Crater Population and Resurfacing at the Martian North Pole

Introduction: The Martian north polar residual cap (NRC) lies on top of the north polar layered deposits (NPLD). The NRC is about 1m thick and composed primarily of large-grained, dust-poor water ice [1]. The mass balance of the polar cap is uncertain. Long-term monitoring reveals small reversible changes in its extent on an interannual basis [2]. Images with a pixel scale of up to 0.25 m/pixel from the High Resolution Imaging Science Experiment (HiRISE) aboard the Mars Reconnaissance Orbiter (MRO), show brighter, or smallergrained, (i.e. younger) ice superposing darker, or larger-grained, (i.e. older) ice. The lack of dust accumulation indicates that the material composing the NRC accumulated recently. On the other hand, the exposure of darker, larger-grained ice indicates a current state of net ablation. Small pits observed in HiRISE imagery resemble suncups and also suggest recent ablation. The NPLD are believed to preserve a record of seasonal and climatic cycling of atmospheric water and dust and could reveal important information regarding Martian geologic and climatic history. The NRC is often considered new NPLD material. Thus, understanding the NRC’s current behavior and mass-balance in relation to the current climate is an important step in reading the climatic record of the NPLD. One way to do this is to analyze the cratering record of the NRC. Previous studies concluded a NPLD resurfacing age of only ~20-100 Kyr. [3; 4]. However, due to the low resolution and sparse coverage of available imagery, these conclusions were based on 0 or 2 craters respectively. Now, Data from the Context Camera (CTX) aboard the MRO provide almost complete coverage of the NRC and NPLD with pixel scales of ~6 m/pixel. To constrain the processes and rates of NRC resurfacing, we conducted a search for craters within the CTX dataset. Using the NRC crater population data, we will use landscape evolution modeling to investigate the recent (10-20 Kyr) mass-balance history of the NRC.