This iron mineral, called ferihydrite, formed under oxidative conditions during cold, humid periods on early Mars, continuing its transition to the current overheating environment.
This image of Mars Express's high-resolution stereo camera shows Mars glove set on a dark background. The planet's disc has patches of yellow, orange, blue and green, all with a muted gray hue throughout, representing the various compositions of the surface. Image credits: ESA/DLR/FU BERLIN/G. MICHAEL/CC BY-SA 3.0 IGO.
Mars is easily identified in the night sky due to its prominent red tint.
Thanks to a fleet of spacecrafts that have been studying planets over the past decades, this red colour is known to be due to rusty iron minerals in the dust.
In other words, iron bound to the rocks of Mars reacted at one point with water and oxygen in the air, just as how rust on Earth formed.
For more than billions of years, this rusty material, iron oxide — has been broken down into dust around the planet by the wind, a process that continues today.
However, iron oxide has a lot of flavour and the precise chemistry of Mars' rust is heavily debated as it is a window into the environmental conditions of Earth at the time.
And what's closely linked to it is the question of whether Mars has been habitable to date.
Previous studies of the iron oxide components of Martian dust based solely on spacecraft observations found no evidence of water contained within it.
Therefore, planetary researchers say that this particular type of iron oxide is formed under hematite, which is formed under dry surface conditions through reaction with the Martian atmosphere for billions of years after an early wet period on Mars. I had concluded that it had to be.
However, new analysis of spacecraft observations combined with new laboratory techniques shows that Mars' red colour is better matched by iron oxides containing water known as ferihydrite.
Felihydrite usually forms quickly in the presence of cold water, so it must have been formed when Mars was still water on the surface.
The minerals hold a watery signature to this day, despite their spreading down to the ground.
Dr. Adomas Valantinas, a researcher at Brown University, said:
“Ferihydrite, mixed with volcanic rock basalt, has proven to be the most suitable for the minerals found in Martian spacecraft.”
“Mars is still a red planet. It's not only about understanding why Mars is red, but it also means that our understanding has changed.”
“The main meaning is that Mars was rusting faster than before, as ferrihydrite could only form when water was still on the surface.”
“In addition, under current conditions on Mars, ferrihydrite remains stable.”
Mars has acquired its iconic color from the combination of rust and erosion over its 4.6 billion years of history. Image credits: ESA/ATG Europe/Valantinas et al. , doi: 10.1038/s41467-025-56970-z.
Other studies have also suggested that ferrihydrite may be present in Mars' dust, but the current study has been the first comprehensive study through a unique combination of space mission data and new laboratory experiments. Provide evidence.
The authors used an advanced grinder machine to create replica Mars dust, achieving realistic dust grain sizes equivalent to 1/100th of human hair.
To make a direct comparison, the samples were then analyzed using the same technology as the spacecraft orbiting the spacecraft, and ultimately identified ferrihydrite as the best match.
“This study is the result of a complementary dataset from a fleet of international missions exploring Mars at orbital and ground levels,” says Dr. Colin Wilson, PhD, Trace Gas Orbiter (TGO) from ESA and Mars Express Project Scientist. said.
Mars Express's dust mineralogy analysis helped to show that even the highly dusty regions of the planet contain water-rich minerals.
Also, thanks to TGO's unique trajectory, you can see the same area at different lighting conditions and angles. Researchers can unravel the particle size and composition essential to replicate the correct dust size in the lab.
Data from NASA's Mars Reconnaissance Orbiter and ground-based measurements from NASA's Mars Rovers Curiosity, Pathfinder and opportunity also helped to assert ferrihydrite.
“We are eagerly awaiting the results of our upcoming missions, including ESA's Rosalind Franklin Rover and sample returns from NASA/ESA Mars.
“Some of the samples that have already been collected by NASA's Perseverance Rover and are waiting for their return to Earth contain dust. Putting these precious samples into the lab will result in dust. You can accurately measure the amount of ferihydrite contained and what this means to understand the history of water and the potential for life on Mars.”
“This research is an opening opportunity for the door,” said Dr. Jack Mustard, a planetary scientist at Brown University.
“It gives us a better opportunity to apply the principles of mineral formation and conditions and tap time.”
“More importantly, the return of samples from Mars, which are currently being collected through patience.”
Survey results It will be displayed in the journal Natural Communication.
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A. Valantinas et al. 2025. Detection of ferrihydrite in the red dust of Mars records ancient cold and wet conditions on Mars. Nut commune 16, 1712; doi:10.1038/s41467-025-56970-z
Source: www.sci.news
