¹Eugene G. Grosch,²Janice L. Bishop,³Christian Mielke,⁴Alessandro Maturilli,⁴Jörn Helbert
American Mineralogist 106, 672–684 Link to Article [http://www.minsocam.org/MSA/AmMin/TOC/2021/Abstracts/AM106P0672.pdf]
¹Geology Department, Rhodes University, Grahamstown/Makhanda 6140, South Africa 2
²Carl Sagan Center, SETI Institute and NASA-Ames Research Center, Mountain View, California 94043, U.S.A. 3
³GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam 4
⁴Institute for Planetary Research, DLR, Rutherfordstrasse 2, 12489, Berlin-Adlershof, Germany
Copyright: The Mineralogical Society of America

Characterization of terrestrial analog sites is critical for detection and determination of clay mineralogy in remote sensing studies of Mars aimed at geological, hydrological, and potentially biological
investigations. In this study, we investigate a suite of hydrothermally altered early Archean rocks from
the Barberton greenstone belt (BGB) of South Africa as potential petrological, mineralogical, and
spectral analogs to hydrothermally altered metabasalts and mafic-ultramafic intrusions in the martian
subsurface and impact craters. We present the first spectral imaging measurements on exceptionally
well-preserved early Archean mafic-ultramafic rocks from the BGB, with the aim of studying their
clay mineralogy and spectral signatures. Multiple spectral analyses were conducted on different
sample textures (rock powders, crushed rocks, and rock slabs) appropriate for Mars rover and remote
sensing exploration. Visible/near-infrared (VNIR) and mid-IR reflectance spectra were acquired on
particulate samples, while VNIR spectral imaging data were collected on rock slabs. Mid-IR emission
spectra were measured for the rock slabs and grains. Spectral features are compared from these different spectral techniques to identify the minerals present in the samples and compare macroscale vs.
microscale detections. The measured spectra reveal absorption bands that correspond to clay mineralogy of the serpentine and chlorite mineral groups, consistent with petrographic observations, as well
as magnetite, olivine, quartz, feldspar, and Al-phyllosilicate. The spectral data acquired in this study
expand the reference spectra data set for remote sensing studies. The implications of this study are that
rocks from early Archean greenstone belts, such as those of the BGB, serve as potential clay-bearing
petrological analogs for hydrothermal environments on Mars.

¹L.Mandon,^2,3P.Beck,¹C.Quantin-Nataf,¹E.Dehouck,⁴A.Pommerol,⁴Z.Yoldi,⁴R.Cerubini,¹L.Pan,¹M.Martinot,⁵V.Sautter
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114517]
¹Univ Lyon, Univ Lyon 1, ENSL, CNRS, LGL-TPE, F-69622 Villeurbanne, France
²Université Grenoble-Alpes, CNRS, IPAG, UMR, 5274 Grenoble, France
³Institut Universitaire de France, France
⁴Space Research & Planetary Sciences Division, Physikalisches Institut, Universität Bern, Bern, Switzerland
⁵Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, Muséum National d’Histoire Naturelle, 75005 Paris, France
Copyright Elsevier

In the next decade, two rovers will characterize in situ the mineralogy of rocks on Mars, using for the first time near-infrared reflectance spectrometers: SuperCam onboard the Mars 2020 rover and MicrOmega onboard the ExoMars rover, although this technique is predominantly used in orbit for mineralogical investigations. Until successful completion of sample-return missions from Mars, Martian meteorites are currently the only samples of the red planet available for study in terrestrial laboratories and comparison with in situ data. However, the current spectral database available for these samples does not represent their diversity and consists primarily of spectra acquired on finely crushed samples, albeit grain size is known to greatly affect spectral features. Here, we measured the reflected light of a broad Martian meteorite suite as a means to catalogue and characterize their spectra between 0.4 and 3 μm. These measurements are achieved using a point spectrometer acquiring data comparable to SuperCam, and an imaging spectrometer producing hyperspectral cubes similarly to MicrOmega. Our results indicate that point spectrometry is sufficient to discriminate the different Martian meteorites families, to identify their primary petrology based on band parameters, and to detect their low content in alteration minerals. However, significant spectral mixing occurs in the point measurements, even at spot sizes down to a few millimeters, and imaging spectroscopy is needed to correctly identify the various mineral phases in the meteorites. Additional bidirectional spectral measurements on a consolidated and powdered shergottite confirm their non-Lambertian behavior, with backward and suspected forward scattering peaks. With changing observation geometry, the main absorption strengths show variations up to ~10–15%. The variation of reflectance levels is reduced for the rock surface compared to the powder. All the spectra presented are provided in the supplementary data for further comparison with in situ and orbital measurements.