Scattering Properties of Large Irregular Cosmic Dust Particles at Visible Wavelengths

Abstract

The effect of internal inhomogeneities and surface roughness on the scattering behavior of large cosmic dust particles is studied by comparing model simulations with laboratory measurements. The present work shows the results of an attempt to model a dust sample measured in the laboratory with simulations performed by a ray-optics model code. We consider this dust sample as a good analogue for interplanetary and interstellar dust as it shares its refractive index with known materials in these media. Several sensitivity tests have been performed for both structural cases (internal inclusions and surface roughness). Three different samples have been selected to mimic inclusion/coating inhomogeneities: two measured scattering matrices of hematite and white clay, and a simulated matrix for water ice. These three matrices are selected to cover a wide range of imaginary refractive indices. The selection of these materials also seeks to study astrophysical environments of interest such as Mars, where hematite and clays have been detected, and comets. Based on the results of the sensitivity tests shown in this work, we perform calculations for a size distribution of a silicate-type host particle model with inclusions and surface roughness to reproduce the experimental measurements of a dust sample. The model fits the measurements quite well, proving that surface roughness and internal structure play a role in the scattering pattern of irregular cosmic dust particles.

Retrieving Dust Grain Sizes from Photopolarimetry: An Experimental Approach

“…Further, the position of DLP max spans from 75°for the samples consisting of smaller particles to 140°for the pebble. The shift of DLP max toward larger phase angles with increasing size is in agreement with the computed results for Gaussian random spheres in the geometric optics regime (Liu et al 2015;Escobar-Cerezo et al 2017). A large α max of about 140°is also observed in the K 1 -band images of the debris disk HR 4796A obtained in the polarimetric mode of the Gemini Planet Imager (Perrin et al 2015;Arriaga et al 2020).…”

Analogues of interplanetary dust particles to interpret the zodiacal light polarization

“…Our past and present laboratory measurements with PROGRA2 (Hadamcik et al, 2007a;2009b) have shown the importance of the presence of carbonaceous particles when trying to simulate cometary particles (with a global low-albedo). The precise numerical modelling of the irregular Sahara sand particles as possible cosmic dust, by Escobar et al (2017), has shown the importance of irregularities on the surface for polarization measurements, and can produce very excellent correlation with the experimental phase curves. Nevertheless, such modelling effort for mixtures of particles of different materials and structures seems to be out of reach for the time being.…”

Experimental phase function and degree of linear polarization of cometary dust analogues

“…Since these quantities are intimately related to the nature of the particles, laboratory data are used as a reference for comparison and interpretation, allowing a correct analysis of the observational data (Muñoz et al 2000;Volten et al 2006;Muñoz et al 2017). Modeling of the interaction between electromagnetic radiation and particles in turn, supports the experiments, helping to discriminate unambiguously dust features corresponding to specific observables (Liu et al 2015;Zubko 2015;Escobar-Cerezo et al 2017). All these different approaches (observations, laboratory experiments and theoretical simulations) provide essential contributions to the investigation of the behavior of dust particles as radiation scatterers.…”