The ferridrite on Mars is discovered, a mineral indicating the presence of water for a more time than as hypothesized. A key clue for past habitability.
Mars, the “red planet”, is easily recognizable in the night sky for its characteristic reddish shade. This iconic color has long been attributed to the presence of iron minerals oxidized in the dust that covers the surface of the planet. Thanks to the space missions of the last decades, scientists have discovered that the iron in the Marzian rocks has reacted with liquid water or with atmospheric oxygen, forming iron oxides, in a process similar to terrestrial rust. Over the years, this material has shattered powder and spread throughout the planet thanks to the Marzian winds, a phenomenon that still continues today.
However, the exact chemistry of this “Martian rust” has been the subject of scientific debate. Understanding how it has formed is crucial to reconstruct the environmental conditions of the past and to determine if Mars has ever been habitable. Previous studies, based on the observations of the space probes, suggested that the iron oxide present on the Martian surface was mainly hematite, a mineral that forms in dry conditions. This would have implied that the liquid water had disappeared from Mars billion years ago, leaving the planet arid and inhospitable.
The new discovery: Ferridrite
A recent analysis, conducted by an international team of researchers, has revolutionized this interpretation. By combining spatial missions data with new laboratory techniques, scientists have discovered that the red color of Mars is better explained by the presence of ferridrite, a type of iron oxide that contains water. Unlike the hemite, ferridrite is quickly formed in the presence of cold water, suggesting that Mars still had liquid water when this mineral has formed.
“We were trying to recreate the Martian dust in the laboratory using different types of iron oxide,” explains Adomas Valantinas, the main author of the study and post-dental researcher at Brown University (USA), previously at the University of Bern (Switzerland). “We discovered that ferridrite mixed with basalt, a volcanic rock, perfectly corresponds to the minerals observed by the space probes on Mars”.
Hematite and ferridrite
For those who have little confidence with minerals and chemical reactions:
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Henmatite (Fe₂o₃) It can form in different environments, including sedimentary, metamorphic and hydrothermal ones. In sedimentary contexts, as Mars could have been, the water is crucial for the transport and precipitation of the dissolved iron. However, it can also form in environments with poor availability of water, such as oxidation areas, or in hydrothermal environments with water rich in minerals.
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The ferridrite (fe₂o₃ · 0.5h₂o) It is a hydrated iron oxide, that is, it contains water molecules in its structure. Its formation is closely linked to aquatic environments at low temperature, such as soils, sediments and underground waters. It develops in conditions of abundant water, being a product of oxidation and iron hydrolysis in solution.
While hematite can also form in relatively dry environments, ferridrite requires a more substantial presence of water.
Implications for the history of Mars
If the presence of Ferridrite will be confirmed 100%, it would mean that Mars has “rusty” much earlier than we thought, when the water was still abundant. In addition, this mineral remains stable in the current Marzian conditions, preserving his watery signature up to the present day. This discovery redefines our understanding of the color of Mars and offers new perspectives on its geological history and on its possible past habitability.
An international teamwork
The study is based on data from different space missions, including The ESA (Tgo) Trace Gas of ESA, Mars Express, the Mars Reconnaissance Orbiter of NASA and Rover Curiosity, Pathfinder and Opportunities. “This study is the result of an international collaboration and complementary data sets,” says Colin Wilson, scientist of the Tgo and Mars Express project of ASA. “Thanks to the single orbit of Tgo, which allows us to observe the same region in different lighting conditions, we managed to precisely determine the composition and size of the dust particles”.
Future perspectives
The search on Martian dust does not stop there. The next missions, such as the Rosalind Franklin of ASA Rosalind and the NASA-ESA Mars Sample Return mission, could provide further clues.
“Some samples already collected by NASA’s Rover Perseverance contain Martian dust,” adds Wilson. “Once on earth, we will be able to analyze them in the laboratory and precisely measure the amount of ferridrite present, opening new windows on the history of water and the potential habitability of Mars”.
