Letter to the Editor

Composition of organics on asteroid (101955) Bennu

¹ NASA Goddard Space Flight Center, Greenbelt, MD, USA
e-mail: hannah.kaplan@nasa.gov
² Southwest Research Institute, Boulder, CO, USA
³ Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN, USA
⁴ NASA Ames Research Center, Moffett Field, CA, USA
⁵ LESIA, Observatoire de Paris, Université PSL, CNRS, Université de Paris, Sorbonne Université, 5 Place Jules Janssen, 92195 Meudon, France
⁶ Department of Geography, University of Winnipeg, Winnipeg, Canada
⁷ INAF-Arcetri Astrophysical Observatory, Florence, Italy
⁸ Department of Physics, Ithaca College, Ithaca, NY, USA
⁹ Department of Physics, University of Central Florida, Orlando, Florida, USA
¹⁰ Northern Arizona University, Flagstaff, AZ, USA
¹¹ Institut Universitaire de France (IUF), Paris, France
¹² Planetary Science Institute, Tucson, AZ, USA
¹³ Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA

Received: 23 April 2021
Accepted: 30 July 2021

Abstract

Context. The Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) mission detected an infrared absorption at 3.4 μm on near-Earth asteroid (101955) Bennu. This absorption is indicative of carbon species, including organics, on the surface.

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 that have features near 3.4 μm (3.2 to 3.6 μm) 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.