Comparative Analysis of Polarization in Interstellar Comet 3I/ATLAS with Distant Solar System Comets

Abstract We analyze polarimetric measurements of the interstellar Comet 3I/ATLAS reported recently by Z. Gray et al. Comparison with distant solar system comets suggests no significant difference in the microphysics of the dust populating its coma. The extended range of the polarimetric phase function places constraints on the real part of refractive index of particles in the 3I/ATLAS coma at Re( m ) ≈ 1.387 ± 0.085, suggesting the presence of a considerable amount of water ice, exceeding volume of Mg-rich silicates by several times.