Fracture geometry and topology and their spectral signatures at OxiaPlanum, Mars

The European Space Agency (ESA) Rosalind Franklin rover Mission (RFM) is expected to land at Oxia Planum, Mars in 2030. Orbital spectral data and imagery reveal layered, clay-rich sedimentary deposits, often overlain by or interbedded with a dark, more resistant rock rich in mafic minerals [e.g., 1, 2]. The 1:30k scale geologic map of the landing site [1] associates two geologic units to their VNIR color and fracture spacing; Apuzzo et al. [3] studied directional statistics of fractures in selected regions of interest. However, complete quantitative fracture metrics over the RFM landing area are not yet available. Since at least 35% of the landing site is covered by fractures [3], a comprehensive study of fractures, and the composition of their hosting bedrock, is critical for elucidating whether formation mechanism, alteration history, and/or mineralogy vary across the Oxia Planum site.

Here, we present fracture density (number of fractures/m^2) and topological connectivity of fractures within an unbiased collection of 33 approximately 500x500 m square windows spaced along transects over the center of the predicted landing footprint of the RFM. Multiple windows overlap with Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) spectral cubes for which Fe,Mg-clay abundance has been qualitatively estimated [2]. Fractures are mapped manually as linear segments in QGIS software, using visual interpretation of High Resolution Imaging Science Experiment (HiRISE) images (0.3 m/px) in the red spectral range. We map at 1:1250 scale resulting in a minimum resolvable fracture length of about five pixels, or 1.5 m. The NetworkGT QGIS software plugin [4] is used to extract node connectivity, fracture orientations, and fracture lengths.

Topological analysis of node types and fracture-bounded polygon shapes is then leveraged to aid in interpreting (1) changes in fracture behavior across previously mapped unit boundaries, and (2) formation mechanisms of the fracture networks, following [5]. We also compare fracture mapping within and outside specific clay-rich areas of interest [2, 6] to determine if they have unique mechanical or formation characteristics. Preliminary analysis
indicates that fracture density is often higher within more clay-rich areas, and that the majority of mapped fractures are “I-node”, meaning they terminate without connecting to another fracture. Where fractures do connect, three- and four-sided polygon shapes dominate. We compare these findings with previous topological network characterization [e.g., 5] to enhance our interpretation of the possible scenarios of formation and current unit composition at Oxia Planum, considering topological characteristics will better constrain our understanding of past aqueous activity. Our results will support the better selection of analog materials for terrestrial drill testing before mission launch, and help inform drill site selection when the rover reaches Mars’ surface.

References: [1] Fawdon et al. (2024) Journal of Maps 20, 2302361. [2] Brossier et al. (2022) Icarus 386, 115114. [3] Apuzzo et al. (2025) PSS 267, 106169. [4] Nyberg et al. (2018) Geosphere 14(4) 10.1130/GES01595.1. [5] Silver et al. (2025) PNAS 22 (10) e2411738122. [6] Altieri et al. (2026), this conference.

Acknowledgements: This work is funded by the Italian Space Agency (ASI) [Grant ASI-INAF n. 2023–3–HH.0].