r/science • u/GeoGeoGeoGeo • 1d ago
Astronomy New research now argues that ferrihydrite, a hydrous ferric oxyhydroxide, not hematite is responsible for Mars' red colour
https://news.uark.edu/articles/75743/new-research-makes-strongest-case-yet-for-why-mars-is-red#:~:text=If%20you%20know%20one%20thing%20about%20Mars%20it's%20probably%20this:%20it's%20red.&text=New%20research%20by%20an%20international%20team%20of,fact%20responsible%20for%20the%20Mars'%20color:%20ferrihydrite.9
u/GeoGeoGeoGeo 1d ago
Research Paper (open access): Detection of ferrihydrite in Martian red dust records ancient cold and wet conditions on Mars
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u/Daybreak74 21h ago
Evidently, that's good news for potential colonization...
Ferrihydrite's high surface area and reactivity make it an effective sorbent for removing pollutants like arsenic, heavy metals (lead, mercury), phosphate, and organic molecules from water.
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u/Cranberryoftheorient 19h ago
Ill ask the dumb question- how did we have the wrong substance in mind for so long? Was it just a guess that we've now confirmed wrong?
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u/GeoGeoGeoGeo 18h ago
Not a dumb question, just a slight misunderstanding of what's being argued, how those conclusions are being drawn, and the margins of error with each interpretation, and why they exist (ie. methodology at the time).
While these findings may appear contradictory, a closer examination reveals that they reflect complementary aspects of Mars’ mineralogical evolution, as well as advancements in instrumentation and analytical techniques.
Early interpretations of Mars’ surface composition relied primarily on data from instruments such as the Thermal Emission Spectrometer (TES) aboard Mars Global Surveyor and the Observatoire pour la Minéralogie, l’Eau, les Glaces et l’Activité (OMEGA) aboard Mars Express. These instruments utilized thermal infrared and visible/near-infrared (VNIR) spectroscopy to identify surface mineralogy. Their sensitivity to crystalline phases with well-defined spectral features enabled the detection of coarse-grained hematite, particularly in localized regions such as Meridiani Planum. The strong spectral signature of hematite in these regions supported interpretations of aqueous alteration under specific geochemical conditions and suggested a link between surface oxidation and the red coloration of the Martian regolith.
However, the limitations of these early methods must be acknowledged. Spectroscopic techniques such as TES and OMEGA are less effective at detecting poorly crystalline or amorphous minerals, which exhibit broad, subtle absorption features rather than sharp, distinctive peaks. As a result, fine-grained, nanophase materials such as ferrihydrite were likely underrepresented or entirely missed in earlier analyses. Additionally, these missions tended to focus on regions with anomalously strong signals, leading to interpretations that emphasized localized rather than global mineralogical processes.
The distinction between these two iron phases also reflects a difference in scale and geological context. Early studies identified hematite in discrete, well-preserved deposits associated with specific geomorphic settings, such as sedimentary bedforms or diagenetically altered rocks. These localized occurrences are important paleoenvironmental indicators but do not necessarily reflect the composition of the globally dispersed dust responsible for the planet’s overall red appearance. In contrast, the 2025 study focuses on the fine-grained, atmospheric dust that blankets most of the Martian surface, offering a more comprehensive view of the mineralogical processes that dominate at a planetary scale.
It is also possible that these two phases are linked in a diagenetic sequence. Ferrihydrite, which precipitates readily from aqueous solutions under oxidizing conditions, is known to transform into hematite over time through dehydration and structural rearrangement. Therefore, the presence of crystalline hematite in localized regions may represent the end product of a broader process that originally produced ferrihydrite on a global scale. This evolutionary relationship suggests that Mars’ surface mineralogy records both an early, wetter epoch and subsequent diagenetic modification in more localized settings.
Ultimately, a sample return mission would be the next step in forming any conclusive findings.
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