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Theses

Les noyaux cométaires et leurs processus d'activité

Abstract : The study of cometary nuclei is of paramount importance to understand the formation and the evolution of the solar system. This thesis presents several methods and models to determine their physical properties (radius, geometric albedo, thermal inertia and active surface fraction) from visible observations, infrared observations and water production rate, and to quantify the activity on their surface. We study the nucleus of comets Hale-Bopp (C/1995 O1), 55P/Tempel-Tuttle, 126P/IRAS, 103P/Hartley 2, 22P/Kopff, 46P/Wirtanen, IRAS-Araki-Alcock (C/1983 H1) and 2P/Encke, of Centaurs Chiron (2060) and Chariklo (1997 CU26), and of sungrazing comets. From this analysis, we find that: (i) the geometric albedo of Centaurs is 0.07-0.11 which is higher than the geometric albedo of LPC (Long Period Comets) and SPC (Short Period Comets) which is 0.04-0.07, (ii) a low albedo is not incompatible with the presence of water ice on the surface, (iii) the thermal inertia of the nucleus is low and is <3 J/K/m2/s1/2, (iv) the perihelion distance, combined with water ice sublimation, is not sufficient to explain the radius differences between sungrazing comets (<0.11 km), SPC (0.6-2.4 km), LPC (3-38 km) and Centaurs (71-118 km), (v) the formation of a crust on the surface of the SPC is highly probable and can explain the variations of the water production rate with the heliocentric distance, and (vi) the activity on the surface of cometary nuclei is not necessarily localized in a few active regions; the activity of small SPC ($\sim$1\ts km) is distributed all over their surface. Localized active regions, as implied by the presence of jets in the coma, only exist on a minority, mostly large, nuclei.
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Olivier Groussin. Les noyaux cométaires et leurs processus d'activité. Autre. Université de la Méditerranée - Aix-Marseille II, 2002. Français. ⟨tel-00124558⟩

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