English: The martian northern plains remain nearly as mysterious today as they seemed 25 years ago during the Viking missions, even though one of those spacecraft--the Viking 2 lander--went to the northern plains. The northern plains are a lowland with fewer impact craters exposed at the surface than the heavily cratered martian southern highlands. Normally, surfaces with fewer craters are considered younger (i.e., they have had less time to accumulate craters). Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) high resolution images have shown that there really are a lot of craters in this region, but most are thinly buried beneath the plains. This low resolution view, covering an area 168 km (104 mi) by 124 km (77 km), shows a few craters at the surface (such as the one at the center of the image), and several circular features that represent craters that are mostly buried beneath the plains. This view was obtained in August 2002; sunlight illuminates the scene from the lower left.