Sedimentary rocks in Bequerel crater: origin as polar layered deposits during high obliquity

Abstract not available

Orientation and distribution of recent gullies in the southern hemisphere of Mars: observations from HRSC/MEX and MOC/MGS data

Abstract not available

First in-situ analysis of dust devil tracks on Earth and their comparison with tracks on Mars

In this study we report about the first in-situ analysis of terrestrial dust devil tracks (DDTs) observed in the Turpan depression desert in northwestern China. Passages of active dust devils remove a thin layer of fine grained material (< ∼63 μm), cleaning the upper surface of coarse sands (0.5–1 mm). This erosional process changes the photometric properties of the upper surface causing the albedo differences within the track to the surroundings. Measurements imply that a removal of an equivalent layer thickness of ∼2 μm is sufficient to form the dark dust devil tracks. Our terrestrial results are in agreement with the mechanism proposed by Greeley et al. (2005) for the formation of DDTs on Mars

Modelling Esker Formation on Mars

International audience&lt;p&gt;&lt;strong&gt;Introduction:&lt;/strong&gt;&amp;#160; Eskers are sinuous sedimentary ridges that are widespread across formerly glaciated landscapes on Earth. They form when sediment in subglacial tunnels is deposited by meltwater. Some sinuous ridges on Mars have been identified as eskers; whilst some are thought to have formed early in Mars&amp;#8217; history beneath extensive ice sheets, smaller, younger systems associated with extant glaciers in Mars&amp;#8217; mid latitudes have also been identified. Elevated geothermal heating and formation during periods with more extensive glaciation have been suggested as possible prerequisites for recent Martian esker deposition.&lt;/p&gt;&lt;p&gt;Here, we adapt a model of esker formation with g and other constants altered to Martian values, using it initially to investigate the impact of Martian conditions on subglacial tunnel systems, before investigating the effect of varying water discharge on esker deposition.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Methods:&lt;/strong&gt; To investigate the effect of these values on the operation of subglacial tunnel systems we first conduct a series of model experiments with steady water discharge, varying the assumed liquid density (r&lt;sub&gt;w&lt;/sub&gt;) from 1000 kgm&lt;sup&gt;-3&lt;/sup&gt; to 1980 kgm&lt;sup&gt;-3&lt;/sup&gt; (the density of saturated perchlorate brine) and ice hardness (A) from 2.4x10&lt;sup&gt;-24&lt;/sup&gt; Pa&lt;sup&gt;-3&lt;/sup&gt;s&lt;sup&gt;-1&lt;/sup&gt; to 5x10&lt;sup&gt;-27&lt;/sup&gt; Pa&lt;sup&gt;-3&lt;/sup&gt;s&lt;sup&gt;-1&lt;/sup&gt; (a temperature range of 0&amp;#176;C to -50&amp;#176;C). We then investigate the impact of variable water discharge on esker formation to simulate very simply a possible release of meltwater from an assumed geothermal event beneath a Martian glacier or ice cap.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Results and Discussion:&lt;/strong&gt;&amp;#160; A key aspect of model behaviour is the decrease in sediment carrying capacity towards the ice margin due to increased tunnel size as ice thins. Our results suggest that Martian parameters emphasise this effect, making deposition more likely over a greater length of the conduit. Lower gravity has the largest impact; it reduces the modeled closure rate of subglacial tunnels markedly as this varies with overburden stress (and hence g) cubed. Frictional heating from flowing water also drops, but much less sensitively. Thus, for a given discharge, the tunnels tend to be larger, leading to lower water pressure and a reduction in flow power. This effect is amplified for harder ice. Higher inferred fluid density raises the flow power, but by a smaller amount.&lt;/p&gt;&lt;p&gt;These effects are clearly seen in the variable discharge experiments. Sediment is deposited on the falling limb of the hydrograph, when the tunnels are larger than the equivalent steady-state water discharge would produce. Sediment deposition occurs much further upglacier from the glacier snout, and occurs earlier on the falling limb leading to longer periods in which deposition occurs.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Conclusions:&lt;/strong&gt; Our results suggest that esker formation within a subglacial meltwater tunnel would be&amp;#160;more likely on Mars than Earth, primarily because subglacial tunnels tend to be larger for equivalent water discharges, with consequent lower water flow velocities. This allows sediment deposition over longer lengths of tunnel, and to greater depths, than for terrestrial systems. Future work will use measured bed topography of a mid-latitude esker to assess the impact of topography on deposition patterns and esker morphology, and we will expand the range of discharges and sediment supply regimes investigated.&lt;/p&gt

Possible Transport of Basal Debris to the Surface of a Mid-Latitude Glacier on Mars

International audience&lt;p&gt;&lt;strong&gt;Introduction:&lt;/strong&gt; We observe internal flow structures within a viscous flow feature (VFF; 51.24&amp;#176;W, 42.53&amp;#176;S) interpreted as a debris-covered glacier in Nereidum Montes, Mars. The structures are exposed in the wall of a gully that is incised through the VFF, parallel to its flow-direction. They are near to the glacier terminus and appear to connect its deep interior (and possibly its bed) to arcuate flow-transverse foliations on its surface. Such foliations are common on VFF surfaces, but their relation to VFF-internal structures and ice flow is poorly understood. The VFF-internal structures we observe are reminiscent of up-glacier dipping shear structures that transport basal debris to glacier surfaces on Earth.&lt;/p&gt;&lt;p&gt;Subglacial environments on Mars are of astrobiological interest due to the availability of water ice and shelter from Mars&amp;#8217; surface radiation environment. However, current limitations in drilling technology prevent their direct exploration. If debris on VFF surfaces contains a component of englacial and/or subglacial debris, those materials could be sampled without access to the subsurface. This could reduce the potential cost and complexity of future missions that aim to explore englacial and subglacial environments on Mars.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Methods: &lt;/strong&gt;We use a 1&amp;#160;m/pixel digital elevation model (DEM) derived from 25&amp;#160;cm/pixel High Resolution Imaging Science Experiment (HiRISE) stereo-pair images, and a false-colour (merged IRB) HiRISE image. We measured the dip and strike of the VFF-internal structures using ArcGIS 10.7 and QGIS software. We also input the DEM (and an inferred glacier bed topography derived from it) into ice flow simulations using the Ice Sheet System Model, assuming no basal sliding and present-day mean annual surface temperature (210K).&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Results and Discussion: &lt;/strong&gt;The VFF-internal structures dip up-glacier at ~20&amp;#176; from the bed. This is inconsistent with their formation by bed-parallel ice-accumulation layering without modification by ice flow. The VFF-internal structures and surface foliations are spectrally &amp;#8216;redder&amp;#8217; than adjacent VFF portions, which appear &amp;#8216;bluer&amp;#8217;. This could result from differences in debris concentration and/or surficial dust trapping between the internal structures and the bulk VFF. Modelling experiments suggest that the up-glacier-dipping structures occur at the onset of a compressional regime as ice flow slowed towards the VFF terminus.&lt;/p&gt;&lt;p&gt;In cold-based glaciers on Earth, up-glacier-dipping folds are common approaching zones of enhanced ice rigidity near the glacier margin. Where multiple folds co-exist, the outermost typically comprises basal ice with a component of subglacial debris entrained in the presence of interfacial films of liquid water at sub-freezing temperatures. In polythermal glaciers, debris-rich up-glacier-dipping thrust faults form where sliding wet-based ice converges with cold-based ice.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Conclusions: &lt;/strong&gt;We propose that the observed up-glacier-dipping VFF-internal structures are englacial shear zones formed by compressional ice flow. They could represent transport pathways for englacial and subglacial material to the VFF surface. The majority of extant mid-latitude VFF on Mars are thought to have been perennially cold-based; thus we favour the hypothesis that the VFF-internal structures are folds formed under a cold-based thermal regime. Under this mechanism, the outermost surface foliation, and its corresponding VFF-internal structure, is the most likely to contain subglacial debris.&lt;/p&gt

Internal Structure of a Glacier on Mars Revealed by Gully Incision

International audienceDebris transport from / A Mars glacier bed to / Flowlines on surface

Cats, connectivity and conservation: incorporating datasets and integrating scales for wildlife management

Understanding resource selection and quantifying habitat connectivity are fundamental to conservation planning for both land-use and species management plans. However, datasets available to management authorities for resource selection and connectivity analyses are often highly limited and fragmentary. As a result, measuring connectivity is challenging, and often poorly integrated within conservation planning and wildlife management. To exacerbate the challenge, scale-dependent resource use makes inference across scales problematic, resource use is often modelled in areas where the species is not present, and connectivity is typically measured using a source-to-sink approach, erroneously assuming animals possess predefined destinations. Here, we used a large carnivore, the leopard Panthera pardus, to characterise resource use and landscape connectivity across a vast, biodiverse region of southern Africa. Using a range of datasets to counter data deficiencies inherent in carnivore management, we overcame methodological limitations by employing occupancy modelling and resource selection functions across three orders of selection, and estimated landscape-scale habitat connectivity – independent of a priori source and sink locations – using circuit theory. We evaluated whether occupancy modelling on its own was capable of accurately informing habitat connectivity, and identified conservation priorities necessary for applied management. We detected markedly different scale-dependent relationships across all selection orders. Our multi-data, multi-scale approach accurately predicted resource use across multiple scales and demonstrates how management authorities can more suitably utilise fragmentary datasets. We further developed an unbiased landscape-scale depiction of habitat connectivity, and identified key linkages in need of targeted management. We did not find support for the use of occupancy modelling as a proxy for landscape-scale habitat connectivity and further caution its use within a management context. Synthesis and applications. Maintaining habitat connectivity remains a fundamental component of wildlife management and conservation, yet data to inform these biological and ecological processes are often scarce. We present a robust approach that incorporates multi-scale fragmentary datasets (e.g. mortality data, permit data, sightings data), routinely collected by management authorities, to inform wildlife management and land-use planning. We recommend that management authorities employ a multi-data, multi-scale connectivity approach—as we present here—to identify management units at risk of low connectivity

3D Morphometries of Eskers on Mars, and Comparisons to Eskers in Finland

International audienceIntroduction: We present new, high-resolution measurements of the 3D morphometries of eskers associated with debris-covered glaciers in the Phlegra Mon-tes [1] and NW Tempe Terra [2] regions of Mars' northern mid-latitudes. We compare them with the ancient south polar 'Dorsa Argentea' eskers on Mars [3], and first large database (n > 20,000) of 3D morphome-tries of terrestrial eskers, from SW Finland [4]. Eskers are ridges of glaciofluvial sediment deposited by meltwater flowing through tunnels within or beneath glaciers. They are vital tools for reconstructing the dynamics, extent, and environmental drivers of wet-based glaciation on Earth and Mars. For example, reconstructions of Mars' climate conditions at the Noa-chian-Hesperian transition [e.g., 5] have relied heavily upon insights from the Dorsa Argentea eskers [e.g., 3], which record basal melting of a large south polar ice sheet ~3.5 Ga. Morphometric studies of candidate eskers on Mars are vital both for testing hypotheses of their origins as eskers [e.g., 3], and for informing insights into the magnitude and dynamics of meltwater flows that formed them [e.g., 5-6]. Previously, such work has been limited by a lack of large-scale surveys of the 3D morphometries of eskers on Earth, to which the martian landforms can be compared. A new database comprising >20 000 measurements of 3D esker morphometries from SW Finland provides new opportunities for such-comparisons, which we exploit in this study [4]. Methods: We used 1-2 m/pixel digital elevation models generated from High Resolution Imaging Science Experiment (HiRISE) images to measure esker heights (H) and widths (W) from cross-sectional tran-sects spaced at 10 and 20 m intervals along the Phlegra Montes and NW Tempe Terra eskers, respectively (fol-lowing [3]). We calculated average slopes across cross-sectional transects (θ) as: tan −1 (H/0.5W). We classified transects into sharp-, multi-, and round-crested morphologies according to the scheme of [6]. The NW Tempe Terra esker comprises two 'stacked' esker ridges (see [7], this conference) which we treat separately in the present study. Storrar and Jones [4] obtained similar H, W, and θ measurements at 10 m intervals along ~70 km of Qua-ternary-aged eskers in SW Finland, using 2 m/pixel elevation data from airborne LiDAR