Identifying Biomarkers and Habitability Indicators on Polygonal Structures using Laser Mass Spectrometry
Authors: Knecht Luca N. , Gruchola Salome , Keresztes Schmidt Peter , de Koning Coenraad P. , Tulej Marek , Wurz Peter , Thomas Nicolas , Cockell Charles S. , Riedo Andreas 
Published: March 2024

The search for signatures of life beyond Earth has been a primary motivator in the field of space science. The question of the ideal exploration site for the search of such signatures for life remains unanswered, despite an increase in space missions dedicated to the understanding of the formation of the Martian surface and its environmental history. The present space exploration missions focus on formerly subaqueous environments, such as water bodies and deltaic structures [1,2]. While these sites have the capability to bury organic material due to rapid sedimentation, the preservation of biosignatures in those high-energy settings is often compromised by oxidizing fluids and gases [3]. Conversely, tranquil settings, such as ancient lakes, might be more suited for biomarker preservation. Many of these lakes were saline and formed salt deposits when they dried out. During salt precipitation, biomarkers can be buried and shielded from the harsh radiation prevailing on the Martian surface. Thus, these evaporites have been previously suggested as important sites for the search for life on Mars [4]. Such salt deposits on the surface of Mars have been identified numerously, displaying distinctive polygonal surface features, visible from orbit by e.g., CRISM or HiRISE imaging [5]. Similar polygonal structures are also found at Mars analogue sites in salt deposits on Earth, like in the Atacama Desert [6] or in the Boulby Mine, United Kingdom.&#160;This contribution presents the results of our study focused on the polygonal structures within the halite deposits of the Boulby Mine. The measurements were performed using a space-prototype laser ablation ionisation mass spectrometer (LIMS) [7,8]. The polygons show two optically distinct features, consisting of dark edges and light interiors. For both features, interior and edge, the chemical composition was determined using LIMS and compared. A specific focus was placed on the difference in abundance of the CHNOPS elements, as they serve as biomarkers. A significant increase in CHNOPS and other biologically relevant minor and trace elements, necessary e.g., for the maintenance and formation of life, was observed at the polygonal edges. This shows that the edges of polygonal structured salt deposits are preferential sites for element accumulation. As a result, the edges of salt deposits might be more habitable to life as we know it and could serve as promising sites for detecting signatures of life in future in-situ space exploration missions.&#160;[1] Mangold, N. et al., 2020, https://doi.org/10.1089/ast.2019.2132[2] Vasavada, A. R., 2022, https://doi.org/10.1007/s11214-022-00882-7[3] Hays, L. E., 2017, https://doi.org/10.1089/ast.2016.1627[4] Rothschild, L. J., 1990, https://doi.org/10.1016/0019-1035(90)90188-F[5] El-Maarry, M. R. et al., 2013, https://doi.org/10.1002/2013JE004463[6] Sager, C. et al., 2021, https://doi.org/10.1016/j.geomorph.2020.107481[7] Riedo, A. et al., 2012, https://doi.org/10.1002/jms.3104[8] Tulej, M. et al., 2021, https://doi.org/10.3390/app11062562