Inferring properties of dust within small bodies of the solar system through observations and simulations of the linear polarization of scattered solar light

Measuring properties of solar light scattered by dust on the surfaces of asteroids and within dust clouds (cometary comae, zodiacal cloud) is often a technical challenge, since the signals need to be isolated from any contaminating source on the line of sight. However, measurements of linear polarization are of major interest, since they enable comparisons between data obtained at different distances from the Sun and the observer on a given object or on various objects. They provide some classifications and efficiently complement unique in situ and sample return missions. Some clear observational trends can be pointed out, from the results obtained, mostly on relatively bright objects, by various teams all over the world. It is worth mentioning that all polarimetric phase curves present a shallow negative branch in the backscattering region, with some significant dispersion of the inversion angle for asteroids, and that the wavelength dependence at a fixed phase angle is, for a given object, mostly linear in the visible domain; besides, changes in the properties of the dust within cometary comae are identified through imaging polarimetry. Promising interpretations of the observed variations of the polarization are inferred from experimental and numerical simulations with irregular compact grains and aggregates of dust particles. They already provide information on the structure, composition, and size distribution of dust within the zodiacal cloud and within comae that are monitored over a wide range of phase angles, as well as comparisons between the properties of asteroidal regoliths and those of some meteorites.