Water and hydroxyl on asteroid Bennu: Reconciling remote observations with OSIRIS-REx sample analysisOPEN ACCESS 

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Hannah H. Kaplan, Amy A. Simon, Victoria E. Hamilton, Joshua P. Emery, Dennis Reuter, Andy J. López-Oquendo

MAPS, Version of Record online: 14 October 2026

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“This study investigates the spatial distribution and spectral characteristics of the broad hydration feature near 3 μm across the surface of asteroid (101955) Bennu using OVIRS (OSIRIS-REx Visible and InfraRed Spectrometer) data. We analyzed multiple global OVIRS data sets obtained at different times throughout the Bennu day, revealing variations in band depth with wavelength, as well as wavelength-dependent correlations with temperature and other surface properties. Our analysis distinguishes between the behavior of the 2.74-μm and 3.0-μm features, which contribute to a broad 3-μm region absorption, suggesting they may have different origins or respond differently to surface conditions. The 2.74-μm band depth shows strong negative correlation with temperature and positive correlation with albedo and hydroxyl, whereas the 3.0-μm band depth exhibits primarily weak relationships with other spectral and surface parameters, such as temperature, albedo, and UV/visible spectral slope, indicating that these features probe different aspects of the surface materials. These findings demonstrate that space weathering likely plays a strong role within the hydration band. Specifically, temperature and time-of-day dependencies observed at 2.74-μm point to an active hydroxyl cycle on Bennu’s surface driven by solar wind hydrogen implantation, hydroxylation, and subsequent thermal desorption. Conversely, the distinct behavior of the 3.0-μm band suggests it may serve as an indicator of surface composition, including the phosphate minerals recently found in the returned sample; however, the lack of correlation with other expected diagnostic spectral features, such as a bluer UV/visible slope, currently leaves this relationship inconclusive.”

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