[P-CG10] Small Solar System Bodies: General and Mars Satellite Sample Return Mission

[PCG10-P08] Gravity science investigation of Ceres from Dawn

*Ryan Park¹ (1.Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA、2.IMCCE, Observatoire de Paris, Paris, France、3.Massachusetts Institute of Technology, Cambridge, MA, USA、4.Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY, USA、5.University of Toulouse, Toulouse, France、6.UCLA, Los Angeles, CA, USA.)

キーワード：Ceres, Dawn, Dwarf planet

R.S. Park¹, A.S. Konopliv¹, B.G. Bills¹, N. Rambaux², J.C. Castillo-Rogez¹, C.A. Raymond¹, A.T. Vaughan¹, A. Ermakov³, M.T. Zuber³, R. Fu⁴, M.J. Toplis⁵, C.T. Russell⁶, ¹Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA (e-mail [e-mail]); ²IMCCE, Observatoire de Paris, Paris, France; ³Massachusetts Institute of Technology, Cambridge, MA, USA; ⁴Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY, USA; ⁵University of Toulouse, Toulouse, France; ⁶UCLA, Los Angeles, CA, USA.
The Dawn gravity science investigation utilizes the DSN radiometric tracking of the spacecraft and on-board framing camera images to determine the global shape and gravity field of Ceres. The gravity science data collected during Approach, Survey, and High-Altitude Mapping Orbit phases were processed. Currently, the latest gravity field called CERES08A is available, which is globally accurate to degree and order 5. Combining the gravity and shape data gives the bulk density of 2163+-8 kg/m³. The low Bouguer gravity at high topography area, or vice versa, indicates that the surface of Ceres is likely compensated and that its interior presents a low-viscosity layer at depth. The degree 2 gravity harmonics show that the rotation of Ceres is very nearly about a principal axis. This is consistent with hydrostatic equilibrium at the 3% level. This infers that the mean moment of inertia of Ceres is , implying some degree of central condensation. Based on a simple two-layer model of Ceres and assuming carbonaceous chondrites and hydrostatic equilibrium, the core size is expected to be ~280 km with corresponding average thickness of the outer shell of ~190 km and density of ~1950 kg/m³.