Mars has long fascinated us with its striking red color, even prompting the ancient Romans to name the planet after their god of war. Now, recent international research is challenging existing theories about what really created the planet’s iconic reddish hue.
The new findings, detailed in a paper published in Nature Communications, suggest that ancient Martian water played a crucial role in shaping the planet’s crimson landscape.
Mars’ high iron content reacted with water—either in liquid or vapor form—over billions of years, producing iron oxide, or rust. This rust eventually disintegrated into fine dust, which was carried across the planet by Martian winds, giving Mars its characteristic color.
Deciphering the Chemistry Behind Mars’ Red Dust
While uncrewed landers and orbital spacecraft have confirmed that iron oxide is responsible for Mars’ coloration, scientists continue to debate the exact chemical processes behind it. Understanding how Martian iron oxidized could provide insights into the planet’s ancient environment—and whether it was ever capable of supporting life.
Until now, no spacecraft observations have detected water within Martian dust, leading researchers to conclude that hematite, a dry-formed iron oxide, was the most likely culprit. Hematite takes billions of years to develop under arid conditions, meaning Mars would have acquired its red color only after its early wet period had ended.
A New Kind of Red on Mars
However, this hematite-based theory is based entirely on spacecraft data rather than direct laboratory tests. A Mars sample return mission, a planned joint effort between NASA and the European Space Agency (ESA), has yet to be executed. Now, a new analysis of NASA and ESA data using novel laboratory techniques suggests that the red dust on Mars more closely resembles ferrihydrite, a water-containing iron oxide, rather than hematite.
Ferrihydrite forms quickly when iron interacts with cool water, suggesting that surface water played a more significant role in Mars’ oxidation than previously thought. Over time, this ferrihydrite weathered into dust and spread across the Martian surface, contributing to its deep red hue.
“The project was an international collaboration between several European and North American universities,” lead author Adomas Valantinas told The Debrief. He began the project at the University of Bern in Switzerland, using ESA’s Trace Gas Orbiter (TGO) data, before concluding his work as a postdoctoral researcher at Brown University in the United States. “Importantly, this project showcases how international collaboration is vital when exploring fundamental questions about our Solar System,” he added.
Replicating Mars in the Lab
While earlier studies had suggested that ferrihydrite might be present on Mars, this research is the first to combine laboratory experiments with spacecraft data to provide strong evidence. The team used an advanced grinding machine to create dust particles 1/100th the thickness of a human hair, mimicking Martian dust conditions. These samples were then analyzed using the same techniques employed by orbiting spacecraft.
“The contents of our replica dust were informed by regolith and dust measurements from NASA’s Curiosity rover, which used multiple instruments including a reflectance spectrometer, an X-ray diffraction machine, and an alpha particle X-ray spectrometer,” Valantinas explained. “To match these properties in our laboratory samples, we used a reflectance spectrometer and X-ray diffraction to determine mineralogy, electron microscopy to analyze particle size, and electron microprobe measurements to verify chemistry.”
“This approach ensured our replica dust matched the Martian material not just in color but also in chemistry, mineralogy, and physical properties,” Valantinas added. “We found that ferrihydrite mixed with basalt, a volcanic rock, best fits the minerals seen by spacecraft at Mars.”
Implications for Mars’ History—And Its Potential for Life
Valantinas explains that while Mars remains the Red Planet, new findings have changed our understanding of why it is red. The discovery of ferrihydrite, which forms in the presence of water, suggests that Mars’ surface rusted much earlier than previously believed. Additionally, this mineral remains stable under current Martian conditions, indicating that traces of its watery past persist today.
Although the recent research does not directly confirm the existence of past life on Mars, it strengthens the case for ancient habitability. If Mars’ red dust formed in the presence of liquid water, then conditions may have been more favorable for life than previously assumed.
“The discovery suggests Mars had two key ingredients needed for life as we know it: liquid water and stable environmental conditions that persisted long enough to leave a planet-wide chemical signature,” Valantinas said. “The cold, wet conditions identified would have been similar to certain environments on Earth where microbial life thrives. However, the presence of suitable conditions doesn’t necessarily mean life existed – it simply indicates that early Mars had environments where life, as we understand it, could potentially have survived.”
The paper “Detection of Ferrihydrite in Martian Red Dust Records Ancient Cold and Wet Conditions on Mars” appeared on February 25, 2025, in Nature Communications.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.