The various ages of Occator crater, Ceres: Results of a comprehensive synthesis approach

Abstract

The 90.5-km Occator crater, with its peculiar and unique bright spots, is one of the most prominent and renowned feature on Ceres. Occator attracted broad public attention in scientific media as it is proposed to exhibit signs of post-impact cryovolcanic activity. In order to understand the time sequence of deposition, several attempts were made during DAWN's primary mission by different research groups to date geomorphologic key units using superposed crater densities. Resulting absolute model formation ages for Occator's ejecta and its interior lobate deposits range from 200 Ma to 78 Ma and about 100 Ma to 6.9 Ma, but were based on different cratering chronology models, measurements on image data at varying resolution, and different statistical and methodological approaches. Here we present the results of a comprehensive approach of determining absolute model formation ages for Occator. This is achieved by using the best resolved Framing Camera image data, by careful treatment of secondary crater admixture and the natural variability of crater detection and sizes by different crater analysts, and by applying appropriate, objective criteria for count area selection. In this context, we evaluate previously published model ages and explain why our results are likely to yield more consistent and robust information about the formation age of Occator. We also show that, in contrast to previous publications, CSFDs measured on Occator’s less competent ejecta blanket, and its more competent cryovolcanic- or impact melt related interior lobate deposits (ILDs), are so similar to each other, that the slight differences might rather be explained by different scaling parameters in different target materials or that the ILDs have formed almost contemporaneously or only shortly after the Occator forming impact.