Concentrations of potassium and thorium within Vesta’s regolith

摘要: Abstract The globally-averaged concentrations of radioelements K and Th within Vesta’s regolith are determined from gamma ray spectra acquired by Dawn’s Gamma Ray Neutron Detector (GRaND). Spectra measured GRaND’s bismuth germanate (BGO) scintillator, while in close proximity to Vesta, analyzed. Improvements data reduction analysis methods enable detection quantification Th. Ample precision is achieved using the entire set Dawn during 5 months low-altitude operations. A simple, analytic model, which can be applied measurements Vesta Ceres, used determine radioelement counting rates. Systematic errors evaluated simulated for representative vestan meteorite compositions. Concentrations global regolith, GRaND, consistent with eucrite-rich howardite, distinct most achondrites, all chondrites, Mars meteorites. K/Th ratio (900 ± 400) similar average howardite (approximately 1200). These data, along major element ratios nuclear spectroscopy, strongly support hypothesis that parent body HEDs. depletion moderately-volatile elements implied early accretion a hot, incompletely condensed solar nebula and/or, less likely, subsequent removal volatiles energetic collisions or degassing magmas.