Editors’ Highlights are summaries of recent papers by AGU’s journal editors.
Source: Journal of Geophysical Research: Planets
Magnetic measurements from the Mars Global Surveyor and Mars Atmosphere and Volatile Evolution (MAVEN) orbiters indicate that localized regions of the Martian crust, particularly within the planet’s southern hemisphere, exhibit field strengths approximately ten times higher than the Earth’s crustal field at the same altitude. The origin of these magnetic anomalies has been an enduring mystery.
Early in Mars’ history, migration of hot fluids may have chemically altered the planet’s crust via a process called serpentinization. Serpentinization reactions are known to produce significant quantities of the mineral magnetite (Fe3O4) from primary grains of the mineral olivine ((Mg,Fe)2SiO4). When such magnetic minerals form in the presence of a planetary field, they record remanent magnetizations that may be preserved over geological time.
Bultel et al. [2025] explore the hypothesis that serpentinization created enough magnetite while the ancient Martian magnetic field was active (i.e., during the pre-Noachian and Noachian periods prior to 3.7 billion years ago) to explain the strong crustal magnetism observed today. The authors present geophysical models that estimate the crustal abundance of serpentinization-derived magnetite required to produce the fields observed at Mars’ strongest magnetic anomalies as well as at the location of the InSight lander. The resulting estimates are compared to the results of novel thermodynamic models that predict the amount of magnetite produced via serpentinization for plausible Martian crustal compositions.
Histogram showing values of saturation remanent magnetization (Mrs) measured for various classes of martian meteorites. Mrs is the maximum magnetization that may be preserved within a given rock sample after an applied saturating magnetic field (typically > 1 Tesla in intensity) is removed. Higher Mrs values may correlate with higher magnetic mineral abundances if magnetic mineral compositions, grain sizes, and shapes are otherwise consistent between samples. The cross-hatched region represents the minimum Mrs values that would be required to account for the observed magnetic field at the InSight landing site if one or more crustal layers there (inferred from seismic data) preserved serpentinization-related magnetization initially acquired in a 50 μT field. The four dashed vertical lines correspond to the minimum thicknesses of magnetized crustal layers to account for the strongest observed magnetic anomalies on Mars under the same conditions of magnetization acquisition. Credit: Bultel et al. [2025], Figure 8
The study concludes that serpentinization could be responsible for Martian magnetic anomalies if certain conditions are met. Alteration of dunite can in principle produce enough magnetite to explain the strongest anomalies if the layer of magnetized crust is sufficiently thick (>10 kilometers). Alteration of pyroxenites or basaltic shergottites produces lower magnetite concentrations, but it could still explain the crustal field intensity at the InSight landing site if water-rock ratios were sufficiently high.
The prospect of widespread serpentinization on early Mars is of interest from both magnetic and astrobiological perspectives. In addition to magnetite, serpentinization produces molecular hydrogen that may be used as an energy source by microbes. This correlation hints at the potential for high-resolution, near-surface magnetic measurements (such as from a helicopter or rover) to be used to identify regions that may have been habitable on ancient Mars.
Citation: Bultel, B., Wieczorek, M., Mittelholz, A., Johnson, C. L., Gattacceca, J., Fortier, V., & Langlais, B. (2025). Aqueous alteration as an origin of Martian magnetization. Journal of Geophysical Research: Planets*, 129, e2023JE008111.*https://doi.org/10.1029/2023JE008111
— Sonia Tikoo, Associate Editor, JGR: Planets
Text © 2025. The authors. CC BY-NC-ND 3.0
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