Experimental phase function and degree of linear polarization curve of olivine and spinel and the origin of the Barbarian polarization behaviour

ABSTRACT We explore experimentally possible explanations of the polarization curves sunlight reflected by Barbarian asteroids. Their peculiar are characterized a large-inversion angle, around 30°, which could be related to presence FeO-bearing spinel embedded in Calcium–Aluminum inclusions. In order test this hypothesis, we have measured phase function and degree linear six samples Mg-rich olivine spinel. For each material, analysed light scattering properties millimeter-sized grain two powdered with size distributions micrometer range. The three show well-defined negative branch an inversion angle located 24°–30°. contrast, case samples, is highly dependent on particle tends decrease for larger sizes. identify macroscopic geometries as explanation evident differences between millimeter samples. Although behaviour near backscattering Barbara asteroid similar that our mm-sized sample random orientation, similarity result part from crystal retro-reflection rather than composition. This ongoing experimental project devoted separately several components CV3-like meteorites, representative Barbarians composition, disentangle their contributions these objects.