نبذة مختصرة : International audience ; Introduction: Gullies on Mars are geologically young landforms that resemble terrestrial gullies [1]. Martian gullies are often carved within a mantling unit in the mid-to high-latitudes of Mars [2]. This mantle is a relief-muting unit [3] that is proposed to be composed of a mixture of dust and water ice that recurrently deposited during Mars' periodic high-obliquity excursions [4]. The formation mechanism of gullies is key to understand Mars' recent climate: previous works, focused on gullies carved into the mantling unit, have suggested meltwater sourced from the volatile-rich surface as one plausible gully-forming scenario (e.g. [5,6]). Other works, focused on the mantle, have studied gullies to infer the thickness of the mantle deposits [7] and provide constraints on Mars' near surface water ice volume. To test the effect of the substrate nature and slope-orientation on gully formation, we inspect individual gully alcoves in Utopia Planitia in the northern plains of Mars, record their orientation, the nature of the substrate, and calculate their incision depths. Approach: We consider gullied hillslopes in Utopia Planitia, a region with abundant occurrences of ice-rich mantling material [8]. We used HiRISE images at 25-50cm/pixel [9] in a sinusoidal projection as a basemap. We inspected every gullied hillslope that we previously mapped in a previous abstract [10] using [11]'s gullied landforms global dataset (Figure 2). We focused our study on individual gully alcoves displaying a V-shaped incision profile with straight walls (Figure 1). We recorded the substrate nature, either mantle deposits or bedrock, and we measured the width of the alcove wall at its widest part, We calculated the associated incision depth, assuming a 20° cross-profile slope as observed by [12]. Finally, we record the upslope to downslope orientation value of each studied alcove.
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