Daily temperature changes reveal compositional variation on asteroid (101955) Bennu

Carbonaceous rubble pile asteroid 101955 Bennu was observed by the OSIRIS-REx Thermal Emission Spectrometer (OTES) at different times of the day with different surface temperatures. Prior results from OSIRIS-REx revealed that hydrated minerals are ubiquitous on Bennu, and OTES showed that Bennu’s surface is dominated by highly hydrated minerals, such those found in the bulk matrix of CI, CM and some CR carbonaceous chondrite meteorites. In this work, we analyzed the OTES spectroscopic behavior in response to the change in temperatures throughout the day, and we detected anomalous temperature-dependent variations of mid-infrared (5.71 to 100 µm) spectroscopic features. Correlating temperature-dependent variation of infrared features with mineralogical composition, we identified that 9% of Bennu surface is dominated by anhydrous minerals. This discovery further constraints Bennu's origin and evolutionary history. Bennu is made up of material reaccumulated after a catastrophic disruption of very different parent bodies. This identifies it as possible source of heterogeneous meteorite fall such as Kaidun and Almatha Sitta.