HiRISE: Tangential craters in Ptolemaeus Crater

This image shows two small craters, just touching on their rims, in the much larger Ptolmaeus Crater, which is located in the Martian Southern hemisphere. These craters are called “tangential craters.” The more degraded and filled-in crater is approximately 3 kilometers in diameter, and there is an unusual feature near the center. A closeup shows…. [More at link]