Chaos Blocks on Europa: An Analysis of Orientation and Size Distributions

Abstract:

Chaos regions on Europa are hypothesized to be among the youngest features on the surface. Therefore, it is crucial to understand chaos formation in order to determine if they are sites of recent or current geological activity. If chaos formation is an ongoing process, the terrain would be an important target of further study by Europa Clipper to understand the internal processes present at Europa. Previously, Leonard et al. (2020) mapped Conamara Chaos and Moytura Regio at a regional scale, identifying differences between the chaos morphologies in each region. Here we extend these initial results by mapping Murias Chaos in the Leading Hemisphere and Dyfed Regio in the Trailing Hemisphere, to better understand the extent of morphological differences between geographically-distinct chaos regions. We find that chaos morphology lies on a spectrum where the two endmembers are characterized as platy and knobby, based on the number of blocks identified as plates relative to the amount of matrix material. We define blocks as pieces within chaos having clear boundaries and topographic relief, distinguished from finer grained matrix, while plates are blocks that display evidence of preexisting terrain. We also determine the orientation of blocks to understand whether there are trends that have implications for chaos formation. Our initial results suggest that preexisting tectonic fabric can influence block orientation for Murias Chaos but not in Dyfed Regio, perhaps indicating that some (but not all) chaos formation involves exploitation of preexisting fractures, as found for Murias Chaos and Conamara Chaos. We also tested whether the size distribution of chaos blocks could be fit by a fragment size distribution (FSD) function per fragmentation theory, to help understand the fracture processes that could be dominating block formation. We present preliminary results of size distributions and fits with an FSD function based on the terrestrial ice literature compared with a linear fit in log-log space. The measured orientation and size distribution of chaos blocks may indicate underlying regional differences of preexisting tectonic fabric influences, thermal processes, or rheology.