In 2015, the NASA Dawn mission arrived at Ceres to investigate the only dwarf planet in the inner solar system and to determine the influence of planetary size and the role of water in planetary evolution. Not only did the Dawn mission reveal that Ceres has areas with organic molecules, in its final phase that took the spacecraft into a series of low-passing orbits above the surface, Dawn found evidence that Ceres is an active ocean world. The results of Dawn’s investigation are summarized in a collection of papers in the journal Nature.

After Dawn arrived at Ceres, it identified large bright spots known as faculae in Occator crater. These faculae are composed of a significant amount of sodium carbonate, a type of salt that likely formed in warm alkaline waters. The low-passing orbits of the spacecraft at 35 kilometers above the surface allowed acquisition of high-resolution data from the faculae and cryovolcanoes in Occator crater using a pair of panchromatic cameras, visible and infrared mapping spectrometers, and a gamma-ray and neutron detector. The high-resolution spectral data of the largest facula show that it also contains a hydrated sodium chloride mineral known as hydrohalite, which is concentrated at the center of the facula. Hydrohalite requires the presence of liquid water and hydrothermal activity to form and will dehydrate in less than 100 years, suggesting it must have been emplaced recently (De Sanctis et al.). Furthermore, an analysis of the geologic relationships and physical properties of features within Occator crater using high-resolution images indicates that the faculae were likely emplaced in an impact-induced hydrothermal system (Scully et al.). Evidence of cryovolcanism that initiated less than 9 million years ago and continued on for millions of years provides further evidence of a long-lasting, deep-seated brine source (Nathues et al.), and gravity data are consistent with an extensive, deep, brine reservoir under Occator crater (Raymond et al.). The discovery of Ceres as an active ocean world, albeit one with a greater abundance of rocky and non-icy materials than the oceans of Enceladus and Europa, further increases the number of places in the solar system that may be capable of supporting life and expands our understanding of ocean worlds in the solar system. READ MORE