Astronomy and Astrophysics – Astrophysics
Scientific paper
Sep 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995a%26a...301..613o&link_type=abstract
Astronomy and Astrophysics, v.301, p.613
Astronomy and Astrophysics
Astrophysics
36
Comets: General, P/Harrington-Wilson
Scientific paper
A comet nucleus is a porous aggregate of ices and dust in which solar heating causes the sublimation of volatiles and the ejection of dust particles lifted by the flow of the escaping gases. We present a numerical model that solves the heat conduction and the gas diffusion equations throughout a porous comet nucleus made of H_2_O ice, CO_2_ ice and dust particles of different sizes. The equations are coupled via the source terms, which describe the sublimation and recondensation of ices as latent heat or mass exchanges. The ejection of dust particles is allowed when the drag exerted on a grain by the outflowing gas is stronger than the gravitational pull of the nucleus. Unbound grains that cannot be ejected form a layer of dust that darkens the comet nucleus, that, in turn, absorbs a larger fraction of the incoming solar energy. The calculations are performed under the assumption that the gas in the pore network acts as a perfect gas, and that sublimation and recondensation are instantaneous in order to keep local thermodynamic equilibrium. We investigate the influence of different model parameters on the gas and dust emission, and on the formation of a dust crust. The results show that the fraction of large grains in the dust size distribution is critical in determining the final fate of the comet nucleus, that can either disintegrate completely or turn into an inactive, asteroid-like object due to the formation of a thick, insulating dust crust. The variability of the albedo can determine a cyclic pattern in the comet activity, alternating phases of gas and dust emission, and phases in which the comet is dormant.
Capaccioni Fabrizio
Capria Maria Teresa
Coradini Angioletta
Espinasse Sylvie
Federico Cinzia
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