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Investigating Compositional Variations of S-Complex Near-Earth Asteroids: (1627) Ivar

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Investigating Compositional Variations of S-Complex Near-Earth Asteroids: (1627) Ivar University of Central Florida STARS Electronic Theses and Dissertations, 2004-2019 2018 Investigating compositional variations of S-complex near-Earth asteroids: (1627) Ivar Jenna Jones University of Central Florida Part of the Physics Commons Find similar works at: https://stars.library.ucf.edu/etd University of Central Florida Libraries http://library.ucf.edu This Doctoral Dissertation (Open Access) is brought to you for free and open access by STARS. It has been accepted for inclusion in Electronic Theses and Dissertations, 2004-2019 by an authorized administrator of STARS. For more information, please contact [email protected]. STARS Citation Jones, Jenna, "Investigating compositional variations of S-complex near-Earth asteroids: (1627) Ivar" (2018). Electronic Theses and Dissertations, 2004-2019. 5838. https://stars.library.ucf.edu/etd/5838 INVESTIGATING COMPOSITIONAL VARIATIONS OF S-COMPLEX NEAR-EARTH ASTEROIDS: (1627) IVAR by JENNA L. JONES B.S. University of Little Rock at Arkansas, 2008 A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Physics in the College of Sciences at the University of Central Florida Orlando, Florida Spring Term 2018 Major Professor: Yanga R. Fernández © 2018 Jenna Jones ii ABSTRACT We seek to investigate the complexity and heterogeneity of the surfaces of near-Earth asteroids (NEAs). In particular, we are studying the S-complex NEAs, which account for a large portion of the observed near-Earth objects. Here we present our results for (1627) Ivar, an Amor class NEA with taxonomic type Sqw. In 2013, Ivar’s large size and close approach to Earth (minimum distance 0.32 AU) provided an opportunity to observe the asteroid over many different viewing angles for an extended period of time. We collected delay-Doppler radar images and Doppler spectra using the Arecibo Observatory’s 2380 MHz radar, and, by incorporating an extensive lightcurve collection, we have constrained the shape and spin state. In addition, we observed Ivar using NASA’s IRTF’s SpeX mode to gather rotationally resolved reflected and thermal spectra in the near-IR regime. We have created a high-resolution shape model, and we have found Ivar to have a sidereal period of 4.7951689 ± 0.0000026 hours with a pole at ecliptic longitude and latitude 336°, +37° (± 6°) respectively. We also show that Ivar is more elongated than previous studies suggests, with dimensions along the principal axis 15.15 x 6.25 x 5.66 ± 10%. This model has been incorporated into our thermal modeling code, SHERMAN, in order to determine which reflective, thermal, and surface properties best reproduce our numerous and rotationally resolved spectra. Primarily, we vary thermal inertia, geometric albedo, and crater fraction (surface roughness) although SHERMAN has many parameters that are allowed to vary. Our findings show that Ivar’s thermal observations cannot be reproduced with a homogeneous model, but rather a heterogeneous model with a thermal inertia spot, and possibly different crater fraction values, needs to be applied in order to reproduce all of the spectra. Due to the variations in observing geometry for our thermal spectra, the properties of this spot are well constrained. We iii find that, with this spot, that the values of thermal inertia, geometric albedo, and crater fraction are 80 ± 20 J m-2 s-1/2 K-1, 0 – 0.3, and 0.27 ± 0.02, respectively. This work shows the advantage of having many datasets for deep study of an individual NEA, and with these results, we will learn more about the detailed regolith and surface properties of Ivar and how those properties compare to those of other NEAs. iv ACKNOWLEDGMENTS I would like to thank my advisors, Yanga Fernández and Ellen Howell, for their support and guidance throughout the course of this dissertation research, without whom this work would not have been possible. I consider myself very lucky to have been able to work with them both and I am grateful that I was given the opportunity to work on this exciting research topic. I also want to thank my other committee members, Humberto Campins and Dan Britt, and collaborators who contributed to the work in this dissertation. I want to thank my husband who has always encouraged me throughout my career and was always willing to listen to my practice presentations and read my paper drafts for the nth time. I also want to thank all my friends and family who have always supported me. v TABLE OF CONTENTS LIST OF FIGURES ....................................................................................................................... ix LIST OF TABLES ........................................................................................................................ xv CHAPTER 1: INTRODUCTION ................................................................................................... 1 1.1 Motivation ........................................................................................................................................... 1 1.2 Background ......................................................................................................................................... 2 1.2.1 Why Study Asteroids? .................................................................................................................. 3 1.2.2 S-Type Asteroids .......................................................................................................................... 4 1.3 Shape Modeling Asteroids .................................................................................................................. 6 1.4 Thermal Modeling Methods ............................................................................................................... 8 1.4.1 Standard Thermal Model and Fast Rotating Model ..................................................................... 9 1.4.2 Near-Earth Thermal Model ........................................................................................................ 10 1.4.3 Thermophysical Model .............................................................................................................. 10 1.5 NEA 1627 Ivar ................................................................................................................................... 12 CHAPTER 2: OBSERVATIONS ................................................................................................. 15 2.1 Radar Data......................................................................................................................................... 15 2.2 Lightcurve Data ................................................................................................................................. 19 2.3 Reflected and Thermal Data ............................................................................................................. 22 CHAPTER 3: SHAPE MODELING ............................................................................................ 27 3.1 SHAPE ................................................................................................................................................ 27 3.2 Shape-Modeling Process ................................................................................................................... 27 3.3 Modeling Surface Detail .................................................................................................................... 29 3.4 Testing Degree of Smoothness ......................................................................................................... 31 3.5 Spin Rate and Ecliptic Pole ................................................................................................................ 36 3.6 Shape Model ..................................................................................................................................... 39 3.7 Radar Albedo and Polarization Ratio ................................................................................................ 50 3.8 Gravitational and Surface Properties ................................................................................................ 53 vi CHAPTER 4: SHERMAN ............................................................................................................ 58 4.1 SHERMAN and Initializations ............................................................................................................ 58 CHAPTER 5: THERMAL MODEL OF IVAR ............................................................................ 63 5.1 Homogeneous Model........................................................................................................................ 63 5.1.1 Group 1 ...................................................................................................................................... 63 5.1.2 Group 2 ...................................................................................................................................... 66 5.1.3 Results of the Homogeneous Model ......................................................................................... 68 5.2 Heterogeneous Model ...................................................................................................................... 68 5.2.1 May Observations ...................................................................................................................... 69 5.2.2 August Observation...................................................................................................................
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