Other
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p31d1724w&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P31D-1724
Other
[5400] Planetary Sciences: Solid Surface Planets
Scientific paper
NIR spectral signatures of phyllosilicates were recognized on Mars with wide distributions from orbit by OMEGA (on Mars Express orbiter) and CRISM (on Mars Reconnaissance Orbiter) observations. On the ground, geochemical and spectral features related to phyllosilicates were identified in rocks at two locations on Columbia Hill at Gusev crater using the data obtained by the Mars Exploration Rover (MER) Spirit. Furthermore, Opportunity rover is currently approaching the Cap of York at Endeavour crater on Meridiani Planum, where the signatures of phyllosilicates (and hydrous sulfates) were seen by CRISM. Laser-Induced Breakdown spectroscopy (LIBS) and Laser Raman spectroscopy will be used for the first time in rover missions in ChemCam on the NASA-MSL (Mars Science Laboratory) and in RLS on the ESA-ExoMars, respectively. As demonstrated by our previous studies, they are very powerful tools for characterizing the geochemistry and mineralogy aspects of the secondary minerals from aqueous alterations, especially hydrous sulfates. This study investigates the potential of LIBS and Raman spectroscopy for identifying and characterizing a variety of phyllosilicates, especially clays. Clay standards from the Clay Mineral Society were used. The LIBS measurements were made in a Planetary Environment and Analysis Chamber (PEACh) under Mars atmospheric pressure and composition, using 1064 nm as the excitation laser wavelength, same as ChemCam. The Raman measurements were made in ordinary laboratory environment using 532 nm as the excitation wavelength, same as RLS. The LIBS data were processed using custom automated software. We performed quantitative analysis of the spectra in order to evaluate the effectiveness of our method in: (a) discriminating between phyllosilicates and other silicates; (b) classifying different types of phyllosilicates (i.e., serpentine, chlorites, clays); and (c) correlating the LIBS-derived elemental abundances with the real chemical compositions of phyllosilicates. At this stage, we concentrated on investigating the LIBS peak area ratios of the Si and H emissions at 390.5 and 656.3 nm, respectively. The results from the first set study are encouraging, and we will be able to support the ChemCam investigation on MSL to classify rocks at distances. As for molecular characterization, we found that examining the Raman spectral patterns and spectral peak positions allows to: (1) classify di-octahedral and tri-octahedral phyllosilicates using the position of Si-O-Si peaks near 700 cm-1; (2) identify a variety of phyllosilicates and clays using H2O/OH peaks in 3000-4000 cm-1 and the fundamental vibration modes of polymerized SiO4 in 1150-200 cm-1; (3) characterize the Fe content in phlogopite-biotite-lepidomelane series using the relative intensities of two Raman peaks near 360 cm-1 and 550 cm-1. These results imply that laser spectroscopy (LIBS and Raman) will be powerful tools for identify, classify, and characterize phyllosilicates on Mars.
Sobron Pablo
Wang Anzhong
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