Volume 643, November 2020
|Number of page(s)||6|
|Section||Letters to the Editor|
|Published online||03 November 2020|
Letter to the Editor
Phoebe’s differentiated interior from refined shape analysis⋆
IMCCE, CNRS, Observatoire de Paris, PSL Université, Sorbonne Université, 77 Ave. Denfert-Rochereau, 75014 Paris, France
2 Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
Accepted: 19 September 2020
Context. Phoebe is an irregular satellite of Saturn, and its origin, from either between the orbits of the giant planets or the Kuiper Belt, is still uncertain. The extent of differentiation of its interior can potentially help inform its formation location because it is mainly determined by heat from 26-aluminum. The internal structure is reflected in the shape, assuming the body is relaxed to hydrostatic equilibrium. Although previous data analysis indicates Phoebe is close to hydrostatic equilibrium, its heavily cratered surface makes it difficult to tease out its low-order shape characteristics.
Aims. This paper aims to extract Phoebe’s global shape from the observations returned by the Cassini mission for comparison with uniform and stratified interior models under the assumption of hydrostatic equilibrium.
Methods. The global shape is derived from fitting spherical harmonics and keeping only the low-degree harmonics that represent the shape underneath the heavily cratered surface. The hydrostatic theoretical model for shape interpretation is based on the Clairaut equation developed to the third order (although the second order is sufficient in this case).
Results. We show that Phoebe is differentiated with a mantle density between 1900 and 2400 kg m−3. The presence of a porous surface layer further restricts the fit with the observed shape. This result confirms the earlier suggestion that Phoebe accreted with sufficient 26-aluminium to drive at least partial differentiation, favoring an origin with C-type asteroids.
Key words: planets and satellites: interiors / planets and satellites: individual: Phoebe / methods: numerical
Table A.1 is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (188.8.131.52) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/643/L10
© N. Rambaux and J. C. Castillo-Rogez 2020
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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