Temporal changes in the Cerberus region of Mars: Mariner 9 and Viking comparisons

As in seen from comparisons of Mariner 9 images obtained in 1972 and Viking Orbiter 1 images obtained in 1978, several changes have occurred in the Cerberus region of Mars. Changes in the boundary of the low albedo feature resulted in an increase of the total area of Cerberus by slightly more than 1%, although the southwestern boundary had shifted as much as 90 km. Relative darkening of Cerberus has resulted in a more uniform tone, and is accompanied by the disappearance of dark filamentary markings. Although several bright streaks within Cerberus changed in length, neither lengthening nor shortening of the streaks predominated. However, changes in streak direction indicate a clockwise rotation of mean streak azimuth between 1972 and 1978. These changes in the outline and appearance of Cerberus can best be explained by eolian redistribution and removal of bright material during major dust storms. Volcanic flow fronts which show through the albedo feature indicate that the contrast between Cerberusand the surrounding light plains is not due to a difference in lithology, but to the distribution of surficial deposits. Because of local topographic influences on the regional atmospheric circulation patterns, it is probable that Cerberus will retain a similar appearance and location.