The Effects of Melt on Impact Craters on Icy Satellites and on the Dynamics of Io's Interior
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The Effects of Melt on Impact Craters on Icy Satellites and on the Dynamics of Io's Interior Item Type text; Electronic Dissertation Authors Elder, Catherine Margaret 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 19:33:28 Link to Item http://hdl.handle.net/10150/556825 THE EFFECTS OF MELT ON IMPACT CRATERS ON ICY SATELLITES AND ON THE DYNAMICS OF IO’S INTERIOR by Catherine Margaret Elder 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 2015 2 THE UNIVERSITY OF ARIZONA GRADUATE COLLEGE As members of the Dissertation Committee, we certify that we have read the disser- tation prepared by Catherine Margaret Elder, titled The effects of melt on impact craters on icy satellites and on the dynamics of Io’s interior and recommend that it be accepted as fulfilling the dissertation requirement for the Degree of Doctor of Philosophy. Date: 7 April 2015 Adam Showman Date: 7 April 2015 Shane Byrne Date: 7 April 2015 Isamu Matsuyama Date: 7 April 2015 Alfred McEwen Date: 7 April 2015 Randy Richardson Final approval and acceptance of this dissertation is contingent upon the candidate’s submission of the final copies of the dissertation to the Graduate College. I hereby certify that I have read this dissertation prepared under my direc- tion and recommend that it be accepted as fulfilling the dissertation requirement. Date: 7 April 2015 Dissertation Director: Adam Showman 3 STATEMENT BY AUTHOR This dissertation has been submitted in partial fulfillment 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 acknowledgment 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: Catherine Margaret Elder 4 ACKNOWLEDGEMENTS First, I thank my advisor, Adam Showman, for all his help and career advice over the years. Adam is always excited about science with an enthusiasm that few professors have, so meeting with him to discuss my research was always fun. In addition to Adam, I would like to thank Shane Byrne and Christopher Hamilton for mentoring and helping me navigate the search for a postdoc position. Thanks to Randy Richardson for always being the person on my committee to step back and ask what I need to do next to continue making progress. And thanks to Alfred McEwen and Isamu Matsuyama for providing many useful suggestions and helping me see the implications of my research in a broader context. I would also like to thank my other co-authors. Most recently, Paul Tackley, who taught me how to use his mantle convection code and helped me interpret the results. Thanks to Jay Melosh and Veronica Bray who were my first advisors when I started graduate school. Veronica in particular worked closely with me on the project and encouraged me to develop career skills such as writing proposals and reviewing papers. My path to LPL started at Cornell where I was welcomed into the planetary science community by the faculty and the graduate students. The graduate students treated me as a peer and gave me a glimpse into what grad school would be like. They are still some of the people I most look forward to seeing at conferences. Among the faculty, I would especially like to thank Jim Bell for helping me select classes, summer internships, and ultimately a grad school. He also led the first geology trip I ever attended where I saw an impact crater and volcanoes for the first time. Also thanks to all my physics buddies at Cornell who made problem sets a lot more fun and do-able. While in grad school, I have been lucky enough to have the support of many friends near and far. I thank them all for their support and making life more fun. In particular, I would like to thank the LPL grad students who were here at the same time as me for their advice, camaraderie, and friendship. Finally, I would like to thank my family: my sister, Jean, for her friendship and support, and my parents. I am very thankful that my parents believed me when I was nine years old and told them that I wanted to be an astronomer when I grew up. They bought me a telescope even though light pollution in Boston is terrible, gave me astronomy books, and took me to ‘Astronomy day’ at the Boston Museum of Science every year. And Casey, who I met early in grad school and who has been my main source of moral support and encouragement since then. I am so happy that whether I have a good day or a bad day, I always get to go home to Casey and the cats. 5 DEDICATION To my parents, who always encouraged my interest in astronomy. 6 TABLE OF CONTENTS LISTOFFIGURES ................................ 9 LISTOFTABLES ................................. 11 ABSTRACT .................................... 12 CHAPTER1 Introduction ........................... 14 1.1 Planetaryheatloss ............................ 14 1.1.1 Mantleconvection. 15 1.1.2 MarsandtheMoon........................ 16 1.1.3 Earth ............................... 17 1.1.4 Venus ............................... 17 1.1.5 Io.................................. 18 1.2 Surface processes as a window to the interior . .... 19 1.2.1 Surface expression of mantle convection . 20 1.2.2 Crater morphology as a probe of the subsurface . 21 1.3 Mapofthedissertation. 23 CHAPTER 2 The theoretical plausibility of central pit crater formation via meltdrainage .................................. 24 2.1 Introduction................................ 24 2.2 Meltvolume................................ 25 2.3 Fracturevolumeestimate. 28 2.4 Meltdrainage ............................... 31 2.4.1 Fracturedistribution . 32 2.4.2 Drainage through plane parallel fractures . 33 2.5 Results................................... 41 2.6 Discussion ................................. 46 2.6.1 Differences between rock and ice . 46 2.6.2 Limitationsandassumptions. 47 2.6.3 The role of viscous dissipation . 50 2.6.4 Mars................................ 51 2.6.5 Othericysatellites . 51 2.7 Conclusions ................................ 54 7 TABLE OF CONTENTS – Continued CHAPTER 3 Melt migration in Io’s convecting mantle . .... 56 3.1 Introduction................................ 56 3.2 Themodel................................. 61 3.2.1 Meltsegregation . .. .. 61 3.2.2 Convective scaling laws . 65 3.2.3 Melt segregation and convection . 71 3.3 Results................................... 72 3.4 Discussion ................................. 80 3.4.1 ComparisontoEarth . 80 3.4.2 Comparisontoobservations . 83 3.5 Conclusions ................................ 84 CHAPTER 4 Convection in Io’s partially molten mantle . ..... 86 4.1 Introduction................................ 86 4.2 Model ................................... 90 4.2.1 Rheology ............................. 92 4.2.2 Composition............................ 93 4.2.3 Meltinganderuption . 93 4.2.4 Tidalheating ........................... 96 4.3 Results................................... 97 4.3.1 Statisticalsteadystatebehavior . 97 4.3.2 Tidal heating distribution . 105 4.3.3 Eruptionparameterization . 106 4.3.4 Influence of reference viscosity . 108 4.3.5 Influence of permeability . 109 4.3.6 Heatingrate............................ 110 4.4 Discussion ................................. 112 4.5 Conclusion................................. 118 CHAPTER 5 Comparison of the one-dimensional model and the two- dimensional numerical simulations . 120 5.1 Directcomparison............................. 120 5.2 Convective scaling laws . 122 5.3 Meltmigrationmodel. 126 5.4 SummaryofComparison . 128 CHAPTER 6 Conclusions and Future Work . 130 6.1 Centralpitcraterformation . 130 6.2 DynamicsofIo’smantle . 132 8 TABLE OF CONTENTS – Continued 6.2.1 Melt generation and migration in an upwelling column of man- tleonIo.............................. 133 6.2.2 Mantle convection in Io’s partially molten mantle . .... 134 6.2.3 Comparison of results to observations . 135 REFERENCES................................... 137 9 LIST OF FIGURES 2.1 Isiscentralpitcrater . 24 2.2 Asketchofcentralpitcraterformation . 26 2.3 Widthsofimpactgeneratedfractures . 34 2.4 Asketch ofmelt drainagethroughfractures . 36 2.5 Dependence of drainage velocity on fracture width . ...... 38 2.6 Solidification dependence on initial temperature . ....... 44 2.7 Fractured, melted, drained and observed pit volumes . ...... 45 2.8 Volume of melt able to drain on different bodies . 46 2.9 Volumeofslushabletodrain . 47 2.10 Volume of melt able to drain on different icy satellites . ........ 52 2.11 Volume of melt generated on different icy satellites . ....... 52 3.1 AsketchofIo’smantle . .. .. 60 3.2 Radialprofilesforthenominalcase . 74 3.3 Radial profiles for 25% eruption efficiency . 80 3.4 The effect