What colored Mars red?
Large parts of the surface of Mars are colored red. New findings about the origin of the color provide an insight into the history of our neighboring planet.
Mars rusted earlier than previously assumed
(Image: ESA/DLR/FU Berlin/G. Michael)
The red planet is easily recognizable, even with the naked eye, in the night sky. Iron oxide – or simply rust – is responsible for its characteristic color. But this is not what was previously assumed.
The crust of Mars consists mainly of basalt, i.e., gray rock. One component of basalt is iron. This is presumably released during erosion and oxidized. The rust-red dust then spread across the planet.
According to a recent study in the journal Nature Communications, the Martian rust consists of ferrihydrite, which requires the presence of water to form. Until now, researchers had assumed that it was hematite, which is formed under dry conditions.
Data from orbit and the surface analyzed
The previous assumptions were based on data collected by spacecraft from orbit. The team led by Adomas Valantinas has now analyzed data collected by Mars rovers in addition to data from orbit from probes such as the Mars Reconnaissance Orbiter of the US space agency NASA and the European probes Mars Express and the Trace Gas Orbiter.
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The team then tested in the laboratory which iron oxide the observed signatures matched. To do this, they mixed ferrihydrite and hematite with basalt rock. “We tried to recreate Martian dust in the laboratory by using different types of iron oxide,” said Valantinas. “We found that ferrihydrite mixed with basalt, a volcanic rock, was the best match for the minerals observed by spacecraft on Mars.”
Mars has been red for a very long time
This means that the red color is much older than previously thought. If the rust were made of hematite, it would only have formed after the water had disappeared. It would have formed over a period of several billion years during the cold and dry phase of Mars' history, which continues to this day.
Ferrihydrite forms much faster. This requires the presence of water and oxygen, although it is not clear where this comes from.
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“As ferrihydrite could only form when water was still present on the surface, Mars rusted earlier than we previously thought,” Valantinas summarized. His team and he are now waiting for upcoming missions such as the European ExoMars mission with the Rosalind Franklin rover or the European-American Mars Sample Return. The results should make it possible to gain further insights into what colors Mars red.
(wpl)
