THE GEOLOGIC AND STRATIGRAPHIC CONTEXT OF THE BRIGHT SPOTS IN OCCATOR CRATER ON CERES

When the Dawn spacecraft arrived at Ceres in March 2015, distinctive bright spots were observed on the surface, the brightest of which occurred in the 92-km-diameter Occator crater (Nathues et al., 2015; Russell et al., 2016). The presence of such bright, apparently fresh, material on the surface of a dwarf planet that accreted a few million years after the beginning of the solar system (e.g. McCord et al., 2011) was intriguing – the Dawn Science Team pondered whether recently active processes took place on this ancient body, and whether they were still occurring today. Since the Occator bright spots were first observed, Dawn’s Framing Camera has subsequently observed them at a high spatial resolution (35 m/pixel), which revealed the central Occator bright spot is located in a ~9 km wide and ~700 m deep pit (Schenk et al., 2016). Furthermore, data from Dawn’s Visible-Infrared Mapping Spectrometer led to the interpretation that the Occator bright spots are mostly made of sodium carbonates (De Sanctis et al., 2016). Occator crater was mapped as a part of the systematic geologic mapping campaign of Ceres, during which Ceres’ surface was divided into fifteen quadrangles (Williams et al., 2016; Roatsch et al., 2016). Occator crater is included in the geologic maps of two quadrangles: Occator and Ezinu (Buczkowski et al., 2016; Scully et al., 2016). However, additional detailed mapping of Occator crater and the Occator bright spots is necessary in order to further interpret their formation mechanism. Here we present a detailed geologic map of Occator crater, in which we identify the Occator bright spots as bright lobate material. This bright lobate material is concentrated into two regions: in the central pit and in the east-northeasterly portion of the crater floor. On the basis of cross-cutting relationships, we find that the crater terrace material, hummocky crater floor material and crater central peak material are the oldest units within the crater. They are cross-cut by a variety of lobate materials, including the bright lobate material, which have lobate margins and surface textures that suggest they were emplaced as flows. Our detailed geologic mapping of Occator crater is ongoing, and will provide important geologic and stratigraphic contextual information for the further interpretation of the Occator bright spots.