It Was a Dark and Stormy Night
Repeat imaging of Mercury's south pole has revealed that a number of craters in the south contain permanently shadowed regions. Because Mercury has only a very small axial tilt, the topography of crater rims, as accentuated in the inset image (shown with five times the vertical exaggeration of the actual topography), blocks sunlight from ever reaching portions of the floors of some polar craters.
Date acquired: August 03, 2011
Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington