Miniaturized Raman Spectrometers for Space Applications: the Detectability of Biomarkers in Geological Matrices Relevant to Mars Exploration

A Raman spectrometer will be utilized on a planetary exploration mission for the first time when the ExoMars rover is launched in 2018. A Raman spectroscopy instrument was selected for inclusion on the ExoMars mission because of its ability to assess the habitability and to search for evidence of life on Mars. Indeed Raman spectrometers have the capability to detect geological substances which are inorganic molecules and inorganic molecular ions constituting the rocky surface of Mars. Information on the nature of rocks present on the surface of Mars will provide information about the habitability of the planet. Besides the detection of geomarkers, Raman spectrometers have the ability to detecting potential biological-derivative substances, often referred to as biomarkers. These biomarkers are organic molecules originating from extent or extinct living organisms. In preparation for ExoMars, it is crucial to study the detection capability of miniaturized Raman spectrometers (specifically developed for space missions and therefore compromised by the associated challenging constraints such as minimal power budget, mass budget, data budget and overall envelope) on both lab synthetic samples and natural terrestrial analogues samples.
We present here a systematic comparison of the capability of a number of Raman spectrometer designs/configurations to detect biomarkers in geological matrices that are relevant to the Martian surface and subsurface. In particular, we will compare spectral images recorded with benchtop instruments and a Raman Laser Spectrometer prototype developed at the University of Leicester to optimize/characterize the camera system that will be used for the ExoMars mission. Several parameters such as the excitation wavelength, the number of spectra recorded per sample and selection of optimal operating modes will be discussed. As an example, the habitability of desert varnish in the context of planetary exploration will be discussed in detail. Desert varnish are mineral coatings comprising clay, iron oxide and manganese oxide which are associated with living organisms in many stable extreme environment on Earth. Desert varnish are recognized as terrestrial analogue samples for martian surface because similar mineral formation have been recently identified on Mars.