Extensive water ice within Ceres' aqueously altered regolith: Evidence from nuclear spectroscopy

T H Prettyman; N Yamashita; M J Toplis; H Y McSween; N Schörghofer; S Marchi; W C Feldman; J Castillo-Rogez; O Forni; D J Lawrence; E Ammannito; B L Ehlmann; H G Sizemore; S P Joy; C A Polanskey; M D Rayman; C A Raymond; C T Russell

doi:10.1126/science.aah6765

Extensive water ice within Ceres' aqueously altered regolith: Evidence from nuclear spectroscopy

Science. 2017 Jan 6;355(6320):55-59. doi: 10.1126/science.aah6765. Epub 2016 Dec 15.

Authors

T H Prettyman¹, N Yamashita², M J Toplis³, H Y McSween⁴, N Schörghofer⁵, S Marchi⁶, W C Feldman², J Castillo-Rogez⁷, O Forni³, D J Lawrence⁸, E Ammannito⁹, B L Ehlmann^{7

10}, H G Sizemore², S P Joy⁹, C A Polanskey⁷, M D Rayman⁷, C A Raymond⁷, C T Russell⁹

Affiliations

¹ Planetary Science Institute, 1700 East Fort Lowell, Suite 106, Tucson, AZ 85719-2395, USA. prettyman@psi.edu.
² Planetary Science Institute, 1700 East Fort Lowell, Suite 106, Tucson, AZ 85719-2395, USA.
³ Institut de Recherche d'Astrophysique et Planétologie, CNRS, Université Paul Sabatier, Toulouse 31400, France.
⁴ Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN 37996-1410, USA.
⁵ University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA.
⁶ Southwest Research Institute, Boulder, CO 80302, USA.
⁷ Jet Propulsion Laboratory (JPL), California Institute of Technology, Pasadena, CA 91109-8099, USA.
⁸ Johns Hopkins University, Applied Physics Laboratory, Laurel, MD 20723, USA.
⁹ Earth Planetary and Space Sciences, University of California, Los Angeles, Los Angeles, CA 90095-1567, USA.
¹⁰ Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA.

PMID: 27980087
DOI: 10.1126/science.aah6765

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.