¹Jeremy Brossier,¹Francesca Altieri,¹Maria Cristina De Sanctis,¹Alessandro Frigeri,¹Marco Ferrari,¹Simone De Angelis,¹Enrico Bruschini,¹Monica Rasmussen,¹Janko Trisic Ponce
Journal of Geophysical Research: Planets (in Press) Open Access Link to Article [https://doi.org/10.1029/2025JE009393]
¹Institute for Space Astrophysics and Planetology (IAPS), National Institute of Astrophysics (INAF), Rome, Italy
Published by arrangement with John Wiley & Sons

Extensive research over the past two decades has shown that early Mars likely had a warmer,wetter climate with widespread water activity. Ferromagnesian (Fe,Mg‐rich) clay deposits are compellingmarkers of these ancient environments, helping reconstruct Mars’ hydrologic evolution, assess past habitability,and guide future exploration. This study analyzes hyperspectral data from the Compact ReconnaissanceImaging Spectrometer for Mars (CRISM) aboard NASA’s Mars Reconnaissance Orbiter, focusing on regionsalong the Martian crustal dichotomy—where clay deposits occur at the boundary between the ancient southernhighlands and the younger northern lowlands. We systematically surveyed ∼1500 CRISM targeted observations(1–2.6 μm) to identify ferromagnesian clays, distinguish them from other hydrated minerals, and characterizecompositional differences between Fe‐ and Mg‐rich species using diagnostic absorptions around 1.4, 2.3, and2.4 μm. Results reveal spatial variations in clay mineralogy: Fe‐rich nontronites are prevalent around MawrthVallis, while Mg‐rich saponites are more locally distributed in Nili Fossae and Libya Montes. Oxia Planum—the Rosalind Franklin rover landing site—exhibits more compositionally intermediate clays such asvermiculites and ferrosaponites. These differences may reflect variations in the iron and magnesium abundanceor in the iron oxidation state. Moreover, a recurring absorption near 2.5 μm suggests co‐occurring carbonateslike magnesite and siderite, increasing the potential for biosignature preservation. These findings refine ourunderstanding of Mars’ aqueous history and offer an important mineralogical context for future rover andsample return missions. They also emphasize the need for a next‐generation orbital imaging spectrometer tosucceed CRISM and extend its legacy.