Light Scattering Effects of Cometary Dust Catherine Master [email protected] Science, Discovery, and the Universe Electrical Engineering Thank you to Dr. Ludmilla Kolokolova for allowing me to participate in your research and for teaching me all about cometary dust. Thank you also to SDU for providing me with the opportunity to work on this project. INTRODUCTION DATA FINDINGS METHODOLOGY CONCLUSION BCCA r = 3.83mm V v /V = 98.6% 16x64 r = 2.67mm V v /V = 94.6% 64x16 r = 3.43mm V v /V = 97.5% 8x128 r = 2.83mm V v /V = 95.5% 128x8 r = 3.36mm V v /V = 97.3% 4x256 r = 2.42mm V v /V = 92.8% 256x4 r = 3.34mm V v /V = 97.2% 2x512 r = 2.23mm V v /V = 90.7% 512x2 r = 2.75mm V v /V = 95.1% 32x32 r = 3.26mm V v /V = 97.0% 2x32x16 r = 3.35mm V v /V = 97.3% 2x16x32 r = 3.19mm V v /V = 96.8% BPCA r = 1.92mm V v /V = 85.5% (Below) Chart depicting old models (red) in comparison to new models (green) (Below) Two older models of dust particles, BPCA (left) and BPCCA (right) (Below) Brightness and Polarization plots for old models, in comparison to plots for new models (Red filter, Dust) P min , % a min, ° a 0, ° P max , % a max, ° Pol. Color , % Color P min , % a min, ° a 0, ° P max , % a max, ° Pol. Color , % Color -0.19 - -0.88 6 - 8 10 - 13 61.0 - 67.3 85 – 91 6.3 - 11.3 0.003 - 0.01 -0.20 - -0.93 5 - 7 8 - 13 78.8 - 91.6 88 – 94 6.2 - 8.9 -0.001 - -0.012 Prior to NASA’s Rosetta mission, researchers used a simplified model of cometary dust to depict its structure. The previous models all concluded that cometary dust was comprised of small clusters of particles. However, data collected from the Rosetta mission, which involved a study of the comet 67P, introduced new information suggesting that the models were over simplified and that the dust had a more complex structure. The goal of this project was to develop a new model of the cosmic dust that correlates to the data collected from the Rosetta mission. Producing a more accurate model of the dust would further astronomers’ understanding of cometary dust, as well as help advance other areas of research. The conclusion of NASA’s Rosetta mission, which conducted an exploratory study of the comet 67P, presented astronomers with new information that changed their current understanding of cometary dust. Previously, it was assumed that cosmic dust had a fairly simple structure made up of small clusters of particles. However, data from the Rosetta mission suggested that the dust had a more complex structure. The goal of this project was to address the data collected by developing and testing a variety of different aggregates in order to develop a more accurate model of the dust. Eleven different spherical clusters, each cluster comprising of 1024 particles, were tested. After comparing the brightness and polarization curves of each aggregate to prior models, it can be determined that cometary dust is indeed composed of a more complex, hierarchal structure. This discovery completely changes the way astronomers understand cosmic dust and can be used in future experiments involving comets. After conducting trials for all 11 aggregates for red filter dust, red filter ice, blue filter dust, and blue filter ice, it was determined that there was a significant change in brightness and polarization values. As depicted by the plots below, the polarization values for 16x64 spheres, 32x32 spheres, and 8x128 spheres were all lower than the BPCA and BCCA curves, while the 2x16x32 spheres resembled the BCCA curve and the 2x512 spheres was between the BPCA and BCCA curves. Alternately, the brightness values for the 2x16x32 spheres and 2x512 spheres diverged the most from the BPCA and BCCA curves but the 16x64 spheres, 32x32 spheres, and 8x128 spheres were more similar. The charts below includes the polarization min/max values and their corresponding angles, as well as the color and polarimetric color for both the red filter dust and red filter ice aggregates. Other members of the research team were responsible for both creating the data files used to model the aggregates, and running the trials. A ballistic approach was used to build the aggregates. Mackowski’s T-Matrix code for parallel computing MSTM3 was used and the computations for the trials were conducted using NASA’s HEC supercomputer cluster, Pleiadas. The following parameters were used for the modelling: The radius of monomers: a m =0.1 μm Wavelengths 0.66 μm and 0.44 μm The number of monomers: N=1024 The refractive index for the dust (based on in-situ data for comet Halley): 1.88-i0.47 at l=0.44 μm 1.98-i0.48 at l=0.66 μm silicate 31.76%, iron 2.56%, carbonaceous materials 65.68% (1/3 organic refractory, 2/3 amorphous carbon) for ice 1.32-i1.10 -5 at l=0.44 μm 1.31-i1.10 -6 at l=0.66 μm The data analysis portion of the project used the following procedure: 1. Using data collected from the trials for each aggregate, determine the brightness and polarization values for each phase angle on Microsoft Excel 2. Plot the brightness and polarization curves for all phase angles, and for (0-25) degrees using MATLAB 3. Create charts to analyze properties of each aggregate such as max/min polarization angle, color, and polarimetric color (Below) Brightness and polarization plots for five different aggregates comparing BCCA and BCA curves to new data Images produced by Dr. Kolokolova Chart produced by Dr. Kolokolova Charts produced by Dr. Kolokolova (Below) Images of cometary dust using hierarchal model (left) produced by Dr. Kolokolova, (right) produced by Alexander Seizinger