PROGRESS ON GLOBAL GEOLOGIC MAPPING OF PLUTO AND TETHYS

We provide an update on two mapping efforts led by the lead author of this abstract that will result in the publication of two US Geological Survey Scientific Investigations Maps (SIMs). The first is a global SIM at 1:7M scale for the >75% of Pluto’s surface that was imaged by New Horizons. This map has undergone revision in response to USGS review and we expect to resubmit it by the time of GSA Connects 2023. Our mapping defines a very wide range of landforms and surface ages across Pluto, and we have identified five geological time periods based on stratigraphic relations and crater ages of mapped units. Our map illustrates that the range of surface ages appears to originate from a complex interplay of effects deriving from the distribution of Pluto's surface volatile ices in response to atmospheric, geographic, and topographic constraints, onto which are superimposed endogenic effects including the ancient ridge-trough tectonic system spanning virtually the entire encounter hemisphere, and the relatively recent terrains south of Sputnik Planitia that are tentatively interpreted as cryovolcanic.

The second map is a global SIM of Tethys at 1:5M scale. This project began in June 2023, so we will present on early progress in updating the global grayscale and color mosaics and stereo digital elevation (DEM) model to be used as base maps, and on how we anticipate the resulting geological map to be scientifically illuminating. Tethys, which features tectonism, potential cryovolcanic resurfacing, and very differential relaxation states of large impact features, belongs to an important class of mid-sized saturnian satellites that display evidence for endogenic activity that is intermediate between the heavily cratered saturnian satellites and the highly active Enceladus. This class is vital to understanding how icy worlds become ocean worlds or not. The currently publicly available global mosaic was generated in April 2014, and we will update it with five Cassini mosaics that were obtained after that date. We will also use these additional mosaics to create new stereo pairs that will allow us to significantly improve upon the existing global DEM of Tethys. We will first map and classify linear and impact structures, and proceed to map geologic units and determine their ages by identifying stratigraphy and calculating crater densities.