Study suggests the real reason why Mars is red

The red color of the planet Mars has always fascinated scientists, but now a new discovery could change the explanation that had been used until now to explain this vivid hue: it may be due to the iron mineral ferrihydrite , instead of hematite as previously thought.

The results of a study published Tuesday in the journal Nature Communications and led by researchers from Brown University in the United States and the University of Bern in Switzerland suggest that water-rich ferrihydrite may be the cause of the reddish color of the dust covering Mars . Ferrihydrite is an iron oxide mineral that forms in water-rich environments. On Earth, it is often associated with processes such as the weathering of volcanic rocks and ash.

Although scientists had long suspected ferrihydrite was the reason for Mars' red color, the theory has been held back until now, when researchers have managed to make Martian dust in the lab by mimicking observational data from NASA 's Mars Reconnaissance Orbiter, along with ground measurements from NASA's Curiosity, Pathfinder and Opportunity rovers.

Final confirmation will come from analysis of the Mars samples currently being collected by the Perseverance spacecraft, along with results from upcoming missions such as the European Space Agency's (ESA) Rosalind Franklin rover and NASA/ESA's Mars Sample Return.

More habitable than previously thought

The discovery would indicate that Mars was, in the past, wetter and potentially more habitable than previously thought, since, unlike hematite, which usually forms in warmer and drier conditions, ferrihydrite forms in the presence of cold water .

Researchers believe Mars may have once had an environment capable of supporting liquid water – an essential ingredient for life – and then transitioned from a wet environment to a dry one billion years ago. Over that time, this oxidised material – iron oxide – would have broken down into dust and been spread across the planet by winds, a process that continues today.

"Mars is still the Red Planet, but our understanding of why it is red has been transformed. The main implication is that since ferrihydrite could only have formed when there was still water on the surface, Mars oxidized earlier than we thought ," said lead author Adomas Valantinas, a researcher at Brown University, formerly at the University of Bern.