New Constraints on the Abundance and Composition of Organic Matter on Ceres

Near-infrared reflectance spectra from the Dawn mission at Ceres were recently found to exhibit a 3.4 mu m absorption indicative of the presence of aliphatic organic compounds. Constraints on abundance and composition of these organics are necessary to inform discussions of their origin. We model reflectance spectra of organic-bearing regions on Ceres using laboratory spectra of insoluble organics of known composition extracted from terrestrial sedimentary rocks (i.e., kerogens) and carbonaceous chondrite meteorites (i.e., insoluble organic matter, IOM). The 3.4 mu m aliphatic organic absorptions observed in Dawn near-infrared data are stronger than those observed in lab spectra of carbonaceous chondrites, and modeling requires 45% to 65% spectral fraction of IOM to fit spectra from Ceres. The spectral fraction of kerogen necessary to fit the same Ceres spectra ranges from 5% to 15% depending on the hydrogen to carbon ratio of the kerogen. Any proposed mechanism of organic delivery or formation on Ceres should explain the presence of highly concentrated IOM or why the composition is distinct from meteorite-derived IOM if lower organic abundances are considered more plausible.