Comment on “Is the D/H ratio in the comet coma equal to the D/H ratio in the comet nucleus?” by M. Podolak, Y. Mekler, and D. Prialnik

In a recent Icarus note, Podolak et al. (2002, Icarus 160, 208-211) proposed a model, which results in a significant enrichment in the D/H ratio in the coma relative to that in the comet nucleus. This conclusion contradicts to the typical HDO/H₂O ice-vapor fractionation, with a smaller or equal D/H in the vapor. It is based on an error in the relationship for sublimation flux, which adversely affects all conclusions of Podolak et al. (2002, Icarus 160, 208-211). Due to the very low diffusion in the H₂O ice, the HDO/H₂O ratio in the coma should closely match this ratio in the nucleus.