GLOBAL GEOLOGIC MAPPING OF CERES

We are creating a global geologic map of Ceres using the Dawn Framing Camera (FC) LAMO mosaic (35 m/pix) as our base, the HAMO-based DTM (136.7 m/pixel) for topography, and VIR Mapping Spectrometer and GRaND data for composition. Structures, contacts, and geologic units are identified primarily from the FC mosaic; the topographic and spectral datasets inform the map by characterizing features and units. This map follows the mapping standards set by the USGS and will be published as a Special Investigation Map (SIM) at 1:3M scale for the equatorial region (+/- 60° lat) and 1:1.5M scale for the polar regions (>60° N/S lat).

Ceres exhibits ~17 km of relief (~-7.5 to 9.5 km) with broad expanses of low-lying terrains separated by areas of elevated terrains. Low-lying terrains are shaped by definite (e.g., Urvara, Yalode, Kerwan) and putative (e.g., Vendimia Planitia) large-diameter impact structures that form basins and broad plains, whereas elevated terrains are formed by Hanami Planum and the rim structures of impact craters.

Impact craters are the most prevalent features on Ceres and have caused most of the visible modification of the surface. Craters range in size from the limits of resolution to larger structures – Urvara (170 km), Yalode (260 km), and Kerwan (284 km) – and exhibit “fresh” to moderately degraded morphologies. Most craters exhibit circular to nearly circular shapes; some craters have rims that display polygonal planform shapes reflecting buried structures and/or mass wasting of crater rim and wall materials.

Structurally, Ceres exhibits impact-derived features (rims, crater chains) and sets of linear to arcuate features – such as troughs and pit chains – that dissect the surface. Troughs are steep-walled, wide, relatively deep, and they are found in parallel sets oriented radial to large craters (e.g., Dantu, Occator, Urvara, Yalode). Pit chains display steep walls, are narrower and shallower than troughs, and some are oriented radial to impact craters. Pit chains are formed by connected circular to ovate depressions that do not display raised rims.

Preliminary mapping of geologic units shows that three major unit types – plains, uplands, and impact materials – represent the surface. LAMO image resolutions are allowing most geologic units to be identified and characterized by their albedo and surface texture.