Dehydration rate of the glycine‐MgSO₄·5H₂O complex and the stability of glycine expelled from the complex by in situ Raman spectroscopy under Mars‐relevant conditions

Abstract

In this work, we studied the dehydration process of the glycine‐MgSO4·5H2O complex under Mars‐relevant conditions (99% CO2 and 0.6% H2O under ultra violet (UV) irradiation exposure at 7‐mbar pressure and high vacuum conditions: 8 × 10−5 and 5 × 10−5 mbar) by in situ Raman spectroscopy inside a planetary atmosphere and surface chamber (PASC). This work provides quality Raman spectra taken under simulated planetary conditions (to be integrated in a database), as Raman spectroscopy forms part of the current and upcoming NASA and ESA Mars planetary missions. The results demonstrate that Raman spectroscopy can be used to calculate rates of dehydration of the glycine‐MgSO4·5H2O compound to study the chemical stability with respect to photodecomposition (1) of metal‐bound glycine molecules forming the complex and (2) glycine expelled from the complex, both under Mars‐simulated conditions; finally, Raman spectroscopy can also be used to quantify intermolecular interactions in terms of local pressures. Importantly, advanced detection of water molecules as part of a complex with astrobiological interest under planetary conditions plays a crucial role in planetary missions.

Impact of UV radiation on the Raman and infrared spectral signatures of sulfates, phosphates and carbonates: Implications for Mars exploration

“…A Martian-like CO 2 atmosphere was not introduced into the chamber to prevent absorption of UV by CO 2 and contamination from air. Previous studies have shown that a few mbars of CO 2 have no influence on the UV induced degradation of amino acids (ten Kate et al, 2006), nor on the UV induced dehydration of sulfates (Bonales et al, 2022). Of note, all the samples have been introduced into the Martian chamber and exposed to the pressure and temperature conditions of the experiments for 15 hours before being exposed to UV radiation.…”

“…Of note, all initially hydrated starting materials do not show anymore Raman features attributed to hydration at the end of the present experiments. Yet, neither Morris and Lauer (1980) nor Yen et al (1999) observed UV photodehydration, but Bonales et al (2022) experimentally showed that exposure to UV enhances the kinetics of dehydration. Dehydration may be a direct consequence of the simulated Martian conditions.…”

“…The evolution of the IR spectral signatures of sulfates, phosphates or carbonates experimentally exposed to simulated Mars surface UV radiation conditions has been investigated by a rather limited number of authors (Bish et al, 2003;Cloutis et al, 2007Cloutis et al, , 2008Poitras et al, 2018;Turenne et al, 2022). An even lower number of studies have been dedicated to the evolution of their Raman spectral signatures (Bonales et al, 2022). Of note, extrapolating laboratory results to natural settings remains difficult, in particular because geological timescales cannot be replicated in the laboratory, questioning the intrinsic relevance of laboratory experiments.…”