OSIRIS-REx spectral analysis of (101955) Bennu by multivariate statistics

Description

The NASA New Frontiers asteroid sample return mission Origins, Spectral Interpretation, Resource Identification, andSecurity–Regolith Explorer (OSIRIS-REx) has provided a large amount of data on the asteroid (101955) Bennu, including high-quality spectra obtained by the OSIRIS-REx Visible and InfraRed Spectrometer (OVIRS).Aims.To better constrain the surface properties and compositional variations of Bennu, we studied the visible and near-infraredspectral behavior across the asteroid surface by means of a statistical analysis aiming to distinguish spectrally distinct groups, ifpresent.Methods.We applied theG-mode multivariate statistical analysis to the near-infrared OVIRS spectra to obtain an automatic statisticalclustering at different confidence levels.Results.The statistical analysis highlights spectral variations on the surface of Bennu. Five distinct spectral groups are identified at a2σconfidence level. At a higher confidence level of 3σ, no grouping is observed.Conclusions.The results at a 2σconfidence level distinguish a dominant spectral behavior group (group 1, background) and foursmall groups showing spectral slope variations, associated with areas with different surface properties. The background group containsmost of the analyzed data, which implies a globally homogeneous surface at the spectral and spatial resolution of the data. The smallgroups with redder spectra are concentrated around the equatorial ridge and are associated with morphological surface features suchas specific craters and boulders. No significant variation is detected in the band area or depth of the 2.74μm band, which is associatedwith hydrated phyllosilicate content. The spectral slope variations are interpreted as a consequence of different regolith particle sizes,and/or porosity, and/or space weathering, that is, the presence of more or less fresh material. The OSIRIS-REx mission primarysampling site, Nightingale, and a boulder known as the Roc, are redder than the background surface.

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