Identifying Icy Chaos and Chaotic Regions on Europa in Low-resolution Images Using a Statistical Approach

One of Europa's most iconic features is chaos, loosely characterized as an area with clear disruption of older terrain, low albedo, and a hummocky surface. Chaos is thought to be a response to near surface liquid water generated by heating within or below Europa's ice shell. Though multiple heat transport models are consistent with chaos formation, no one mechanism fully explains all instances of chaos. The models do make predictions for the global distribution of chaos, but maps have been limited to the <10% of the surface for which there is imagery of sufficient resolution to confidently identify chaos features by eye. One goal of this work is to enable more widespread mapping by developing a quantitative method for identifying chaos features in lower resolutions images ( 1km/pix), for which we have near global coverage. The ability to locate and characterize chaos in more locations on Europa can inform development of the Europa Multiple Flyby Flagship. First, we have mapped and categorized small-scale surface disruptions in regional image mosaics of Europa ( 250 m/pix) and applied a statistical tool called discriminant function analysis to identify quantitative metrics that separate chaos from other features: a high perimeter to area ratio, generally low normalized reflectance values, and moderate eccentricity. We will discuss how these results inform our understanding of chaos and its relationship to other types of small-scale surface disruptions. Next, we test our approach by applying the technique to identify chaos in the low-resolution portion of the USGS basemap and ground-truthing the results against the higher-resolution E11 image mosaics. If successful, we will have a method to accurately distinguish chaos features from other types of small-scale surface disruptions even in lower-resolution imagery, providing constraints on the formation of chaos and enabling a better estimate of the potentially habitable volume present within Europa's ice shell.