LINKED NODE POINT CLOUDS TO EXAMINE FRACTURE PATTERNS WITHIN A MARS CRATER

Polygonal fracture patterns are common on Mars and bear similarities with those found in permafrost on Earth. Rather than using line segments, examining the Mars polygonal fracture pattern intersection points (nodes) can characterize preferred orientation and spacing geometries simultaneously. Plotting the relative position of linked nodes creates “fingerprints”. These fingerprints take different shapes depending on the orientation and spacings of the fractures. Highly organized fingerprints will have prominent clusters while unorganized fingerprints will have more diffuse clusters.

A Mars crater located at 582758.55m E, 7731149.47m N (WGS 84 zone 59N) is the area of focus for this study because of the availability of high-resolution imagery, specifically using HiRISE imagery from University of Arizona, and because a distinctive and variable polygonal fracture pattern is seen within the crater. Using Google Earth Pro, the linked nodes were located as latitude and longitude and then transformed into UTM equivalents. Multiple node fingerprint plots were created from various subareas because of their differing pattern. There is a shift from 90° angles between linking segments to 120° angles between linking segments from exterior to interior of the crater. The exterior fingerprint plot has distinct, organized, and elongated clusters (petals) that trend north-south as well as east-west. The preferred orientations are not simply aligned with radial or concentric lines for the crater. The centers of the clusters are at different distances as a reflection of the rectangular shape of the polygons. The interior of the crater has less distinct, less organized, diffuse clusters with weak northeast and southwest preferred orientations. The transition subarea has intermediate preferred orientations and degree of organization. On the node plots, there is a zone of exclusion in the middle, at around 50 units and less. This zone is due to the size of the craters and not due to a resolution sensing bias. Further research will look at the Shannon entropy values. The change in polygon shape and organization could be due to slope related stresses, changes in thickness of crater fill, or reactivation of structures beneath the crater.