* Astronomy

Title: Ring-mould craters in lineated valley fill and lobate debris aprons on Mars: Evidence for subsurface glacial ice
Authors: Ailish M. Kress, James W. Head

Ring-mould craters (RMCs), concentric crater forms shaped like a truncated torus and named for their similarity to the cooking implement, are abundant in lobate debris aprons (LDA) and lineated valley fill (LVF) in the northern mid-latitudes on Mars, but are not seen in surrounding terrain. LDA and LVF have been interpreted to form by flow of debris, but uncertainty remains concerning the mechanism of flow, with hypotheses ranging from pore-ice-assisted creep of talus to debris-covered glaciers. RMCs average less than a few hundred meters in diameter and occur in association with normal bowl-shaped impact craters whose average diameters are commonly less than RMCs. On the basis of their morphologic similarities to laboratory impact craters formed in ice and the physics of impact cratering into layered material, we interpret the unusual morphology of RMCs to be the result of impact into a relatively pure ice substrate below a thin regolith, with strength-contrast properties, spallation, viscous flow and sublimation being factors in the development of the ring-mould shape. Associated smaller bowl-shaped craters are interpreted to have formed within a layer of regolith-like sublimation till overlying the ice substrate. Estimates of crater depths of excavation between populations of bowl-shaped and ring-mould craters suggest that the debris layer is relatively thin. These results support the hypothesis that LDA and LVF formed as debris-covered glaciers and predict that many hundreds of meters of ice remain today in LDA and LVF deposits, beneath a veneer of sublimation till. RMCs can be used in other parts of Mars to predict and assess the presence of ancient ice-related deposits.

Source

Planetary scientists have often puzzled over the origins of the Martian landscape, including its so-called hemispheric dichotomy, a pronounced difference in the thickness of the planet's crust between its northern lowlands and highlands of the south. Another curious feature is an elevated region near the equator called the Tharsis Rise, capped by volcanic peaks located in a relatively straight line.
A new study seeks to unify those features by showing how thickness variations in the planet's outer layers may have given birth to the Tharsis Rise. The new model proposes that even though the Red Planet may not have Earth's multiple plates, its single fused outer shell, or lithosphere, may still rotate relative to the planet's center. The study's results were published this week in the online edition of Nature Geoscience.

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Survol d'une région en 3D où sont visibles des roches sédimentaires, témoins de climat cyclique dans l'atmosphère et à la surface de Mars. Vidéo réalisée à partir des images prisent par la sonde Mars Reconnaissance Orbiter de la NASA.

Avalanches Rumble on Mars at Spring
Billowing down the cliffs of the red planet, scientists have spotted a strangely Earth-like phenomenon -- snowy avalanches near Mars' north pole.
Led by Patrick Russell of the University of Berne in Switzerland, a team of researchers first noticed the avalanches in February while combing through images from the Mars Reconnaissance Orbiter's high resolution camera, HiRISE.

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