Astronomy and Astrophysics – Astrophysics
Scientific paper
Jun 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...286..659t&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 286, no. 2, p. 659-682
Astronomy and Astrophysics
Astrophysics
53
Amorphous Materials, Carbon Monoxide, Comet Nuclei, Dust, Ice, Matrix Materials, Thermochemistry, Water Vapor, Astronomical Models, Crystallization, Granular Materials, Thermal Conductivity
Scientific paper
New experimental results related to the physical characteristics of the material components of the cometary nuclei as well as new ideas about several aspects of the modelling of the thermochemical process in the interior of this objects lead us to make a new attempt to analyse the physical evolution of Jupiter family comets over time scales comparable to their lifetime. A new model is described in this paper where we present results concerning the evolution of Jupiter family comets and make comparisons with previous models. Our model of the cometary material includes a porous solid matrix and vapor filling the pores. As basic constituents of the solid matrix we consider three omnipresent species: dust, water ice (in two phases: amorphous and crystalline), and H2O vapor. In addition to the above, we include one substance more volatile than H2O, CO, initially trapped in the amorphous matrix. We improved on the earlier models by accounting for the state of near saturation attained by the vapor inside the nucleus, by including a separate treatment of an unsaturated surface layer and by explicitly including the erosional velocity of the surface. As far as physical parameters are concerned, our basic improvements on earlier models were: 1) the representation of this matrix as an aggregate of micron-sized core-mantle grains; 2) the adoption of a very low thermal conductivity of the amorphous ice mantles; and 3) a correct account of the energetics of gas release and the allowance for condensation of CO ice. Concluding on the behavior of Jupiter family comets, we find that the complete crystallization of a sizeable nucleus with an initial radius of several km should take approximately 104 years. This means that Jupiter family comets with our assumed properties should still retain their CO, although in most cases buried deep below the nuclear surface.
Greenberg Mayo J.
Rickman Hans
Tancredi Gonzalo
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