Print button

Abstract EANA2025-33


Chemical and Mineralogical Characterization of the Cave of Loulé (Portugal) – a Potential Planetary Field Analogue for Mars

Miguel Quiaios (1), Manuel Francisco Pereira (2), Carlos Cordeiro (3), Ana Sofia P. S. Reboleira (4)*, Zita Martins (1)*
(1) Centro de Química Estrutural, Institute of Molecular Sciences and Department of Chemical Engineering, Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, (2) Centro de Recursos Naturais e Ambiente (CERENA), Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, (3) BioISI - Instituto de Biossistemas e Ciências Integrativas, Faculdade de Ciências da Universidade de Lisboa, Portugal, (4) Centre for Ecology, Evolution and Environmental Changes (CE3C) & CHANGE – Global Change and Sustainability Institute, and Departamento de Biologia, Faculdade de Ciências, Universidade de Lisboa, Lisboa, Portugal. * - These authors share senior authorship.


Mars is one of the most well studied planets in the search of habitable environments beyond the Earth [1]. Subsurface environments on Mars, particularly caves, are of interest because they offer protection from the planet’s harsh surface conditions, including radiation and extreme temperatures, allowing the preservation of putative biosignatures of past and present life. Planetary field analogues, i.e., terrestrial sites that replicate key physical, geological, or chemical characteristics of certain extraterrestrial environments, serve as valuable tools for pre-mission planning, including instrument testing and scientific protocol refinement. Since no single site on Earth can exactly replicate the Mars, identifying diverse analogues is essential, as each may offer insights into different environmental characteristics [3].

We studied the Cave of Loulé, Portugal, which has high concentrations of atmospheric CO2 and Rn, and low O2, making it a compelling planetary field analogue of Martian caves [4]. Fieldwork was performed in two different seasons: November 2024 and March 2025. We employed X-ray diffraction (XRD), X-ray fluorescence (XRF), elemental analysis-isotope ratio mass spectrometry (EA-IRMS), and Fourier-transform ion cyclotron resonance mass spectrometry analysis (FT-ICR-MS) to characterize the chemistry, mineralogy, and metabolomics of cave sediments. Preliminary mineralogical results show that the sediments are predominantly composed of quartz, hematite, and kaolinite, consistent with minerals identified or inferred on the Martian regolith [5], [6], [7]. Carbon and nitrogen isotopic data revealed δ15N ranging from 3.094‰ to 9.907‰, and δ13C from -28.850‰ to -9.358‰, indicating spatial variability in biogeochemical processes within the cave, that suggest localized differences in nitrogen and carbon fixation by plant and microbial life present in each room [8], [9], [10]. Ongoing metabolomics and additional isotopic analyses on seasonally distinct samples aim to further understand the environment within the cave, ultimately allowing the assessment of its relevance for astrobiological studies as a planetary field analogue.

References:

[1]        A. De Morais, et al. (2015) In Planetary Exploration and Science, pp. 147–245.

[2]        V. Marcheselli (2022) Tecnoscienza, 13, 25-45.

[3]        F. Foucher, et al. (2021) Planetary and Space Science, 197, 105162.

[4]        A. Reboleira, Personal communication.

[5]        V. E. Hamilton, et al. (2003) Geophysical Research Letters, 30, 1915.

[6]        M. B. Wyatt, et al. (2002) Nature, 417, 263–266.

[7]        J. F. Bell, et al. (2000) Journal of Geophysical Research: Planets, 105, 1721–1755.

[8]        N. Planavsky, et al. (2011) In Encyclopedia of Astrobiology, pp. 241–245.

[9]        M. H. O’Leary (1988) BioScience, 38, 328–336.

[10]      G. Fiorentino, et al. (2015) Vegetation History and Archaeobotany, 24, 215–227.

 

Acknowledgments:

This work was supported by the Prize Belmiro de Azevedo-FCT (2023.10009.PRIZE), and the Chair in Sustainability of Subterranean Ecosystems – Loulé at the Faculty of Sciences of the University of Lisbon. Financial support from Fundação para a Ciência e a Tecnologia (FCT) is acknowledged by BioISI (UIDB/04046/2020 - https://doi.org/10.54499/UIDB/04046/2020; UIDP/04046/2020 - https://doi.org/10.54499/UIDP/04046/2020), CHANGE (LA/P/0121/2020 - https://doi.org/10.54499/LA/P/0121/2020), CQE (UIDB/00100), CE3C (UIDB/00329/2025), IMS (LA/P/0056/2020), CERENA (UIDB/04028/2020). This work is framed within the College on Polar and Extreme Environments (Polar2E) of the University of Lisbon.