Origin and evolution of Castalia Macula, an anomalous young depression on Europa

Abstract

Europa's Castalia Macula region was comprehensively imaged by the Galileo spacecraft on several orbits, at both local and regional resolutions and with different illumination geometries. Using these datasets we have mapped and identified the different geological units within the Castalia area, and derived digital elevation models (DEMs) of the topography within most of the Castalia Macula region. Using these data sets in combination allows us to map the geology and topography of this area in greater detail than perhaps any other site on Europa. Castalia Macula consists of unusually dark and reddish material, most of which is confined to a broad topographic depression 350 m deep located between two large uplifted domes 900 and 750 m high, to the north and south, respectively. The preservation of topography at the bottom of Castalia Macula indicates that dark material initially filled the depression to a certain depth but was subsequently removed via drainage, resulting in a dark stain up to the original equipotential surface. Superposition and topographic relationships suggest that the Castalia Macula plains deposit formed prior to uplift of both domes, and at least two distinct episodes of chaos formation have occurred near and on top of the northern dome. It appears that Castalia Macula is comparatively young and was active relatively recently, therefore it could provide an ideal place to sample material that has recently been erupted from the subsurface, and may have been in communication with Europa's ocean. These factors combine to make Castalia Macula a very attractive site for a future Europa lander.