Characterizing the Morphology of Chaos on Europa

Chaos terrain represents a type of feature unique to Europa and covers approximately one third of the satellite's surface. Two endmember models have been proposed for its formation: one suggests it forms through melting of the surface by liquid water from the subsurface ocean; the second suggests that chaos forms from the upwelling of thermally or compositionally buoyant diapirs. The formation of chaos disrupts preexisting surfaces and it has been observed that the magnitude of this disruption varies from one feature to another. Based on the morphological characteristics of different prominent and well-imaged regions of chaos (i.e., Conamara and Murias), this feature-type has been subdivided into endmember classes (Greeley et al., 2000). Conamara chaos is defined by kilometer-scale blocks of preexisting ridged plains material that have been tilted, translated and rotated with respect to one another within a generally lower-albedo matrix of hummocky material. Approximately 60% of the preexisting terrain has been replaced with or converted into matrix material (Spaun et al., 1998). In contrast, Murias chaos appears to be comprised purely of matrix material, with no hint of blocks of preexisting material or tectonic structure (Figueredo et al. 2002). The morphological characteristics of these two types of chaos have been commonly used to establish criteria for examining formation models. However, additional distinct morphologies of chaos have been proposed and the abundance/distribution of chaos morphologies is not well known. Understanding the importance of these various morphologies could provide valuable insight regarding the formation and evolution of this unique feature-type. To that end, we have systematically mapped the global distribution of chaos using image data at resolutions from ~1 km/pixel to 10 m/pixel and covering a range of viewing geometries. From this, we have categorized variations in morphology using the relative abundance of plates within a given feature as a defining characteristic and, using this map, we examine potential trends in the distribution of chaos morphologies.