Direct Detection of Hydrogen Reveals a New Macroscopic Crustal Water Reservoir on Early Mars

Abstract The next great leap in Martian exploration is the return of samples to Earth. Maximizing their scientific value requires non‐destructive analytical techniques for early three‐dimensional characterization. Neutron computed tomography (CT), highly sensitive to hydrogen, complements conventional X‐ray CT and enables the detection of hydrous phases. The distribution and nature of hydrous phases are central to understanding the habitability, climatic and geological evolution, and potential biosignatures of Mars. Using the only Martian crustal material available on Earth, the NWA 7034 meteorite and its pairs, we demonstrate that combined neutron, X‐ray, and X‐ray diffraction CT enables non‐destructive, sample‐wide hydrogen mapping, revealing the distribution and petrographic contexts of hydrous phases. We identify hydrogen‐rich iron oxyhydroxides within ancient igneous clasts, representing a macroscopic mineralogical water reservoir. These alteration assemblages closely resemble those observed by the Perseverance rover in Jezero crater, indicating that such hydrated phases may constitute a widespread near‐surface water reservoir on early Mars.