The geology of the Nawish quadrangle of Ceres: The rim of an ancient basin

Abstract

Herein we present the geology of the Nawish quadrangle, located in the equatorial region of dwarf planet Ceres, named after one of the most prominent craters of the area. Geologic mapping was based on the image mosaics and digital terrain models derived from Dawn Framing Camera data. Interpretation of geologic units was supported by supplemental data, such as the multi spectral color images from the Framing Camera, and the spectral parameters derived from the Visible and Infrared Spectrometer (VIR) data, as well as Dawn gravity data. There is not a primary feature that dominates the geology of Nawish quadrangle, but rather several terrains overlap, and their relations explain the geology of the area. Crater size frequency distributions show that Nawish quadrangle is dominated by two distinct time domains. The central and eastern part of the quadrangle is topographically elevated, which we define as cratered highlands, and contains the older domain. The western lowlands show two younger domains related to impact craters Kerwan and Dantu, including the Kerwan smooth material and Dantu ejecta. This variation of elevation within the Nawish quadrangle is more than the half of the global topographic altitude variation on Ceres. Analysis and comparison of the topography of the Nawish quadrangle with surrounding ones shows that this quadrangle is dominated by the topography of the rim sector of a large, > 800 km ancient impact basin, most likely the putative Vendimia Planitia. The Nawish quadrangle thus represents a sector of Ceres which has not undergone large-scale, post-Kerwan, intermediate age-events, but rather represents a place on Ceres where a well-preserved relict of old cerean crust can be studied, together with ejecta from more recent impact events.

The mineralogy of Ceres’ Nawish quadrangle

“…Sm resembles the cratered terrains morphology, with a lower amount of craters with a diameter >15 km and a higher albedo. The crater size-frequency counts demonstrate that the sm unit is younger than the crt (1 Ga) (Frigeri et al, 2018b).…”

“…4). Nawish quadrangle topography is computed as the height over an ellipsoid with a semi-major axis of 482 km and a semi-minor axis of 446 km, showing an elevation ranging between -3800 m and 5900 m (Frigeri et al, 2018b). …”

“…Details concerning the production of such maps are reported in Frigeri et al (2018a, this issue). The boundary of some geological units has been drawn (white curves: CRT = cratered terrains, C = crater material, SM = smoothed material, for details see Frigeri et al, 2018b). The map is superimposed over the FC images using a transparence of 25%.…”

“…4) of the quadrangle (Frigeri et al, 2018b) indicates the presence of three major units, cratered terrains (crt) which dominate the eastern highlands, smooth material (sm), characterizing the western lowlands, and crater material (c) typical of the crater ejecta of big impacts.…”

“…It is heavily cratered, and the crater counting reveals an age of ~2 Ga (Frigeri et al, 2018b). In crt, large craters show degraded rims, while small craters display more prominent rims (Frigeri et al, 2018b).…”