Re: interesting Martian photos
The high-centered polygons may be analogs to raised polygonal features seen on Mars. The center is raised and the sides are troughs in this case. For low-centered polygons the center is lowered and the sides are ridges.
This page may give an indication of how one type can transform into the other:
Ice Wedges, Polygons, and Pingos
http://www.mapcruzin.com/arctic_refuge/permcycl.html
This page shows the formation of pingoes, but the process shown by which an area can be alternatively raised and lowered by freeze-thaw cycling may be analogous to how low and high centered polygons transform into each other.
Bob Clark