Aeolian Landforms in the ExoMars 2028 Landing Site

Kurzfassung

Intro & Methods ESA’s ExoMars Rosalind Franklin Mission will land a rover at Oxia Planum to search for signs of life on Mars [1, 2]. Bright bedforms (Transverse Aeolian Ridges [TARs]), and erosive wind-formed ridges (Periodic Bedrock Ridges [PBRs]) have been documented in the landing site [3-6]. In this study, we compare automated and manual mapping of aeolian features in CTX (6 m/pixel), CaSSIS (5 m/pixel) and HiRISE (25 cm/pixel) images in the landing site with sand fluxes from the NASA Ames GCM [7] obtained with the Martian Surface/Atmosphere Web Interface [8]. In particular, we focus our attention on bright bedforms, ridges and wind streaks. Since these features are widespread on Mars, the observations made here on ridge and bedform are also relevant to other areas and landing sites [9-13]. Results Different aeolian features are observed in the landing area thanks to the new automatic mapping methodology employed in this work (Fig. 1a). Wind streaks (n = 87) were manually mapped on the CTX image mosaic [15] in a GIS environment. Most of the mapped streaks are bright-toned (n = 85), indicating winds originating from the NNW–NNE (Fig. 1b, c). A few dark-toned streaks (n = 2), formed by winds from the E–ESE, were also identified. Bright bedforms (TARs) were automatically mapped within the study area using the method described in [16]. They are widespread, especially in the SE, suggesting a higher sand supply and availability. Ridges (PBRs) were automatically mapped as well (Fig. 1a). These features are bright-toned as they are directly carved into the clay-enriched Noachain bedrock [4-6]. Together with the bright-toned ridge set, here we identified a new class of WNW–ESE-oriented cratered ridges (Fig. 1d). These features are mostly located in the NW of the study area but can also be found elsewhere. Theses sets of ridges display Y-junctions, can be found inside degraded impact craters, and may be locally covered by boulders from nearby impacts [4]. However, unlike PBRs, they are not directly carved into the underlying bedrock (Fig. 1d). Discussion The consistent orientation of bright wind streaks in the study area suggests contemporary regional winds predominantly blowing from the north, corresponding to the return flows of the Hadley cell circulation [17]. We also identified a secondary mode formed by winds from the ESE. Interestingly, a bimodal sand flux direction is also predicted by the GCM (Fig. 1e), with one mode (~172°–188°) closely matching the observed bright-toned wind streak orientations (Fig. 1b, c). This, along with no observed changes in orientation or modification of the bright streaks, indicates that these winds continue to blow at the surface and/or that winds from other directions are not strong or frequent enough to rework the wind streaks. Bright bedforms (TARs) are likely relict or static features shaped by past wind conditions [4, 5]. This is supported by the GCM-predicted bedform orientation (red line in Fig. 1e), which does not align with either the observed TARs’ orientation or that of the older periodic bedrock ridges (PBRs) [4-6]. The newly segmented “Ridge 2” class of landform has previously been interpreted as precursor bedforms that initiated the formation of the underlying PBRs [4]. This interpretation is supported by (1) the close spatial association between PBRs and the “ridge 2” class, and (2) their similar orientation. However, in the example shown in Fig. 2, the ridges are located on a flat bedrock surface and are not associated with PBRs. The morphology of the “Ridge 2” class varies across the study area, with some ridges appearing subdued and eroded making them similar to ghost-dune pits [18]. Alternatively, such a relationship between positive and subdued morphologies might represent an assemblage of erosional scars and bedforms, similar to those observed at Meridiani Planum (see Fig. 6b in [10]). In this scenario, ridges are thought to have migrated southwest, leaving behind erosional scars. Detailed examination of the relationships among ridges and TARs by the RFM rover will be crucial for advancing our understanding of ridges and PBR formation mechanisms [19, 20], the winds responsible for shaping TARs, and broader Martian climatic changes [9, 10].