A Study of Composition, Texture and Space Weathering Effects on Asteroid (101955) Bennu*

The focus of our work has been asteroid (101955) Bennu, target of NASA’s OSIRIS-REx mission. The first part of our work was creating two-component laboratory simulations of the asteroid surface’s texture and composition. We found a physical model whose composition and texture best fit the near-infrared spectrum of the asteroid, as observed from the spacecraft: a dry mixture of 90% saponite (SAP105) with 10% carbon lampblack (LCA101) dissolved in a 1:2 powder to water slurry, then baked and broken into rough chunks.

 

Next, we worked on constraining space weathering processes on the asteroid. Qualitative and quantitative analyses of previous work and mission findings have led to our preferred hypothesis: the major agent of surface evolution on Bennu is dehydration of phyllosilicates and nanophase magnetite opaque formation due to surface irradiation. 

 

Nakauchi et al. 2021 (Icarus Vol. 355, 114140) suggest that there are distinct peaks at 2.72 μm, 2.77 μm, and 2.85 μm, each of which correspond to OH, H₂O, and Si-OH, respectively. We are writing a machine learning algorithm that will fit Gaussians at each peak, and are hoping to compare the depth of each Gaussian when applied to irradiated and unirradiated sample spectra to see exactly which type of hydration feature is attenuated.