Geological Society of America

T110 The Geology of Dwarf Planet Ceres

Monday, 26 September 2016
8:00 AM - 12:00 PM
Room 201

ELEMENTAL CONSTRAINTS ON CERES' EVOLUTION

Paper number: T110-5
Program: Technical Sessions
Time: 8:55 AM – 9:10 AM

Authors

Thomas H. Prettyman Presenting Author
Planetary Science Institute, Tucson, AZ
David J. Lawrence
Johns Hopkins University Applied Physics Laboratory, Laurel, MD
Eleonora Ammannito
University of California, Los Angeles, Los Angeles, CA
Bethany Ehlmann
California Institute of Technology, Pasadena, CA
Hanna Sizemore
Planetary Science Institute, Tucson, AZ
Steven P. Joy
University of California, Los Angeles, Los Angeles, CA
Carol A. Polanskey
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA
Marc D. Rayman
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA
Carol A. Raymond
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA
Christopher T. Russell
University of California, Los Angeles, Los Angeles, CA
Naoyuki Yamashita
Planetary Science Institute, Tucson, AZ
Michael Toplis
Centre National de la Recherche Scientifique, Toulouse
Harry Y. McSween
University of Tennessee, Knoxville, TN
Norbert Schorghofer
Honolulu, HI
Simone Marchi
Southwest Research Institute, Boulder, CO
William C. Feldman
Planetary Science Institute, Tucson, AZ
Julie C. Castillo-Rogez
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA
Olivier Forni
Centre National de la Recherche Scientifique, Toulouse

Abstract

The Gamma Ray and Neutron Detector (GRaND) onboard the Dawn spacecraft globally mapped the elemental composition of Ceres’ regolith, providing new information about interior processes that shaped Ceres. The bombardment of surface materials by galactic cosmic rays makes gamma rays and neutrons. Gamma rays are also made by the decay of natural radioelements (K, Th, U) found in silicate minerals. At low altitude, GRaND measures the leakage spectrum of gamma rays and neutrons, which are sensitive to the composition of the uppermost meter of the regolith within broad spatial regions (several 100 km in scale). The data show that Ceres’ regolith is hydrogen rich, with an equatorial composition (Fe, K, C) similar to that of aqueously altered CI/CM chondrites. These meteorites contain hydrogen in the form of water and hydroxyl bound to phyllosilicate minerals with concentrations similar to that observed by GRaND. This is consistent with the inference by Dawn’s Visible and Infrared (VIR) Spectrometer that phyllosilicates are a major component of the surface. At high latitudes, the concentration of hydrogen is elevated, likely due to pervasive water ice very near the surface, as predicted by ice stability modeling (Fanale and Salvail, 1989). The elemental data support global-scale alteration of accreted material by the action of water within Ceres’ interior; however, due to Ceres’ large size, various processes such as convection may have separated brine-rich liquid from solid residues, resulting in chemical fractionation. If so, then the elemental composition of the regolith should deviate from altered carbonaceous chondrites, which formed in an environment with limited fluid flow. In this presentation, we describe the latest elemental measurements of Ceres by GRaND and show how these measurements constrain regolith processes and interior evolution.

Fanale, F. P. and J. R. Salvail (1989), The water regime of asteroid (1) Ceres, Icarus, Vol. 82, Issue 1, pp. 97-110, doi:10.1016/0019-1035(89)90026-2.

Geological Society of America Abstracts with Programs. Vol. 48, No. 7

doi: 10.1130/abs/2016AM-283851

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