Mineral discovery sheds light on Mars' fiery past

For years, scientists studying Mars from orbit have noticed odd patterns in some sulfate-rich regions. These spots had a unique spectral fingerprint – something that didn’t match any known mineral. Now, researchers think they’ve figured out why.

A study has identified an unusual type of iron sulfate on the Martian surface that may represent a completely new mineral.

The team behind this discovery comes from the SETI Institute and NASA’s Ames Research Center in California’s Silicon Valley. Their findings offer new insight into how Mars has changed over time, especially under the influence of heat and water.

Mars dust holds an intriguing record

The researchers focused on two regions that stood out in orbital data due to unusual sulfate signatures: Aram Chaos and the plateau above Juventae Chasma.

“We investigated two sulfate-bearing sites near the vast Valles Marineris canyon system that included mysterious spectral bands seen from orbital data, as well as layered sulfates and intriguing geology,” said Dr. Janice Bishop, senior research scientist at the SETI Institute.

The idea was to understand how these odd signatures formed. The scientists combined lab work with satellite data and uncovered a rare ferric hydroxysulfate that hadn’t been confirmed on Mars before.

It’s a unique type of iron sulfate that forms only in specific environments, with the potential to reshape our knowledge of Mars’ recent geology.

On the edge of Juventae Chasma

The Juventae Plateau, perched just above the 5-kilometer-deep Juventae Chasma, shows signs of water from long ago. Dry channels wind across the surface, hinting at a wetter past. But the key finding wasn’t the water – it was what the water left behind.

In one small, low-lying patch, scientists spotted hydrated ferrous sulfates. These included ferric hydroxysulfate, which appeared in meter-thick layers both above and below basaltic rock. The pattern suggests they formed from pools of water that later evaporated – and were then heated by lava or volcanic ash.

“Investigation of the morphologies and stratigraphies of these four compositional units allowed us to determine the age and formation relationships among the different units,” said study co-author Dr. Catherine Weitz, senior scientist at the Planetary Science Institute.

A messy past with a message

Aram Chaos lies northeast of Valles Marineris. It’s one of Mars’ many chaotic terrains – broken-up, rugged landscapes thought to have been shaped by ancient floods. When the water disappeared, it left behind layered deposits of iron and magnesium sulfates.

In this region, the upper levels hold polyhydrated sulfates. Beneath them are layers of monohydrated sulfates and ferric hydroxysulfate. From orbit, each of these sulfates gives off a different spectral signature, allowing scientists to map their presence using an instrument called CRISM.

Lab testing showed that heating polyhydrated sulfates to 50°C creates monohydrated ones. At temperatures above 100°C, ferric hydroxysulfate starts to form. That supports the idea that geothermal heat reshaped the minerals after their initial formation.

Monohydrated and polyhydrated sulfates cover large areas, while ferric hydroxysulfate appears in only a few small patches. Those patches likely mark the warmest areas in the past, possibly still hiding deeper mineral layers below.

Ongoing oxidation of Mars’ minerals

The research team replicated these Martian conditions in the lab. They heated rozenite (an iron sulfate with four water molecules) and watched it transform to szomolnokite (with one water molecule) and then to ferric hydroxysulfate, which contains OH instead of H₂O in its chemical structure.

“Our experiments suggest that this ferric hydroxysulfate only forms when hydrated ferrous sulfates are heated in the presence of oxygen,” said postdoctoral researcher Dr. Johannes Meusburger.

“While the changes in the atomic structure are very small, this reaction drastically alters the way these minerals absorb infrared light, which allowed identification of this new mineral on Mars using CRISM.”

The reaction is simple but revealing. It uses oxygen gas and produces water: Mars’ atmosphere is mostly carbon dioxide, but it still has enough oxygen to make this reaction possible. That means oxidation of iron minerals continues today, slowly and quietly.

Is it a new mineral?

“The material formed in these lab experiments is likely a new mineral due to its unique crystal structure and thermal stability,” said Bishop. “However, scientists must also find it on Earth to officially recognize it as a new mineral.”

Structurally, this mineral is close to szomolnokite. But it forms more easily from rozenite – especially in oxygen-rich, high-heat environments. And those conditions, it turns out, may not be as ancient as once assumed.

The transformation into ferric hydroxysulfate only happens above 100°C. That’s far hotter than Mars’ surface today. So. if these minerals formed recently, it implies there were geothermal or volcanic heat sources still active during the Amazonian period, less than 3 billion years ago.

Significance of minerals on Mars

This discovery shows that some parts of Mars may have been chemically and thermally active more recently than previously thought.

The sulfates at Aram Chaos and Juventae Plateau weren’t just frozen in place from ancient floods – they were altered later by heat and oxygen.

That adds a new layer to the story of Mars. It suggests there were pockets of energy and chemical change long after the planet’s surface dried out. And where there’s change, there’s always the potential for something more – possibly even the ingredients for life.

The full study was published in the journal Nature Communications.

Image Credit: NASA/ JPL-Caltech/ University of Arizona

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