Space mystery solved: This is why Mars is red, according to scientists

A study published in Nature Communications journal this week gave the clearest indication yet as to why Mars is the only planet in our solar system that has a rusty red hue.

Iron oxides present in Martian dust

The study, which was funded by NASA, suggests that a water-rich iron mineral may explain Mars’ reddish dust. By using photographic images of dust samples on Mars, researchers were able to recreate their own Martian dust in a laboratory, using a mix of various different iron oxide-hydroxide minerals. But one in particular, ferrihydrite, gives the planet its iconic color.

The findings also offer clues and insights into Mars’ history, past climate and habitability. Ferrihydrite forms in the presence of cool water and at lower temperatures than other minerals (for example hematite). It suggests that Mars may have once been able to harbor liquid water - billions of years before its environment transitioned from wet to dry.

Mars' has a wet and cool environment around three billion years ago

“The fundamental question of why Mars is red has been considered for hundreds if not for thousands of years,” Adam Valantinas, the study’s lead author explains. “From our analysis, we believe ferrihydrite is everywhere in the dust and also probably in the rock formations, as well. We’re not the first to consider ferrihydrite as the reason for why Mars is red, but we can now better test this using observational data and novel laboratory methods to essentially make a Martian dust in the lab.”

The prevalence of ferrihydrite on Mars suggests that the mineral formed during a cold, wet period during the planet’s nascent stage under oxidative conditions, followed by a transition to the current hyper-arid environment. The new findings challenge previous models of continuous dry oxidation and indicates that “ancient Mars experienced aqueous alteration before transitioning to its current desert state”.

Over billions of years, ferrihydrite decomposed, breaking down into hyperfine ferrihydrite-basalt dust particles which settled all over the planet’s surface, giving it a rusty red color.

Scientists will get a clearer idea about the exact composition of Mars' surface and soil through samples collected from the Mars Sample Return program - a series of planned missions which should be complete by the early 2030s.

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