Ubiquitous Carbon-Bearing Minerals on Asteroid Bennu

During fall 2019, NASA’s OSIRIS-REx spacecraft captured this image, which shows one of asteroid Bennu’s boulders with a bright vein that appears to be made of carbonate. The image within the circle (lower right) shows a focused view of the vein. Credit: NASA/Goddard/University of Arizona.

Carbonaceous chondrite meteorites preserve volatiles and carbonaceous matter, the key ingredients of life, from the early solar system. These meteorites show spectral similarities to the C-type asteroids that are also thought to be enriched in carbon. NASA’s OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer) spacecraft collected samples from one such asteroid, the near-Earth asteroid (101955) Bennu. OSIRIS-REx is equipped with a visible and infrared spectrometer (OVIRS) that allows detection of carbon-bearing minerals and organic species by mapping wavelengths from 0.4 to 4.3 microns. Amy Simon of NASA’s Goddard Space Flight Center and coauthors recently reported the results of this mapping of Bennu by the OSIRIS-REx spacecraft. The team found that carbon-bearing compounds are detected globally on the surface of Bennu via a 3.4-micron absorption feature. They also detected a global 2.74-micron absorption feature, indicative of hydrated phyllosilicates, suggesting the similarly ubiquitous presence of aqueously altered materials on Bennu. The mapping results also show that the carbon-bearing compounds are a mixture of organics and carbonates, varying greatly in abundance, across Bennu’s surface. The observed variations suggest a complex collisional and mixing history for the asteroid. The ubiquitous presence of organics implies that most of the material on Bennu’s surface is freshly exposed (within the last few million years), because organic compounds are rapidly destroyed by the harsh radiation environment to which the surface is subjected. The samples collected by the spacecraft in October likely contain these carbon-bearing minerals and organic materials. OSIRIS-REx will leave Bennu next year and head back to Earth. It will arrive in September 2023 and eject the sample return capsule, which will parachute to a landing in the Utah desert. The samples returned from the asteroid Bennu are likely the leftovers of planet formation processes, and their study will help improve our understanding of the earliest times in the solar system. READ MORE