Mars: Rethinking red planet’s trademark color

For centuries, scientists have been captivated by Mars' distinctive red hue, but new research suggests that its color may not stem from rust-like hematite, as previously thought. Instead, a groundbreaking study indicates that ferrihydrite—an iron-rich mineral that forms in water—may be the true source of Mars' red dust. This discovery reshapes our understanding of the planet’s history, suggesting it was once much wetter and potentially habitable.

Mars has long fascinated both researchers and the public, earning the nickname the “Red Planet” due to its striking appearance. However, as an article by SciTechDaily lays out, the reason behind this coloration has been debated for centuries. Scientists traditionally attributed it to hematite, a mineral formed in dry, oxidizing conditions. Now, new findings challenge this assumption, linking Mars' color to ferrihydrite, which forms in the presence of water.

A recent study published in the Nature Communications journal by researchers from the American Brown University and the Swiss University of Bern provides strong evidence that ferrihydrite, not hematite, is responsible for Mars' signature red hue. Using data from Mars orbiters, rovers, and laboratory experiments, the study presents a compelling case for a wetter past on the planet.

Adomas Valantinas, a postdoctoral researcher at Brown University and one of the study’s authors, explains: “The fundamental question of why Mars is red has been debated for thousands of years. Our analysis suggests ferrihydrite is widespread in Martian dust and likely in rock formations as well.” While ferrihydrite had been considered before, this study provides the strongest proof yet, using innovative lab techniques to recreate Martian dust.

Ferrihydrite: Evidence of a watery past

Ferrihydrite is an iron oxide mineral that forms in water-rich environments. On Earth, it is associated with volcanic rock weathering and sedimentary deposits in lakes or oceans. Unlike hematite, which forms under drier, warmer conditions, ferrihydrite requires the presence of cool water. The article states that this suggests Mars once had an environment capable of sustaining liquid water—an essential ingredient for life.

This discovery strengthens the idea that Mars transitioned from a wet planet to the dry, cold desert we see today. “To understand whether Mars was ever habitable, we need to analyze the conditions under which these minerals formed,” Valantinas said. The study implies that Mars’ red dust formed in an environment with both oxygen and liquid water, dramatically different from the planet’s current state.

Advanced techniques reveal new clues

The research team used multiple Mars missions to gather data, analyzing observations from NASA’s Mars Reconnaissance Orbiter, the European Space Agency’s Mars Express, and ground-based measurements from rovers like Curiosity, Pathfinder, and Opportunity. By comparing spectral data with laboratory simulations, they were able to match ferrihydrite’s properties to the red dust covering Mars.

To replicate Martian conditions, the team ground ferrihydrite and basalt to submicron sizes—one-hundredth the width of a human hair—allowing them to study how light interacts with these particles. Their results closely matched spectral readings from Mars’ surface, reinforcing the theory that ferrihydrite plays a key role in the planet’s coloration.

Awaiting final confirmation

While the study presents strong evidence, definitive proof will come only when Mars samples are returned to Earth. NASA’s Perseverance rover is currently collecting samples for a future return mission. “This study opens the door to understanding Mars' climate history,” said Brown planetary scientist Jack Mustard. “But once we have those samples, we can finally confirm whether this theory is correct.”

This new perspective on Mars’ red color not only changes our understanding of the planet’s past but also deepens the mystery of whether it once supported life.

By Nazrin Sadigova