201-7 Centimeter-Scale Polygonal Terrain on Mars: Constraints on Polygonal Ground Formation from the Curiosity Rover

Session: The G.K. Gilbert Award Session: Geology of Mars, Mercury, Asteroids, and Icy Satellites in Honor of Scott Murchie

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Since 2022, the Mars Science Laboratory (MSL) Curiosity rover has been exploring the layered sulfates, a wide-spread stratigraphic unit that has been observed from orbit across Mars. However, despite its common occurrence, the formation of this unit remains cryptic. Curiosity’s ascent up Mount Sharp is one of two in situobservations of this unit to date, providing an opportunity to delineate the surface processes responsible for generating this strata, and its record of the past climate. 

Throughout this portion of the traverse, the rover has crossed several distinct horizons of patterned, polygonal ground with regular, cm-scale polygon sizes. Polygonal ground is common on Earth and is often found in sedimentary rocks that have undergone either: desiccation; compaction and hydraulic fracturing; convection; or repeated freeze-thaw cycles (e.g. Goehring, Phil. Trans. R. Soc., 2013; Lasser et al. Phys. Rev. X, 2023). However, the recent occurrences of polygonal ground in the layered sulfates are not easily attributable to any of these commonly understood mechanisms. Here we explore the different physical characteristics of these polygons to better understand how they formed, and what their repeated presence means for the past environments at Mount Sharp, and on Mars. 

We report trends from 20 workspaces covering 4 distinct polygonal horizons encountered on the traverse spanning ~150 m in elevation. Within the sulfate-bearing unit, polygon spacing varies between 3.5 and 8 cm in diameter, which is consistent with observations over 200 m lower down in stratigraphy (e.g. Rapin et al., Nature, 2023). However, for these recent intervals, polygon spacing increases with elevation. On average, polygons have a depth-to-diameter ratio ranging from 2:1 to 3:1. Measurements of junction angles across all horizons peak with a normal distribution at 120^o (n=383), with a similar distribution to angles observed by Rapin et al., Nature (2023). These data combined with analyses of fracture orientation and grainsize are used to constrain the environments leading to formation in the layered sulfates.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

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