Mercury: Santa Maria Rupes compressional scarp 3.5
A 200km-wide Mariner 10 image showing detail of an area near the upper centre of the incoming hemispheric view. A compressional scarp known as Santa Maria Rupes cuts slightly obliquely from top to bottom of this view. It cuts through, and therefore post-dates, the 25 km diameter crater near the centre.
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Image Credit: NASA.  

Apart from impact cratering, which must be continuing to the present day, the youngest event identified in Mercury's global record is the formation of a number of sinuous features known as lobate scars. These range from 20 to 500 km in length, and up to 2 km in height. They are regarded as unmistakable signs of compression of Mercury's lithosphere, indicating where the edge of a tract of lithosphere has been thrust over an adjacent tract. Summing up the deformation indicated by all the observed lobate scars indicates a reduction in Mercury's radius of between 1 and 2 km. This would have been caused either by contraction of Mercury's mantle as it cooled, or by solidification of a previously liquid part of the core.  
David A Rothery Return to top of page