Future exploration of Ceres as an ocean world

After 2 years in orbit around Ceres, the Dawn spacecraft, in the last phase of its extended mission (June-October 2018), reached closer to Ceres’ surface, down to 35 km, and performed imaging, infrared spectroscopy, elemental spectroscopy, and gravity science at resolutions never achieved before at an icy body1. The focus was on Occator crater, a ~20-million-year old crater revealed earlier in the mission to be a site of recent evaporite exposure (faculae), primarily as sodium carbonate spread over >100 km2 2. This discovery raised a debate in the community as to whether that activity could stem from a deep brine layer or from melt produced as a result of heat generated by the impact that created the crater, or both. Liquids from an impact melt chamber and evolve on different timescales than those from deeper (>40 km) reservoirs: the former would start warm as a result of impact heat, up to 100oC, but freeze over a few million years because of its close proximity to the surface. On the other hand, a perennial brine layer could be maintained by the presence of salts at sub-zero temperature if it were deep enough for internal heat to slowly leak through a thick crust.