Orbital detection and implications of akaganéite on Mars

The martian surface bears the mineralogical record of ancient sub-surface and surface aqueous alteration environments. While most of the chemical alteration produced phyllosilicates, hydrated sulfates and chlorides, other less common compounds provide key constraints on localized geochemical settings, and help refine the geological evolution of the planet. Using orbital imaging spectroscopy data, we report the detection of the iron chlorine hydroxide akaganéite (β-FeOOH, Cl) at several locations of Mars. Akaganéite is known to form in highly saline and chlorinated aqueous environments, and its occurrence in at least three basins of Mars suggests the existence of near-marine (lagoon-like) evaporitic settings early in Mars' history. As a frequently biogenic mineral, the in-depth study of akaganéite and its relationship with other minerals will also provide an additional benchmark for the assessment of pre-biotic to biotic activity on Mars.