Why is Mars is red? Scientists think they've figured it out

Mars has fascinated observers for centuries with its striking red hue, shining brightly in our night skies. Research from multiple space agencies suggests that this distinctive color comes primarily from iron in the planet’s rocks, which contributes to its dusty appearance.

Despite decades of exploration, we still do not know exactly why the surface of Mars appears red. A new study suggests that Mars’s earliest environment may hold the key to understanding its famous color.

Adomas Valantinas, a postdoctoral researcher at Brown University, began this research at the University of Bern in Switzerland.

“What we want to understand is the ancient Martian climate, the chemical processes on Mars – not only ancient – but also present,” explained Valantinas.

“Then there’s the habitability question: Was there ever life? To understand that, you need to understand the conditions that were present during the time of this mineral formation.”

Along with collaborators, he compared data from multiple spacecraft and tested basalt mixtures with various iron oxides in the lab.

Mars’s red dust may come from water

Scientists have often linked Mars’s color to hematite, a type of iron oxide believed to form under dry conditions.

However, the latest research points to ferrihydrite, a water-rich iron mineral that can only arise in the presence of cool liquid water.

Ferrihydrite can retain hints of water in its molecular structure, providing a record of damp conditions long ago.

By testing rock powders in a specialized laboratory setup, the team discovered that ferrihydrite, combined with basalt, replicated Martian dust more convincingly than other mixes.

“These new findings point to a potentially habitable past for Mars and highlight the value of coordinated research between NASA and its international partners when exploring fundamental questions about our solar system and the future of space exploration,” said Geronimo Villanueva from NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and co-author of this study.

Shifting environment of Mars

“We were trying to create a replica Martian dust in the laboratory using different types of iron oxide,” said Valantinas.  

If ferrihydrite took shape when Mars had a thicker atmosphere and steady surface water, then the planet’s environment transitioned earlier than scientists once believed.

This suggests Mars was once very different from its dry, cold self today, noted the researchers.

Mars now has a thin atmosphere that makes liquid water on its surface improbable for long stretches.

Past rover missions including Curiosity and Opportunity found signs of ancient streams and lakes, but current conditions are much less forgiving.

The presence of ferrihydrite indicates that water likely existed on Mars when the mineral first formed.

Many experts believe that these liquid conditions faded away several billion years ago as Mars lost much of its atmospheric protection.

Spread of red dust on Mars

Wind is still a dominant force on Mars, shaping and distributing dust across vast distances. Over time, these movements broke down iron oxides and spread them around the planet.

Persistent dust storms continue to swirl, obscuring ground views and leaving rovers coated in fine debris.

Despite the harsh environment, the original water-rich signature of ferrihydrite may remain locked in the dust grains.

The NASA-ESA Mars Sample Return program aims to gather Martian rocks, dust, and regolith for deeper inspection on Earth.

Scientists hope to confirm the exact mineral makeup of these samples and see if ferrihydrite dominates the red dust.

Probing collected material with high-precision instruments could pin down when water was truly abundant.

Such details may refine our picture of whether early Mars had conditions that could have supported life.

Red dust points to life and water on Mars

Several lines of evidence, including ancient lakebeds, clay minerals, and valley networks, point to a past where water was not a fleeting visitor.

This latest ferrihydrite finding strengthens the argument that Mars underwent a cool and moist period well before it dried out.

The researchers noted that understanding these iron minerals unlocks a chapter in Mars’s history that we’re just beginning to unravel.

The color we see today might hide clues about a time when oxygen and water were abundant.

“We eagerly await the results from upcoming missions like ESA’s Rosalind Franklin rover,” said Colin Wilson, ESA’s Mars Express project scientist. He expects the future findings to shed more light on Mars’s watery transformation.

Many questions remain about how this wet period influenced the potential for simple life-forms to emerge.

Researchers across the world will keep watching, testing, and wondering what else Mars has hidden in its dusty past.

The study is published in the journal Nature Communications.

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