For decades, spacecraft and rovers have gathered data pointing to a familiar explanation behind Mars' redness: the rusting of iron minerals, namely iron oxide, in the planet's dust. That's the same compound that gives your standard "rust" on Earth its red color.
Scientists already knew that on Mars, over billions of years, iron oxide has been ground into dust and carried across the planet by powerful winds, a process still shaping the Martian landscape today. However, not all iron oxides are the same, so experts have long debated the precise nature of Martian rust. Understanding how this rust formed offers a crucial glimpse into the planet’s past environment — was it once warm and wet, or always cold and dry? And, more importantly, did it ever support life?
What they found was that the best match for Mars' red dust is a combination of basaltic volcanic rock and a water-rich iron oxide called ferrihydrite.
This discoveries is intriguing because ferrihydrite typically forms rapidly in the presence of cool water — meaning it must have originated when liquid water still existed on Mars' surface.
Even after billions of years of being ground into dust and scattered by Martian winds, ferrihydrite has retained its watery signature, offering a tantalizing clue about Mars' ancient past.
"The major implication is that because ferrihydrite could only have formed when water was still present on the surface, Mars rusted earlier than we previously thought," said Valantinas. "Moreover, the ferrihydrite remains stable under present-day conditions on Mars."
Data from NASA's Mars Reconnaissance Orbiter along with ground-based measurements from the Curiosity, Pathfinder and Opportunity rovers further support the identification of ferrihydrite. These observations provide crucial evidence that Mars’s red dust retains a signature of its watery past, reinforcing the idea that liquid water once played a key role in shaping the planet’s surface.
Source: www.space.com
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