A distinctive terrain named cryptic region which is characterized by regions of low albedo and low temperature has been identified oil the Martian south polar cap. In this zone, many fan- and spider-shaped features of km-scale appeared following the sublimation of the CO2 frost layer. These peculiar features were apparently caused by a wind-blown system of dust-laden jets. During the warming period starting at L-s similar to 180, the seasonal ice cap regresses and fans and spiders appear in sequence. These surface features are repeatable events that tend to occupy the Same areas front year to year. In this Study, We use the Mars Orbiter camera (MOC) narrow-angle images to produce a statistical Study of the time distributions of the fans and spiders as functions of L, and as functions of the topography. The time variations and spatial distributions of these features are further correlated with the CO2 ice coverage measured by the Mars Orbiter laser altimeter (MOLA) instrument. We have documented that most of the falls are found in the early spring with L-s <230 and the fans and spiders coexist at L-s = 250 +/- 20. It is also found that there is a strong dependence oil latitude and altitude with falls and spiders most often observed at high latitude (>83 S) and high altitude (>2500 m). Our statistical result also indicates that the occurrence of fans is highly correlated with the thickness of the CO2 frost thus providing support for the venting model. (C) 2009 Elsevier Ltd. All rights reserved.
