Widespread carbon-bearing materials on near-Earth asteroid (101955) Bennu

(101955) Bennu is a dark asteroid on an Earth-crossing orbit, thought to have assembled from the fragments of an ancient collision. We use spatially-resolved visible and near-infrared spectra of Bennu to investigate its surface properties and composition. In addition to a hydrated phyllosilicate band, we detect a ubiquitous 3.4-micron absorption feature, which we attribute to a mix of organic and carbonate materials. The shape and depth of this absorption feature vary across Bennu’s surface, spanning the range seen among similar main-belt asteroids. Its distribution does not correlate with temperature, reflectance, spectral slope, or hydrated minerals, although some of those characteristics correlate with each other. The deepest 3.4-micron absorptions occur on individual boulders. The variations may be due to differences in abundance, recent exposure, or space weathering.