Origins of Martian Red

Mars has long mesmerized scientists and dreamers alike with its vivid red glow. Traditionally, this ruddy hue was blamed on a dry, rust-like mineral called hematite. However, a recent study published in Nature Communications led by researchers from Brown University and the University of Bern points to a surprising culprit: ferrihydrite.

Ferrihydrite is an iron oxide that forms in water-rich environments—a stark contrast to the arid conditions required for hematite. Using data from NASA’s Mars Reconnaissance Orbiter, the European Space Agency’s Mars Express and Trace Gas Orbiter, and ground-level rover measurements from Curiosity, Pathfinder, and Opportunity, the team crafted a detailed picture of Martian dust. Laboratory simulations, replicating the fine sub-micron particles found on Mars, confirmed that ferrihydrite’s light reflection properties closely match the planet’s distinctive red surface.

Postdoctoral fellow Adomas (Adam) Valantinas, who began this work during his Ph.D. at the University of Bern, explains, “From our analysis, we believe ferrihydrite is everywhere in the dust—and also probably in the rock formations as well.” The team's main breakthrough was proving its role using both observational data and lab-created Martian dust. This discovery suggests that Mars once harbored cooler, wetter conditions, a scenario that might have supported liquid water and, by extension, life.

The implications are profound. Unlike hematite, which forms in warmer, drier settings, the presence of ferrihydrite hints at an ancient Martian climate where water and oxygen interacted with iron, painting the planet red. As Martian winds dispersed this dust, it sculpted the look we see today.

Although these findings open a new chapter in understanding Mars’ past, confirmation awaits the return of samples collected by the Perseverance rover—a tangible key to unlocking the Red Planet’s long-held secrets.