# Experimental phase function and degree of linear polarization of cometary dust analogs

## TL;DR

This study experimentally characterizes the phase function and polarization of cometary dust analogs, comparing results with observational data to understand dust grain properties and composition.

## Contribution

It provides new experimental phase and polarization curves for various cometary dust analogs at 520 nm, aiding in interpreting comet and asteroid observations.

## Key findings

- Measured phase functions show typical behavior for micron-sized cosmic dust.
- Significant differences found when comparing with comet 67P data, suggesting larger dust chunks.
- Polarization curves are similar to ground-based observations, with polarization angle depending on grain composition.

## Abstract

We present experimental phase function and degree of linear polarization curves for seven samples of cometary dust analogues namely: ground pieces of Allende, DaG521, FRO95002 and FRO99040 meteorites, Mg-rich olivine and pyroxene, and a sample of organic tholins. The experimental curves have been obtained at the IAA Cosmic Dust Laboratory at a wavelength of 520 nm covering a phase angle range from 3{\deg} to 175{\deg}. We also provide values of the backscattering enhancement (BCE) for our cometary analogue samples. The final goal of this work is to compare our experimental curves with observational data of comets and asteroids to better constrain the nature of cometary and asteroidal dust grains. All measured phase functions present the typical behavior for \mu m-sized cosmic dust grains. Direct comparison with data provided by the OSIRIS/Rosetta camera for comet 67P Churyumov-Gerasimenko reveals significant differences and supports the idea of a coma dominated by big chunks, larger than one micrometer. The polarization curves are qualitatively similar to ground-based observations of comets and asteroids. The position of the inversion polarization angle seems to be dependent on the composition of the grains.We find opposite dependence of the maximum of the polarization curve for grains sizes in the Rayleigh-resonance and geometric optics domains, respectively.