Planetary and Space Science 56 (2008) 1977–1991 Quasi-3-D model to describe topographic effects on non-spherical comet nucleus evolution J. Lasue a,Ã , M.C. De Sanctis b , A. Coradini c , G. Magni b , M.T. Capria b , D. Turrini c , A.C. Levasseur-Regourd a a UPMC Univ Paris 06, UMR 7620, Ae´ronomie CNRS-IPSL, BP 3, F-91371 Verrie`res, France b Istituto di Astrofisica Spaziale e Fisica Cosmica, INAF, Rome 00133, Italy c Istituto di Fisica dello Spazio Interplanetario, INAF, Rome 00133, Italy Received 15 January 2008; received in revised form 25 August 2008; accepted 27 August 2008 Available online 3 September 2008 Abstract A new quasi three-dimensional code is presented and used to explore the thermal evolution of non-spherical-shape cometary nuclei. Calculations are done for spherical nuclei with different obliquities, spherical nuclei with crater-like depressions and spheroid-shape nuclei. The results obtained for both the gas and dust fluxes agree with previous simulations. Local dust crust formation can occur when the comet is located far from the Sun (around 3.5 AU), creating active and inactive areas on the surface. For a given set of parameters, the H 2 O production rate is comparable to the one observed for comets. A pre–post-perihelion asymmetry exists for H 2 O, CO 2 and CO production rates. It is shown that crater-like depressions can be erased within the lifetime of a comet and that spheroid-shape nuclei have a higher production rate than equal area spherical nuclei. r 2008 Elsevier Ltd. All rights reserved. Keywords: Comets; Nucleus; Composition; Interiors; Thermal histories 1. Introduction Cometary nuclei are icy bodies considered as the most primitive remnants of the solar system formation. As a consequence, their study can improve our insight on the processes that occurred during the initial stages of the protosolar nebula. The international space mission Rosetta launched in 2004 by ESA (European Space Agency) will study the onset of the activity from near the aphelion to the perihelion of the comet 67P/Churyumov–Gerasimenko, providing thus insights both on its origin and on its evolution. This goal will be achieved through the use of instruments designed to make a tomography-like measure- ment of the interior inhomogeneities of the nucleus (Kofman et al., 2007) and observations and spectral analyses of the surface and gas emissions (Coradini et al., 2007). In order to prepare adequately the arrival and the landing of the mission, both remote observations and numerical models of the nucleus and its activity are required to give as much prior information as possible to prevent damages to the spacecraft and analyze the output data with a high precision. In this regard, numerical models of thermal evolution of cometary nuclei remain a cornerstone for the interpretation and, within limits, prediction of cometary activity and evolution (Huebner et al., 2006). Numerical models of cometary evolution have been developed during the last two decades thanks to the increase in computational power. Initial models used a one- dimensional representation of an ideal spherical nucleus (e.g., Fanale and Salvail, 1984; Herman and Podolak, 1985; Espinasse et al., 1991). They gave valuable insights on the cometary activity, taking progressively into account the crystallization of ice, the contribution of different volatiles and the heat and matter flows through a porous matrix of ice and dust. The first models were based on the ‘‘fast-rotator’’ approximation. However to obtain a correct surface temperature and its change with the rotation, the obliquity ARTICLE IN PRESS www.elsevier.com/locate/pss 0032-0633/$ - see front matter r 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.pss.2008.08.020 Ã Corresponding author. Tel.: +33 1 44 27 21 63; fax: +33 1 44 27 37 76. E-mail address: jeremie.lasue@aerov.jussieu.fr (J. Lasue).