^1,2Maggie McAdam,^2,3Annika Gustafsson
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114592]
¹NASA Ames Research Center, United States of America
²Northern Arizona University, United States of America
³Lowell Observatory, United States of America
Copyright Elsevier

We present rotationally resolved spectroscopy of asteroid (93) Minerva using the Lowell Discovery Telescope with the Near-Infrared High Throughput Spectrograph (NIHTS). We obtained spectroscopy over ~34% of the asteroid’s rotation period. Minerva has been shown to be spectrally similar to primitive carbonaceous chondrites (e.g., McAdam et al., 2018, Icarus 306, 32–49) indicating it has amorphous materials on its surface. The extent to which these materials appear over Minerva’s surface could provide constraints on the asteroid’s formation time and/or directly relate the asteroid to a chemical group of carbonaceous chondrite meteorites. Parent asteroids are thought to preserve primitive meteorites in either an outer shell of material or by avoiding parent body processing (e.g., accreting after the peak heat flux of 26Al or before the introduction of exogenous 26Al to the Solar System). These two scenarios are expected to have different properties: the no processing scenario produces an asteroid with a compositionally homogenous surface and interior while the outer shell scenario would have compositionally distinct surface and interior. Over the observed region, we report that Minerva’s surface appears to have amorphous materials, potentially indicating a homogeneous surface. However, more data are needed to determine Minerva’s compositional uniformity and which formation scenario is most appropriate.

¹S.M.Ferrone et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114579]
¹LESIA-Observatoire de Paris, Université PSL, CNRS, Université de Paris, Sorbonne Université, Paris, France
²Department of Physics and Astronomy, Ithaca College, Ithaca, NY, USA
Copyright Elsevier

The OSIRIS-REx Visible and InfraRed Spectrometer (OVIRS) onboard the Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) spacecraft detected ~3.4-μm absorption features indicative of carbonates and organics on near-Earth asteroid (101955) Bennu. We apply a Kolmogorov-Smirnov similarity test to OVIRS spectra of Bennu and laboratory spectra of minerals to categorize 3.4-μm features observed on Bennu as representing either carbonates or organics. Among the 15,585 spectra acquired by OVIRS during high-resolution (4 to 9 m/spectrum footprint) reconnaissance observations of select locations on Bennu’s surface, we find 544 spectral matches with carbonates and 245 spectral matches with organics (total of 789 high-confidence spectral matches). We map the locations of these matches and characterize features of Bennu’s surface using corresponding image data. Image data are used to quantitatively characterize the albedo within each spectrometer footprint. We find no apparent relationships between spectral classification and surface morphological expression, and we find no correlation between carbon species classification and other spectral properties such as slope or band depth. This suggests either that carbonates and organics are ubiquitous across the surface of Bennu, independent of surface features (consistent with findings from laboratory studies of carbonaceous chondrites), or that the observations do not have the spatial resolution required to resolve differences. However, we find more organic spectral matches at certain locations, including the site from which the OSIRIS-REx mission collected a sample, than at others. Higher concentrations of organics may be explained if these materials have been more recently exposed to surface alteration processes, perhaps by recent crater formation.