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The intimate mixture of ice and silicate within the uppermost few kilometres of Ceres influences its geology and the evolution of its subsurface. Both ground ice and cryovolcanic processes have been hypothesized to form geologic terrains on Ceres, including within Occator crater, where they have been suggested to influence the post-impact surface evolution. Both types of processes involve the presence and expression of volatiles and brines, such that distinguishing between them could be difficult. Here, we use images and topography data from the NASA Dawn mission to investigate the morphology, age and distribution of mounds and hills within Occator crater, and infer their origin. The shapes and relative ages of many of these features suggest that they formed as impact-induced water-rich flows that covered the crater floor refroze in a manner similar to the formation of periglacial ice-cored mounds on Earth called pingos. We suggest that impacts on Ceres produced hydrologic conditions for surface changes in the absence of cryovolcanic processes. Our findings imply that cryo-hydrologic processes extend beyond Earth and Mars, and have been active on Ceres in the geologically recent past. Mounds within Ceres’s Occator crater may have formed by freezing of water-rich impact-induced melt, by a process analogous to that of pingo formation on Earth, according to an analysis of data from NASA’s Dawn mission.

This paper focuses on the identification and distribution of compositional units and their stratigraphic relationships in the Fejokoo quadrangle of Ceres (Ac-5) located between 21–66°N and 270–360°E and named after one of its prominent and well-preserved impact craters, Fejokoo (centered at 26°N and 312°E). In this quadrangle, we observed that hydroxylated- (OH-rich) and ammoniated- (NH4-rich) phyllosilicates are present everywhere, in various abundances; low abundance is observed on bright terrains and higher abundances are observed on lobate materials associated with craters. Carbonates are mostly correlated with the high-albedo areas surrounding Oxo (359.7°E, 42.2°N) and other major craters, and are mixed with Ceres’ most common surface composition type (i.e. low albedo, phyllosilicate-rich material). There are a few locations where carbonates and phyllosilicates co-exist, indicating a range of geological or chemical processes produced them in co-existence. No correlation between the surface composition and the age of the craters was found. Instead, the composition observed on impact craters depends on the size of the impact and the composition of the different stratigraphic layers excavated. The compositional interpretation inferred from Dawn's visible-infrared spectrometer data of the Fejokoo quadrangle is consistent with the presence of an internal ocean that produced carbonates and phyllosilicates via aqueous alteration of minerals.

The Dawn Framing Camera repeatedly imaged Ceres’ North Pole quadrangle (Ac-1 Asari, latitudes >66°N) at a resolution of ∼35 m/pixel through a panchromatic filter, enabling the derivation of a digital terrain model (DTM) and an ortho-rectified mosaic. Using this dataset, a photo-geologic map and stratigraphy, complemented with absolute model ages of impact craters, were produced. We identified the following key surface features: an ancient 4.5 km high isolated dome with a non-impact origin; recent lobate materials on crater interiors possibly formed as high-speed flows of collapsed rim material; and recent bright areas in permanently shadowed regions (PSRs), which we interpret as ice accumulation mostly by infall of exogenic material. Crater morphologies and dimensions do not differ from those in other quadrangles, suggesting the widespread influence of a rheologically weak target during the crater formation process. There is a paucity of lobate materials associated with impact cratering, in contrast to previous identifications with lower spatial resolution imagery.

Dawn is the first spacecraft to visit and orbit Ceres, the largest object in the asteroid belt and the only dwarf planet in the inner Solar System. The Dawn science team undertook a systematic geologic mapping campaign of Ceres’ entire surface. Here we present our contribution to this mapping campaign, a geologic map and geologic history of the Ezinu quadrangle, located in the northern mid latitudes from 21–66° N and 180–270° E. From our map, we reconstruct the geologic history of Ezinu quadrangle, which is dominated by impact cratering. Large impact craters that formed a few hundreds to tens of millions of years ago, such as Datan, Messor, Ninsar and Occator, are surrounded by ejecta and contain the products of mass wasting (hummocky crater floor material and talus material) and crater-wall collapse (terrace material). Two of these large impact craters are the sources of lobate flows, which we interpret as melt flows emplaced after the ballistically deposited ejecta. Morphological evidence suggests these lobate flows are rich in water–ice-bearing material that was excavated during the formation of the impact craters. There are only a few localized occurrences of lobate flows, suggesting that the water–ice-bearing source materials have restricted extents and/or are deeply buried within Ceres’ subsurface. The quadrangle also contains a variety of linear features: secondary crater chains are formed by the impact of locally and globally sourced material and pit chains and grooves are formed by the collapse of surficial materials into sub-surface fractures. The Ezinu quadrangle contains the northern portion of Occator crater, which is the host crater of prominent bright regions called faculae. Our geologic analysis therefore also provides context for the future investigation of Occator and its intriguing faculae.

Prior to the arrival of the Dawn spacecraft at Ceres, the dwarf planet was anticipated to be ice‐rich. Searches for morphological features related to ice have been ongoing during Dawn's mission at Ceres. Here we report the identification of pitted terrains associated with fresh Cerean impact craters. The Cerean pitted terrains exhibit strong morphological similarities to pitted materials previously identified on Mars (where ice is implicated in pit development) and Vesta (where the presence of ice is debated). We employ numerical models to investigate the formation of pitted materials on Ceres and discuss the relative importance of water ice and other volatiles in pit development there. We conclude that water ice likely plays an important role in pit development on Ceres. Similar pitted terrains may be common in the asteroid belt and may be of interest to future missions motivated by both astrobiology and in situ resource utilization., Key Points Fresh complex craters on Ceres host distinctive pitted terrains that are morphologically similar to pitted materials on Mars and VestaPitted terrains on Ceres likely form via the rapid volatilization of molecular H2O entrained in impact materialsPitted terrains may be common morphological markers of volatile‐rich near‐surface material in the asteroid belt

Landslides are among the most widespread geologic features on Ceres. Using data from Dawn's Framing Camera, landslides were previously classified based upon geomorphologic characteristics into one of three archetypal categories, Type 1(T1), Type 2 (T2), and Type 3 (T3). Due to their geologic context, variation in age, and physical characteristics, most landslides on Ceres are, however, intermediate in their morphology and physical properties between the archetypes of each landslide class. Here we describe the varied morphology of individual intermediate landslides, identify geologic controls that contribute to this variation, and provide first‐order quantification of the physical properties of the continuum of Ceres's surface flows. These intermediate flows appear in varied settings and show a range of characteristics, including those found at contacts between craters, those having multiple trunks or lobes; showing characteristics of both T2 and T3 landslides; material slumping on crater rims; very small, ejecta‐like flows; and those appearing inside of catenae. We suggest that while their morphologies can vary, the distribution and mechanical properties of intermediate landslides do not differ significantly from that of archetypal landslides, confirming a link between landslides and subsurface ice. We also find that most intermediate landslides are similar to Type 2 landslides and formed by shallow failure. Clusters of these features suggest ice enhancement near Juling, Kupalo and Urvara craters. Since the majority of Ceres's landslides fall in the intermediate landslide category, placing their attributes in context contributes to a better understanding of Ceres's shallow subsurface and the nature of ground ice., Key Points Landslides on Ceres have a wide range of morphologiesSubsurface ice affects the formation of most landslides on Ceres and influences their morphologyCeres has widespread ground ice with ice enhancements near the poles and within Juling and Kupalo craters

High-resolution mapping of Ceres, Vesta and the icy satellites of Saturn, Uranus and Pluto reveals a rich variety of well-preserved impact crater morphologies on these low gravity bodies. These objects provide a natural laboratory to study effects of composition on crater formation processes under similar surface gravity conditions (though mean impact velocities vary by several factors). Simple craters occur on all these bodies but subtle differences in morphology on Ceres and Vesta are recognized. Immature complex craters (with large floor mounds but not terraces or conical central peaks) occur on Vesta and while smaller than predicted are consistent with its silicate composition. Asymmetric simple craters (with incomplete scarp development) on all bodies are likely related to differential overburden stresses in the rim, and their occurrence is consistent with lower crustal strength on icy bodies including Ceres. Immature and mature complex craters exhibit increasing degrees of complexity, including spiral floor deformation patterns (related to failure in converging floor material), central peaks, and impact melt. Cerean crater morphologic types and simple-complex transition diameters are smaller than on Vesta but similar to those on icy satellites, indicating a much weaker rheology for Ceres' outer layers under impact conditions. These are consistent with geophysical indications of a low-density water ice and probably clathrate rich outer shell. Fluidized floor deposits (impact melt or melt-solid mixtures) are significant in craters >25 km across on Ceres but absent on Saturn satellites. Central pit craters are common on Ceres (at diameters of ~75 to 150 km consistent with gravity scaling from the larger Galilean satellites) but are absent on Saturnian satellites and Charon. The contrasting impact melt and central pit behaviors on Ceres and Saturn's moons is contrary to expectation given the higher impact velocities at Saturn but might be related to lower internal temperatures, or the higher fraction of non-ice material on Ceres. The correlation or scaling of transition diameters to surface gravity is near −0.65 rather than −1, perhaps due to increased porosity on lower gravity bodies. The fundamental similarity of crater morphologies on Ceres and icy satellites, however, indicates that the weaker rheology of water ice results in similar craters even if the non-(ice+clathrate) components are as high as ~30 vol%.

H2O-rich materials are locally exposed at the surface of Ceres as discovered from infrared reflectance spectra of the Visible and InfraRed mapping spectrometer (VIR) of the Dawn mission. Nine locations on Ceres exhibit diagnostic absorption bands of the H2O molecule at 2.00, 1.65 and 1.28 μm. The detections are all consistent with H2O ice mixed with low-albedo components. All the reported H2O exposures occur at latitudes poleward of 30° in fresh craters near rim shadows, have a surface area < 7 km2, and are associated with one or more surface features such as a morphological flow or landslide, fractures, high albedo, or a pole-facing slope (one case is confirmed to be adjacent to persistent shadow). In four occurrences, these detections are associated with small (< 0.1 km2) high-albedo areas that can be recognized in high-resolution imagery (∼35 m/pixel) from the Framing Camera (FC). Since all these observations are compatible with an H2O-rich subsurface, the replenishment of surficial H2O likely comes from the ice that is present underneath. In four other occurrences, H2O is detected on walls and floors of fresh impact craters, either in the shadow or adjacent to shadows, which suggests that local thermodynamical conditions may also favor the concentration of H2O in these areas.

NASA's Dawn spacecraft arrived at Ceres on March 6, 2015, and has been studying the dwarf planet through a series of successively lower orbits. Throughout these mission phases Dawn obtained photographic, mineralogical, elemental abundance, and gravity data. Ceres is the largest object in the asteroid belt with a mean diameter of ∼940 km. The Dawn Science Team conducted a geologic mapping campaign for Ceres similar to the one that was implemented on the asteroid Vesta (Dawn's previous target), including production of a Survey- and High Altitude Mapping Orbit (HAMO)-based global map, and a series of 15 Low Altitude Mapping Orbit (LAMO)-based quadrangle maps. In this paper we present the LAMO-based geologic map of the Ac-5 Fejokoo Quadrangle (21–66°N and 270–360°E) and discuss its implications. The Ac-5 quadrangle is primarily composed of ancient cratered terrain punctuated with several moderately fresh impact craters of geologic interest, six large tholi that are possibly cryovolcanic in origin, and an abundance of flows that well represent the full spectrum of mass wasting features observed on Ceres. The Fejokoo quadrangle hosts the majority of Oxo crater, the site of the first spectroscopic detection of H2O ice on the surface of Ceres. The H2O detection is closely related to two distinctive morphological units interpreted as possible high water ice content landslides. These observations and interpretations are consistent with ground ice mediated surface processes on Ceres.

The Dawn spacecraft arrived at dwarf planet Ceres in spring 2015 and imaged its surface from four successively lower polar orbits at ground sampling dimensions between ∼1.3 km/px and ∼35 m/px. To understand the geological history of Ceres a mapping campaign was initiated to produce a set of 15 quadrangle-based geological maps using the highest-resolution Framing Camera imagery. Here we present the geological map of the Ac-10 Rongo Quadrangle, which is located at the equator encompassing the region from 22°N to 22°S and 288° to 360°E. The total relief within the quadrangle is 11.1 km with altitudes ranging from about −7.3 km to +3.8 km. We identified nine geological units based on surface morphology and surface textural characteristics. The dominant and most widespread unit is the cratered terrain ( crt ) representing ancient reworked crustal material. Its consistent formation age across the quadrangle is 1.8 Ga. Two edifices (unit th ), Ahuna Mons and an unnamed tholus within Begbalel Crater, are interpreted to be of (cryo)volcanic origin. The southwest portion of the quadrangle is dominated by ejecta material ( Ye ) emplaced during the formation of the 260-km diameter Yalode impact basin at about 580 Ma. Rayed crater ejecta material ( cr ) is dominant in the eastern part of the quadrangle but also occurs in isolated patches up to a distance of 455 km from the 34 km diameter source crater Haulani. The remaining five geological units also represent impact crater materials: degraded rim ( crdeg ), bright crater ( cb ), hummocky floor ( cfh ), talus ( ta ), and crater ( c ) materials. Widespread Yalode and Haulani ejecta materials can potentially be utilised as stratigraphic markers. Therefore, it is essential to consistently map their full areal extent and to date their formations using impact crater statistics.

INTRODUCTION Dwarf planet Ceres’ low average-density (2162 ± 3 kg m −3 ) indicates that it must contain considerable water. Water is likely a key component in the chemical evolution and internal activity of Ceres, possibly resulting in a layer of ice-rich material and perhaps liquid in the mantle. Mineral hydroxides (OH-bearing) and hydrates (H 2 O-bearing), such as clays, carbonates, and various salts, would be created. These hypotheses were supported by the detection of hydroxyl (OH)–rich materials, OH-bearing molecule releases, H 2 O vapor molecules, and haze. However, the presence of H 2 O on the surface has not previously been confirmed. The detection and mapping of H 2 O on Ceres is one objective of the Dawn spacecraft, in orbit around Ceres since March 2015. RATIONALE The purpose of the Dawn space mission at Ceres is to study the geology, geophysics, and composition remotely by means of high-resolution imagery and spectrometry. Dawn’s Visible and InfraRed Mapping Spectrometer (VIR) measures the sunlight scattered by the surface of Ceres in a range of wavelengths between 0.25 and 5.1 μm. The position and shape of absorption features in VIR reflectance spectra are sensitive to the surface mineral and molecular composition. In spectroscopy, absorption bands at 2.0, 1.65, and 1.28 μm are characteristic of vibration overtones in the H 2 O molecule. RESULTS Dawn has detected water-rich surface materials in a 10-km-diameter crater named Oxo, which exhibit all absorption bands that are diagnostic of the H 2 O molecule (see the figure). These spectra are most similar to those of H 2 O ice, but they could also be attributable to hydrated minerals. Oxo crater appears to be geologically very young (~1 million to 10 million years); it has sharp rims and its floor is almost devoid of impacts, suggesting a recent exposure of surface H 2 O. The high latitude and morphology of the Oxo crater protects much of the surface area from direct solar illumination for most of the cerean day, presenting favorable conditions for the stability of water ice or heavily hydrated salts. CONCLUSION Four ways to create or transport H 2 O on Ceres are considered: (i) Exposure of near-surface H 2 O-rich materials by a recent impact or an active landslide seems most consistent with the presence of both mineral hydrates and water ice. (ii) Release of subsurface H 2 O may occur on Ceres, similar to release on comet nuclei, but may never recondense on the surface. (iii) Infall of ice-bearing objects is not likely to deposit water on Ceres, because the H 2 O molecule likely would dissociate upon impact. (iv) Implantation of protons from the solar wind on the surface is not a probable origin of OH on Ceres because of the low flux of solar wind charged particles. We therefore conclude that surface H 2 O or hydrated minerals are the most plausible explanation. Dawn VIR infrared observations of Oxo crater on Ceres demonstrate the detection of H 2 O at the surface. ( A ) Reflectance spectrum collected where absorption bands of H 2 O at 1.28, 1.65, and 2 μm are the strongest (in blue) compared with a laboratory spectrum of H 2 O ice (black). The lab spectrum is scaled and vertically shifted for clarity. ( B ) Perspective view of Oxo crater observed by the Dawn Framing Camera (FC), where the two high-albedo areas right next to the scarps contain H 2 O-rich materials.