THE SURFACES OF THE MAJORITY OF SOLAR SYSTEM BODIES ARE COVERED BY A LAYER OF DUST OR SMALL ICY PARTICLES. SPACEBORNE AND GROUNDBASED OBSERVATIONS OF THOSE OBJECTS DEMONSTRATE A WIDE RANGE OF THEIR SPECTRAL AND PHOTOMETRIC CHARACTERISTICS WHICH INDICATES A DIVERSITY OF THE COMPOSITION SIZE AND PACKING OF THOSE PARTICLES. IF WE HAD AN OPPORTUNITY TO REPRODUCE THE SPECTRAL AND PHOTOMETRIC DATA VIA COMPUTER MODELING WE COULD REVEAL THE SURFACE DUST AND ICE PARTICLE PHYSICAL PROPERTIES AND THUS BETTER UNDERSTAND THE FORMATION AND EVOLUTION OF THE BODIES. HOWEVER THERE IS STILL NO TOOL FOR COMPUTER MODELING OF LIGHT SCATTERING BY SUCH SURFACES THAT SATISFIES BOTH (A) THE POLARIMETRY/SCATTERING COMMUNITY S DESIRE FOR A SOLUTION THAT IS NOT SEMI-EMPIRICAL AND FULLY INCLUDES THE PHYSICAL AND CHEMICAL CHARACTERISTICS OF THE SURFACE AND (B) THE PLANETARY COMMUNITY S REQUEST FOR A METHOD THAT DOES NOT REQUIRE EXCESSIVE COMPUTATIONAL RESOURCES AND PROVIDES STABILITY FOR A BROAD RANGE OF DUST LAYER AND ICY REGOLITH PARAMETERS. IN THIS PROJECT WE ARE PLANNING TO DEVELOP AND APPLY A SOFTWARE PACKAGE TO ADDRESS BOTH NEEDS. THE PACKAGE WILL ALLOW MODELING LIGHT SCATTERING BY PARTICULATE SURFACES REPRESENTED BY LAYERS OF RANDOMLY DISTRIBUTED PARTICLES OF ANY SHAPE AND STRUCTURE AND CAN BE APPLIED TO ANY MEDIA FROM DENSELY PACKED TO VERY FLUFFY. THUS THE CODE COULD BE USED TO STUDY LIGHT SCATTERING BY A VARIETY OF SOLAR-SYSTEM BODIES: ASTEROIDS COMETARY NUCLEI TNOS PLANETARY SATELLITES MERCURY ETC. OUR APPROACH IS TO DIRECTLY SIMULATE THE LIGHT-SCATTERING CHARACTERISTICS OF RANDOM REGOLITH LAYERS I.E. TO GENERATE A HIGH ACCURACY SOLUTION TO THE MACROSCOPIC MAXWELL'S WAVE EQUATIONS FOR A LAYER WITH MICROSCOPICALLY DEFINED PHYSICAL AND CHEMICAL CONFIGURATIONS. THE RANDOM CONFIGURATIONS ARE GENERATED WITH MONTE-CARLO METHODS FOR A RECTANGULAR UNIT CELL. THE CODE THEN MODELS A PLANE-PARALLEL LAYER BY PERIODICALLY REPEATING THE UNIT CELL IN THE LATERAL PLANE TO INFINITY. THE PROPERTIES OF THE RANDOM MEDIUM ARE OBTAINED BY AVERAGING OVER MULTIPLE RANDOMLY SAMPLED CONFIGURATIONS. THE PERIODIC PLANE-PARALLEL DDA FORMULATION USED IN THE PROJECT HAS BEEN RECENTLY DEVELOPED AND CODED BY CO-I MACKOWSKI THE AUTHOR OF THE MULTI-SPHERE T-MATRIX CODE A VERSION OF WHICH WAS DEVELOPED UNDER NASA GRANT NNX09AM97G. THIS FORMULATION USES A RECIPROCAL SPACE (RS) REPRESENTATION OF THE POLARIZABILITY DISTRIBUTION THAT ENABLES A WINDOWING SCHEME WHICH SIGNIFICANTLY REDUCES THE TOTAL NUMBER OF DEGREES OF FREEDOM RELATIVE TO THE TRADITIONAL DIRECT SPACE APPROACH OF DDSCAT [1]. THE RS FORMULATION ALSO ENABLES THE APPLICATION OF A PRECONDITIONING SCHEME DURING THE SOLUTION OF THE DDA INTERACTION EQUATIONS WHICH REDUCES CONSIDERABLY THE NUMBER OF ITERATIONS REQUIRED TO OBTAIN A SOLUTION. CO-I MACKOWSKI HAS ALREADY SUCCESSFULLY TESTED THIS APPROACH [2] AND WILL FINALIZE THE CODE DURING THE FIRST YEARS OF THE GRANT PERIOD. WE ARE PLANNING TO APPLY THE CODE TO FURTHER WORK ON UNDERSTANDING THE OPPOSITION EFFECT USING DATASETS ALREADY IN HAND FROM OUR PREVIOUS GRANTS AND PDS: SPECTRA OF ICY SATELLITES (ACQUIRED UNDER OPR GRANT NNX16AH35G) AND ROSETTA OSIRIS DATA FOR THE NUCLEUS OF COMET 67P/CHURYUMOV GERASIMENKO [3]. COMPARISON WITH OUR PREVIOUS ESTIMATES AND WITH THE RESULTS OBTAINED BY OTHER GROUPS WILL BE USED TO TEST THE CODE AND POLISH IT TO THE POINT THAT IT CAN BE PUT ONLINE FOR COMMUNITY USE. THE NEW TECHNIQUE WILL ALLOW US TO OBTAIN A BETTER CHARACTERIZATION OF THE PARTICLES THAT COVER THE ICY SATELLITES AND THE COMETARY NUCLEUS. 1. B. DRAINE P. FLATAU 1994 DISCRETE-DIPOLE APPROXIMATION FOR SCATTERING CALCULATIONS JOSA A 11 1491-1499. 2. D. MACKOWSKI THE DDA THE RTE AND THE COMPUTATION OF SCATTERING BY PLANE PARALLEL LAYERS OF PARTICLES JQSRT IN PRESS. 3. N. MASOUMZADEH ET AL. OPPOSITION EFFECT ON COMET 67P CHURYUMOV-GERASIMENKO USING ROSETTA OSIRIS IMAGES A&A DOI: 10.1051/0004-6361/201629734