How Did an Ancient Climate on Mars Trap Sulfates ?

Curiosity rover and the Franco-American ChemCam instrument have mapped a thick formation of sulfate nodules, enabling an international team—including CNRS researchers—to reveal a succession of wet and dry climates on Mars dating back more than 3.5 billion years. This climate evolution is far from a monotonous aridification and resembles Earth’s semi-arid regions.

On a 6-kilometer-high sedimentary massif, the Curiosity rover is traversing layers enriched with sulfate salts. Using data from the Franco-American ChemCam instrument, an international team led by William Rapin has shown that these sulfates formed within sediments 200 meters thick during climate fluctuations more than 3.5 billion years ago. These results, published in the journal JGRP, indicate that the salts crystallized, forming nodules, each time the water table evaporated.

ChemCam has enabled the high-resolution mapping of fine sedimentary structures exposed within a 1.5-kilometer radius of the rover, revealing traces of ancient dune fields crisscrossed by ephemeral rivers. At each stop, the instrument also analyzes the chemical composition of the soil and reveals a population of nodules rich in calcium and magnesium sulfates. Mapping of these nodules indicates that they formed through evaporation when the water table was close to the surface.

 

Until now, orbital data suggested a gradual disappearance of water from the surface of Mars and a transition to a strictly arid climate.

The new Curiosity data presented here, however, reveal a prolonged succession of dry and wet climates, as indicated by the sulfate nodules. This study thus proposes a new model for the accumulation of sulfates on Mars, linked to surface climates rather than to weathering by deep, late-stage groundwater.[/caption]

This model resembles semi-arid regions on Earth, where dune fields are subject to alternating wet and dry periods. Mars, like Earth, may therefore have experienced rapid climatic fluctuations. Martian sulfates are thus not merely markers of the end of wet environments, but are rather associated with the presence of water near the surface.

  

Bibliographic reference : “Stratigraphic Partitioning of Evaporites Through the Clay‐Sulfate Transition in Gale Crater, Mars”, W. Rapin, G. Dromart, Gwénaël Caravaca, J. Schieber, D. Rubin, L. Edgar, Sanjeev Gupta, A. Roberts, T. Magnin, B. Clark, L. Kah, R. Sheppard, M. Loche, O. Gasnault, D. Burtt, E. Dehouck, Stéphane Le Mouélic, A R Vasavada. Journal of Geophysical Research: Planets 131.9 (2026): e2026JE009783. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2026JE009783

French laboratories involved : Institut de Recherche en Astrophysique et planétologie (IRAP – OMP),  Laboratoire Géosciences environnement Toulouse (GET – OMP),  Institut d’astrophysique spatiale (IAS – OSUPS), Laboratoire de planétologie et géosciences (LPG – OSUNA), Laboratoire de Géologie de Lyon : Terre, Planètes, Environnement (LGL-TPE – OSUL)

Article published on October 22, 2026, by CNRS-INSU

 

Published on November 5th, 2026