Morphometric trends and implications for the formation of araneiform clusters

Araneiforms are an exotic type of feature exclusive to the Martian south polar terrain which have no known direct Earth analog. The dilation and recession of the seasonal CO2 ice deposit has long been hypothesized to be responsible for their gradual formation. However, high south polar latitude araneiforms have not been observed to form or extend in the present day and it is unclear whether they are growing below the limits of high resolution imagery, or whether they formed in a paleoclimate. Furthermore, it is unclear what physical factors govern the distinct araneiform morphologies, which often appear in discrete 'clusters', showing non-random spatial distribution. While qualitative observations of morphology have been reported, there has been a paucity of quantitative measurements of the many physical controls that govern araneiform activity and morphology. Here we present the results of a survey designed to initiate a quantitative morphometric approach to exploring some of the factors which may influence araneiform morphologies. We survey distinct clusters within 3 sites in the Martian south polar regions representing unique araneiform morphologies ranging from 'fat' to 'thin' to starburst' in order to test the relationship between vent spacing and diameter to morphology found in experimental results. Using the diameters of their central pits as proxies for their starting vent diameters, we find that the level of branching of these dendritic features appears to be correlated with (i) inferred vent spacing and (ii) inferred vent diameter. We suggest that the individual araneiforms within such distinct clusters may have formed contemporaneously, and that vent geometry reflects at least one control on their distinct morphologies. We surveyed and measured araneiforms in three HiRISE images and we have observed and characterized new morphologies at eight sites in HiRISE and CTX images between lat=-87.521 degrees N and lon=162.39 degrees E and lat=-74.7 degrees N, lon=168.41 degrees E in order to investigate if there are any trends in araneiform morphology with latitude. For the sites we studied, we find no discernable relationship between morphology and latitude, though we caution that a more extended survey is needed to confirm this observation on the broader scale. Additionally, from this survey, we report six new araneiform morphologies; 'fan', 'linear', 'spiky', 'segmented', 'flowing' and 'sunflower'. (c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC license (http://creativecommons .org /licenses /by-nc /4 .0/).