Layered Ejecta Craters in the Candidate Landing Areas of China's First Mars Mission (Tianwen-1): Implications for Subsurface Volatile Concentrations

One important scientific objective of China's first Mars mission (Tianwen-1) is to investigate the martian surface soil characteristics and water-ice distribution. Layered ejecta craters (LECs) on Mars are characterized by their fluidized ejecta deposits which have been interpreted to indicate volatiles in the substrate where the impact occurred. Thus, they have potential to serve as important planetary exploration sites/targets of geological significance. In this study, we estimated the absolute model ages (AMAs) of 68 LECs with diameters >4 km using the Context Camera (an instrument onboard the Mars Reconnaissance Obiter, MRO) images in the two candidate landing areas of Tianwen-1 mission, aiming to reveal temporal-spatial variation of the regional subsurface volatiles, in particular water ice. The results from a combination of the derived AMAs and the ejecta mobility (EM) values for the southern Utopia-Isidis Planitia (SUIP) and southern Chryse Planitia (SCP) show that the LECs in both regions plausibly have formed throughout the Amazonian and Hesperian periods. However, the subsurface volatile concentrations might have undergone different evolution histories: SUIP shows a relatively stable trend with time, while there seems a general downward trend in SCP. The presence of the fresh similar to 1.5-km-diameter LECs suggests that volatile concentrations might have been at depth less than 150 m. We conclude with a discussion of recommendations for Tianwen-1 and future explorations that have the ability to effectively detect any signs of past and present water/ice on Mars, which contain a wealth of information of past and recent climate.

Automated summary

This study estimated the age of layered ejecta craters (LECs) on Mars and analyzed the variation of subsurface volatiles, particularly water ice. The results indicate that the LECs in the two candidate landing areas of the Tianwen-1 mission formed during the Amazonian and Hesperian periods. However, the concentrations of subsurface volatiles have undergone different evolution histories in different regions.