New 3D thermal evolution model for icy bodies application to trans-Neptunian objects (original) (raw)

A&A 529, A71 (2011)

1 LESIA, Observatoire de Paris – Section Meudon, 2 Place J. Janssen, 92195 Meudon Principal Cedex, France
2 UCLA, Department of Earth and Space Sciences, 595 Charles E. Young Drive East, Los Angeles CA 90095, USA
e-mail: aguilbert@ucla.edu
3 Los Alamos National Laboratory, Space Sciences and Applications, ISR-1, Mail Stop D-466, USA
4 Lunar and Planetary Institute, 3600 Bay Area Boulevard, Houston TX 77058, USA
5 Università di Perugia, Dipartimento di Scienze della Terra, 06123 Perugia, Italy
6 INAF-IFSI, via del Fosso del Cavaliere, 00133 Roma, Italy
7 INAF-IASF, via del Fosso del Cavaliere, 00133 Roma, Italy
8 Jet Propulsion Laboratory, 4800 Oak Grove Drive, MS 183-301, Pasadena, CA 91109, USA

Received: 3 February 2010
Accepted: 4 February 2011

Abstract

Context. Thermal evolution models have been developed over the years to investigate the evolution of thermal properties based on the transfer of heat fluxes or transport of gas through a porous matrix, among others. Applications of such models to trans-Neptunian objects (TNOs) and Centaurs has shown that these bodies could be strongly differentiated from the point of view of chemistry (i.e. loss of most volatile ices), as well as from physics (e.g. melting of water ice), resulting in stratified internal structures with differentiated cores and potential pristine material close to the surface. In this context, some observational results, such as the detection of crystalline water ice or volatiles, remain puzzling.

Aims. In this paper, we would like to present a new fully three-dimensional thermal evolution model. With this model, we aim to improve determination of the temperature distribution inside icy bodies such as TNOs by accounting for lateral heat fluxes, which have been proven to be important for accurate simulations. We also would like to be able to account for heterogeneous boundary conditions at the surface through various albedo properties, for example, that might induce different local temperature distributions.

Methods. In a departure from published modeling approaches, the heat diffusion problem and its boundary conditions are represented in terms of real spherical harmonics, increasing the numerical efficiency by roughly an order of magnitude. We then compare this new model and another 3D model recently published to illustrate the advantages and limits of the new model. We try to put some constraints on the presence of crystalline water ice at the surface of TNOs.

Results. The results obtained with this new model are in excellent agreement with results obtained by different groups with various models. Small TNOs could remain primitive unless they are formed quickly (less than 2 Myr) or are debris from the disruption of larger bodies. We find that, for large objects with a thermal evolution dominated by the decay of long-lived isotopes (objects with a formation period greater than 2 to 3 Myr), the presence of crystalline water ice would require both a large radius (>300 km) and high density (>1500 kg m-3). In particular, objects with intermediate radii and densities would be an interesting transitory population deserving a detailed study of individual fates.

Key words: Kuiper belt: general / diffusion / methods: numerical