THE PHYSICAL AND CHEMICAL PROPERTIES OF THE SURFACE OF VENUS by Stewart David Nozette B.S. The University of Arizona (1979) SUBMITTED TO THE DEPARTMENT OF EARTH AND PLANETARY SCIENCES IN PARTIAL FULFILLMENT OF THE REQUIREMENTS OF THE DEGREE OF DOCTOR OF PHILOSOPHY AT THE MASSACHUSETTS INSTITUTE OF TECHNOLOGY November 1982 @ MASSACHUSETTS INSTITUTE OF TECHNOLOGY 1982 Signature of Author .. .. D&epartment of rth and Planetary Sciences November 2, 1982 . Certified by. lJohn Lewis, Thesis Supervisor Certified by. ordon Pettengill, Th is Supervisor Accepted by . Ted Madden Chairman, Department Committee MASSACHUSETTS INSTITUTE OF TECHNOLOSY MAR 14 1993 AchieS I IRRARIES THE PHYSICAL AND CHEMICAL PROPERTIES OF THE SURFACE OF VENUS by Stewart David Nozette Submitted to the Department of Earth and Planetary Sciences on November 2, 1982, in Partial Fulfillment of the Requirements of the Degree of Doctor of Philosophy ABSTRACT Exoerimental studies of aeolian transport on Venus, using a scale-modeling technique, indicate that observed surface winds are sufficient to move sedimentary particles of about 0.3 mm or less in diameter. Measurements of radar reflectivity indicate that portions of the surface are covered by material with low bulk density, possibly wind-blown sediments. Transport of chemically weathered material by wind may also affect the local composition of the lower atmosphere. The buffering of atmospheric gases in some regions of the surface is only Possible for a restricted mineral assemblage. Radar determination of the surface dielectric constant by the Pioneer Venus radar mapper for at least one area of the surface, Theia Mons, suggests that the surface contains conductive material, probably iron sulfides. Laboratory measurements of the dielectric constants of terrestrial sulfide bearing rocks indicate that sulfide inclusions present at 15% by weight Provide a good match to the dielectric constant inferred for Theia Mons. Theia Mons and other high-dielectric constant areas could be a source of sulfur bearing compounds previously suggested to explain the composition of the clouds of Venus. In this thesis one possible model for geochemical transport is presented, transport of weathering products from high to low elevation. However, we are still ignorant of the relative importance of this Process, and of the possible existence of others. Further insight into the physical and chemical nature of Venus will have to await more detailed exploration by spacecraft and laboratory investigation of chemical weathering. Thesis Supervisors: John S. Lewis Title: Professor of Planetary Science Gordon H. Pettengill Professor of Planetary Physics ACKNOWLEDGEMENTS I must acknowledge many people who played a crucial role in the preparation of this thesis. I would like to express my gratitude to all members of my thesis committee, especially John Lewis and Gordon Pettengill, for their guidance and attention to this work. I must also express extreme gratitude to Peter Ford for his unique talents, and thorough understanding and tutelage, of the various aspects of the Pioneer Venus radar data reduction. I would also like to thank Eric Eliason, for his brief tour through the land of image processing, and for supplying the images used in my thesis. I must also thank John Southard for providing a reasonable experiment to study aeolian transport on Venus. I also thank M. B. Fegley and Ron Prinn for enlightening discussions. In addition, I must thank W. Westphal for aid in dielectric measurements. It would be impossible to mention all of the individuals responsible for the success of the Pioneer Venus Project, which supplied the data that form the basis of this thesis. Therefore, I would like to extend my gratitude to all members of the Pioneer Project, both at NASA Ames, and NASA Headquarters, especially Larry Colin and Henry Brinton. I would also like to thank Laurel Wilkening, and Geoff Briggs, for their encouragement in a time of rapidly changing direction for the U.S. space program. Most importantly, I would like to extend my warmest appreciation to my parents, Morris and Helen Nozette, for their unyielding support through the tough times, and ups and downs of the NASA planetary program. More than anything, this thesis is a product of their support. My gratitude is also extended to Mr. Francis Doughty, Ms. Barbara Langford, and to Ms. Dorothy Frank for typing and preparing the thesis. TABLE OF CONTENTS Page I. Introduction 8 II. Interaction Between Atmosphere and Surface A. Purpose 12 B. Structure of the Venus Atmosphere 12 C. Composition of the Venus Atmosphere 21 D. Composition of the Venus Surface 39 1. Venera Landings 39 E. Chemical Weathering on Venus 48 1. Methodology of Study 48 2. Variation of Weathering Over the Surface for Idealized and 55 Petrologically Realistic Reactions 3. Kinetic Effects 73 F. Conclusions and Directions for Future Work 77 III. Radar Investigation A. Background 79 B. Earth Based Radar Observations 1. Arecibo 81 2. Goldstone 87 C. Pioneer Venus Radar Observations 1. Experiment Description and Operation 88 D. Pioneer Venus Radar Results 1. Global Altimetry and Roughness 90 2. Global Reflectivity 120 E. Dielectric Properties of Materials 1. Previous Work 126 2. Experimental Results 133 Page F. Conclusions and Directions for Future Work 137 IV. Aeolian Transport on Venus A. Previous Theoretical Studies 140 B. Types of Aeolian Features 142 C. Scaling Theory 143 1. Other Fluid Dynamical Considerations 146 2. Experimental Methods 147 3. Experimental Results 150 D. Conclusions and Directions for Future Work 157 VI. Appendices A. Thermodynamic Data 159 B. Macroscopic Properties of Dielectrics 161 C. Measurement of Dielectric Constants 163 VII. References 164 Table of Figures Figure Title Page 1. Temperature vVs. Altitude on Venus 16 2. Pressure vVs. Altitude on Venus 18 3. Comparison of Pioneer and Venera Temperature Profiles 18 4. Equilibrium Abundances of Sulfur Gas 33 5. Venus Sulfur Cycle 37 6. Composition of Various Solar System Rocks 43 7. Venera Surface Panoramas 45 8. Carbon-Dioxide Weathering Reactions 56 9. Water Weathering Reactions 59 10. Sulfur-Carbon Monoxide Equilibrium 62 11. Phlogopite Formation 66 12. Hydrogen Fluoride-Water Equilibrium 68 13. Hydrogen Chloride-Water Equilibrium 68 14. Altitude Dependence of Weathering 71 15. Arecibo Radar Image 85 16. Topography of Venus and Earth 92 17. Contours of Venus Topography 94 18. Earth Topography at Pioneer Venus Resolution 96 19. Detailed Topography 101 20. Pioneer Venus Radar Images 103 21. Pioneer Venus Hagfors' Constant Map 106 22. Detailed Topography of Maxwell Montes 108 23. Detailed Topography of Ishtar Terra 111 24. Topography of Diana Chasm 113 6 Figure Title Page 25. Detailed Topography of Beta Regio 118 26. Reflectivity of Venus 122 27. Reflectivity Vs. Roughness for Theia Mons and Sedna Planitia 124 28. Wind Tunnel Facility 148 29. Wind Transport of Sediment in Tunnel 155 List of Tables Table Title Page 1. Venus Spacecraft Exploration 11 2. Spectroscopic Water Abundance Determination 26 3. In Situ Water Abundance Determination 27 4. Sulfur Dioxide Abundance Determination 29 5. Venera Determination of Venus Surface Composition 47 6. Reactive Components of the Venus Atmosphere 52 7. Summary of Chemical Weathering Reactions 53 8. Dielectric Properties of Selected Rocks 128 I. Introduction In the first two and a half decades of space exploration no fewer than nineteen separate spacecraft have been launched toward Venus. In spite of this extensive exploration, our understanding of the Venus surface remains sketchy and incomplete. The harsh and challenging surface conditions, and the obscuring clouds, have hindered direct observation. Yet, some conclusions are possible. This work represents a compilation of previous knowledge about the nature of the Venus surface, integrated with new ideas. A synthesis is attempted of our knowledge about the surface-atmosphere interaction on Venus, including: spacecraft radar observation, laboratory investigation of the dielectric properties of rocks, theoretical speculation on the chemistry of Venus, and experimental studies of surface aeolian transport. Such a synthesis requires an approach in the true spirit of planetary science and exploration, combining physics and chemistry with astronautics and engineering. Unfortunately, there exist many gaps in our understanding of Venus. These gaps may remain for at least six years, due to a hiatus in Venus exploration by the United States. The present hiatus serves as a useful time to look back on what has been learned, and to devise some new theories which can help us understand our present data and offer predictions which may be tested in the future. NOW. The thesis is divided into three major sections. The first will review our current knowledge of the physical and chemical nature of the Venus atmosphere, and present some new ideas regarding the chemical interaction between atmosphere and surface with particular attention to using Pioneer Venus and Venera data in a model of chemical weathering on Venus. This section will address such questions as: what minerals are stable on which portions of the Venus surface, and what role does the surface play in regulating the composition of the Venus atmosphere? The second section will focus on physical studies of the Venus surface made by the Pioneer Venus radar mapper, though measurements of radar altitude, roughness, and dielectric constant which allow new speculations on the gross physical and chemical characteristics of a large