^1,2Miguel Arribas Tiemblo,¹Pedro Rayo,¹María-Paz Martín-Redondo,¹Felipe Gómez
Journal of Geophysical Research (Planets)(in Press) Open Access Link to Article [https://doi.org/10.1029/2025JE009070]
¹Centro de Astrobiología (CAB), CSIC-INTA, Madrid, Spain
²Universidad de Alcalá de Henares (UAH), Madrid, Spain
Published by arrangement with John Wiley & Sons

Amino acids are an extremely heterogeneous group of biomolecules essential for life on Earth. Their biosignatures are expected to be easily degraded on the Martian surface as the absence of a thick atmosphere and a magnetosphere leads to most of the solar radiation directly reaching its surface. To determine the preservation of amino acids in the Martian regolith, and their detectability, we exposed protein-sourced and free amino acids to UV-B radiation. This was done while in contact with different particle size ranges of two Martian regolith simulants. Bulk analysis through High Performance Liquid Chromatography (HPLC) showed that UV-B radiation led to little damage across all samples, mainly targeting sensitive amino acids like tyrosine, histidine, tryptophan and methionine. The two Martian simulants were divided into five particle size ranges. Smaller particles (<0.045 mm) led to higher recoveries than bigger ones (>0.500 mm), likely through their high specific surface area. Raman spectroscopy offered localized surface information, which HPLC was unable to. One of the simulants (MMS-2) is rich in iron oxides like hematite, which likely prevented any detection by absorbing the excitation wavelength of the laser. Irradiation also led to widespread loss of signal of all amino acids. Overall, the limitations of both techniques were compensated by each another, which allowed for the precise characterization of the chemical alterations suffered by amino acids in these conditions.

^1,2Erbin Shi,²Alian Wang,³I-Ming Chou,¹Zongcheng Ling
Journal of Geophysical Research (Planets)(in Press) Open Access Link to Article [https://doi.org/10.1029/2024JE008867]
¹Shandong Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, School of Space Science and Physics, Institute of Space Sciences, Shandong University, Weihai, China
²Department of Earth & Planetary Sciences and McDonnell Center for the Space Sciences, Washington University in St. Louis, St. Louis, MO, USA
³CAS Key Laboratory of Experimental Study Under Deep-Sea Extreme Conditions, Institute of Deep-Sea Science and Engineering, Chinese Academy of Sciences, Sanya, China
Published by arrangement with John Wiley & Sons

Ferric sulfate minerals have been identified by orbital and landed missions at multiple locations on Mars and are the most common minerals in the Acid Mine Drainage (AMD) system on Earth. The occurrences and the speciation of ferric sulfates are very sensitive to variations in environmental conditions, such as temperature (T), relative humidity (RH%), redox potential (Eh), and potential of hydrogen ions (pH). In this study, two phase boundaries among kornelite, paracoquimbite, and ferricopiapite were experimentally derived in T–RH% space, using the well-established humidity buffer technique. The phase transformation and phase identification during experiments were determined by the gravimetric measurements and laser Raman spectroscopy, respectively. The two new phase boundaries clearly defined the edges of the stable fields of paracoquimbite that were ambiguously determined in a previous study. From the experimental data, we derived the entropy, enthalpy, and Gibbs free energy of the two reactions, and calculated the enthalpy changes and Gibbs free energy changes for each water of crystallization (either enter or escape from the structure) of these hydrous ferric sulfates. When compared with the same parameters of hydrous metal (Fe3+, Fe2+, Cu2+, Mg2+, Ni2+, Zn2+, Co2+, Mn2+, Cd2+, and Na+) sulfates derived by previous hydration/dehydration studies, we found a strong consistency, especially the Gibbs free energy changes. This finding implies the very consistent energetic barriers for the hydration/dehydration of those sulfates, post their first hydration/dehydration, regardless of their difference in cation and crystal structure.