and deimos, the smaller, outter moon. viking could observe boulders on the moon's surface. study of the surface indicates that mars has experienced periodic change of climate. the best evidence is seen in the strange solar patterns of mars. the dark bands are buried ground within the north polar ice cap. on each scar are numerous small terraces, indicated by eroded small rock. this is an area of terrain about 40 miles across. it is believed the large scars represent two different cycles of climate change, which occur simultaneously. because of mars' osceolation around the sun, it is alternately warm in cold for tens of thousands-millions of years. during the cold time, mixtures of dust and ice were deposited in a series of near-horizontal layers, obscuring the underlying typography. then, a time of warmer climate followed and erosion set in. cutting deep valleys into the icy mass of the polar caps. after the erosion cycle, new layers were laid down. another episode of erosion followed. this oblique truncating of one set of terraces obscure few gated by another indicates the