Mapping Mars . ... Credit Copyright: Malin Space Science Systems , MGS , JPL , NASA Explanation: This month, the Mars Global Surveyor (MGS) spacecraft began its primary mission to the red planet. Orbiting about once every two hours at an altitude of over 200 miles, instruments onboard MGS now regularly explore the Martian surface and atmosphere. ... Water-ice clouds can be seen hovering over the surface while the north polar cap is visible at the top of each image. ... NASA Official: Jay Norris. ...