Morphometrics of polygonal ground on Earth and Mars: Assessing formation mechanisms from orbit

Abstract

Polygonal ground patterns are meter-to-decameter-scale landforms commonly observed on Earth, Mars, and other planetary bodies. They can form through a variety of processes (periglacial, desiccation, volcanic, jointing) and provide insight into geological and environmental conditions that can influence habitability. We focus on the morphometric analysis of these patterns to determine diagnostic signatures which may be used to remotely distinguish between the different formation mechanisms, particularly when in-situ observations are not available. We conducted a survey of patterned ground at 17 Earth sites and 12 Mars sites to determine the diameter distributions, junction angles, junction valencies, circularities, and aspect ratios to determine the characteristics of each polygon type. Our results showed common clustering of morphometric characteristics amongst similar polygon types, though some ambiguities remain between formation endmembers. The size-frequency distributions and the ratio of 90° to 120° junction angles were strong indicators of formation process. The junction angle ratio also reveals the “maturity” of the networks due to periodic or episodic refracturing. Junction valency, circularity, and aspect ratios, also proved valuable as statistical indicators. Our analysis of polygonal patterns located in the Jezero crater floor and margin unit, along with two sites located at Terby crater, are consistent with both volcanic and tectonic jointing processes. Analysis of Mawrth Vallis is strongly suggestive of desiccation. These findings suggest that similar physical mechanisms control polygon formation across planetary bodies, and the study of these patterns on Mars can provide key insights into its geological and climate history, providing clues to potential habitability.