Séminaire
It has long been recognized that the layers contained within the North Polar Layered Deposits (NPLD) are fundamental to our understanding of atmospheric deposition and thus climatic processes on Mars. Until recently, the focus had been on outcrops of exposed layers within the spiral troughs that dominate the ice cap surface. However, modification of the troughs by wind affects depositing layers, leaving an outcrop record that must be interpreted hand in hand with trough morphology and not independent from it.
The spiral troughs found NPLD of Mars are intriguing features that have been the source of much literature and debate since their discovery during the Mariner 9 mission. In order to fully explain the troughs' features, a hypothetical model must explain many aspects. Here we interpret the spiral troughs as belonging to a class of features called cyclic steps, which have well understood characteristics. In this context, we provide evidence for active surface evolution from visual observations and demonstrate that katabatic winds and katabatic jumps in the flow, explain all aspects of troughs.
Cyclic steps require specific conditions to form and persist. The governing principles are well understood, so the existence of cyclic steps within the polar ice on Mars provides unique, scientifically useful insights into the development of the ice cap and into Mars’ recent climate. We use this new interpretation to better characterize spiral troughs and atmospheric conditions in Mars’ recent past.