On the extremely low polarization in Comet C/2023 P1 (Nishimura)

On September 6 and 7 of 2023, we measured the degree of linear polarization of Comet C/2023 P1 (Nishimura) with the R filter. Our observations reveal an extremely low amplitude of positive polarization. Our modeling suggests Mg-rich silicate dust particles are the dominant species in the coma; whereas, an alternative explanation is that such low positive polarization in comets is attributed to the depolarizing effect of their gaseous emission. These two alternative explanations predict dramatically different polarimetric responses at small phase angle that can be discriminated in future polarimetric observations of Comet C/2023 P1 (Nishimura).