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Ice deposits on the North Pole of Mercury: insights from crater morphometry

Presentation #116.06 in the session Mercury (Poster + Lightning Talk)

Published onOct 23, 2023
Ice deposits on the North Pole of Mercury: insights from crater morphometry

The morphometry of impact craters is a key tool to investigate the physical properties and evolution of planetary surfaces, and thus to reveal variations in the effective strength, porosity, and stratigraphy within the crust, and/or information about the composition, like the presence of volatile material [1]. On the other hand, a lower crater depth than the statistical value predicted by measurements (e.g., [2]) can be (also) due to resurfacing processes like magma infilling, isostatic adjustment, and/or degradation.

In this work, we analysed the morphometry of >10 km impact structures located on the North Pole of Mercury, which exhibits Permanently Shadowed Regions (PSRs), suggested to host water ice deposits [3]. These craters can be classified into three groups [4]: (i) complex morphology (central peak), (ii) no-complex morphology (no central peak), (iii) incomplete complex morphology (flat floor and small central peak). Our final goal is to unravel whether a steady state accumulation due to water-bearing micrometeoroid flux might have affected the north-pole surface rheology.

We firstly compared the depth-to-diameter ratios (d/D) of the north-pole craters with those located all around the planet [2]. Crater depth and diameter were calculated as the mean of four profiles of the MESSENGER-derived Digital Terrain Models (DTMs) for each crater. The d/D trend of craters is similar to that on the [2] database.

On the other hand, we found that the central peak, one of the distinctive characteristics of complex craters, develops in craters larger than 13−25 km, a range which is a bit larger than what expected for the onset the complex morphology on Mercury (about 12 km, e.g. [2]). We interpret this different behaviour to be ascribed to a lower effective strength of the (younger) smooth plains, where water ice, brought through a continuous flux, could have been embedded into regolith.

Acknowledgement: This activity has been realized under the BepiColombo ASI-INAF contract no 2017- 47-H.0

References: [1] Stopar J. D. et al. (2017) Icarus, 298, 34-48; [2] Susorney H. C. M. et al. (2016); Icarus, 271, 180-193. [3] Chabot N. L. et al. (2018) JGR Planets, 123(2), 666-681; [4] Bertoli S. et al. (subm.) GFT&M.

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