accomplishments during this time, however, let us first answer the question:
why do we need to investigate the Moon from space?
In lifting instruments for any kind of astronomical observations from the ground
to above the main atmospheric air mass (in practice, to 200 km or higher), we aim
at freeing ourselves from two limitations imposed by it: namely, its absorption (which
prohibits transmission to ground of a very large part of the entire spectrum of extra
terrestrial light sources); and its turbulence (which causes the index of refraction to
fluctuate along the line of sight, and thus 'spoils our seeing'). For many types of
astronomical work both these obstacles are of comparable importance; but in lunar
studies the second one is of paramount significance.
The atmospheric absorption itself restricts lunar ground-based work but little;
for most part of the sunlight scattered by the Moon passes through the 'optical
window' of transmission of our atmosphere between 3000-10000 A without much
change. The thermal radiation of the Moon itself occurs mainly in the near infrared.
However, its maximum emission at daylight temperatures happens to fall within the
8-12 Jl. infrared window offair atmospheric transparency, so that its direct measure
ments are again possible from the ground; and only at lunar nighttime does lunar
thermal emission migrate towards longer wavelengths which no longer penetrate
the atmosphere. In the transition region of near infrared between wavelengths of
1-5 J1., the spectrum of the Moon has recently been traced with the aid of balloons
(cf. Wattson and Danielson, 1965). On the other hand, in the ultraviolet (below the
limit of atmospheric ozone absorption) the lunar reflectivity becomes again so low
(cf. Lebedinsky et al., 1967a, b) that not much can be learned from observations in
this domain even at altitudes from which such observations can be made.
While, therefore, terrestrial atmospheric absorption does not restrict ground-based
lunar work in any essential respect, the atmospheric turbulence causing 'bad seeing'
is a very different matter. In actual fact, the optical effects of ever-present turbulence
seldom permit ground-based telescopes with apertures in excess of20 inches to attain
the resolution permissibly by geometrical optics; and the smallest details on the lunar
surface actually discernible by our terrestrial telescopes from the distance of the
Earth are seldom less than half a kilometre in size.
For the first 200 years oflunar astronomy, atmospheric degradation of images was
2 THE MOON IN THE POST-APOLLO ERA
of but secondary concern to the observers wrestling with the optical and mechanical
imperfections of their instruments. Technology marched on, however, and the stage
at which the 'atmospheric seeing' became the limiting factor was reached some time
around the turn of this century. It set off an exodus of the old astronomical obser
vatories away from large cities - an exodus which by now has almost been completed
- but by itself this move proved to be a mere temporary expedient. By now - in the
Fig. 1.1. A schematic view of the Russian space station (Luna 3) which photographed for the first time
the far side of the Moon on 7 October 1959 (U.S.S.R. Acad. Sci. photograph).