ARM: Asteroid Reflection Model

Abstract

Asteroid Reflection Model (ARM) is a newly developed model that simulates reflected radiation and polarization on an asteroid's surface. The working principle behind the model is radiative transfer using Fourier series expansions of reflection matrices. Input models and parameters are: a triangle polyhedron shape model of an asteroid, a surface scattering model, and the desired asteroid location and orientation and the phase angle. Output parameters are the reflected Stokes vector and the degree and direction of polarization, for each individual surface facet and disk-integrated. ARM is fully verified. Generated phase-polarization curves are validated using polarimetric data of four asteroids, including (3200) Phaethon, for which various surface scattering models are deployed. These phase-polarization curves are fit to the Phaethon data, but this did not result in a good match for any of the surface scattering models, since they fail to simulate the opposition effect. However, the effect of the shape, orientation and the rotational motion is clearly visible in the results, as is the relation between wavelength and polarization. Finally, it was concluded that the polarization is favored over the flux when determining an asteroid's surface characteristics and shape, and that both flux and polarization can be used together when determining its size.