Why is Mars red? Scientists say they were wrong – and now finally have the answer
Mars, our closest planetary neighbour, has long been known as the 'Red Planet' – but a new discovery has turned the reason for its distinctive colouring on its head.
New research suggests that Mars' recognisable rusty hue comes from a water-rich iron mineral called ferrihydrite – and isn’t, in fact, the result of a dry mineral known as hematite, which was previously believed.
Because of the absence of liquid water on the surface, it's long been thought that the planet’s redness came from 'dry' iron oxides, such as hematite. But this new analysis says iron oxides containing water, known as ferrihydrite, are actually a better match.
This new study, published in Nature Communications, is also important as it implies that Mars went ‘rusty’ earlier than previously thought.
Adomas Valantinas, of Brown University in the US, an author of the study, said: "Mars is still the red planet. It's just that our understanding of why Mars is red has been transformed."
The idea this is the origin of the planet's red colour isn’t completely new – but scientists say this study is the first time that such 'Martian dust' has been recreated, and the idea ‘proven’ using observations.
The only way to know for certain is by taking samples from Mars itself. Nasa’s Perseverance Rover is currently collecting soil and rock from the planet so they can be brought back to Earth on a future mission. When this happens, we’ll be able to say for sure.
Adomas Valantinas added: "The fundamental question of why Mars is red has been thought of for hundreds if not for 1000s of years.
"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 a Martian dust in the lab."
It’s also an interesting discovery for Mars because ferrihydrite forms in the presence of cool water, which is essential for life, and suggests it may have had an environment capable of sustaining water before it eventually became a dry planet.
"The study is a door-opening opportunity," said Jack Mustard, a senior author on the study.
"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."
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