MASTER'S THESIS Solar Wind Proton Reflection from the Moon Data Analysis of the SARA Instrument Charles Lue Master of Science in Engineering Technology Space Engineering Luleå University of Technology Department of Computer Science, Electrical and Space Engineering MASTER’S THESIS Solar Wind Proton Reflection from the Moon Data Analysis of the SARA Instrument Charles Lue Luleå University of Technology MSc Programme in Space Engineering Division of Space Technology, Department of Computer Science, Electrical and Space Engineering ii Abstract The Moon has neither a strong magnetic field nor a dense atmosphere to stand- off the solar wind. However, some areas of the lunar crust are permanently magnetized and several studies indicate that these magnetic anomalies can form mini-magnetospheres, partially deflecting the solar wind. Here, ion data from the SARA instrument onboard Chandrayaan-1 is analyzed, to improve the understanding of the interaction dynamics between the solar wind protons and the Moon. A clear and strong interaction is observed between the solar wind protons and the lunar magnetic anomalies. ~50 % of the incoming solar wind protons are reflected above the strongest magnetic anomalies. An average of ~1 % of the solar wind protons are reflected over the entire lunar far-side. This implies that the regolith in magnetic anomaly areas is partially protected from proton precipitation, and that the near-Moon plasma environment is highly influenced by the magnetic anomalies. Even small (<100 km), weak (<3 nT at 30 km altitude) magnetic anomalies reflect some of the solar wind protons, which is surprising considering the large gyro radius of a proton in such a field. Further studies are required to understand the reflection mechanism. iii iv Sammanfattning Månen har varken ett starkt magnetfält eller en tät atmosfär som kan stå emot solvinden. Vissa områden av månens skorpa är dock permanent magnetiserade och flera studier antyder att dessa magnetiska anomalier kan forma mini- magnetosfärer som delvis böjer av solvinden. Här analyseras jon-data från SARA-instrumentet ombord på Chandrayaan-1 för att förbättra förståelsen av hur solvindsprotoner interagerar med månen. En stark interaktion påvisas mellan solvindsprotonerna och månens magnetiska anomalier: ~50 % av de inkommande solvindsprotonerna reflekteras ovanför de områden där de starkaste magnetiska anomalierna finns. Ett genomsnitt av ~1 % av de inkommande solvindsprotonerna reflekteras av de magnetiska anomalierna på den från jorden bortvända sidan av månen. Detta innebär att månens finkorniga ytlager delvis skyddas från protonnedfall i områden med magnetiska anomalier, samt att plasmamiljön runt månen starkt påverkas av de magnetiska anomalierna. Även små, svaga magnetiska anomalier (~3 nT vid 30 km altitud) reflekterar en del av solvindsprotonerna, vilket är överraskande med tanke på den stora gyroradien för en proton i ett sådant fält. Vidare studier krävs för att förstå mekanismen bakom reflektionen. v vi Acknowledgements I am very grateful to the SARA instrument team and the Swedish Institute of Space Physics (IRF) for the opportunity to work with their data. I am especially grateful for the honor to work closely with the reputable, talented and enthusiastic people of the Solar System Physics and Space Technology (SSPT) research program at IRF Kiruna. My deepest gratitude goes to my thesis supervisor, Dr. Yoshifumi Futaana for invaluable encouragement, guidance and teachings. I owe special thanks to Prof. Stas Barabash and Dr. Martin Wieser for sharing their insight, support and advice. I am also very thankful to the staff and students at Luleå University of Technology (LTU) for making the education greatly enjoyable. I thank my thesis examiner Dr. Martin Bohm, who has given me great advice; my thesis coordinator Dr. Johnny Ejemalm; and my education administrator Ms. Maria Winnebäck at LTU’s Department of Space Science (IRV). They have been extremely helpful with practical matters related to the thesis studies. I also thank the ACE MAG instrument team and the ACE Science Center for providing their interplanetary magnetic field data; and the WIND SWE instrument team and the MIT Space Plasma Group for providing their solar wind plasma data. Last, but not least, I thank my supportive family. Parts of this thesis were published by: Charles Lue, Yoshifumi Futaana, Stas Barabash, Martin Wieser, Mats Holmström, Anil Bhardwaj, M. B. Dhanya, and Peter Wurz (2011), Strong influence of lunar crustal fields on the solar wind flow, Geophys. Res. Lett. 38, L03202, doi:10.1029/2010GL046215. vii viii Table of Contents 1 Introduction ...................................................................................................... 5 1.1 Background ................................................................................................. 5 1.2 Purpose ....................................................................................................... 7 1.3 Delimitations............................................................................................... 7 2 Current Knowledge ........................................................................................... 9 2.1 Solar Wind Interactions with Solar System Objects ..................................... 9 2.1.1 The Solar Wind ..................................................................................... 9 2.1.2 Interactions with Dynamo Powered Magnetic Fields .......................... 11 2.1.3 Interactions with Unprotected Atmospheres ...................................... 11 2.1.4 Interactions with Unprotected Crusts ................................................. 12 2.2 Lunar Interaction Conditions ..................................................................... 13 2.2.1 Plasma Environment at the Lunar Orbit .............................................. 13 2.2.2 Effects of UV-Irradiation ..................................................................... 13 2.2.3 Lunar Magnetic Anomalies ................................................................. 13 2.3 Current View of the Solar Wind-Moon Interaction ................................... 14 2.3.1 IMF Interaction with the Lunar Core ................................................... 14 2.3.2 Interaction with the Lunar Atmosphere .............................................. 15 2.3.3 Interaction with Unmagnetized Lunar Crust ....................................... 15 1 2.3.4 Interaction with Magnetic Anomalies ................................................. 15 3 Instrumentation .............................................................................................. 19 3.1 Chandrayaan-1 .......................................................................................... 19 3.2 SARA ......................................................................................................... 20 3.3 SWIM ........................................................................................................ 21 3.4 Field of View ............................................................................................. 22 4 Analysis ........................................................................................................... 25 4.1 Data Selection ........................................................................................... 25 4.2 Data Extraction ......................................................................................... 25 4.3 Differential Directional Flux ...................................................................... 27 4.4 Identifying Particle Populations ................................................................ 28 4.5 Directional Flux ......................................................................................... 28 4.6 Selenographic Mapping ............................................................................ 29 4.7 Space Environment Comparison ............................................................... 30 4.8 Temperature Calculation .......................................................................... 30 4.9 Distribution Function and Flux .................................................................. 31 5 Results ............................................................................................................ 33 5.1 Orbit Plots ................................................................................................. 33 5.2 Particle Populations .................................................................................. 34 5.3 Selenographic Plots ................................................................................... 38 5.4 Spectrographic Plots ................................................................................. 40 5.5 Space Environment Plots .......................................................................... 41 2 5.6 Reflection Fraction .................................................................................... 43 5.7 Directional Flux Compared to Crustal Magnetism ..................................... 43 6 Conclusions and Discussion ............................................................................. 45 6.1 Interpretation of the Results ..................................................................... 45 6.2 Implications .............................................................................................. 47 6.3 Speculations on the Reflection Mechanism .............................................. 47 6.3.1 Fluid-Like Deflection ..........................................................................