Spectral Characterization of Analog Samples in Anticipation of OSIRIS-REx’s Arrival at Bennu: A Blind Test Study

K.L. Donaldson Hanna, D.L. Schrader, E.A. Cloutis, G.D. Cody, A.J. King, T.J. McCoy, D.M. Applin, J.P. Mann, N.E. Bowles, J.R. Brucato, H.C. Connolly Jr., E. Dotto, L.P. Keller, L.F. Lim, B.E. Clark, V.E. Hamilton, C. Lantz, D.S. Lauretta, S.S. Russell, P.F. Schofield

Available online 25 October 2018



• A suite of chondritic meteorites and mineral mixtures that are possible Bennu analogs are spectrally characterized across VNIR and TIR wavelengths.
• Different types of meteorites can be identified from one another by the presence or absence of diagnostic absorption features that are characteristic of specific minerals and compositional properties, in spite of them sharing low overall reflectance.
• The most diagnostic VNIR spectral regions for identifying different meteorites are the 0.6 – 1.3 and 2.7 – 3.0 μm and the most diagnostic spectral features in the TIR are the Christiansen features, fundamental vibration bands, and transparency features.
• Comparing spectra of chondritic meteorite and physical mineral mixtures indicates that simple physical mixing of mineral phases is ineffective at reproducing the low overall albedo of the meteorites.
• We observe that the thermal infrared spectral effects due to the simulated asteroid environment vary with meteorite type.”

“We present spectral measurements of a suite of mineral mixtures and meteorites that are possible analogs for asteroid (101955) Bennu, the target asteroid for NASA’s Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer (OSIRIS-REx) mission. The sample suite, which includes anhydrous and hydrated mineral mixtures and a suite of chondritic meteorites (CM, CI, CV, CR, and L5), was chosen to characterize the spectral effects due to varying amounts of aqueous alteration and minor amounts of organic material. Our results demonstrate the utility of mineral mixtures for understanding the mixing behavior of meteoritic materials and identifying spectrally dominant species across the visible to near-infrared (VNIR) and thermal infrared (TIR) spectral ranges. Our measurements demonstrate that, even with subtle signatures in the spectra of chondritic meteorites, we can identify diagnostic features related to the minerals comprising each of the samples. Also, the complementary nature of the two spectral ranges regarding their ability to detect different mixture and meteorite components can be used to characterize analog sample compositions better. However, we observe differences in the VNIR and TIR spectra between the mineral mixtures and the meteorites. These differences likely result from (1) differences in the types and physical disposition of constituents in the mixtures versus in meteorites, (2) missing phases observed in meteorites that we did not add to the mixtures, and (3) albedo differences among the samples. In addition to the initial characterization of the analog samples, we will use these spectral measurements to test phase detection and abundance determination algorithms in anticipation of mapping Bennu’s surface properties and selecting a sampling site.”