Boulder Distribution Analysis of Impact Craters in the Tharsis Region And
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Louisiana State University LSU Digital Commons LSU Master's Theses Graduate School 12-15-2017 Boulder Distribution Analysis of Impact Craters in the Tharsis Region and Elysium Planitia, Mars Nicole Button Louisiana State University and Agricultural and Mechanical College, [email protected] Follow this and additional works at: https://digitalcommons.lsu.edu/gradschool_theses Part of the Other Physical Sciences and Mathematics Commons Recommended Citation Button, Nicole, "Boulder Distribution Analysis of Impact Craters in the Tharsis Region and Elysium Planitia, Mars" (2017). LSU Master's Theses. 4379. https://digitalcommons.lsu.edu/gradschool_theses/4379 This Thesis is brought to you for free and open access by the Graduate School at LSU Digital Commons. It has been accepted for inclusion in LSU Master's Theses by an authorized graduate school editor of LSU Digital Commons. For more information, please contact [email protected]. BOULDER DISTRIBUTION ANALYSIS OF IMPACT CRATERS IN THE THARSIS REGION AND ELYSIUM PLANITIA, MAR A Thesis Submitted to the Graduate Faculty of the Louisiana State University and Agricultural and Mechanical College in partial fulfillment of the requirements for the degree of Master of Science in The Department of Geology and Geophysics by Nicole E. Button B.S., Cornell University, 2012 May 2018 Acknowledgements First and foremost, I would like to thank my advisor Dr. Suniti Karunatillake. Without him, I would not have learned about the career opportunities in planetary science and may not have pursued my passion in this field of science. I appreciate the undergraduate and graduate research that I have participated in because of him as well as his continued support the past years, particularly during my graduate program. I also appreciate the financial support for a research assistantship and travel from the Mars Data Analysis Program (MDAP) Grant NNX13AI98G through NASA from the start of my graduate program until August 2016. I would also like to acknowledge the support of my committee, Dr. Karen Luttrell, Dr. Peter Doran, and Dr. Carol Wicks. All members in the Planetary Science Laboratory, including graduate students Don Hood and David Susko, have provided research guidance and support throughout the past years, for which I am extremely grateful. Thank you to the undergraduate researchers that measured boulders at the two Martian impact craters – Chris Diaz, Sarah Zadei, Vaibhav Rajora, Allison Barbato, and Michael Piorkowski. Lastly, I would like to thank my family and friends for their support during my graduate career. ii Table of Contents Acknowledgements…………………………………………………………………………ii Abstract……………………………………………………………………………………..iv 1. Introduction………………………………………………………………………………1 2. Methods…………………………………………………………………………………..7 3. Results……………………………………………………………………………………15 4. Discussion………………………………………………………………………………..28 5. Conclusions………………………………………………………………………………36 References…………………………………………………………………………………..38 Appendix A: Data Management Plan……………………………………………………….44 Appendix B: Raw Data……………………………………………………………………...45 Vita…………………………………………………………………………………………..198 iii Abstract Crater counting is an accepted method for dating the surface of a planetary body. An older landscape will have a higher areal density of craters due to exposure of impacts occurring over a longer time period. Since each initial impact only forms one primary crater, secondary craters need to be excluded in the crater counting method to appropriately catalog only distinct impact events. However, small primary craters may be difficult to distinguish from secondary craters. Understanding physical features of impact craters, such as the ejecta blanket, would improve the planetary community’s ability to differentiate between the two types of craters. Boulder distribution analysis of individually measured boulders in an ejecta blanket includes the comparison of a boulder’s area to its distance from the crater, the comparison of a boulder’s axial ratio to its distance from the crater, and the cumulative size frequency distribution. Krishna and Kumar (2016) applied boulder distribution analysis to Censorinus Crater on the Moon. Through cumulative size frequency distribution and power-law fit to calculate the largest negative b-value, they determined the impact direction. On Mars, boulder distribution analysis has yet to be applied to impact craters observed in high resolution images. This study investigated two Martian impact craters using boulder distribution and improved the technique of previous boulder distribution studies by incorporating error propagation. These craters were: 1. a speculated primary crater located in the Tharsis region that was approximately 175 m in diameter (Banks, 2008), and 2. a speculated secondary crater located in Elysium Planitia that was approximately 320 m in diameter (Hart & Gulick, 2010; McEwen et al., 2005). Variations and similarities between the two types of craters on the Martian surface could provide insight about the typical boulder distribution for each crater type and the impact direction. For a secondary crater, the impact direction may indicate its associated primary crater. At these two Martian impact craters, the power-law fit to the cumulative iv size distribution frequency, boulder population density, and presence of a forbidden zone, defined as a region where ejecta is absent or nearly absent for an oblique impact, did not conclusively indicate the impact direction of either crater. While this study serves as a starting point for understanding the boulder distribution patterns around small Martian primary and secondary craters, it also motivates future work to determine whether the impact direction is indeterminable for small craters and to establish a database of Martian primary and secondary craters for which boulder distribution was applied. v 1. Introduction Craters play an important role in determining the age of a planetary surface (Fassett, 2016; McEwen & Bierhaus, 2006; Robbins & Hynek, 2011a). Older terrain on a planetary body is expected to have a higher areal density of craters relative to a newly formed surface (Hartmann & Neukum, 2001; Robbins & Hynek, 2014), such as resurfacing from volcanic activity, since craters form randomly in time across a planetary body (Robbins & Hynek, 2014). However, secondary craters can form on a planetary body following the initial impact when the velocity of the ejecta is high enough (McEwen & Bierhaus, 2006). The term velocity is used throughout this study because the impact direction is a key component of the impact crater formation, particularly with the formation of secondary craters. Robbins and Hynek (2011b) define secondary craters as typically having one or more of the following properties: 1. clustered within troughs that extend radially from the primary crater or adjacent to the primary crater (McEwen & Bierhaus, 2006; Robbins & Hynek, 2014), 2. highly asymmetric (McEwen & Bierhaus, 2006) or biaxial symmetry with one of the symmetry axes pointing to the primary crater, and 3. presence of a herring-bone ejecta pattern that points to the primary crater (Hargitai & Kereszturi, 2015; McEwen & Bierhaus, 2006). Secondary craters of large impact craters have been discovered thousands of kilometers from the associated primary crater (Preblich et al., 2007; Robbins & Hynek, 2011a, 2014). Smaller distant craters are referred to as “background secondaries” (Robbins & Hynek, 2011b, 2014). In addition, secondary craters typically have a shallower depth than a primary crater of the same size due to the lower impact velocity (McEwen et al., 2005; McEwen & Bierhaus, 2006; Melosh, 1984; Robbins & Hynek, 2011b). The lower impact velocity associated with secondary craters also produces larger boulders 1 than primary craters of the same size (Gwendolyn D. Bart & Melosh, 2007). Table 1 presents the differences between primary and secondary craters of similar size. Table 1. Characteristics of primary and secondary craters compiled from Bart and Melosh (2007), McEwen and Bierhaus (2006), Robbins and Hynek (2011b, 2014), and Robbins et al. (2017). Characteristic Primary Crater Secondary Crater Depth (equal diameters) Deeper Shallower Boulder size Smaller Larger Across a planetary Location body Usually clustered adjacent to a primary crater or within troughs that extend radially from a primary crater Additional Presence of a herring-bone ejecta pattern that Characteristics points to the primary crater Highly elliptical crater with the long axis pointing towards a primary crater Crater rim may be absent in the uprange direction Secondary craters produced from the same primary crater form in the same geologic instant as the initial impact and are spatially distributed around a central source (Robbins & Hynek, 2014). Since impacts forming secondary craters are not independent events, secondary craters can contaminate the primary crater population in crater counting and affect the results of dating a planetary body through this method (Gwendolyn D. Bart & Melosh, 2007; Bierhaus et al., 2005, 2012; Calef et al., 2009; McEwen & Bierhaus, 2006; Robbins et al., 2014; Robbins & Hynek, 2011a, 2014; Werner et al., 2009; Xiao, 2016; Xiao & Strom, 2012). Zunil Crater is a large primary crater located at 7.69°N, 166°E that produced approximately 107 secondary craters, some up to 1600 km away (McEwen et al., 2005). It was the first rayed crater discovered on Mars using the Thermal Emission Imaging System (THEMIS) onboard the 2 2001 Mars Odyssey orbiter (Christensen et al., 2004;