Experimental phase function and degree of linear polarization of cometary dust analogues
Jan 2019 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◦ to 175◦. We also provide values of the
backscattering enhancement 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 behaviour for μm-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.
MNRAS, 484:2198, 2019