Periodic Bedrock Ridges in the Equatorial Region of Mars: Insights from a Global Study

Periodic bedrock ridges (PBRs) are interpreted as repeating, symmetrical, meter- to decameter-scale linear ridges observed on Earth and Mars [1-6]. In situ and orbital observations of PBRs on both planets suggest that PBRs develop transverse to dominant or long-term winds [7] and are eroded directly into cohesive substrate [5-7]. As a result, PBR orientation can be used as proxies to reconstruct past climatic conditions (i.e. paleowind directions), and their expression on the landscape can lend insight into the environments in which they have formed.

To date, PBR identification and documentation has been largely opportunistic and limited to a single site on Earth in northwestern Argentina [7] and at 11 sites in four regions on Mars: Valles Marineris and the Medusae Fossae Formation [1], the MSL Curiosity landing site at Gale crater [e.g. 2,3], and around the circum-Chryse basin, including at Oxia Planum [4-6], the 2030 landing site of ESA’s ExoMars Rosalind Franklin rover.

A recent study in the circum-Chryse basin [5] noted that PBRs were often found on Fe/Mg phyllosilicate- (clay) bearing terrain. In situ and orbital observations of PBRs at Gale crater have similarly been found to be eroded into Fe/Mg rich clay-bearing materials [2,8]. This raises the possibility that PBRs could be found in other clay-bearing terrains on Mars, and that their formation may be tied to the mechanics of this surface.

Building on these observations, this research investigates PBRs on Fe/Mg phyllosilicate-bearing terrain in an equatorial band between 20° S and 20° N on Mars as detected by OMEGA (Observatoire pour la Mineralogie, l’Eau, les Glaces et l’Activite) and CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) instruments [9] onboard ESA’s Mars Express and NASA’s Mars Reconnaissance Orbiter, respectively.

A systematic survey of 3922 HiRISE images that overlapped Fe/Mg phyllosilicate signatures from the Mars Orbital Catalogue of Aqueous Alteration Signatures [9] was undertaken in a GIS. We identified 1526 HiRISE where PBRs were either confirmed or necessitated further investigation. From this detailed analysis, we have identified over 350 new sites where PBRs are found. Our investigation to date has revealed a diversity of form, expression, and distribution not currently described in the literature, and will be reported on at this meeting.

Overall, this work investigates the nature of PBRs found on clay-bearing terrain across the equatorial region of Mars to (i) elucidate the controls on distribution and expression on the landscape, and (ii) offer insights into the hydrologic, aeolian, and climate conditions on Mars across vast spatial and temporal scales.

[1] Montgomery et al. (2012). J. Geophys. Res. Planets, 117(E3); [2] Stack et al. (2022). J. Geophys. Res. Planets, 127(6); [3] Bretzfelder et al. (2024). Icarus, 408; [4] Favaro et al. (2021). J. Geophys. Res. Planets, 126(4); [5] Favaro et al. (2024). EPSL, 626,118522; [6] Silvestro et al. (2021). Geophys. Res. Letters, 48(4); [7] Hugenholtz et al. (2015). Aeolian Research, 18. [8] He et al. (2022). J. Geophys. Res. Planets, 127(9); [9] Carter et al. (2023). Icarus, 389.