J/A+A/643/L10ivo://CDS.VizieR/J/A+A/643/L10doi:10.26093/cds/vizier.36439010CDSRambaux N.Castillo-Rogez J.C.2021-05-03T08:55:36Z2020-11-03T06:47:05ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frsolar-systemsolar-system-planetsPhoebe 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-aluminium. 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. 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. 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). We show that Phoebe is differentiated with a mantle density between 1900 and 2400kg/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.2020A&A...643L..10Rhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/643/L10CatalogResearchIsServedByTAP VizieR generic servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/643/L10https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/643/L10http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/643/L10https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/643/L10https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/643/L10http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/643/L10GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapdefaultJ/A+A/643/L10/tablea1Coefficients of the spherical functionsDegreeDegreestat.fit.paramintrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintOrderOrderstat.fit.paramintATopographic coefficients of the spherical functions (cosine term)kmstat.fit.paramdoubleBTopographic coefficients of the spherical functions (sine term)kmstat.fit.paramdoublee_AFormal uncertainty on A (sigmaA)kmstat.errordoublee_BFormal uncertainty on B (sigmaB)kmstat.errordouble