Surface regolith model of near-Earth asteroid (3200) Phaethon
The near-Earth asteroid (3200) Phaethon displays activity as it comes close to the Sun and is presumed to be the progenitor of the Geminids meteor shower. Both CM- and CY-meteorites have been suggested as possible meteorite analogues for Phaethon. Previous spectral and polarization measurements of Phaethon indicate possible surface heterogeneity in the regolith properties. By combining mineral components and their size fractions, we present a regolith model for Phaethon that reproduces the spectral, polarization, and geometric albedo measurements presented in various studies, with the aim of quantitatively characterizing the surface material and structure, as well as the regolith heterogeneity. The best fit model able to produce the measurements is constructed from large olivine particles with troilite inclusions and small scale surface roughness, mixed with smaller, porous troilite aggregates comprised of monomers resembling interplanetary dust. Our model suggests that the different spectral and polarization responses of the regolith are caused by changes in the size and amount of the small dark troilite particles. Based on the amount of troilite in the regolith model, we propose that CM-meteorites are the preferable meteorite analogue for Phaethon.