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Author(s): M. C. De Sanctis (corresponding author) [1]; F. Capaccioni [1]; M. Ciarniello [1]; G. Filacchione [1]; M. Formisano [1]; S. Mottola [2]; A. Raponi [1]; F. Tosi [1]; D. [...]

Telescopic observations have detected an exosphere around Ceres, composed of either water vapor or its photolytic products. Proposed mechanisms for its formation include sublimation or sputtering from solar energetic particles of buried ice, surface ice, or an optically thin seasonal polar cap. We estimate the amount of water vapor produced by known exposures of water ice, detected in Dawn spacecraft image and spectral data and by ice exposures from subresolution impact craters. We use thermal and sublimation modeling to take into account slope, orientation, and, in the case of water ice within craters, shadowing due to crater walls. We use a Monte Carlo approach to calculate the number of ice‐exposing impacts, where they occur on Ceres' surface, and how long the ice within the impact crater remains bright (e.g., less than one monolayer of sublimation lag). We find that the observed water ice patches on Ceres could account for ~0.06 kg/s of water vapor to (with Oxo crater as the main contributor) and that ice‐exposing impacts that remain bright in appearance after one Ceres year supply 0.08–0.56 kg/s of vapor, depending on the regolith volume fraction of the ice. While water ice has not been detected to date at Occator crater, if it were present we find that Occator is unlikely to be a major contributor of vapor. We find a typical background water vapor production rate from all of Ceres, combining surface and buried ice, of about a few tenths of a kilogram per second. Plain Language Summary: Ceres, the closest dwarf planet to the Sun, may be periodically surrounded with water vapor. This water vapor could be coming from water ice, either exposed at the surface or buried, undergoing temperature changes during Ceres' day and year. Vapor could also be released from ice that is bombarded by solar energetic particles. In this paper, we calculate how much water vapor could be produced from ice currently exposed on the surface of Ceres due to changes in temperature. We calculate the water vapor produced from observed surface water ice patches identified in Dawn spacecraft mission data. We also calculate water vapor produced from likely water ice patches that are exposed to space after a new impact crater forms but are too small to be seen by the Dawn spacecraft's instruments. We find that from these sources plus water vapor produced from buried water ice tables (calculated in other papers), about a few tenths of a kilogram per second of water vapor is likely to be escaping Ceres at the present day. Key Points: Observed exposed water ice patches on Ceres can contribute a few 10s of g/s of water vapor to the exosphereSubresolution impact craters can generate new surface water ice patches that increase the total water vapor productionModeled vapor production from both surface and buried ice suggests a lower typical rate than previously inferred by telescopic studies [ABSTRACT FROM AUTHOR]

In this study, the solubility of acetylene (or ethyne, C 2 H 2 ) and ethylene (or ethene, C 2 H 4 ) in liquid methane (CH 4 ) and ethane (C 2 H 6 ) has been experimentally determined at Titan surface temperature (90 K) and pressure (1.5 bars). As predicted by theoretical models, the solubilities of acetylene and ethylene are very large at Titan temperature and these species are most likely to be abundantly present in the lakes and as evaporites on the shores or dry lake beds. Our results indicate the solubility of 4.9 × 10 −2 mole fraction for acetylene in methane and 48 × 10 −2 mole fraction in ethane; for ethylene, 5.6 × 10 −1 mole fraction in methane and 4.8 × 10 −1 mole fraction in ethane. Assuming the mole fractions from atmospheric models in the lower stratosphere and equilibrium with the surface, we determined that the lakes on Titan that cover ∼400,000 km 2 are not saturated. The liquid lakes on Titan act as an important reservoir for both acetylene and ethylene. Assuming difference of methane and ethane content in the lakes at different latitudes, the difference in solubility in liquid methane and ethane, solutes in lakes may change with the temporal evolution (such as; evaporation and condensation) over seasons and geological time scales. [ABSTRACT FROM AUTHOR]

Highlights • The most prominent surface feature in quadrangle Ac-H-6 is crater Haulani. • Negative visual to near-infrared spectral slopes are observed in crater Haulani'ejecta and in other small unnamed craters. • Mg- and NH 4 -phyllosilicates are depleted in crater Haulani's floor and bright ejecta. • Mg- and NH 4 -bearing mineral phases correlate only in Haulani crater's area. • Ca- and Na-carbonates are most abundant in bright material found in crater Haulani. Abstract Ac-H-6 'Haulani' is one of five quadrangles that cover the equatorial region of the dwarf planet Ceres. This quadrangle is notable for the broad, spectrally distinct ejecta that originate from the crater Haulani, which gives the name to the quadrangle. These ejecta exhibit one of the most negative ('bluest') visible to near infrared spectral slope observed across the entire body and have distinct color properties as seen in multispectral composite images. Besides Haulani, here we investigate a broader area that includes other surface features of interest, with an emphasis on mineralogy as inferred from data obtained by Dawn's Visible InfraRed mapping spectrometer (VIR), combined with multispectral image products from the Dawn Framing Camera (FC) so as to enable a clear correlation with specific geologic features. Our analysis shows that crater Haulani stands out compared to other surface features of the quadrangle. Albedo maps obtained in the near infrared range at 1.2 µm and 1.9 µm reveal that the floor and ejecta of Haulani are indeed a patchwork of bright and dark material units. Visible to near-infrared spectral slopes display negative values in crater Haulani's floor and ejecta, highlighting bluish, younger terrains. Diagnostic spectral features centered at ∼2.7 µm and ∼3.1 µm respectively indicate a substantial decrease in the abundances of magnesium-bearing phyllosilicates and ammoniated phyllosilicates in crater Haulani's floor and bright ejecta. Similar, but less prominent, spectral behavior is observed in other geologic features of this quadrangle, while the general trend in quadrangle Ac-H-6 for these two mineral species is to increase from the northwest to the southeast. However, it is worth noting that the correlation between the ∼2.7 µm and ∼3.1 µm spectral parameters is generally strong in the Haulani crater's area, but much weaker elsewhere, which indicates a variable degree of mixing between these two major mineral phases in moving away from the crater. Finally, the region of crater Haulani displays a distinct thermal signature and a local enhancement in calcium and possibly sodium carbonate minerals, which is hardly found in the rest of the quadrangle and is likely the result of intense hydrothermal processes following the impact event. These evidences all together confirm the young age of crater Haulani, as they have not been erased or made elusive by space weathering processes. [ABSTRACT FROM AUTHOR]

Highlights • We present a method for thermal removal from Ceres spectra. • Most of the crater floors are devoid of volatiles due to the impact events. • Na-carbonates on Ikapati crater are likely preexistent to impact event. • We present the map of abundance of organic aliphatic material in Ernutet crater. • Organic rich-regions show different compositions pointing to a complex environment. Abstract Ceres has been explored by NASA/Dawn spacecraft, which allowed for the discovery of the main mineralogical and compositional characteristics of Ceres' surface. Here, we use mainly data from the Visible and InfraRed imaging spectrometer (VIR) in order to investigate the main spectral characteristics of the quadrangle Ac-H-2 Coniraya, one of the 15 quads in which Ceres' surface has been divided. Coniraya quadrangle is characterized by the presence of mostly highly degraded impact craters of diameters between 50 and 200 km and clusters of small to midsize impact craters. Although the composition over the quadrangle appears to be quite uniform, significant differences have been detected between different craters by spectral parameters analysis and spectral modeling. Ernutet crater presents two regions with very peculiar band at 3.4 µm, typical of organics aliphatic material. One region result to be correlated with larger amount of carbonates, the other region does not present such correlation. Ikapati crater shows strong absorption bands at 4.0 µm, indicating the presence of Na-carbonates in the floor and ejecta. Ikapati, Gaue and other craters present smaller spectral features of NH 4 and/or OH stretching, suggesting a volatile depletion process induced by the heating of the impact event. [ABSTRACT FROM AUTHOR]

Highlights • Sodium carbonates are found in bright material in ejecta craters. • Mineralogy of quadrangle Nawish using the band at 2.7, 3.1 and 3.9 µm. • Correlation between age of terrains and the mineralogy. Abstract Quadrangle Ac-H-08 Nawish is located in the equatorial region of Ceres (Lat 22°S-22°N, Lon 144°E- 216°E), and it has variable mineralogy and geology. Here, we report on the mineralogy using spectra from the Visible and InfraRed (VIR) mapping spectrometer onboard the NASA Dawn mission. This quadrangle has two generally different regions: the cratered highlands of the central and eastern sector, and the eastern lowlands. We find this dichotomy is also associated with differences in the NH 4 -phyllosilicates distribution. The highlands, in the eastern part of the quadrangle, appear depleted in NH 4 -phyllosilicates, conversely to the lowlands, in the north-western side. The Mg-phyllosilicates distribution is quite homogeneous across Nawish quadrangle, except for few areas. The 2.7 µm band depth is lower in the south-eastern part, e.g. in the Azacca ejecta and Consus crater ejecta, and the band depth is greatest for the Nawish crater ejecta, and indicates the highest content of Mg-phyllosilicates of the entire quadrangle. Our analysis finds an interesting relationship between geology, mineralogy, topography, and the age in this quadrangle. The cratered terrains in the highlands, poor in NH 4 phyllosilicates, are older (̴2 Ga). Conversely, the smooth terrain, such as with Vindimia Planitia, is richer in ammonia-bearing phyllosilicates and is younger (̴1 Ga). At the local scale, Ac-H-8 Nawish, displays several interesting mineralogical features, such as at Nawish crater, Consus crater, Dantu and Azzacca ejecta, which exhibit localized Na-carbonates deposits. This material is superimposed on the cratered terrains and smooth terrains and shows the typical depletion of phyllosilicates, already observed on Ceres in the presence of Na-carbonates. [ABSTRACT FROM AUTHOR]