The Formation and Evolution of Bright Spots on Ceres

Abstract

a b s t r a c tThe otherwise homogeneous surface of Ceres is dotted with hundreds of anomalously bright, predominantly carbonate-bearing areas, termed "faculae," with Bond albedos ranging from ∼0.02 to > 0.5. Here, we classify and map faculae globally to characterize their geological setting, assess potential mechanisms for their formation and destruction, and gain insight into the processes affecting the Ceres surface and near-surface. Faculae were found to occur in four distinct geological settings, associated predominantly with impact craters: (1) crater pits, peaks, or floor fractures (floor faculae), (2) crater rims or walls (rim/wall faculae), (3) bright ejecta blankets, and (4) the mountain Ahuna Mons. Floor faculae were identified in eight large, deep, and geologically young (asteroid-derived model (ADM) ages of < 420 ± 60 Ma) craters: Occator, Haulani, Dantu, Ikapati, Urvara, Gaue, Ernutet, and Azacca. The geometry and geomorphic features of the eight craters with floor faculae are consistent with facula formation via impact-induced heating and upwelling of volatile-rich materials, upwelling/excavation of heterogeneously distributed subsurface brines or their precipitation products, or a combination of both processes. Rim/wall faculae and bright ejecta occur in and around hundreds of relatively young craters of all sizes, and the geometry of exposures is consistent with facula formation via the excavation of subsurface bright material, possibly from floor faculae that were previously emplaced and buried. A negative correlation between rim/wall facula albedo and crater age indicates that faculae darken over time. Models using the Ceres crater production function suggest initial production or exposure of faculae by large impacts, subsequent dissemination of facula materials to form additional small faculae, and then burial by impact-induced lateral mixing, which destroys faculae over timescales of less than 1.25 Gyr. Cumulatively, these models and the observation of faculae limited to geologically young craters indicate relatively modern formation or exposure of faculae, indicating that Ceres' surface remains active and that the near surface may support brines in the present day.

Thermal Evolution of the Impact‐Induced Cryomagma Chamber Beneath Occator Crater on Ceres

“…Here we are interested in the origin of the bright salt‐rich surface deposits called faculae, which are observed widely on Ceres' surface (De Sanctis et al, ; Li et al, ; Longobardo et al, ; Stein et al, ). The faculae associated with large impact craters have been preferentially related to the brine reservoir located at the base of the crust (Buczkowski et al, ; Nathues et al, ; Quick et al, ).…”

“…The Occator faculae are generally interpreted as cryovolcanic deposits formed by brine fountaining (Quick et al, ; Ruesch et al, ; Scully, Buczkowski, et al, ). The source of the brine is either thought to be impact heating of the crust (Bowling et al, ), a preexisting crustal brine pocket (Stein et al, ), or a deeper brine reservoir in the mantle (Quick et al, ). Given Cerealia Facula's location in the center of Occator Crater, impact‐induced processes (partial melting and pervasive fracturing) must have played a major role in its formation.…”

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

“…3 bottom). This value is arguably greater than surroundings (Stein et al, 2017) and greater than the average albedo of Ceres (Thangjam et al, 2018). Clusters of bright spots are present on crater Heneb's floor and in the Azacca and Dantu crater materials.…”

Ceres’ Ezinu quadrangle: a heavily cratered region with evidence for localized subsurface water ice and the context of Occator crater

“…There are many small impact craters that do not have bright ejecta blankets and interiors, which indicates that the bright-spotforming materials are spatially restricted within Ceres' subsurface. Stein et al (2018) propose that bright-spot-forming materials are formed as brine precipitates in impact craters, broadly similar to the faculae in Occator crater ( De Sanctis et al, 2016 ), and are then buried and mixed into the subsurface until they are excavated by impacts and mass wasting. Thus, it is likely that some of the bright spots in Ezinu quadrangle are excavated brine precipitates.…”