An insight to the cryospheric level in Mars: Case study from the Thaumasia Minor

Abstract

The presence of a subsurface Martian cryosphere has been widely acknowledged. Rampart craters and outflow channels are thought to be the prominent geomorphic signatures in support of the presence of this cryospheric layer. Valley networks, on the other hand, are thought to be the signatures of precipitation, seasonal meltwater flow due to glacial melting and/or groundwater sapping. A rampart crater essentially has an asymmetric lobate-shaped ejecta blanket around it. In the present study area within Thaumasia Minor, situated near the equatorial region of Mars, rampart craters are present while outflow channels are absent. Therefore, the rampart craters are the only windows to locate the existence and extent of the cryospheric level in the area. It has been observed that these rampart craters remained unaffected by surface fluvial activities. Rampart Craters, both Single Layered Ejecta craters (SLE) and Multiple Layered Ejecta craters (MLE) present in Thaumasia Minor were identified, mapped and dated. Excavation depths were calculated (with respect to the areoid) for all craters of varied ages. The excavation depth data sets were used to draw statistical surfaces for MLE craters and SLE craters. It was concluded from the comparative analysis of the excavation depths (between the MLE and SLE craters situated in the relatively higher altitudes within TM) at different time intervals, the base of the Martian cryosphere was at greater depths prior to ~2Ga than it was around 0.5Ga in the study area. This suggests that within the study area the Martian cryosphere did evolve with time and our study of the excavation depths of the craters suggests that the cryosphere must have thinned out as time progressed.