Thermal physics of asteroids. II. Polarization of the thermal microwave emission from asteroids.
Abstract
The thermal microwave emission of the atmosphereless asteroids is the result of a radiative transport process extending to a depth of some wavelengths into the surface material. The possibility of polarization in the disc integrated microwave emission is investigated. The heat diffusion of the diurnal insolation is considered, and the radiative transport equation is solved for the resulting vertical temperature profile. When transmitted through the surface the radiation is polarized according to Fresnel's equations. The transmission coefficients are modified by the surface roughness, which results in a lower degree of polarization and an increased emissivity for the regions closer to the limb. It is demonstrated how the polarization and its orientation depends on the physical properties of the surface as well as the global geometry. The levels of polarization found range from a few percent to some tens of percent; maximized by a highly elongated shape, low surface roughness, a spin vector perpendicular to the line of sight and a high dielectrical constant. The orientation of the polarization is not in general parallel to the spin vector as suggested by Redman et al. (1996AJ....109.2869R). The electrical vector and the spin vector coincide only for special geometries or when the time average of the Stokes vector is considered.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- November 1996
- Bibcode:
- 1996A&A...315..625L
- Keywords:
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- ASTEROIDS: POLARIZATION;
- INFRARED: SOLAR SYSTEM