The red color of Mars might have an earlier, wetter origin
Scientists reckon the red hue of Mars might have originated in an earlier period in the planet’s past when liquid water was widespread on the surface.
The research, published in Nature Communications, suggests that the planet’s red color is best matched by iron oxides containing water, known as ferrihydrite. The previous leading theory was that the iron oxide was hematite which had been formed under dry surface conditions. Ferrihydrite, on the other hand, usually forms quickly in the presence of water.
The implication is that Mars must have “rusted” earlier than previously believed.
The ferrihydrite theory has been proposed in other studies [PDF]. However, the latest research builds on observations from a variety of spacecraft, including the European Space Agency’s (ESA) veteran Mars Express spacecraft and the Trace Gas Orbiter (TGO).
Data from NASA’s Mars Reconnaissance Orbiter and ground-based measurements from Mars rovers Curiosity, Pathfinder, and Opportunity were also used.
Scientists drew upon this information in laboratory experiments, grinding and mixing samples before analyzing the results with the same techniques used by the robotic explorers. They concluded that ferrihydrite was the best match.
A lead author of the study, Adomas Valantinas, a postdoc at Brown University in the US, said: “We were trying to create a replica Martian dust in the laboratory using different types of iron oxide. We found that ferrihydrite mixed with basalt, a volcanic rock, best fits the minerals seen by spacecraft at Mars.”
Colin Wilson, ESA’s TGO and Mars Express project scientist, said: “This study is the result of the complementary datasets from the fleet of international missions exploring Mars from orbit and at ground level.
“We eagerly await the results from upcoming missions like ESA’s Rosalind Franklin rover and the NASA-ESA Mars Sample Return, which will allow us to probe deeper into what makes Mars red.”
Some of the samples collected by NASA’s Perseverance rover include dust, which can be analyzed on Earth to determine the ferrihydrite content, assess implications for Mars’s water history, and evaluate the possibility of life.
Valantinas said: “Mars is still the Red Planet. It’s just that our understanding of why Mars is red has been transformed. 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.”
ESA commented: “The exact chemistry of Martian rust has been intensely debated because how it formed is a window into the planet’s environmental conditions at the time.
“And closely linked to that is the question of whether Mars has ever been habitable.” ®
