New Data Shows Mars' Red Hue May Have Come From A Different Source Than Previously Thought

Yahoo

03-03-2025

Scientists may finally know what gives Mars its red hue, and it's turned the previous theory on its head.
It has long been thought that the Red Planet got its coloring due to rusted iron minerals within the dust on the surface. Since observations by spacecraft didn't detect any evidence of water on the planet, it was believed that the iron oxide came from hematite, forming through reactions with the planet's atmosphere over billions of years, CNN reported. This theory meant that the hematite would have formed later in Mars' history after the planet's lakes and rivers disappeared.
But new findings published in February in the journal Nature Communications have shown that iron within Mars' rocks may have reacted with both water and oxygen to create iron oxide, just like what happens on Earth. That iron oxide broke down over billions of years, creating the planet's famous red dust.
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'There are ways to form oxidized iron without water, and some proposed dry processes include surface oxidation like the oxidation rinds that form in rocks in the Antarctic Dry Valleys, and surface oxidation by abrasion as the surface is blasted with sand grains over long periods. But there are also lots of ways to oxidize with water too, including in soils and lakes,' Briony Horgan, co-investigator on the Perseverance rover mission and professor of planetary science at Purdue University, told CNN.
The type of iron oxide now believed to be responsible for Mars' coloring is called ferrihydrite, which forms quickly in cool water, and likely formed on the planet when water was still present on the surface before the planet chilled significantly, NASA reported.
Scientists used data collected by the European Space Agency's Mars Express orbiter, the ExoMars Trace Gas Orbiter and NASA's Mars Reconnaissance Orbiter and several NASA rovers.
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The scientists also recreated dust similar to that found on Mars using different types of iron oxide and grinding it finely similar to the dust on the planet. They then compared their creations to dust from Mars' surface.
The findings change our understanding of Mars and its history. Ferrihydrite lending to Mars' red coloring could mean that there was more widespread water across the planet than previously thought. Both water and oxygen are important resources for a planet to host life, and for water to be present, the planet was likely at a more habitable temperature.