Scientists might have found a brand-new mineral on Mars

Each mineral has its own crystal structure and physical properties. Familiar examples include gypsum and hematite. Scientists analyze data from orbiting spacecraft to identify minerals on the Martian surface and reconstruct the environmental conditions that produced them. For nearly two decades, researchers have been puzzled by layered iron sulfates on Mars that show unusual spectral signals. A new investigation led by Dr. Janice Bishop, senior research scientist at the SETI Institute and NASA’s Ames Research Center in California’s Silicon Valley, has now identified and characterized an uncommon ferric hydroxysulfate phase. The team combined laboratory experiments with orbital observations of Mars to better understand these materials. Their results provide new clues about the roles of heat, water, and chemical reactions in shaping the Martian landscape.

“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 Bishop.

Study Sites Near Valles Marineris

The research focused on two areas close to Valles Marineris, one of the largest canyon systems in the solar system. One location is Aram Chaos, situated northeast of the canyon system where ancient water once flowed toward lower terrain to the north. The second site lies on the plateau above Juventae Chasma, a 5-km-deep canyon located just north of Valles Marineris.

Juventae Plateau (above Juventae Chasma)

This region near the cliffs of Valles Marineris preserves signs of a wetter past. Ancient channels carved by flowing water cross the landscape. Scientists found sulfate minerals concentrated in a small low area that likely formed when pools of sulfate-rich water gradually evaporated. As the water disappeared, hydrated ferrous sulfates were left behind.

These minerals, including ferric hydroxysulfate, occur in thin layers roughly a meter thick that sit both above and below basaltic materials. Their position suggests they were later exposed to heat from lava or volcanic ash after they originally formed.

“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 Dr. Catherine Weitz, a co-author on the study and Senior Scientist at the Planetary Science Institute.

Evidence From Aram Chaos

Sulfate minerals are widespread throughout the Valles Marineris region, especially in rugged landscapes called chaotic terrains. Scientists believe these areas formed when massive floods reshaped the surface long ago. As the water evaporated, it left layered deposits of iron and magnesium sulfates that provide evidence of a much wetter Mars in the past.

In one chaos terrain that formed within an ancient impact crater, the uppermost layers contain polyhydrated sulfates. Beneath them lie layers of monohydrated sulfates and ferric hydroxysulfate.

How Heat Transformed Martian Sulfates

Each of these sulfate types has a unique spectral signature that can be detected from orbit using the CRISM instrument. At first, the arrangement of these mineral layers was difficult to explain. Laboratory experiments helped solve the puzzle. Researchers found that heating polyhydrated sulfates to 50°C converts them into monohydrated forms. When temperatures exceed 100°C, ferric hydroxysulfate forms. These results indicate that geothermal heat likely altered the minerals after they were deposited.

Polyhydrated and monohydrated sulfates appear across large areas of the region. Ferric hydroxysulfate is much rarer and occurs only in a few small locations. Scientists suspect that warmer geothermal sources once existed beneath these areas, producing the conditions needed to create this mineral. Additional deposits could remain buried under layers of monohydrated sulfates.

Laboratory Experiments Reveal Mineral Transformations

Researchers at the SETI Institute and NASA Ames performed laboratory experiments to trace how these minerals evolve. The process begins with rozenite (Fe²⁺SO₄·4H₂O), which contains four water molecules in each unit cell. Heating transforms it into szomolnokite (Fe²⁺SO₄·H₂O), which contains only one water molecule. Continued heating produces ferric hydroxysulfate, where OH replaces H2O in the mineral 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 at NASA Ames. “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.”

Oxygen and Chemical Reactions on Mars

This chemical reaction requires oxygen gas and generates water (Equation 1). Mars currently has a thin atmosphere dominated by CO₂, yet it still contains enough oxygen for this reaction to occur and for other forms of iron to oxidize as well.

Equation 1: 4 Fe²⁺SO₄·H₂O + O₂ → 4 Fe³⁺SO₄OH + 2H₂O

“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.”

Clues to Mars’ Geological Activity

The newly identified ferric hydroxysulfate has a crystal structure similar to szomolnokite, a monohydrated ferrous sulfate. However, it appears to form more readily from rozenite, which contains four water molecules.

The transformation from hydrated ferrous sulfates to ferric hydroxysulfate occurs only when temperatures exceed 100°C, far hotter than typical Martian surface conditions. The sulfates observed at Aram Chaos and Juventae, including ferric hydroxysulfate, probably formed more recently than the surrounding terrain. Researchers suggest they may date to the Amazonian period (<3 billion years ago).

The findings indicate that volcanic heat at the Juventae Plateau and geothermal energy beneath Aram Chaos could convert common hydrated sulfates into ferric hydroxysulfate. This discovery suggests that parts of Mars have remained chemically and thermally active more recently than previously believed, offering new insights into the planet’s evolving surface and its possible ability to support life.

The paper, Characterization of Ferric Hydroxysulfate on Mars and Implications of the Geochemical Environment Supporting its Formation, is published in Nature Communications.