Vaduz, an unusual fresh crater on Mars: Evidence for impact into a recent ice-rich mantle
A fresh, 1.85 km diameter impact crater in the midlatitudes of Mars (38°N) named Vaduz exhibits distinctive crater-related geological subunits (facies) extending up to ∼15 radii from the rim crest and perched >10 m above the adjacent plains. Knobby terrain fringing and underlying the facies is interpreted as degraded thermal contraction crack polygons, consistent with an ice-rich mantle buried by ejecta. The almost complete regional disappearance of this ice-rich unit, and consequent lowering of regional topography by over ten meters, is interpreted to mean that the ice-rich mantle was formed by climate-related deposition of snow, ice, and dust during recent periods of high obliquity. Transition to lower obliquity, and the attendant poleward retreat of the mantling unit, is the most likely cause of the regional loss of the ice-rich layer. The depth of this crater, relative to the thickness of the ice-rich unit, indicates that the impact event excavated bedrock and that Vaduz can be classified as an excess ejecta crater. Excavated silicate regolith and fragmented target debris appear to have been an important factor in the armoring mechanism.