Composition of Organics on Asteroid (101955) Bennu

Context: The Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) mission detected an infrared absorption at 3.4μm on near-Earth asteroid(101955) Bennu. This absorption is indicative of carbon species, including organics, on the sur-face. Aims: We aim to describe the composition of the organic matter on Bennu by investigating the spectral features in detail. Methods: We use a curated set of spectra acquired by the OSIRIS-REx Visible and InfraRed Spectrometer (OVIRS) that have features near 3.4μm (3.2 to 3.6μm) attributed to organics. We assess the shapes and strengths of these absorptions in the context of laboratory spectra of extraterrestrial organics and analogs. Results: We find spectral evidence of aromatic and aliphatic CH bonds. The absorptions are broadly consistent in shape and depth with those associated with insoluble organic matter in meteorites. Given the thermal and space weathering environments on Bennu, it is likely that the organics have not been exposed for long enough to substantially decrease the H/C and destroy all aliphatic molecules.