Carbonates and Organics on Asteroid (101955) Bennu (Invited Speaker)

The Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) mission has found evidence of widespread carbon-bearing materials on asteroid (101955) Bennu. Spectra collected by the OSIRIS-REx Visible and InfraRed Spectrometer (OVIRS) have a series of absorption features near 3.4 µm that we attribute to carbonates (minerals that contain -CO₃), organics (other carbon-bearing compounds), and mixtures of the two. In addition, we identify bright, meter-long and centimeters-wide, linear features in PolyCam images that we interpret as veins. We propose that the carbonates are hosted in these veins based on the expected mineralogy from meteorite data and the modeled percentage of total carbonate on Bennu, which is consistent with the extent of veins in the OVIRS field of view. The strongest organic spectral features on Bennu are correlated with darker and redder materials, suggesting that the organics and carbonates are associated with different lithologies and potentially have distinct alteration histories. Outside of the 3.2–3.6 µm region, spectra from OVIRS and the OSIRIS-REx Thermal Emission Spectrometer (OTES) suggest that the surface is dominated by Fe/Mg-phyllosilicates, indicating that Bennu is compositionally consistent with the most aqueously altered carbonaceous chondrite meteorites, the CM and CI types [1]. The interpreted carbonate compositions are similar to the carbonates in CMs and CIs. The organic features on Bennu are also well-fit with laboratory spectra of organics from these meteorites. Evidence of carbonates, organics, and associated geological features are present in the primary and back-up sample sites, suggesting that the OSIRIS-REx mission will likely return a sample with these materials. Carbonates and organic compounds returned from Bennu will greatly advance our understanding of early hydrothermal processes on asteroids and the prebiotic material required for the emergence of life.

1. Hamilton et al., Evidence for widespread hydrated minerals on asteroid (101955) Bennu, Nature Astronomy (2019).