Tools for Robotic In Situ Optical Microscopy and Raman Spectroscopy on Mars Authors: Schoen, C. H.; Dickensheets, D. L. Affiliation:
AA(Detection Limit), AB(Montana State Univ.)

Abstract

Robotic missions to Mars require remote diagnostic tools for detecting evidence of former life. Laser Raman spectroscopy is eminently suitable for this quest as its light-scattering principle permits nonintrusive analysis. Integration of Raman spectroscopy with optical microscopy correlates biochemical and morphological data. Vibrational Raman spectra identify component moieties of unknown target biomolecules such as pigments involved in photosynthesis and UV-protection. Antarctic desert analoges of potential early Mars habitats support localized anaerobic photosynthetic bacteria and widespread cyanobacteria containing chlorophyll as a primary pigment. Chlorophyll and accessory pigments (e.g. phycocyanin) autofluoresce at visible wavelengths (e.g. 530 nm). Although valuable for epifluorescence microscopy, this interferes with Raman spectra by producing curved baselines and instrument saturation. Fourier Transform Raman spectroscopy (FTRS) with near-IR excitation avoids most fluorescence while producing distinct and unique spectra for a wide range of wavenumbers. These spectra identify key moieties, such as the porphyrin nucleus of chlorophyll, which can be detected in whole communities from deserts with features common to potential habitats of early Mars.