A thermal modelling of cometary activity with a crystallized water ice nucleus

Abstract

Arguments are presented to suggest that surface layers of the nuclei of periodic comets consist of crystallized rather than amorphous water ice and thermal modelling of such nuclei is presented. The rate of sublimation of water from a rotating nucleus is found to be greater than that from a uniformly heated nucleus. When the model is applied to P/Halley, the sublimation rate at perihelion is found to be 8.1 x 10" mol s-' for a nucleus rotating with a period of 50 hours and 7.6 x lo*' for a uniformly heated nucleus on the premise that the effective radius of the nucleus is 2.5 km. The total sublimation of water per revolution is 5.38 x 1O36 molecules for P/Halley and 3.91 x 1O36 molecules per P/Crommelin. The result so obtained is discussed in relation to the observational data.

Water outburst activity in Comet 17P/Holmes

“…The phase transition from amorphous water ice (2.3 g cm -3 ) to the crystalline allotrope with a density of 0.94 g cm -3 , occurs at a temperature near pulverize the ice (e.g. Prialnik and Bar-Nun, 1992, for comet P/Halley crystallization of amorphous ice model; see also Yabushita and Hatta, 1987;and Patashnick et al, 1974). Any volume element that undergoes this irreversible (exothermic) phase transition increases its temperature by about 45 K. Gronkowski (2007) has reviewed the potential sources of energy of cometary outbursts and concluded that the hypothesis concerning the amorphous water ice transformation appears to be the most probable one.…”