18-1 Volcanic Resurfacing and Impact Cratering History of Mercury’s Smooth Plains

Session: Surface Processes Across the Solar System

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Abstract:

The geologic history of the planet Mercury is analogous to Earth’s Moon: a significant proportion of the planet has been resurfaced by basaltic lava flows (the smooth plains), and it is densely covered in impact craters. Like the Moon, most of Mercury’s volcanic activity is though to have occurred billions of years ago, with age estimates placing the peak of effusive volcanism at ~3.7-3.8 Ga. Thus, the size-frequency distribution of impact craters superposed on Mercury’s smooth plains can be used to estimate the age(s) that volcanic resurfacing took place. Impact craters also record erosion rates and how they evolve through time. This process, known as topographic diffusion, causes a gradual reduction in relief and roughness over time. The primary mechanism through which topographic diffusion occurs on Mercury, the Moon, and other airless Solar System bodies is the progressive bombardment of subsequent impacts in an effect known as “sandblasting.” The topographic diffusion rate is therefore directly correlated to the impactor flux. Mercury has a significantly higher average impact velocity than the Moon, and impact crater degradation is estimated to occur much more quickly as a result.

The exact rate at which topographic diffusion occurs on Mercury is not currently known, nor is the full range of potential mechanisms. Processes such as thermal cycling from Mercury’s extreme diurnal temperature contrasts or greater energy partitioning into secondary impact processes could play outsized roles in the degradation of impact craters relative to the Moon. In order to address these questions, we use visible imagery and laser altimetry data from the NASA MESSENGER mission that orbited Mercury from 2011-2015. High-resolution topographic information is necessary to accurately assess and model impact crater diffusion, but the spatial coverage and data quality from MESSENGER vary widely. We have leveraged improvements to NASA’s Ames Stereo Pipeline to generate topography from MESSENGER stereo pairs. This will allow us to assess the three-dimensional shapes of impact craters at a smaller size range than before, specifically at diameters ~1-5 km that are most sensitive to impact-driven degradation. Our goal is to better constrain topographic diffusion rates on Mercury’s smooth plains and to derive independent estimates for the age of its volcanic resurfacing.

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