Detection of ferrihydrite in Martian red dust records ancient cold and wet conditions on Mars

• Published in: Nature communications Vol. 16; no. 1; pp. 1712 - 16
• Main Authors: Valantinas, Adomas, Mustard, John F., Chevrier, Vincent, Mangold, Nicolas, Bishop, Janice L., Pommerol, Antoine, Beck, Pierre, Poch, Olivier, Applin, Daniel M., Cloutis, Edward A., Hiroi, Takahiro, Robertson, Kevin, Pérez-López, Sebastian, Ottersberg, Rafael, Villanueva, Geronimo L., Stcherbinine, Aurélien, Patel, Manish R., Thomas, Nicolas
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 25.02.2025; Nature Publishing Group; Nature Portfolio
• Subjects: 147/135; 639/33/445/209; 639/33/445/330; Arid zones; Basalt; Cold; Color; Deserts; Dust; Earth Sciences; Ferric hydroxide; Habitability; Hematite; Humanities and Social Sciences; Infrared analysis; Infrared spectra; Iron oxides; Mars; Mars dust; Mineralogy; multidisciplinary; Near infrared radiation; Oxidation; Planetology; Science; Science (multidisciplinary); Sciences of the Universe; Mars; ferrihydrite
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-025-56970-z

Iron oxide-hydroxide minerals in Martian dust provide crucial insights into Mars’ past climate and habitability. Previous studies attributed Mars’ red color to anhydrous hematite formed through recent weathering. Here, we show that poorly crystalline ferrihydrite (Fe 5 O 8 H · nH 2 O) is the dominant iron oxide-bearing phase in Martian dust, based on combined analyses of orbital, in-situ, and laboratory visible near-infrared spectra. Spectroscopic analyses indicate that a hyperfine mixture of ferrihydrite, basalt and sulfate best matches Martian dust observations. Through laboratory experiments and kinetic calculations, we demonstrate that ferrihydrite remains stable under present-day Martian conditions, preserving its poorly crystalline structure. The persistence of ferrihydrite suggests it formed during a cold, wet period on early Mars under oxidative conditions, followed by a transition to the current hyper-arid environment. This finding challenges previous models of continuous dry oxidation and indicates that ancient Mars experienced aqueous alteration before transitioning to its current desert state. Mars’ distinctive red colour attributed to ferrihydrite, a type of rust mineral. This finding suggests Mars experienced a cold and wet environment before transitioning to its current desert state.