Mars. Mosaic of images taken by the Viking I and II probes showing the northern polar region up to a latitude of +65 degrees. The northern polar cap (white) may extend outward about to the 80 degree latitude circle. The polar deposits are believed to be mixtures of ice and dust. The north polar region is surrounded by a vast, sparsely cratered circumpolar plain, known as Vastitas Borealis, having a diameter of about 10,000 km. Viking I and II were launched in August and September 1975 respectively and they both landed on the martian surface in the following year.