EUROPA’S GLOBAL TRENDS IN MICROCHAOS AND CYCLOIDS WITH IMPLICATIONS FOR GEOLOGIC HISTORY

The first global geologic map of Europa was published by the United Stated Geologic Survey (USGS) as a Scientific Investigation Map (SIM) in 2024 at a scale of 1:15,000,000 (1:15M). The Europa Global 1:15M SIM established four areally extensive primary material unit types (Regional Plains Material, Band Material, Chaos Material, and Crater Material) that are divided into geologic subunits. They also identify structures that are too small areally to be mapped as units but are significant enough (e.g., >15 km wide) to be mapped linearly or with a point: Ridge, Undifferentiated Linea, Band Linea, High Relative Brightness Band Linea, Cycloid, Multi-ring Structure, Microchaos, Trough, Depression Margin, Small Crater (5-10 km diameter), and Central Peak Structure. Here, we explore the global geologic trends and find interesting implications for microchaos and cycloids. An Optimized Hot Spot analysis shows that the global distribution of microchaos is non-uniform and occurs in concentrated clusters in several areas. One potential interpretation of the microchaos clusters, their location, and their association with other geologic units, is that there are stages of microchaos/chaos formation. Cycloids are defined as linear features that, in planform view, appear as a series of arcs connected by sharp cusps. In the rose diagram for the global orientation of all the cycloids mapped on Europa, we see a strong signal around a E-W orientation. The dominant E-W orientation of cycloids is expected due to their hypothesized, and well-accepted formation mechanism from varying diurnal stresses. However, the predicted dominant E-W orientation of cycloids can only be the case if Europa’s ice shell has not undergone large amounts of True Polar Wander (TPW) since the formation of cycloids. Both the formation of cycloids with a dominant E-W global orientation due to tidal stresses and geologically recent TPW cannot be true.