Why is Mars red? Have scientists finally solved this ancient mystery?

It’s a well-known fact that Mars is a red planet.

But for hundreds of years, people have wondered what gives the planet its unique reddish hue.

Scientists at the University of Bern and Brown University appear to have a concrete answer.

They claim that the planet’s dust is made up of rusted iron minerals.

Let’s take a closer look.

The reason behind Mars’ reddish hue

A study published in the journal Nature Communications suggests that the main reason for Mars’ reddish colour could be the water-rich iron mineral ferrihydrite.

The mineral occurs in situations with significant amounts of water. On Earth, it is frequently linked to processes such as the weathering of volcanic ash and rocks.

The study’s theory contradicts the widely accepted notion that the planet’s colour is the result of a dry, rust-like substance called haematite.

The findings were drawn using data from Martian orbiters, rovers, and lab simulations. Prior studies of iron oxide on Mars were based only on spacecraft data and failed to find any indications of water.

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“The fundamental question of why Mars is red has been thought of for hundreds if not thousands of years,” said lead author Adomas Valantinas, a postdoctoral fellow at Brown University  who started the work as a PhD student at the University of Bern, said in a statement.  

“Mars is still the Red Planet. It’s just that our understanding of why Mars is red has been transformed.”

“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 it has never been proven the way we proved it now using observational data and novel laboratory methods to essentially make Martian dust in the lab.”

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A clue into Mars’ past

The latest discovery offers an intriguing hint to Mars’ wetter and perhaps habitable past since ferrihydrite originates in the presence of cool water, as opposed to haematite, which usually forms under warmer, drier conditions.

This implies that the environment on Mars may have been able to support liquid water, which is necessary for life, and that it changed from a wet to a dry state billions of years ago.

“What we want to understand is the ancient Martian climate and the chemical processes on Mars — not only ancient but also present,” said Valantinas, who works in the lab of Brown planetary scientist Jack Mustard, a senior author on the study.

“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.

“What we know from this study is the evidence points to ferrihydrite forming, and for that to happen there must have been conditions where oxygen, from air or other sources, and water could react with iron. Those conditions were very different from today’s dry, cold environment. As Martian winds spread this dust everywhere, it created the planet’s iconic red appearance.”

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‘A door-opening opportunity’

In their analysis, the researchers combined ground-level measurements from rovers such as Curiosity, Pathfinder, and Opportunity with orbital views from NASA’s Mars Reconnaissance Orbiter and the European Space Agency’s Mars Express and Trace Gas Orbiter.

The planet’s dusty surface was captured in great detail by the instruments on the rovers and orbiters.

The researchers compared these results with laboratory tests in which they examined the effects of light on ferrihydrite particles and other minerals in settings that were similar to those on Mars.

“Martian dust is very small in size, so to conduct realistic and accurate measurements we simulated the particle sizes of our mixtures to fit the ones on Mars,” Valantinas said.

“We used an advanced grinder machine, which reduced the size of our ferrihydrite and basalt to submicron sizes. The final size was 1/100th of a human hair, and the reflected light spectra of these mixtures provide a good match to the observations from orbit and red surface on Mars.”

Even while the recent findings are intriguing, scientists acknowledge that they cannot be completely verified until samples from Mars are returned to Earth.

“The study is a door-opening opportunity,” Mustard said in a statement.

“It gives us a better chance to apply principles of mineral formation and conditions to tap back in time. What’s even more important though is the return of the samples from Mars that are being collected right now by the Perseverance rover. When we get those back, we can actually check and see if this is right.”