Effects of airbursts on the surface of Venus Item Type text; Dissertation-Reproduction (electronic) Authors Wood, David Allen Publisher The University of Arizona. Rights Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. Download date 26/09/2021 00:16:46 Link to Item http://hdl.handle.net/10150/289162 INFORMATION TO USERS This manuscript has t>een reproduced from the microfilm master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be from any type of computer printer. The quality of this reproduction is dependent upon the quality of the copy submitted. 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Bell & Howell Informatton arxJ Learning 300 North Zeeb Road, Ann Arbor, Ml 48106-1346 USA 800-521-0600 EFFECTS OF AIRBURSTS ON THE SURFACE OF VENUS by David Allen Wood, Jr. A Dissertation Submitted to the Faculty of the DEPARTMENT OF PLANETARY SCIENCES In Partial Fulfillment of the Requirements For the Degree of DOCTOR OF PHILOSOPHY In the Graduate College THE UNIVERSITY OF ARIZONA 2000 UMf Number 9983856 UMII® UMI Mjcrofomi9983856 Copyright 2000 by Bell & Howell Infomiation and Learning Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. Bell & Howell Information and Leaming Company 300 North Zeeb Road P.O. Box 1346 Ann Arbor, Ml 48106-1346 2 THE UNIVERSITY OF ARIZONA « GRADUATE COLLEGE As members of the Final Examination Committee, we certify that we have read the dissertation prepared bv David Allen Wood, Jr. entitled Effects of Airbursts on the Surface of Venus and recommend that it be accepted as fulfilling the dissertation requirement for the Degree of Doctor of Philosoohv G. Robe«t G. Strom Datete f . ^/u/a d Date , ^ Titao thy D.Wind^ Dace // 4-U-) kxt i-cosi "andall M. Richardson Date C. Wallace Date Final approval and acceptance of this dissertation is contingent upon the candidate's submission of the final copy of the dissertation to the Graduate College. I hereby certify that I have read this dissertation prepared under my direction and recommend that it be accepted as fulfilling the dissertation requirement. (k. Dissertation Director Robert G. Strom D*" STATEMENT BY AUTHOR This dissertation has been submitted in partial fulfiUment of requirements for an advanced degree at The University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library. Brief quotations from this dissertation are allowable without special permission, provided that accurate acknowledgement of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his or her judgment the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from the author. SIGNED. David A. Wood, Jr. , ACKNOWLEDGEMENTS Over the course of your life, you encounter so many people who help shape you and mold you into the person you eventually become. That is why acknowledgements are so difficult to write. Invariably, some one of imi>ortance gets left off such a list, so I issue in advance my humblest apologies to those I don't mention here by name. I want you all to know how very grateful I am for all of the support and encouragement I've received throughout my life. Let me start by thauiking the members of my conmiittee who have given me the benefit of the doubt in trying times. I have done my best and I hope your faith in me has not been misplaced. Thanks especially to Bob Strom and Jay Melosh who devoted special attention to me in the last semester as I worked to fmish. Your patience with me is greatly appreciated. Thanks also go to Jay for providing much needed advice and assistance with the hydrocode simulations. Thanks also to Mike Drake for providing me with an RA so that I could devote all of my energy to this. Many thanks go to Hal Larson, Tim Swindle, and David Hough who gave me unique opportunities to grow and develop as both an undergraduate and a graduate student. These gentlemen are all wonderful mentors. I also want to thank other mentors I have had in the course of my education. Brother Jim Burkholder inspired me in physics, Mr. David Casanova made chemistry personal, and Ms. Donna DeLire fueled my passion for pure mathematics. Had I not been on a science track already, I would have switched because of these fabulous teachers. To my friends, Clark, Janet, and Suzann, I can say only that I am so honored and privileged to have met you. You have been truly loyal fnends, and my life has been enriched because of you. Let me also mention Brad, Kirstin, Heather, Jeni, Marc, Brian, Jim, Celinda, and Pete. Thank you all for the fnendships I have enjoyed with each of you during my stay here. Finally, I am so blessed to have the greatest family in the world. Thank you Mom and Dad, Jeff, Leisha, Bryan and Lindsay, Laurie and Josh, Tim, Lissa and John, and Pam for all the great times I had growing up. To Grandma Wood, Grandma and Grandpa Savary, Gaki, and all of my aunts, uncles, and cousins, it is always a treat to spend time with you. I hope I've made you all proud. To my nephews, Seth, Michael, and Caleb, life will always throw challenges in your path, and no matter how difficult those challenges become, I know you will rise up to meet them. Finally, let me give a very special thank you to Uncle Don for a very difficult favor he provided. DEDICATION For my parents David and Cynthia Wood 6 TABLE OF CONTENTS LIST OF ILLUSTRATIONS 9 LIST OF TABLES 16 ABSTRACT 17 1. THE PROBLEM 18 1.1 INTRODUCTION 18 1.2 IMPACT CRATERING ON AIRLESS SURFACES 19 1.3 IMPACT CRATERING IN THE PRESENCE OF AN ATMOSPHERE 21 1.4 VENUS: A NATURAL LABORATORY FOR IMPACT STUDIES 25 1.5 MAGELLAN SYNTHETIC APERTURE RADAR (SAR) IMAGING 27 1.6 MOTIVATING THE PROBLEM 30 1.7 PRELUDE 34 2. ANALYSIS OF CIRCULAR RADAR ALBEDO FEATURES 35 2.1 INTRODUCTION 35 2.2 SPLOTCHES 36 2.3 DISRUPTED SPLOTCHES 44 2.4 CRATER HALOES 46 2.5 RELATIONSHIPS BETWEEN IMPACT FEATURES 46 2.5.1 Comparing Craters to Haloes 48 2.5.2 Comparing Haloes to Splotches 48 2.6 TERRAIN EFFECTS 68 2.7 SUMMARY 88 3. A HISTORY OF THE PROBLEM 92 3.1 SETTING THE SCENE 92 3.2 AIRBURSTS 93 3.3 SURFACE DAMAGE 94 3.4 EVOLUTION OF ZAHNLE'S CRUSHING MODEL 95 3.5 ALTERNATIVE MODELS 97 3.5.1 Back Venting 97 3.5.2 Parabaloidal Bowshock Model 99 3.5.3 Parabola Degradation Model 100 3.5.4 Impactor Debris Model 101 3.6 THE NEXT STEP 103 7 TABLE OF CONTENTS - CONT 4. THE MODEL 105 4.1 THE UNMODIFIED CRUSHING MODEL 105 4.2 AIRBURSTS 105 4.3 STRONG SHOCK WAVES IN THE VENUSIAN ATMOSPHERE 111 4.3.1 Propagation of Strong Shock Waves 113 4.3.2 Shock Waves Reflected From a Rigid Surface 115 4.3.3 Effects of Airburst Altitude on Shock Reflection 118 4.4 ROCK FRAGMENTATION 120 4.5 WIND TRANSPORT OF SMALL PARTICLES 123 4.6 AIRBURST SCAR MODELS 129 4.6.1 Crushing and Breaking Rock 129 4.6.2 Crushing and Scouring 133 4.6.3 Back Venting 135 4.6.4 Fireball 136 4.6.5 Base Surge 137 4.7 MODEL SYNTHESIS 138 4.8 SUMMARY 140 5. HYDROCODE SIMULATIONS 142 5.1 THE ORIGIN OF HYDROCODES 142 5.2 THE SALE HYDROCODE 143 5.2.1 The Hydrocode Mesh 144 5.2.2 SALE in Lagrangian Mode 144 5.2.3 SALE in Eulerian Mode 145 5.2.4 Artificial Viscosity 146 5.2.5 Alternate Node Coupler 148 5.3 SIMULATING AN AIRBURST 148 5.3.1 The Venusian Atmosphere 149 5.3.2 The Airburst 151 5.3.3 Simulation Conditions 152 5.4 RESOLUTION STUDIES 153 5.4.1 Mesh Size 153 5.4.2 Maximum Time Step 154 5.4.3 Artificial Viscosity 161 5.4.4 Comparison to the Sedov Solution 164 5.5 SUMMARY 168 6. MODEL AND DATA COMPARISONS 169 6.1 METHODS OF ANALYSIS 169 6.2 AIRBURST SIMULAHONS 169 6.3 HYDROCODE SIMULATIONS 177 8 TABLE OF CONTENTS - CONT 6.3.1 Relationship Between Pressure and Radial Wind Velocity 178 6.3.2 Pressures in Rock 188 6.3.3 Radial Wind Velocities 198 6.4 RADII OF DARK AND BRIGHT AIRBURST SCARS 201 6.4.1 Effect of Rarefaction Wind on Dark Region Size 203 6.4.2 Radii of Bright Regions 207 6.4.3 Comparison of Bright and Dark Radii 208 6.5 RANGE OF IMPACTOR SIZES 212 6.6 LIFETIMES OF AIRBURST SCARS 214 6.6.1 Aeolian Redistribution Rate 216 6.6.2 Lifetimes of Radar-Bright Regions 217 6.6.3 Lifetimes of Radar-Dark Regions 218 6.6.4 Estimating the Number of Airbursts Over Time 222 6.7 SUMMARY AND IMPLICATIONS OF CRUSHING AND SCOURING 223 6.8 PROBLEMS WITH THE CRUSHING AND SCOURING MODEL 226 6.9 EXPANDING HORIZONS 228 7.