The image shown here was acquired at 24 m/pixel, the highest resolution that has been obtained for any of Mercury's shadowed polar craters!
The top left panel shows a view of an unnamed crater in Mercury's north polar region, with the crater rim outlined in pink and the edge of the 24-meter/pixel, low-altitude broadband MDIS image in green.
In the large bottom panel, a different stretch has been applied to the same MDIS broadband image, revealing details of the shadowed surface inside the crater. In particular, as highlighted with yellow arrows in the top right panel, the image reveals a region inside the crater that has a lower reflectance. The edge of the low-reflectance region has a sharp and well-defined boundary, even as imaged at this highest resolution of 24 m/pixel.
The sharp boundary suggests that the low-reflectance material is sufficiently young to have preserved a sharp boundary against lateral mixing by impact craters. The sharp boundary matches the location predicted by temperature models for the stability of a surficial layer of volatile, organic-rich material tens of centimeters thick that overlies a thicker layer of water ice.