A new international study, partially funded by NASA, has added to the growing body of evidence suggesting that Mars once had a cool, wet, and potentially habitable climate. The research, published on February 25 in Nature Communications, proposes that the planet’s iconic red dust is largely composed of ferrihydrite, an iron-rich mineral that forms in the presence of water at lower temperatures than previously considered minerals like hematite.
Mosaic of the Valles Marineris hemisphere of Mars projected into point perspective, a view similar to that which one would see from a spacecraft. The distance is 2500 kilometers from the surface of the planet, with the scale being .6km/pixel. The mosaic is composed of 102 Viking Orbiter images of Mars. The center of the scene (lat -8, long 78) shows the entire Valles Marineris canyon system, over 2000 kilometers long and up to 8 kilometers deep, extending form Noctis Labyrinthus, the arcuate system of graben to the west, to the chaotic terrain to the east. Many huge ancient river channels begin from the chaotic terrain from north-central canyons and run north. The three Tharsis volcanoes (dark red spots), each about 25 kilometers high, are visible to the west. South of Valles Marineris is very ancient terrain covered by many impact craters. Credit : NASA
Mars' current atmosphere is too thin and cold to support liquid water for long periods. However, decades of exploration by NASA and international missions have revealed signs of ancient rivers, lakes, and minerals that only form in water, indicating a more temperate past.
This latest study strengthens that idea by identifying ferrihydrite as a key component of Martian dust. According to lead author Adam Valantinas, a postdoctoral fellow at Brown University, ferrihydrite appears to be widespread in both the dust and rock formations on Mars.
“The fundamental question of why Mars is red has been considered for hundreds, if not thousands, of years,” said Valantinas, who began this research as a Ph.D. student at the University of Bern in Switzerland. “We’re not the first to suggest ferrihydrite is the reason, but now we can better test this using observational data and novel laboratory methods to essentially make Martian dust in the lab.”
A Clue to Mars' Potential Habitability
Ferrihydrite's presence suggests that Mars had water-rich environments at lower temperatures than previously thought. This could mean that the planet’s transition from wet to dry conditions occurred more gradually, allowing for extended periods of habitability.
“These new findings point to a potentially habitable past for Mars,” said Geronimo Villanueva, Associate Director for Strategic Science at NASA’s Goddard Space Flight Center, and co-author of the study. “It highlights the value of coordinated research between NASA and international partners when exploring fundamental questions about our solar system.”
To reach their conclusions, the researchers analyzed orbital and ground-level data collected from multiple Mars missions, including NASA’s Mars Reconnaissance Orbiter, ESA’s Mars Express and Trace Gas Orbiter, and NASA rovers like Curiosity, Sojourner, and Opportunity. By studying spectral data of Mars' surface, they compared their findings to laboratory experiments simulating Martian conditions, testing how light interacts with ferrihydrite and other minerals.
Unraveling Mars’ Climate History
Understanding the formation of ferrihydrite on Mars could also help scientists reconstruct the planet’s ancient climate.
“What we want to understand is the ancient Martian climate, the chemical processes on Mars—both past and present,” Valantinas explained. “Then there’s the habitability question: Was there ever life? To answer that, we need to understand the conditions when these minerals formed.”
1Laboratory sample showing simulated Martian dust. The ochre color is characteristic of iron-rich ferrihydrite, a mineral that provides crucial insights into ancient water activity and environmental conditions on Mars. The fine-powder mixture consists of ferrihydrite and ground basalt with particles less than one micrometer in size (1/100th diameter of a human hair) (Sample scale: 1 inch across). Adam Valantinas
Since ferrihydrite requires oxygen and water to react with iron, its formation suggests that early Mars had environmental conditions vastly different from today’s dry and cold landscape. As Martian winds dispersed this dust across the surface, it helped shape the planet’s distinct red appearance.
While this study provides strong evidence for ferrihydrite’s role in shaping Mars’ red hue, researchers emphasize that a definitive answer may come once Martian soil samples are returned to Earth. NASA’s Perseverance rover is currently collecting samples that will be brought back in a future mission.
“The study really is a door-opening opportunity,” said Jack Mustard, senior author and professor at Brown University. “It lets us apply principles of mineral formation to tap back in time. But what’s even more important is the return of the samples from Mars. When we get those back, we can actually check and see if this is right.”
Some of the spectral measurements for the study were conducted at NASA’s Reflectance Experiment Laboratory (RELAB) at Brown University, which is part of NASA’s Planetary Science Enabling Facilities program.
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