title: Extensive water ice within Ceres' aqueously altered regolith: Evidence from nuclear spectroscopy.
abstract: The surface elemental composition of dwarf planet Ceres constrains its regolith ice content, aqueous alteration processes, and interior evolution. Using nuclear spectroscopy data acquired by NASA's Dawn mission, we determined the concentrations of elemental hydrogen, iron, and potassium on Ceres. The data show that surface materials were processed by the action of water within the interior. The non-icy portion of Ceres' carbon-bearing regolith contains similar amounts of hydrogen to those present in aqueously altered carbonaceous chondrites; however, the concentration of iron on Ceres is lower than in the aforementioned chondrites. This allows for the possibility that Ceres experienced modest ice-rock fractionation, resulting in differences between surface and bulk composition. At mid-to-high latitudes, the regolith contains high concentrations of hydrogen, consistent with broad expanses of water ice, confirming theoretical predictions that ice can survive for billions of years just beneath the surface.
authors.affiliation: Planetary Science Institute, 1700 East Fort Lowell, Suite 106, Tucson, AZ 85719-2395, USA. prettyman@psi.edu.
authors.forename: T H
authors.initials: TH
authors.lastname: Prettyman
authors.affiliation: Planetary Science Institute, 1700 East Fort Lowell, Suite 106, Tucson, AZ 85719-2395, USA.
authors.forename: N
authors.initials: N
authors.lastname: Yamashita
authors.affiliation: Institut de Recherche d'Astrophysique et Planétologie, CNRS, Université Paul Sabatier, Toulouse 31400, France.
authors.forename: M J
authors.initials: MJ
authors.lastname: Toplis
authors.affiliation: Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN 37996-1410, USA.
authors.forename: H Y
authors.initials: HY
authors.lastname: McSween
authors.affiliation: University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA.
authors.forename: N
authors.initials: N
authors.lastname: Schörghofer
authors.affiliation: Southwest Research Institute, Boulder, CO 80302, USA.
authors.forename: S
authors.initials: S
authors.lastname: Marchi
authors.affiliation: Planetary Science Institute, 1700 East Fort Lowell, Suite 106, Tucson, AZ 85719-2395, USA.
authors.forename: W C
authors.initials: WC
authors.lastname: Feldman
authors.affiliation: Jet Propulsion Laboratory (JPL), California Institute of Technology, Pasadena, CA 91109-8099, USA.
authors.forename: J
authors.initials: J
authors.lastname: Castillo-Rogez
authors.affiliation: Institut de Recherche d'Astrophysique et Planétologie, CNRS, Université Paul Sabatier, Toulouse 31400, France.
authors.forename: O
authors.initials: O
authors.lastname: Forni
authors.affiliation: Johns Hopkins University, Applied Physics Laboratory, Laurel, MD 20723, USA.
authors.forename: D J
authors.initials: DJ
authors.lastname: Lawrence
authors.affiliation: Earth Planetary and Space Sciences, University of California, Los Angeles, Los Angeles, CA 90095-1567, USA.
authors.forename: E
authors.initials: E
authors.lastname: Ammannito
authors.affiliation: Jet Propulsion Laboratory (JPL), California Institute of Technology, Pasadena, CA 91109-8099, USA.|Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA.
authors.forename: B L
authors.initials: BL
authors.lastname: Ehlmann
authors.affiliation: Planetary Science Institute, 1700 East Fort Lowell, Suite 106, Tucson, AZ 85719-2395, USA.
authors.forename: H G
authors.initials: HG
authors.lastname: Sizemore
authors.affiliation: Earth Planetary and Space Sciences, University of California, Los Angeles, Los Angeles, CA 90095-1567, USA.
authors.forename: S P
authors.initials: SP
authors.lastname: Joy
authors.affiliation: Jet Propulsion Laboratory (JPL), California Institute of Technology, Pasadena, CA 91109-8099, USA.
authors.forename: C A
authors.initials: CA
authors.lastname: Polanskey
authors.affiliation: Jet Propulsion Laboratory (JPL), California Institute of Technology, Pasadena, CA 91109-8099, USA.
authors.forename: M D
authors.initials: MD
authors.lastname: Rayman
authors.affiliation: Jet Propulsion Laboratory (JPL), California Institute of Technology, Pasadena, CA 91109-8099, USA.
authors.forename: C A
authors.initials: CA
authors.lastname: Raymond
authors.affiliation: Earth Planetary and Space Sciences, University of California, Los Angeles, Los Angeles, CA 90095-1567, USA.
authors.forename: C T
authors.initials: CT
authors.lastname: Russell