The development of a miniaturized Raman instrument for the detection of biosignatures on Europa

Abstract

Raman spectroscopy has gained popularity in planetary exploration over the last decade as an exceptionally versatile non-destructive compositional analysis technique that can identify a vast spectrum of molecules including both minerals and biomolecules, and provide information on the molecular structure, material phase as well as atom arrangements. For its many merits, Raman spectroscopy was proposed as one of the model instruments for the Europa Lander mission currently under development at NASA. For their vast oceans possibly harbouring extraterrestrial life, Europa and other Icy Worlds were identified as high priority planetary targets in both ESA’s and NASA’s plans for future planetary exploration. However, contemporary state-of-the-art Raman instruments for planetary exploration were designed for bulk mineral detection on Mars, the most imminent planetary target, and are not compatible with life detection on Europa. This research evaluates the capabilities and limitations of Raman spectroscopy for in-situ detection of biosignatures on Europa in order to identify critical instrument design requirements and enabling technology necessary for the development of a Raman instrument compatible with a landed mission to Europa and its scientific goals. High confidence and high priority biosignatures for the search for life on Europa are identified and a selection of the target molecules is used to study the effects of laser induced damage, fluorescence interference, cryogenically induced spectral changes and the ability of available Raman technology to detect molecules at extremely low concentrations. The research shows that cryogenically induced changes can severely impact the detectability and identifiability of molecules due to Raman shift changes of up to 25 cm^-1, as well as the cryogenically induced increase in the fluorescence noise. On the other hand, the significant narrowing of Raman bands as well as the decrease in the variability of the measurements at low temperatures lead to higher precision and accuracy. Cryogenic temperatures also mitigate the effects of laser damage, increase the SNR in the spectra of some molecules and even allow the detection of highly photosensitive molecules that are unresolvable at higher temperatures. The results also indicate that the spectral resolution necessary for successful detection of biosignatures on Europa could be as high as 2 cm^-1, which is much higher than the resolution of contemporary state-of-the-art Raman instruments for planetary exploration and is particularly problematic for miniaturized instruments. Additionally, detection at extremely low concentrations, as required on Europa, is not achievable using traditional Raman spectroscopy. Based on the identified requirements, two Raman instrument designs compatible with a mission to Europa are proposed. Key enabling technology and future directions for the development of these instruments are identified and discussed. Most notably, Surface Enhanced Raman spectroscopy (SERS) is identified as a critical component of future Raman instruments for planetary exploration. Recent advances in the SERS technology are discussed and a SERS technique compatible with planetary exploration that could allow biosignature detection on Icy Worlds is proposed and described.

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Identifiers

ORCID for Ariana Barbora Vitkova: orcid.org/0000-0001-9872-7811

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