The Formation and Evolution of Ceres' Occator Crater and its Faculae
Abstract
When the Dawn mission explored Ceres from 2015 to 2018, it revealed intriguing bright regions inside the 92-km-diameter Occator impact crater, which were named Cerealia Facula and Vinalia Faculae. Here we synthesize together studies that investigate the driving forces behind the formation of Occator and its faculae, which are presented in a special issue of the journal 'Icarus'. Occator's ejecta blanket, terraces and hummocky floor material formed during and/or immediately after crater formation. The lobate material is interpreted as a slurry of impact-melted water, soluble salts and boulders of unmelted silicates/salts that flowed around the crater interior before solidifying. It is suggested that the central pit formed when an initial liquid water central uplift drained into impact induced fractures. The outer edge of Cerealia Facula is interpreted as a residual salt deposit derived from relatively short-lived impact-induced hydrothermal circulation. The majority of Cerealia Facula is located within the central pit, and is thought to have formed significantly later than Occator, from brines derived from a pre-existing reservoir and/or an impact-induced reservoir. A part of the lobate material was likely inflated by cryomagmatic intrusion, giving it a hummocky texture and forming fractures. It is proposed that brines used these fractures to travel to the surface and form the Vinalia Faculae. The central dome is located in the central pit, along with the majority of Cerealia Facula, and was one of the last features to form in the crater. Small, bright impact craters superpose the faculae, indicating that the faculae have slightly darkened from mixing and/or space weathering. Occator's faculae are the freshest endmember of an evolutionary pathway for Cerean bright regions. Unlike Cerealia and Vinalia Faculae, the majority of bright regions on Ceres are formed from re-excavated material. We find that Ceres is an active world where briny liquids have been mobile in the geologically recent past, driven by either entirely impact-derived or impact and endogenic driving forces. Faculae have likely formed throughout Ceres' history, but Occator's are currently striking because they are geologically young. Part of this work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract to NASA. Government sponsorship acknowledged.
- Publication:
-
42nd COSPAR Scientific Assembly
- Pub Date:
- July 2018
- Bibcode:
- 2018cosp...42E3048S