This area of Hellas Basin has a number of unusual features which are thought to be quite old because of the high crater density. Here a crater has been filled with material. This may be related to volcanic activity on the northwestern rim of Hellas.
However, it might also be related to water and water ice. There is evidence elsewhere that the ground here is ice-rich. HiRISE will investigate this in more detail when Hellas Basin is free from atmospheric dust.
Written by: Nicolas Thomas (5 May 2010)
More info and image formats at http://hirise.lpl.arizona.edu/ESP_017196_1455
Image: NASA/JPL/University of Arizona