Astronomy Picture of the Day . The South Pole of Mars . ... Recorded in September of this year by the Mars Global Surveyor (MGS) spacecraft, the picture shows a region surrounding the 400 kilometer wide martian polar cap in the midst of southern hemisphere spring . During this season the ice cap , predominantly layers of frozen carbon dioxide ( dry ice ) plus some water ice, begins to shrink as the ices change directly from solid to gas (sublimate). ... NASA Official: Jay Norris. ...