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Constraints on Ceres' Internal Structure and Evolution From Its Shape and Gravity Measured by the Dawn Spacecraft
Author(s) -
Ermakov A. I.,
Fu R. R.,
CastilloRogez J. C.,
Raymond C. A.,
Park R. S.,
Preusker F.,
Russell C. T.,
Smith D. E.,
Zuber M. T.
Publication year - 2017
Publication title -
journal of geophysical research: planets
Language(s) - English
Resource type - Journals
eISSN - 2169-9100
pISSN - 2169-9097
DOI - 10.1002/2017je005302
Subject(s) - geology , isostasy , hydrostatic equilibrium , gravity anomaly , geophysics , dwarf planet , gravitational field , physics , spherical cap , spherical harmonics , geodesy , asteroid , lithosphere , geometry , astrobiology , astronomy , seismology , paleontology , mathematics , quantum mechanics , oil field , tectonics
Ceres is the largest body in the asteroid belt with a radius of approximately 470 km. In part due to its large mass, Ceres more closely approaches hydrostatic equilibrium than major asteroids. Pre‐Dawn mission shape observations of Ceres revealed a shape consistent with a hydrostatic ellipsoid of revolution. The Dawn spacecraft Framing Camera has been imaging Ceres since March 2015, which has led to high‐resolution shape models of the dwarf planet, while the gravity field has been globally determined to a spherical harmonic degree 14 (equivalent to a spatial wavelength of 211 km) and locally to 18 (a wavelength of 164 km). We use these shape and gravity models to constrain Ceres' internal structure. We find a negative correlation and admittance between topography and gravity at degree 2 and order 2. Low admittances between spherical harmonic degrees 3 and 16 are well explained by Airy isostatic compensation mechanism. Different models of isostasy give crustal densities between 1,200 and 1,400 kg/m 3 with our preferred model giving a crustal density of 1 , 28 7 + 70 − 87 kg/m 3 . The mantle density is constrained to be 2 , 43 4 + 5 − 8 kg/m 3 . We compute isostatic gravity anomaly and find evidence for mascon‐like structures in the two biggest basins. The topographic power spectrum of Ceres and its latitude dependence suggest that viscous relaxation occurred at the long wavelengths (>246 km). Our density constraints combined with finite element modeling of viscous relaxation suggests that the rheology and density of the shallow surface are most consistent with a rock, ice, salt and clathrate mixture.