The iconic hue of the red planet Mars has fascinated scientists for centuries, but the real reason behind its color may be different than we once thought. A groundbreaking study suggests that Mars' red color is caused not by dry, rust-like hematite as previously thought, but by ferrihydrite - an iron-rich mineral that forms in water. The discovery reshapes our understanding of Mars' history, suggesting that Mars was once wet and potentially habitable.
Mars has fascinated scientists and the public for centuries, primarily because of its striking red color. This unique hue has earned it the well-known nickname "Red Planet." But what exactly gives Mars its iconic color? Scientists have been debating this question ever since they began studying Mars. Now, new research may provide a clear answer - linking Mars' color to its watery past.
A recent study published in Nature Communications, led by researchers at Brown University and the University of Bern, suggests that Mars' red dust comes primarily from ferrihydrite, an iron mineral rich in water. This challenges the long-held belief that Mars' color is caused by hematite, a dry, rust-like mineral. By analyzing data from Mars orbiters, rovers and laboratory simulations, researchers have presented compelling evidence that ferrihydrite, not hematite, is responsible for Mars' iconic red appearance.
"The fundamental question of why Mars is red has been pondered for hundreds if not thousands of years," said Brown University postdoctoral researcher Adomas (Adam) Valantinas, who began the work while working on his PhD at the University of Bern. "Based on our analysis, we believe that hydrothermal minerals are ubiquitous in dust and may also be present in rock formations. We are not the first to consider hydrothermal minerals as the cause of Mars' red color, but it has never been confirmed as we are now using observational data and novel laboratory methods to create Martian dust in the laboratory."
Hydrothermal 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 volcanic ash. Until now, its role in the composition of Mars' surface has been less clear, but the new study suggests it may be an important component of the dust that coats the surface.
The discovery provides an important clue that Mars had a wetter and more habitable past, because unlike hematite, which typically forms in warmer, drier conditions, hydrometeorite formed in the presence of cold water. This suggests that Mars may have once had an environment capable of sustaining liquid water, an essential ingredient of life, and transitioned from a moist to a dry environment billions of years ago.
“What we want to understand is the climate of ancient Mars, the chemical processes on Mars — not just ancient — but current,” said Valantinas, who works in the lab of Brown planetary scientist Jack Mustard, senior author of the study.
"Then there's the question of habitability: Was there ever life? To understand that, you need to understand the conditions under which this mineral formed. What we know from this study is evidence that ferrihydrite is forming, and for that to happen, there have to be conditions where oxygen (from the air or other sources) and water can react with the iron. These conditions are very different from today's dry, cold environment. As Martian winds blow this dust around, it creates the planet's signature red appearance."
The researchers analyzed data from multiple Mars missions, combining orbital observations from NASA's Mars Reconnaissance Orbiter and the European Space Agency's Mars Express and Trace Gas Orbiters with ground-based measurements from rovers such as Curiosity, Pathfinder and Opportunity.
Instruments on orbiters and rovers provide detailed spectroscopic data on Mars' dusty surface. The findings were then compared to laboratory experiments in which the team tested how light interacted with ferrihydrite particles and other minerals under simulated Martian conditions.
"Mars dust has a very small volume, so to make realistic and accurate measurements, we simulated the particle size of the mixture to fit the particle sizes on Mars," Valantinas said. "We used advanced grinders to reduce the size of ferrihydrite and basalt to submicron levels. The final size is 1/100 the size of a human hair, and the reflectance spectra of these mixtures match closely those observed from orbit and on the red surface of Mars."
As exciting as these new discoveries are, researchers know that none of them can be confirmed until Martian samples are brought back to Earth, and the mysteries of the Red Planet's past will remain out of reach.
"This study is an opportunity to open doors," Mustard said. "It gives us a better opportunity to apply principles of mineral formation and conditions back in time. But more importantly the Perseverance rover is currently collecting Martian samples. When we bring those samples back, we can check if this is correct."
Compiled from /scitechdaily