Thu Feb 27 14:50:00 UTC 2025: ## Martian Red Dust Holds Clues to a Cold, Wet Past

**International team of researchers reveals that ferrihydrite, a hydrated iron oxide, is the dominant iron-bearing mineral in Martian dust, challenging previous theories and suggesting a more complex history of water on Mars.**

A new study published in *Nature Communications* reveals a surprising finding about the composition of Martian dust, shedding new light on the planet’s climate history and potential for past habitability. Contrary to previous belief that anhydrous hematite was the primary cause of Mars’ red color, researchers have identified poorly crystalline ferrihydrite (Fe5O8H·nH2O) as the dominant iron oxide-bearing phase.

The research team, involving scientists from various international institutions, combined data from orbital observations (including the Mars Reconnaissance Orbiter’s CRISM and ESA’s Mars Express OMEGA), in-situ measurements from rovers (Mars Exploration Rovers, Mars Pathfinder, and Mars Science Laboratory), and extensive laboratory analyses of submicron ferrihydrite-basalt mixtures. Their spectral analyses strongly support ferrihydrite as the best spectral match to the color of Mars. The addition of magnesium sulfates to these mixtures further replicated the distinctive 3-micron hydration band observed in Martian dust spectra.

Laboratory experiments demonstrated that ferrihydrite remains stable under current Martian conditions, suggesting it formed during a colder, wetter period on early Mars under oxidative conditions, before the planet transitioned to its present hyper-arid state. This challenges the previous model of continuous dry oxidation, indicating instead that Mars experienced significant aqueous alteration before becoming the desert planet we know today.

The abundance of ferrihydrite, estimated at 20-33 wt%, aligns with previous observations of X-ray amorphous iron in Martian soils. The researchers also determined that the dust particles are predominantly submicron in size (<1 µm).

The presence of ferrihydrite raises important questions about the nature of surface oxidation on early Mars and the timing and duration of periods with liquid water. The findings suggest that future Mars Sample Return missions could provide crucial data to further understand the planet’s history and the potential for past life.

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