Large impact craters often have pits on their floors. Some of these (with raised rims) are later impacts, but some are thought to originate immediately after the crater forms when slurries of molten and broken rocks occupy the crater floor.
Bakhuysen Crater, located in Noachis Terra, is thought to be the largest crater that possesses (and has preserved) these pitted materials.
This caption is based on the original science rationale.
Written by: HiRISE Science Team (17 August 2011)
This is a stereo pair with ESP_020731_1570 .
More info and image formats at http://hirise.lpl.arizona.edu/ESP_020309_1570
Image: NASA/JPL/University of Arizona