Analysis of In-Situ Organic and Mineral Compounds Relevant to Martian Astrobiology Using 266 nm Raman Spectroscopy

Abstract:

Raman spectroscopy has become increasingly desirable for astrobiological investigations on Mars due to the potential for stand-off measurements, sensitivity to organic and mineral targets, and detection on unprepared surfaces. While the majority of existing Raman instruments intended for planetary exploration operate in the visible or near infrared, an ultraviolet Raman wavelength offers potential advantages including increased Raman cross section, decreased fluorescence in the Raman window, and increased signal due to resonance with some organics. This work presents a Raman spectrometer with an excitation of 266 nm, designed around the putative requirements of a flight instrument. We demonstrate spatial mapping of organic and mineral compounds on Mars analogue samples from the Canadian Arctic and the Atacama Desert, showcasing the reduced fluorescence and increased scattering efficiency compared to longer wavelengths. The Raman window provided by a 266 nm excitation is advantageously positioned to observe fluorescence bands that are characteristic to terrestrial bacteria yet do not overlap with the Raman signal. We present the potential for time-resolved nanosecond scale gating of the detector in characterizing mineral and organic fluorescence by measuring the fluorescence lifetime of endoliths in gypsum. The characteristic short lifetime of the bacterial fluorescence provides additional information regarding the presence of organic carbon in the sample, and therefore combined Raman-fluorescence measurements may increase the sensitivity of the instrument to organic carbon. This research was carried out at the Planetary Instrumentation Laboratory at York University, and supported in part by both the Canadian Space Agency (CSA) and by the Natural Sciences and Engineering Research Council of Canada (NSERC).