Avoiding misidentification of bands in planetary Raman spectra

• Published in: Journal of Raman spectroscopy Vol. 46; no. 10; pp. 863 - 872
• Main Authors: Harris, Liam V., McHugh, Melissa, Hutchinson, Ian B., Ingley, Richard, Malherbe, Cédric, Parnell, John, Olcott Marshall, Alison, Edwards, Howell G. M.
• Format: Journal Article Web Resource
• Language: English
• Published: Bognor Regis Blackwell Publishing Ltd 01.10.2015; Wiley Subscription Services, Inc; John Wiley & Sons
• Subjects: Ambiguity; astrobiology; Band spectra; Bands; Confusion; geological analogues; Mars exploration; Physical, chemical, mathematical & earth Sciences; Physique, chimie, mathématiques & sciences de la terre; planetary exploration; Raman spectra; space missions; Spectra; spectral band assignment; Spectrometers
• ISSN: 0377-0486; 1097-4555; 1097-4555
• DOI: 10.1002/jrs.4667

Raman spectroscopy has been identified as a powerful tool for astrobiology and remote robotic planetary exploration. It can be used to identify and characterise rock matrices, mineral inclusions and organic molecules and is demonstrably effective at identifying biomarkers, or indicators of biological activity. The ExoMars rover, jointly operated by the European and Russian Federal Space Agencies, will carry the first Raman spectrometer into space when it launches in 2018 and two further Raman instruments have recently been announced as part of the payload onboard the National Aeronautics and Space Administration's Mars 2020 rover. Each of these spectrometers however will, by necessity, have poorer resolution than the most sophisticated laboratory instruments because of mass, volume and power constraints and the space readiness of the requisite technologies. As a result, it is important to understand the minimum instrument specification required to achieve the scientific objectives of a mission, in terms of parameters such as spectral resolution and laser footprint size. This requires knowledge of the target minerals and molecules between which there may be ambiguity when identifying bands in spectra from geological samples. Here, we present spectra from a number of Mars analogue samples that include a range of such molecules, highlighting where such confusion may occur and identifying the most useful bands for differentiation. It is recommended that a Raman spectrometer achieves a resolution of at least 3 cm−1 and covers a spectral range from 100 to 4000 cm−1 in order to differentiate between all of the target molecules presented here. Copyright © 2015 John Wiley & Sons, Ltd. Raman spectra of several terrestrial Mars analogue samples, representative of a range of aspects of Martian geology, are used to illustrate potential sources of ambiguity or confusion, which may arise when analysing Raman spectra returned by future planetary exploration missions. We recommend the minimum operating parameters that should be considered for flight spectrometers, capable of unambiguous differentiation between the mineral and molecular targets presented here.