On the nature of interstellar grains

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

“…The vapour pressure could be large enough to blow off the surface layer and to expose virgin ice to the solar radiation, which would result in the asymmetry of cometary activity. Furthermore, the liquid water could act as a site for replication of micro-organisms in the panspermia of Hoyle et al (Hoyle, 1984;Hoyle and Wickramasinghe, 1979). Finally, the total gas production per revolution can be estimated by summing up the production rate over one orbital period.…”

“…We adopt the temperature dependence of c and K for crystalline ice as given by Klinger (1981). Both c and K have strong temperature dependence.…”

“…First, heat balance at the nuclear surface is related to the gas production rate and hence coma formation. Second, heat conduction within the nucleus may lead to a thermal stress which might result in the fragmentation of the nucleus (Smoluchowski, 1981a).…”

“…First, radio genie heating due to A126 may be sufficient to melt the deep interior (Wallis, 1980). Second, if the amorphous ice is heated to 153 K by solar radiation, a rapid crystallization sets in and releases the energy sufficient to raise the temperature by 37 K in 10 seconds (Smoluchowski, 1981a). Therefore, if a comet approaches the Sun, heating at the surface is expected to transform the surface to crystalline ice, and if the energy released thereby is communicated to the neighbouring layers, such layers are also transformed to Earth, Moon, and Planets 37 (1987) crystalline form.…”

“…In doing so, the observational data of P/Halley will be of particular use, and naturally it is the one to which we pay most of our attention. Sekanina (1985) reported that the rotational period of P/Halley is 52 hours and that the obliquity of the rotational axis is 30 degrees. For the sake of simplicity, the spin axis is taken to be perpendicular to the orbital plane.…”