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Shape Model of Potentially Hazardous Asteroid 1981 Midas from Radar and Lightcurve Observations Macalester Journal of Physics and Astronomy Volume 8 Issue 1 Spring 2020 Article 11 May 2020 Shape Model of Potentially Hazardous Asteroid 1981 Midas from Radar and Lightcurve Observations Riley McGlasson Macalester College, [email protected] Follow this and additional works at: https://digitalcommons.macalester.edu/mjpa Recommended Citation McGlasson, Riley (2020) "Shape Model of Potentially Hazardous Asteroid 1981 Midas from Radar and Lightcurve Observations," Macalester Journal of Physics and Astronomy: Vol. 8 : Iss. 1 , Article 11. Available at: https://digitalcommons.macalester.edu/mjpa/vol8/iss1/11 This Honors Project - Open Access is brought to you for free and open access by the Physics and Astronomy Department at DigitalCommons@Macalester College. It has been accepted for inclusion in Macalester Journal of Physics and Astronomy by an authorized editor of DigitalCommons@Macalester College. For more information, please contact [email protected]. Shape Model of Potentially Hazardous Asteroid 1981 Midas from Radar and Lightcurve Observations Abstract We report observations of potentially hazardous, Apollo-class asteroid 1981 Midas, which passed 0.090 au from Earth (35 lunar distances) on March 21, 2018. During this close approach, Midas was observed by radar both from the Arecibo Observatory on March 21 through 25 (five nights), and from NASA's Goldstone Deep Space Communications Complex on March 19 and 21. These radar observations yielded one-dimensional continuous-wave spectra and two-dimensional delay-Doppler images. In addition, there have been optical lightcurve observations of Midas during four apparitions (1987, 1992, 2004, and 2018), which showed a rotation period of 5.22 hours. Midas has an absolute magnitude of H = 15.2. By combining the lightcurves and radar data, we have constructed a shape model for Midas. This model shows that Midas has two lobes separated by a neck which, at its thinnest point, is about 60% of the width of the lobes. From our model, we also confirm the lightcurve-derived rotation period and show that Midas has dimensions of 3.33 x 1.99 x 1.85 km +/- 10% and a pole position within 6 degrees of (370,-610) in ecliptic longitude and latitude. This honors project - open access is available in Macalester Journal of Physics and Astronomy: https://digitalcommons.macalester.edu/mjpa/vol8/iss1/11 McGlasson: Radar Observations of Asteroid 1981 Midas MACALESTER COLLEGE Shape Model of Potentially Hazardous Asteroid 1981 Midas from Radar and Lightcurve Observations by Riley A. McGlasson in the Department of Physics and Astronomy Advisor: Professor John Cannon March 2020 Published by DigitalCommons@Macalester College, 2020 1 Macalester Journal of Physics and Astronomy, Vol. 8, Iss. 1 [2020], Art. 11 https://digitalcommons.macalester.edu/mjpa/vol8/iss1/11 2 McGlasson: Radar Observations of Asteroid 1981 Midas MACALESTER COLLEGE Abstract Department of Physics and Astronomy by Riley A. McGlasson We report observations of potentially hazardous, Apollo-class asteroid 1981 Mi- das, which passed 0.090 au from Earth (35 lunar distances) on March 21, 2018. During this close approach, Midas was observed by radar both from the Arecibo Observatory on March 21 through 25 (five nights), and from NASA's Goldstone Deep Space Communications Complex on March 19 and 21. These radar ob- servations yielded one-dimensional continuous-wave spectra and two-dimensional delay-Doppler images. In addition, there have been optical lightcurve observations of Midas during four apparitions (1987, 1992, 2004, and 2018), which showed a ro- tation period of 5.22 hours (Mottola et al. 1995; Wisniewski et al. 1997; Muinonen et al. 2007; Franco et al. 2018). Midas has an absolute magnitude of H = 15.2. By combining the lightcurves and radar data, we have constructed a shape model for Midas. This model shows that Midas has two lobes separated by a neck which, at its thinnest point, is about 60% of the width of the lobes. From our model, we also confirm the lightcurve-derived rotation period and show that Midas has dimen- sions of 3:33 × 1:99 × 1:85 km ±10% and a pole position within 6◦ of (37◦; −61◦) in ecliptic longitude and latitude. Published by DigitalCommons@Macalester College, 2020 3 Macalester Journal of Physics and Astronomy, Vol. 8, Iss. 1 [2020], Art. 11 Acknowledgements I would like to thank Dr. Sean Marshall for his guidance in all things shape modeling, and for helping me continue this research from the summer of 2018 through the completion of this paper. Thanks also to the rest of the Arecibo planetary radar group, Drs. Flaviane Venditti and Anne Virkki, for teaching me all about planetary radar during my time at Arecibo. I would also like to give special thanks to Dr. John Cannon, my advisor through- out these 4 years at Macalester. He introduced me to this wonderful world of astronomy, and encouraged me to pursue research opportunities like the one that produced this research. More thanks go to my committee, Drs. Anna Williams, Sean Marshall, and John Cannon, for their invaluable comments on this document. A massive thanks goes also to the residents of OLRI 404 over these past four years, you have pushed and inspired me and I cannot wait to see where you all end up. Thank you also to Lance A. M. Benner, Marina Brozovi´c,Shantanu P. Naidu, Jon D. Giorgini, Betzaida Aponte, Alan W. Harris, James W. Young, Guy Wells, Daniel Bamberger, Jeff Tobak, and Marek Husarik for the use of their unpublished Midas observations. This research was supported by the Arecibo Observatory Research Experience for Undergraduates program, National Science Foundation grant 1559849. This research also was supported by NASA's Near-Earth Object Observations Program through grants NNX13AQ46G and 80NSSC18K1098. The Arecibo Observatory is a facility of the NSF, operated under cooperative agreement by the University of Central Florida in alliance with Yang Enterprises Inc. and Universidad Ana G. Mendez. iv https://digitalcommons.macalester.edu/mjpa/vol8/iss1/11 4 McGlasson: Radar Observations of Asteroid 1981 Midas Contents Abstract iii Acknowledgements iv List of Figures vii List of Tables viii 1 Introduction1 1.1 An Overview of this Thesis ....................... 1 1.2 Motivation ................................ 2 2 The Near-Earth Asteroid Population 3 2.1 Spectral Classification ......................... 3 2.1.1 The SMASSII Taxonomy .................... 4 2.1.2 Bus-DeMeo taxonomy ..................... 8 2.2 Orbital Classification .......................... 8 2.2.1 Potentially Hazardous Asteroids . 10 2.3 Orbital Distribution of Spectral Classes . 12 3 Radar Astronomy 15 4 Observations of 1981 Midas 19 4.1 Lightcurve Observations ........................ 19 4.2 Radar Observations ........................... 20 5 SHAPE Modeling 24 5.1 SHAPE Software ............................ 24 5.2 Modeling Process ............................ 25 5.3 Bad Models ............................... 28 6 Results and Conclusions 31 6.1 Pole Position .............................. 31 6.2 Shape Model .............................. 33 Appendix A Selected Views of Model 35 Bibliography 41 v Published by DigitalCommons@Macalester College, 2020 5 Macalester Journal of Physics and Astronomy, Vol. 8, Iss. 1 [2020], Art. 11 https://digitalcommons.macalester.edu/mjpa/vol8/iss1/11 6 McGlasson: Radar Observations of Asteroid 1981 Midas List of Figures 2.1 SMASSII Taxonomy Spectral Component Plot............ 5 2.2 Average Spectra for the 26 SMASSII Taxonomic Classes . 6 2.3 Average Spectra for all 24 Bus-DeMeo Spectral Classes . 9 3.1 Example Delay-Doppler Images of 1981 Midas . 16 5.1 Progression of three different model types . 26 5.2 Example grid search results ...................... 27 5.3 Example Bad Models .......................... 28 5.4 Bad Northern Model .......................... 29 5.5 Bad Northern Model .......................... 30 6.1 Pole Position 1σ Region ........................ 31 6.2 Pole Position Uncertainty Analysis . 32 6.3 Final Model ............................... 34 A.1 CW Model View ............................ 35 A.2 CW Model View ............................ 36 A.3 Delay-Doppler Model View ....................... 36 A.4 Delay-Doppler Model View ....................... 37 A.5 Delay-Doppler Model View ....................... 37 A.6 Delay-Doppler Model View ....................... 37 A.7 Lightcurve Model View ......................... 38 A.8 Lightcurve Model View ......................... 39 A.9 Lightcurve Model View ......................... 40 vii Published by DigitalCommons@Macalester College, 2020 7 Macalester Journal of Physics and Astronomy, Vol. 8, Iss. 1 [2020], Art. 11 List of Tables 4.1 Lightcurve Observations ........................ 22 4.2 Radar Observations ........................... 23 6.1 Properties of 1981 Midas ........................ 33 viii https://digitalcommons.macalester.edu/mjpa/vol8/iss1/11 8 McGlasson: Radar Observations of Asteroid 1981 Midas CHAPTER 1: Introduction 1.1 An Overview of this Thesis In this thesis, I will describe the shape modeling process and resulting three- dimensional shape model of the potentially hazardous asteroid 1981 Midas. In Chapter2, I provide a review of the existing body of knowledge regarding the near-Earth asteroid population. Chapter3 addresses methods used in radar astronomy, both continuous wave Doppler spectra and delay-Doppler images. This chapter also discusses the capa- bilities of the two telescopes used for radar observations: the Arecibo 305 meter telescope in Puerto Rico and the Goldstone
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