Cryogenic origin of fractionation between perchlorate and chloride under modern martian climate

• Published in: Communications Earth & Environment
• Main Authors: Li, Dongdong, Zhao, Yu-Yan Sara, Meslin, Pierre-Yves, Vals, Margaux, Forget, François, Wu, Zhongchen
• Other Authors: Key Laboratory of Comprehensive and Highly Efficient Utilization of Salt Lake Resources, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining, China, Key Laboratory of Salt Lake Resources Chemistry of Qinghai Province, Xining, China, Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, Center for Excellence in Comparative Planetology, Chinese Academy of Sciences Beijing (CAS), Chengdu University of Technology (CDUT), Institut de recherche en astrophysique et planétologie (IRAP), Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Météorologie Dynamique (UMR 8539) (LMD), Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-École des Ponts ParisTech (ENPC)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Shandong University at Weihai Weihai
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2022
• Subjects: [SDU]Sciences of the Universe [physics]; Arctic
• Online Access: https://hal.sorbonne-universite.fr/hal-03561314; https://hal.sorbonne-universite.fr/hal-03561314/document; https://hal.sorbonne-universite.fr/hal-03561314/file/s43247-022-00345-5.pdf; https://doi.org/10.1038/s43247-022-00345-5

International audience The high perchlorate (ClO 4 −) to chloride (Cl −) ratios observed at the Phoenix landing site, northern polar region of Mars, have been puzzling since detection. However, a lack of understanding of perchlorate-chloride-water systems under cryogenic conditions makes it difficult to assess ClO 4 − /Cl − ratios during deliquescence-related processes. Here we quantitatively evaluate ClO 4 − /Cl − fractionation in deliquescence-induced brines of magnesium-and calcium-perchlorate-chloride salt mixtures under subzero conditions, by measuring solubility data and constructing temperature-dependent thermodynamic models. We find that under specific relative humidity (RH) and temperature (T) conditions, deliquescence of perchlorate-chloride mixtures may form brines with fractionated ClO 4 − /Cl − signatures. Appropriate RH-T, water-limited conditions, and aeolian processes are required to produce and preserve the elevated ClO 4 − /Cl − signatures in soils. Under the present climate, the north polar region can support ClO 4 − /Cl − fractionation and potentially enrich perchlorate for longer periods on global Mars. This highlights the uniqueness of Mars' arctic environment and its implications for modern habitability.