Impact heat driven volatile redistribution at Occator crater on Ceres as a comparative planetary process

Abstract

Hydrothermal processes in impact environments on water-rich bodies such as Mars and Earth are relevant to the origins of life. Dawn mapping of dwarf planet (1) Ceres has identified similar deposits within Occator crater. Here we show using Dawn high-resolution stereo imaging and topography that Ceres' unique composition has resulted in widespread mantling by solidified water-and salt-rich mud-like impact melts with scattered endogenic pits, troughs, and bright mounds indicative of outgassing of volatiles and periglacial-style activity during solidification. These features are distinct from and less extensive than on Mars, indicating that Occator melts may be less gas-rich or volatiles partially inhibited from reaching the surface. Bright salts at Vinalia Faculae form thin surficial precipitates sourced from hydrothermal brine effusion at many individual sites, coalescing in several larger centers, but their ages are statistically indistinguishable from floor materials, allowing for but not requiring migration of brines from deep crustal source(s).

The varied sources of faculae-forming brines in Ceres’ Occator crater emplaced via hydrothermal brine effusion

“…In addition, other fractures within the set, which are now buried, could have also, or alternatively, allowed the faculae-forming brines to reach the surface. There is a candidate-centralized source region, or eruptive crater-like structure, in the center of one of the regions of Vinalia Faculae, which possibly sourced the surrounding bright material 21,40 (Fig. 4).…”

“…This structure consists of a low central rise surrounded by linear depressions, and is discussed in detail in ref. 40 . The structure has straight sides, with two sides parallel to the fractures, suggesting that the weaknesses formed by the set of fractures controlled its shape.…”

“…1b). The XM2 data illustrate that there is no dark material at the base of the~50-100 m deep 40 radiating fractures on top of Cerealia Tholus (Fig. 2a), indicating that the continuous bright material on the uppermost parts of the tholus is ≥50 m thick (Fig.…”

“…While the model ages provide approximate ages for the faculae, and there is some evidence for possible local reactivation/ resurfacing on Cerealia Facula~1-2 million years ago 43 , the model ages cannot precisely quantify the emplacement durations of the faculae. Moreover, the small count areas used for the faculae, which have low crater densities and less large craters, are more susceptible to stochastic cratering variability, contamination by secondary craters and degradation/erasure of small craters than larger areas 40,47 . In addition, the frequently diffuse nature of the deposits make absolute age dating of the faculae notoriously Fig.…”

“…difficult, and prone to relatively large uncertainties 40,47 . Thus, while a shorter period of emplacement for Vinalia Faculae cannot be entirely ruled out, there is no clear evidence supporting this possibility.…”