University of Arkansas, Fayetteville ScholarWorks@UARK Theses and Dissertations 12-2019 An Investigation of Metal Sulfides as the Source of the Low Emissivity Anomaly on the Highlands of Venus Sara Taeko Port University of Arkansas, Fayetteville Follow this and additional works at: https://scholarworks.uark.edu/etd Part of the Biogeochemistry Commons, Geology Commons, and the The Sun and the Solar System Commons Citation Port, S. T. (2019). An Investigation of Metal Sulfides as the Source of the Low Emissivity Anomaly on the Highlands of Venus. Theses and Dissertations Retrieved from https://scholarworks.uark.edu/etd/3479 This Dissertation is brought to you for free and open access by ScholarWorks@UARK. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of ScholarWorks@UARK. For more information, please contact [email protected]. An Investigation of Metal Sulfides as the Source of the Low Emissivity Anomaly on the Highlands of Venus A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Space and Planetary Sciences by Sara Taeko Port Stony Brook University Bachelor of Science in Astronomy/Planetary Science, 2014 Stony Brook University Bachelor of Science in Physics, 2014 December 2019 University of Arkansas This dissertation is approved for recommendation to the Graduate Council. _______________________________ __________________________________ Vincent Chevrier, PhD John Dixon, PhD Dissertation Director Committee Member _______________________________ __________________________________ Julia Kennefick, PhD Adriana Potra, PhD Committee Member Committee Member Abstract Since its detection in the 1960s the source of the unusual radar emissivity signal seen on several highlands on Venus has long eluded researchers. Researchers have determined that a mineral with a high dielectric constant could explain the signal. Using a Venus simulation chamber, we experimentally investigated this enigma to build upon the candidate mineral list that has been compiled over the last several decades. We tested the stability of 8 different minerals and elements at two to three different temperature/pressure regimes in three different gas mixtures meant to simulate the conditions found on Venus for a period of no less than 24 hours. These samples included: Bi/Te/S, Bi2S3/Bi2Te3, Bi2S3/3Te, Pb, PbO, PbS, PbSO4, and Fe7S8. The temperature/pressure regimes simulate the conditions found in the average lowlands, 460°C/95 bar, 4.5 km above the planetary radius, 425°C/75 bar, and 11 km above the planetary radius, 380°C/45 bar. The three tested gases were 100% CO2, 100 ppm of COS in CO2, and 100 ppm of SO2 in CO2. Samples were analyzed via XRD (X-ray Diffraction) and on occasion SEM/EDX (Scanning Electron Microscope/Energy-Dispersive X-ray spectroscopy) or XPS (X-ray Photoelectron Spectroscopy). Additional studies were completed at Okayama University in Japan where we modeled the effect of surface temperature on SO2 abundance and the elevation of the critical altitude (where the emissivity changes) if the source mineral was pyrite (FeS2). Our Bi/Te/S mixture experiments resulted in the formation of numerous minerals but tetradymite (Bi2Te2S) formed in every tested condition. Our lead experiments revealed that PbS and lead carbonates can form in the highland condition. Pyrrhotite was stable at all tested conditions. Our modeling results verified that surface temperature, SO2 abundance, and the critical altitude are all closely correlated. The data collected in this project can be used to better understand the near surface environment on Venus. It provides information on the surface-atmosphere reactions that occurs due to the different gases and temperatures/pressures on Venus. Most importantly, our data expands upon the mineral candidate list and identifies which minerals are stable and could perhaps explain the anomalous radar signal. ©2019 by Sara Taeko Port All Rights Reserved Acknowledgements The research completed in this project was funded by NASA Solar System Workings grant #NNX15AL57G. Additional funding was acquired from National Science Foundation: East Asia Pacific Summer Institutes program, the Japan Society for the Promotion of Science (JSPS), and by the Sturgis International Fellowship. I would like to thank my advisor, Dr. Vincent Chevrier, for all his support and for allowing me to work on this project. I would also like to thank my committee members Dr. John Dixon, Dr. Julia Kennefick, and Dr. Adriana Potra for their support and guidance throughout my graduate career. A special thank you to Walter Graupner for his invaluable insight and assistance while working at the University of Arkansas W.M. Keck Laboratory for Planetary Simulations. I would also like to thank Dr. George Hashimoto for allowing me to intern with him at Okayama University and for Dr. Toru Kouyama who found the opportunity for me. I would like to thank my undergraduate researchers, Austin Chase Briscoe and Alec Fitting for their assistance in the lab. A special thank you to Travis Garmon and Luis Morales for their helpful discussions, and Rachel Slank and Ellen Czaplinski for their assistance in preparing some of the chapters. I also greatly appreciated the use of the Arkansas Nano & Bio Materials Characterization Facility at the University of Arkansas which houses the MRD, Versaprobe, and the SEM/EDX used during this project. I would like to thank the faculty that work there (Dr. Andrian Kuchuk, Dr. Mourad Benamara, and Dr. Betty Martin) for all their help and kind words. I really enjoyed my time there. I would also like to thank the High Density Electronics Center (HiDEC) for allowing me to use their Rigaku XRD which was used to analyze several of my pyrrhotite samples. A special thank you to faculty at Los Alamos National Lab (Dr. Sam Clegg, Adriana Reyes-Newell, Dr. Nina Lanza, and Dr. Patrick Gasda) for analyzing my pyrrhotite samples using the ChemCam. Lastly, I would like to express my gratitude to all the reviewers for their invaluable insight and commentary on my papers. Dedication To my loving and supportive family as well as all my friends who helped and supported me during my time at Stony Brook University and The University of Arkansas. Thank you to my grandmother who ignited my love of science and my father who fostered it. Table of Contents Chapter 1: Introduction ………………………………………………………………………………...1 1.0 Introduction …………………………………………………………………………………..1 1.1 The Radar Reflective Anomaly on Venus ………………………………………..1 1.2 Research Background …………………………………………………………......8 1.2.1 Bismuth, Tellurium, and Sulfur …………………………………………8 1.2.2 Lead …………………………………………………………………......11 1.2.3 Pyrrhotite ………………………………………………………………..12 2.0 Dissertation ………………………………………………………………………………...14 2.1 Goals and Significance ……………………………………………………….…..14 2.2 Dissertation Outline ………………………………………………………….……16 3.0 Methods.…………………………………………………………………………………….16 3.1 Instruments ………………………………………………………………….……..16 3.2 Methodology ……………………………………………………………….………20 4.0 References.…………………………………………………………………………………24 Chapter 2: Investigation into the Radar Anomaly on Venus: The Effect of Venusian Conditions on Bismuth, Tellurium, and Sulfur Mixtures ....……………………………………29 1.0 Abstract.....………………………………………………………………………………….29 2.0 Introduction..………………………..………………………………………………………29 3.0 Methods/Materials………………………………………………………………………….34 4.0 Results………………………………………………………………………………………36 5.0 Discussion…………………………………………………………………………………..40 5.1 Effect of CO2 Gas………………………………………………………………….40 5.2 Effect of Mixed Gases……………….…………………………………………….43 5.3 Stability of Bi2S3, Bi2Te3, and Bi2Te2S……………………………………………44 5.4 Deposition onto the Highlands……………………………………………………47 6.0 Conclusion…………………………………………………………………………………..49 7.0 Acknowledgments………………………………………………………………………….50 8.0 References………………………………………………………………………………….51 Chapter 3: An Experimental Investigation into the Impact of Venusian Temperatures, Pressures, and Gases on Lead and Lead Minerals……………………………………………….55 1.0 Abstract……………………………………………………………………………………...55 2.0 Plain Language Summary…………………………………………………………………56 3.0 Introduction………………………………………………………………………………….56 4.0 Methods……………………………………………………………………………………..60 5.0 Results………………………………………………………………………………………63 5.1 Experiments Completed in 99.999% CO2………………………………….……63 5.2 Experiments Completed in CO2/SO2 and CO2/COS…………………….……..66 6.0 Discussion…………………………………………………………………………………..73 6.1 Experiments Completed in 99.999% CO2……………………………………….73 6.1.1 PbS……………………………………………………………………….73 6.1.2 Pb………………………………………………………………………...74 6.1.3 PbO………………………………………………………………………75 6.1.4 PbSO4………………………………….………………………………...77 6.2 Experiments Completed in CO2/SO2 and CO2/COS……………………………78 6.2.1 Pb………………………………………………………………………...78 6.2.2 PbO………………………………………………………………………79 6.2.3 Comparison Between the Mixed Gas Results………………………..80 6.3 Implications for Venus……………………………………………………………..83 7.0 Summary…………………………………………………………………………………….86 8.0 Acknowledgments………………………………………………………………………….87 9.0 References………………………………………………………………………………….87 10.0 Supplementary Materials…………………………………………………………………93 Chapter 4: Stability of Pyrrhotite under Experimentally Simulated Venus Conditions…….95 1.0 Abstract……………………………………………………………………….……………..95 2.0 Introduction………………………………………………………………….………………95 3.0 Methods……………………………………………………………………………………..99 4.0 Results……………………………………………………………………………………..102 5.0 Discussion…………………………………………………………………………………106 5.1 Previous Work Completed by Others…………………………………………..106 5.2 Comparison with