**3. Ring-mold craters on Ceres**

Ring- mold craters (RMC) are common on lineated and lobated debris aprons, filling valleys, and concentric crater fills on Mars [32–34]. They are interpreted as impacts into ice covered by a thin layer of regolith. Ring-mold craters have diameters between 167 and 697 m and are generally surrounded by a rimless, circular moat. Furthermore, ring-mold craters show a variety of complex interior features. [33] found four morphological types of ring-mold craters: (1) a central pit or bowl; (2) a central plateau; (3) a multiring; and (4) central mound craters.

On Ceres ring-mold craters are located on the southern crater floor of Occator [35]. They predominantly appear on the lobate smooth material; a few craters are found on the terrace material as defined on the geologic maps of [36, 37]. Some ring-mold craters are located on or near the tectonic structure in the southern part of the Occator floor. Ring-mold craters show an almost circular shape seem to be subsiding into the surface, causing less elevated crater rims (**Figure 3**). Numerous ring-mold craters are degraded (**Figure 3**) and contains cracks (**Figure 3D**) or lobate material (**Figure 3E** and **F**). [35] found three classes of ring-mold craters: (1) central pit or bowl craters (**Figure 3A**); (2) central mound craters (**Figure 3B** and **C**); and (3) central plateau craters (**Figure 3B**). They show, that ring-mold craters on Ceres are comparable to those on Mars (e.g., [32, 33, 38]). Both bodies show nearly rimless craters with a circular outer moat and similar interior morphologies, like central pits or bowls, plateaus, and mounds. Moreover, ring-mold craters on both bodies are associated with flow features, lineated valley fills and lobate debris aprons on Mars and lobate materials within Occator on Ceres. The similarities of morphology and location indicate a similar formation process [35]. Although, Martian ring-mold craters with diameters between 697 (mean 225 m; [32]) and 750 m (mean 102 m; [33])

**Figure 3.**

*Ring-mold craters on Ceres. (A) shows a central pit/bowl crater. (B) shows a central plateau (bottom) and a central mound crater (top). (C) shows two central mound craters. (D) shows a ring-mold crater degraded and deformed by cracks. (E) and (F) show craters affected by flow features.*

are smaller than ring-mold craters on Ceres with diameters from ~280 to ~1,520 m with a mean of ~710 m [35]. Ponded material and lobate materials within Occator are supposed to be formed by impact melt or cryovolcanic flows (e.g., [39–41]). Furthermore, thermal modeling and gravity data suggest an extensive deep brine reservoir beneath Occator, which might have been mobilized by the heating and deep fracturing related to the Occator impact. Thus, this process would lead to a long-lived extrusion of brines and the formation of the faculae [15]. Additionally, pre-existing tectonic cracks may provide hints for deep brines migrating and dilatating the crust creating a compositional heterogeneity [15].

Due to the occurrence of frozen oceanic materials rich in sodium carbonate and ammonium chloride at several locations, [26] suggest that oceanic material is frozen in the first 10s of kilometers and possibly shallower. This hypothesis is verified by [35] using the depth to diameter ratio from [42] to estimate the minimum regolith thickness on the basis of bowl-shaped craters sizes which are adjacent to ring-mold craters. The results also conclude an overlying area thickness of several tens of meters suggesting that the smaller bowl-shaped crater do not penetrate to the ice layer. Thus, subsurface ice at Occator is at a relatively shallow depth, below a thin protective layer of regolith, and those impacts hitting the subsurface ice layer form ring-mold craters [35].
