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PLANETARY
SCIENCES
American and Soviet Research
Edited by
Thomas M. Donahue
with
Kathleen Kearney Trivers
David M. Abramson
Proceedings from the US-USSR Workshop
on
PlanetaIy Sciences
January 2-6, 1989
Academy of Sciences of the Union of Soviet Socialist Republics
National Academy of Sciences of the United States of America
National Academy Press
Washington, D.C. 1991
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NOTICE: The project that is the subject of this report was approved by the officers of the
National Academy of Sciences and the Academy of Sciences of the USSR on January 12, 1988. The
members of the committee responsible for the report were chosen for their special competences and
with regard for appropriate balance.
This report has been reviewed by a group other than the authors according to procedures
approved by a Report Review Committee consisting of membem of the National Academy of
Sciences, the National Academy of Engineering, and the Institute of Medicine.
The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distin-
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and technology and to their use for the general welfare. Upon the authority of the charter granted to
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on scientific and technical matters. Dr. Frank Press is president of the National Academy of Sciences.
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associate the broad community of science and technology with the Academy's purposes of furthering
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are chairman and vice chairman, respectively, of the National Research Council.
Library of Congress Catalog Card No. 90-62812
International Standard Book Number 0-309-04333-6
Copies of this report are available from:
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National Research Council
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Washington, D.C. 20418
Additional copies are for sale from:
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S216
Printed in the United States of America
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Foreword
The Academy of Sciences of the USSR and the National Academy
of Sciences of the United States of America sponsored a workshop on
Planetary Sciences at the Institute for Space Research in Moscow, January
2-6, 1989. The purpose of the workshop, which was attended by Soviet and
American scientists, was to examine the current state of our theoretical
understanding of how the planets were formed and how they evolved to
their present state. The workshop assessed the type of observations and
experiments that are needed to advance understanding of the formation and
evolution of the solar system based on the current theoretical framework
In the past, models of the formation and evolution of the planets have
been just that, models. They essentially portrayed possibilities: that events
could have transpired in the way depicted without violating any known
constraints and that, if they did take place, certain consequences would
follow. Now, we may be advancing beyond that stage to the point where it
may be possible to settle fairly definitely on certain scenarios and exclude
others. Assessment of the present state of theories and the observational
base will help determine the extent to which this is the case.
This workshop focused on the present status of observational and
theoretical understanding of the clearing of stellar nebulae, planetesimal
formation, and planetary accretion; the evolution of atmospheres; the rela-
tionship of still existing primitive bodies to these topics; and the relationship
of ground-based and in situ measurements.
As the papers presented at the workshop and published in this volume
show, astronomical observations are now at hand that will reveal the
sequence of events occuring in circumstellar disks with sufficient precision
to define the models of planetary formation. Moreover, theories for the
origin of the solar system have reached a point where it is now possible,
. . .
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indeed it is essential, to examine them in the broader context of the origins
of planetary systems. Until recently, it has not been possible to select among
a range of feasible scenarios the one that is most likely to be correct, in
the sense that it satisfies observational and theoretical constraints. We are
now advancing to that stage.
Similarly, theories for the formation of planetary atmospheres are
becoming more sophisticated and respond to an increasingly complex set
of observational data on relative abundance of atmospheric species and the
state of degassing of the interior of the Earth. But, as the papers presented
here will demonstrate, there is still a way to go before all the questions are
resolved.
The topics discussed at this workshop were timely, and the debate and
discussion were full and informative. The participants learned a great deal,
and the scientific basis for cooperation in planetary sciences was strength-
ened appreciably. The Soviet hosts extended their usual thoughtful and
gracious hospitality to the American delegation, and the entire experience
was memorable and rewarding.
T.M. Donahue
Chairman, NAS/NRC Committee on
Cooperation with the USSR on
Planetary Science
1V
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Contents
FOREWORD
Thomas M. Donahue
ACKNOWLEDGEMENTS
1. THE PROPERTIES AND ENVIRONMENT OF PRIMITIVE
SOLAR NEBULAE AS DEDUCED FROM OBSERVATIONS
OF SOLAR-TYPE PRE-MAIN SEQUENCE STARS
Stephen E. Strom, Susan Edwards, Karen M. Strom
2. NUMERICAL TWO-DIMENSIONAL CALCULATIONS
OF THE FORMATION OF THE SOLAR NEBULA
Peter H. Bodenheimer
3. THREE-DIMENSIONAL EVOLUTION OF EARLY SOLAR
NEBULA
Alan ]? Boss
FORMATION AND EVOLUTION OF THE
PROTOPLANETARY DISK
Tamara ~ Ruzmaikina and RIB. Makalkin
5. PHYSICAL CHEMICAL PROCESSES IN A PROTO-
PLANETARY CLOUD
Avgusta K Lavrakbina
vii
. . .
111
v
1
17
31
44
61
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6. MAGNETOHYDRODYNAMIC PUZZLES IN THE
PROTOPLANETARY NEBULA
Eugene H. Levy
7. FORMATION OF PLANETESIMALS
Stuart] Weidenschilling
8. FORMATION OF THE TERRESTRIAL PLANETS FROM
PLANETESIMALS
George ~ Wetherill
9. THE RATE OF PLANET FORMATION AND
THE SOLAR SYSTEM'S SMALL BODIES
Motor S. Safronov
10. ASTROPHYSICAL DUST GRAINS IN STARS, THE INTER-
STELLAR MEDIUM, AND THE SOLAR SYSTEM
Robm D. Gehrz
11. LATE STAGES OF ACCUMULATION AND
EARLY EVOLUTION OF THE PLANETS
Audrey ~ Amazed and G.~ Pechemikova
12. GIANT PLANETS AND THEIR SATELLITES: WHAT ARE
THE RELATIONSHIPS BETWEEN THEIR PROPERTIES
AND HOW THEY FORMED?
David ~ Stevenson
13. THE THERMAL CONDITIONS OF VENUS
Vladimir 1V Zharkov and V.S. Solomatov
14. DEGASSING
James C. G. Walker
15. THE ROLE OF IMPACTING PROCESSES IN THE
CHEMICAL EVOLUTION OF THE ATMOSPHERE
OF PRIMORDIAL EARTH
Lev Al Mukhin and M.~ Gerasimov
16. LITHOSPHERIC AND ATMOSPHERIC INTERACTION
ON THE PLANET VENUS
Vla~lislav ~ Molkov
.. .
V111
70
82
98
116
126
143
163
174
191
203
218
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17. RUNAWAY GREENHOUSE ATMOSPHERES:
APPLICATIONS TO EARTH AND VENUS
James ~ Hasting
18. THE OORT CLOUD
Leonid S. Marochnik, Lev M. Mukhin, and Roald Z. Sagdeev
19. THE CHAOTIC DYNAMICS OF COMETS AND THE
PROBLEMS OF THE OORT CLOUD
Roald Z. Sagdeev and G.M. Zaslavskiy
234
246
259
20. PROGRESS IN EXTRA-SOLAR PLANET DETECTION 270
Robert ~ Brown
APPENDIX I
List of Participants
APPENDIX II
List of Presentations
IX
289
292
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