Martian north polar cap recession: 2000 Mars Orbiter Camera observations

The wide-angle cameras of the Mars Orbiter Camera (MOC) on the Mars Global Surveyor have recorded the 2000 recession of the seasonal CO2 cap in the north polar region from L-S = 330degrees to 90degrees. In stark contrast to the asymmetric behavior of the south seasonal cap, the seasonal north cap remains relatively circular and uniform until mid-spring when the retreat reaches the circum-polar dune field, which is the one major nonuniformity in the cap. The recession of cap edge latitude versus areocentric longitude (L-S) is very well represented as a linear function until late spring; there is no evidence for the plateau or standstill in the recession curve that has been observed in some prior years. The Lambert albedo of the seasonal frost deposits in the north polar region demonstrates the increase with insolation first observed by Paige in 1985, increasing to approximately 0.57 at L-S = 40degrees. The north polar cap near solstice visually appears smaller than that observed by MOC at the start of mapping in 1999, but later images acquired in summer show the residual cap returning to its more usual shape. The most likely explanation for these changes in albedo is precipitation and subsequent removal of dust on the cap as a result of frequent dust storms near the cap edge. (C) 2001 Elsevier Science.