Lawrence, D.J.D.J.LawrencePeplowski, P.N.P.N.PeplowskiBeck, A.W.A.W.BeckFeldman, W.C.W.C.FeldmanPrettyman, T.H.T.H.PrettymanRussell, C.T.C.T.RussellToplis, M.J.M.J.ToplisWilson, J.T.J.T.WilsonAmmannito, EleonoraEleonoraAmmannitoCastillo-Rogez, J.C.J.C.Castillo-RogezDeSanctis, M.C.M.C.DeSanctisMest, S.C.S.C.MestNeesemann, A.A.Neesemann2022-08-222022-08-222018https://hdl.handle.net/20.500.13025/6191High-energy gamma rays (HEGRs) from Ceres’s surface were measured using Dawn's Gamma Ray and Neutron Detector (GRaND). Models of cosmic-ray-initiated gamma ray production predict that the HEGR flux will inversely vary with single-layer hydrogen concentrations for Ceres-like compositions. The measured data confirm this prediction. The hydrogen-induced variations in HEGR rates were decoupled from the measurements by detrending the HEGR data with Ceres single-layer hydrogen concentrations determined by GRaND neutron measurements. Models indicate that hydrogen-detrended HEGR counting rates correlate with water-free average atomic mass, which is denoted as <A>*. HEGR variations across Ceres’s surface are consistent with <A>* variations of ±0.5 atomic mass units. Chemical variations in the CM and CI chondrites, our closest analogs to Ceres’s surface, suggest that <A>* variations on Ceres are primarily driven by variations in the concentration of Fe, although other elements such as Mg and S could contribute. Dawn observations have shown that Ceres’s interior structure and surface composition have been modified by some combination of physical (i.e., ice-rock fractionation) and/or chemical (i.e., alteration) processes that has led to variations in bulk surface chemistry. Locations of the highest inferred <A>* values, and thus possibly the highest Fe and least altered materials, tend to be younger, less cratered surfaces that are broadly associated with the impact ejecta of Ceres’s largest craters. © 2018 The Authors. Meteoritics & Planetary Science published by Wiley Periodicals, Inc. on behalf of The Meteoritical Society (MET).enjournal article10.1111/maps.13124https://onlinelibrary.wiley.com/doi/10.1111/maps.13124