Dynamic aperture factor analysis/target transformation (DAFA/TT) for Mg-serpentine and Mg-carbonate mapping on Mars with CRISM near-infrared data

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Lin, H., Tarnas, J. D., Mustard, J. F., Zhang, X., Wei, Y., Wan, W., Klein, F., & Kellner, J. R. Dynamic aperture factor analysis/target transformation (DAFA/TT) for Mg-serpentine and Mg-carbonate mapping on Mars with CRISM near-infrared data. Icarus, 355, (2021): 114168, https://doi.org/10.1016/j.icarus.2020.114168.Serpentine and carbonate are products of serpentinization and carbonation processes on Earth, Mars, and other celestial bodies. Their presence implies that localized habitable environments may have existed on ancient Mars. Factor Analysis and Target Transformation (FATT) techniques have been applied to hyperspectral data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) to identify possible serpentine and Mg-carbonate-bearing outcrops. FATT techniques are capable of suggesting the presence of individual spectral signals in complex spectral mixtures. Applications of FATT techniques to CRISM data thus far only evaluate whether an entire analyzed image (≈ 3 × 105 pixels) may contain spectral information consistent with a specific mineral of interest. The spatial distribution of spectral signal from the possible mineral is not determined, making it difficult to validate a reported detection and also to understand the geologic context of any purported detections. We developed a method called Dynamic Aperture Factor Analysis/Target Transformation (DAFA/TT) to highlight the locations in a CRISM observation (or any similar laboratory or remotely acquired data set) most likely to contain spectra of specific minerals of interest. DAFA/TT determines the locations of possible target mineral spectral signals within hyperspectral images by performing FATT in small moving windows with different geometries, and only accepting pixels with positive detections in all cluster geometries as possible detections. DAFA/TT was applied to a hyperspectral image of a serpentinite from Oman for validation testing in a simplified laboratory setting. The mineral distribution determined by DAFA/TT application to the laboratory hyperspectral image was consistent with Raman analysis of the serpentinite sample. DAFA/TT also successfully mapped the spatial distribution of Mg-serpentine and Mg-carbonate previously detected in CRISM data using band parameter mapping and extraction of ratioed spectra. We applied DAFA/TT to CRISM images in some olivine-rich regions of Mars to characterize the spatial distribution of Mg-serpentine and Mg-carbonate-bearing outcrops.This work was supported by the National Natural Science Foundation of China (grant no. 41671360, 41525016, 41902318). JFM and JDT acknowledge NASA support through a subcontract from the Applied Physics Lab for CRISM investigations. H. Lin also acknowledges the support from the key research Program of the Institute of Geology and Geophysics, CAS (IGGCAS-201905). The Headwall imaging spectrometer was acquired using funds to JRK from The Institute at Brown for Environment and Society and Brown University. The DAFA/TT codes are available on GitHub (https://github.com/linhoml?tab=repositories)

Exploring relationships between major element cations and organic preservation in silica

Ancient biosignatures are key to understanding the emergence and evolution of life in its planetary context. Microbes thrived on Earth from at least the early Archean to the present, and similar organisms may have emerged on a warmer, wetter Mars in the past, as well. However, fossil evidence of ancient microbes is often difficult to identify and interpret. Early diagenetic chert preserves numerous examples of microbial biosignatures from the Proterozoic and Archean eons. Despite their presence in the rock record, though, the mechanism behind this biosignature preservation and the biological and abiotic factors that contributed to the precipitation of chert are not well understood. Here, we address these uncertainties through fossilization experiments and analyses of Proterozoic biosignatures and the minerals that preserved them.Fossilization experiments reveal that exopolymeric substances (EPS) produced by some cyanobacteria can promote the precipitation of amorphous silica by using magnesium as a cation bridge. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) maps of biosignatures in Proterozoic chert reveal that the organic matter is commonly associated with magnesium-, calcium-, and aluminum- rich phases. In contrast, chert that does not contain organic matter lacks these cation associations. These combined results suggest that interactions among organic matter and major element cations in seawater may have promoted the preservation of organic matter by chert in marine environments during the Proterozoic.Our findings provide a window into interactions between microbes and their environments on the early Earth and the microbial contribution to geochemical cycles and chert formation. By analyzing these biosignatures and constraining the processes that led to their formation on Earth, we may be better equipped to identify and interpret potential biosignatures in Jezero crater, the landing site of the Mars2020 rover. Based on our results, we suggest that hydrated silica containing calcium, magnesium, and aluminum may be good targets for the Mars 2020 Perseverance rover as potential biosignature-hosting lithologies. If such biosignatures exist, these results will also help us to interpret how organisms may have interacted with the martian environment in the past

Compositionally and density stratified igneous terrain in Jezero crater, Mars

International audienceBefore Perseverance, Jezero crater’s floor was variably hypothesized to have a lacustrine, lava, volcanic airfall, or aeolian origin. SuperCam observations in the first 286 Mars days on Mars revealed a volcanic and intrusive terrain with compositional and density stratification. The dominant lithology along the traverse is basaltic, with plagioclase enrichment in stratigraphically higher locations. Stratigraphically lower, layered rocks are richer in normative pyroxene. The lowest observed unit has the highest inferred density and is olivine-rich with coarse (1.5 millimeters) euhedral, relatively unweathered grains, suggesting a cumulate origin. This is the first martian cumulate and shows similarities to martian meteorites, which also express olivine disequilibrium. Alteration materials including carbonates, sulfates, perchlorates, hydrated silicates, and iron oxides are pervasive but low in abundance, suggesting relatively brief lacustrine conditions. Orbital observations link the Jezero floor lithology to the broader Nili-Syrtis region,suggesting that density-driven compositional stratification is a regional characteristic