Light Scattering Effects of Cometary Dust Catherine Master

cmaster@umd.eduScience, 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

BCCAr = 3.83mmVv/V = 98.6%

16x64r = 2.67mmVv/V = 94.6%

64x16r = 3.43mmVv/V = 97.5%

8x128r = 2.83mmVv/V = 95.5%

128x8r = 3.36mmVv/V = 97.3%

4x256r = 2.42mmVv/V = 92.8%

256x4r = 3.34mmVv/V = 97.2%

2x512r = 2.23mmVv/V = 90.7%

512x2r = 2.75mmVv/V = 95.1%

32x32r = 3.26mmVv/V = 97.0%

2x32x16r = 3.35mmVv/V = 97.3%

2x16x32r = 3.19mmVv/V = 96.8%

BPCAr = 1.92mmVv/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)

Pmin, %

amin,°

a0,°

Pmax, %

amax,°

Pol. Color , %

Color

Pmin, %

amin,°

a0,°

Pmax, %

amax,°

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 useda simplified model of cometary dust to depict itsstructure. The previous models all concluded thatcometary dust was comprised of small clusters ofparticles. However, data collected from the Rosettamission, which involved a study of the comet 67P,introduced new information suggesting that themodels were over simplified and that the dust had amore complex structure. The goal of this project was todevelop a new model of the cosmic dust thatcorrelates to the data collected from the Rosettamission. Producing a more accurate model of the dustwould further astronomers’ understanding of cometarydust, as well as help advance other areas of research.

The conclusion of NASA’s Rosetta mission, whichconducted an exploratory study of the comet 67P,presented astronomers with new information thatchanged their current understanding of cometarydust. Previously, it was assumed that cosmic dust hada fairly simple structure made up of small clusters ofparticles. However, data from the Rosetta missionsuggested that the dust had a more complexstructure. The goal of this project was to address thedata collected by developing and testing a variety ofdifferent aggregates in order to develop a moreaccurate model of the dust. Eleven different sphericalclusters, each cluster comprising of 1024 particles,were tested. After comparing the brightness andpolarization curves of each aggregate to prior models,it can be determined that cometary dust is indeedcomposed of a more complex, hierarchal structure.This discovery completely changes the wayastronomers understand cosmic dust and can be usedin future experiments involving comets.

After conducting trials for all 11 aggregates forred filter dust, red filter ice, blue filter dust, and bluefilter ice, it was determined that there was asignificant change in brightness and polarizationvalues. As depicted by the plots below, thepolarization values for 16x64 spheres, 32x32 spheres,and 8x128 spheres were all lower than the BPCA andBCCA curves, while the 2x16x32 spheres resembledthe BCCA curve and the 2x512 spheres was betweenthe BPCA and BCCA curves. Alternately, the brightnessvalues for the 2x16x32 spheres and 2x512 spheresdiverged the most from the BPCA and BCCA curves butthe 16x64 spheres, 32x32 spheres, and 8x128 sphereswere more similar. The charts below includes thepolarization min/max values and their correspondingangles, as well as the color and polarimetric color forboth the red filter dust and red filter ice aggregates.

Other members of the research team wereresponsible for both creating the data files used tomodel the aggregates, and running the trials. A ballisticapproach was used to build the aggregates. Mackowski’sT-Matrix code for parallel computing MSTM3 was usedand the computations for the trials were conductedusing NASA’s HEC supercomputer cluster, Pleiadas.

The following parameters were used for themodelling:The radius of monomers: am=0.1 µm Wavelengths 0.66 µm and 0.44 µmThe number of monomers: N=1024The 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 ice1.32-i1.10-5 at l=0.44 µm1.31-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