Other
Scientific paper
Oct 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997icar..129..317c&link_type=abstract
Icarus, Volume 129, Issue 2, pp. 317-336.
Other
30
Scientific paper
What is the ultimate fate of a comet? Excluding impacts with other bodies, two possibilities are foreseen: either long-lasting activity, accompanied by nucleus reduction, or the formation of a stable crust that inhibits dust emission and strongly reduces volatile emissions. In the first case the comet could disintegrate, whereas in the second case it could become dormant or extinct, assuming an asteroidal appearance; in both cases the comet could be reactivated. In this paper we present results of a comet evolution model trying to establish the conditions under which the nucleus becomes dormant or extinct and under which it continues its activity up to the consumption of the icy material. Our nucleus model is composed of a mixture of ices of water, CO_2, and CO and dust particles. The H_2O ice can be either amorphous or crystalline; the solid matrix is assumed to be porous. The evolution of the body is determined by the solar energy reaching its surface and by the heat transfer in the interior. The propagation of the heat through the nucleus is modeled by means of the heat transfer and gas diffusion equations, coupled via the condensation-sublimation terms that are seen as sinks or sources of energy and matter, respectively. Particular attention is given to the variations of porosity and to the changes in composition of the superficial layers due to sublimation-condensation phenomena, to gas diffusion processes through the pore system, and to the ejection of dust particles. At the beginning of the evolution of the nucleus the crust is never present and the interior of the comet is not differentiated. We have seen that the evolution can proceed essentially in two ways: (1) if the body is dark and rich in volatiles and the dust grains are fluffy, then the upper layers are usually removed at the same rate at which the CO_2 upper boundary sinks; (2) in the opposite case, sometimes a dusty crust is formed, sometimes not, but in any case the CO_2 interface sinks deeply. We conclude that in the first case the body will remain active for several orbits, while in the second case the gradual reduction of any activity can produce a dormant or extinct comet, maybe with the appearance of an asteroid.
Capaccioni Fabrizio
Capria Maria Teresa
Coradini Angioletta
de Sanctis Maria Cristina
Espianasse S.
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