Consolidated Aeolian Streaks in Oxia Planum: Evidence for Differential Erosion and Topographic Shielding

The ESA ExoMars mission will land at Oxia Planum to search for signs of life on Mars [1, 2]. In this study, we analyze aeolian linear features in the landing ellipse using CTX (6 m/pixel), CaSSIS (5 m/pixel), and HiRISE (25 cm/pixel) imagery.

We identified bright wind streaks oriented towards the S-SSW (mean azimuth 189°), consistent with formative winds blowing from the N-NNE. Their orientation reveals slight variations, allowing us to distinguish distinct sub-populations that appear controlled by the local topography.

In contrast, dark-toned stripes form a 'streaky' pattern with a main NE-SW trend. In the western sector, they consist of elongated dark patches covering the bright, clay-enriched unit (the mission’s main target [2]). Crucially, the presence of small scarps suggests a degree of material consolidation or cementation. These stripes are preferentially preserved in the lee of impact craters (~600 m diameter), suggesting formative winds from the NE, thus differing substantially from the orientation of the nearby bright streaks.

In the SE sector, SSE-oriented dark stripes are associated with a ~2 km diameter impact crater. Both CaSSIS and HiRISE data confirm that these features consist of a dark ejecta blanket preferentially preserved along the crater's southern rim, directly overlying the bright clay-enriched bedrock. Their orientation is slightly divergent but comparable to the bright wind streaks in this area, suggesting control by the current regional wind regime.

We propose that these findings indicate a new class of Martian aeolian feature. Unlike typically described wind streaks, the features presented here appear composed of consolidated material. Specifically, the dark ejecta stripes can be interpreted as 'aeolian preservation streaks'. This feature arises from the differential erosion of a consolidated unit (e.g., crater ejecta blanket) by winds from the N-NNW; the crater rim creates a wind shadow that preserves the ejecta downwind while the surrounding area is removed, exposing the underlying Noachian bedrock.

The orientation of these preservation streaks suggests that a N-NNW wind regime has been dominant in shaping the landscape over geological timescales. Even the dark stripes in the western sector, particularly where clustered behind topographic obstacles, may share this origin. Although their degree of consolidation remains to be definitively determined, their divergence from bright streaks suggests either a different formation timeline or strong local topographic control. These hypotheses regarding consolidated aeolian features and paleo-wind regimes will require crucial in-situ validation by the ESA Rosalind Franklin rover.

[1] Vago J. et al. (2017). Astrobiology, 17. [2] Quantin et al. (2021), Astrobiology, 21.