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The surface of Saturn's moon Enceladus is composed primarily by pure water ice. The Cassini spacecraft has observed present-day geologic activity at the moon's South Polar Region, related with the formation and feeding of Saturn's E-ring. Plumes of micron-sized particles, composed of water ice and other non-ice contaminants (e.g., CO 2 , NH 3 , CH 4 ), erupt from four terrain's fractures named Tiger Stripes. Some of this material falls back on Enceladus' surface to form deposits that extend to the North at ∼40°W and ∼220°W, with the highest concentration found at the South Pole. In this work we analyzed VIMS-IR data to identify plumes deposits across Enceladus' surface through the variation in band depth of the main water ice spectral features. To characterize the global variation of water ice band depths across Enceladus, the entire surface was sampled with an angular resolution of 1° in both latitude and longitude, and for each angular bin we averaged the value of all spectral indices as retrieved by VIMS. The position of the plumes’ deposits predicted by theoretical models display a good match with water ice band depths' maps on the trailing hemisphere, whereas they diverge significantly on the leading side. Space weathering processes acting on Enceladus' surface ionize and break up water ice molecules, resulting in the formation of particles smaller than one micron. We also mapped the spectral indices for sub-micron particles and we compared the results with the plumes deposits models. Again, a satisfactory match is observed on the trailing hemisphere only. Finally, we investigated the variation of the depth of the water ice absorption bands as a function of the phase angle. In the visible range, some terrains surrounding the Tiger Stripes show a decrease in albedo when the phase angle is smaller than 10°. This unusual effect cannot be confirmed by near infrared data, since observations with a phase angle lower than 10° are not available. For phase angle values greater than 10°, the depth of the water ice features remains quite constant within a broad range of phase angle values. [ABSTRACT FROM AUTHOR]

Highlights: [•] We apply the SAM classification method to 85 infrared VIMS cubes of Rhea. [•] We find eight different spectral units. [•] We analyze their distribution on Rhea’ surface. [•] We estimate water ice and contaminants abundance variation, and ice grain size. [•] We compare results obtained for Rhea and Dione. [ABSTRACT FROM AUTHOR]

Highlights: [•] We apply the SAM classification method to 132 infrared VIMS cubes of Dione. [•] We find nine different spectral units. [•] We analyze their distribution on the surface of Dione. [•] We estimate water ice and contaminants abundance variation, and ice grain size. [•] We compare infrared VIMS spectra of Dione and Helene. [Copyright &y& Elsevier]

We have compared spectroscopic data of Sputnik Planitia on Pluto, as acquired by New Horizons' Linear Etalon Imaging Spectral Array (LEISA) instrument, to the geomorphology as mapped by White et al. (2017) using visible and panchromatic imaging acquired by the LOng-Range Reconnaissance Imager (LORRI) and the Multi-spectral Visible Imaging Camera (MVIC). We have focused on 13 of the geologic units identified by White et al. (2017) , which include the plains and mountain units contained within the Sputnik basin. We divided the map of Sputnik Planitia into 15 provinces, each containing one or more geologic units, and we use LEISA to calculate the average spectra of the units inside the 15 provinces. Hapke-based modeling was then applied to the average spectra of the units to infer their surface composition, and to determine if the composition resulting from the modeling of LEISA spectra reflects the geomorphologic analyses of LORRI data, and if areas classified as being the same geologically, but which are geographically separated, share a similar composition. We investigated the spatial distribution of the most abundant ices on Pluto's surface - CH 4 , N 2 , CO, H 2 O, and a non-ice component presumed to be a macromolecular carbon-rich material, termed a tholin, that imparts a positive spectral slope in the visible spectral region and a negative spectral slope longward of ~1.1 μm. Because the exact nature of the non-ice component is still debated and because the negative spectral slope of the available tholins in the near infrared does not perfectly match the Pluto data, for spectral modeling purposes we reference it generically as the negative spectral slope endmember (NSS endmember). We created maps of variations in the integrated band depth (from LEISA data) and areal mass fraction (from the modeling) of the components. The analysis of correlations between the occurrences of the endmembers in the geologic units led to the observation of an anomalous suppression of the strong CH 4 absorption bands in units with compositions that are dominated by H 2 O ice and the NSS endmember. Exploring the mutual variation of the CH 4 and N 2 integrated band depths with the abundance of crystalline H 2 O and NSS endmember revealed that the NSS endmember is primarily responsible for the suppression of CH 4 absorptions in mountainous units located along the western edge of Sputnik Planitia. Our spectroscopic analyses have provided additional insight into the geological processes that have shaped Sputnik Planitia. A general increase in volatile abundance from the north to the south of Sputnik Planitia is observed. Such an increase first observed and interpreted by Protopapa et al., 2017 and later confirmed by climate modeling (Bertrand et al., 2018) is expressed geomorphologically in the form of preferential deposition of N 2 ice in the upland and mountainous regions bordering the plains of southern Sputnik Planitia. Relatively high amounts of pure CH 4 are seen at the southern Tenzing Montes, which are a natural site for CH 4 deposition owing to their great elevation and the lower insolation they are presently receiving. The NSS endmember correlates the existence of tholins within certain units, mostly those coating the low-latitude mountain ranges that are co-latitudinal with the tholin-covered Cthulhu Macula. The spectral analysis has also revealed compositional differences between the handful of occurrences of northern non-cellular plains and the surrounding cellular plains, all of which are located within the portion of Sputnik Planitia that is presently experiencing net sublimation of volatiles, and which do not therefore exhibit a surface layer of bright, freshly-deposited N 2 ice. The compositional differences between the cellular and non-cellular plains here hint at the effectiveness of convection in entraining and trapping tholins within the body of the cellular plains, while preventing the spread of such tholins to abutting non-cellular plains. • The average spectra of Pluto's Sputnik Planitia are analyzed. • The average spectra were modeled by using a Hapke-based modeling. • Correlations between the occurrences of the endmembers in the geologic units were investigated. • A suppression of the strong CH4 absorption bands occurs in units dominated by H2O ice and the blue endmember. [ABSTRACT FROM AUTHOR]

The data returned from NASA’s New Horizons spacecraft have given us an unprecedented, detailed look at the Pluto system. New Horizons' Ralph/MVIC (Multispectral Visible Imaging Camera) is composed of 7 independent CCD arrays on a single substrate. Among these are a red channel (540–700 nm), near-infrared channel (780–975 nm), and narrow band methane channel (860–910 nm). By comparing the relative reflectance of these channels we are able to produce high-resolution methane “equivalent width” (based on the 890 nm absorption band) and spectral slope maps of Pluto’s surface. From these maps we can then quantitatively study the relationships between methane distribution, redness, and other parameters like latitude and elevation. We find Pluto’s surface to show a great diversity of terrains, particularly in the equatorial region between 30°N and 30°S latitude. Methane “equivalent width” also shows some dependence on elevation (while spectral slope shows very little). [ABSTRACT FROM AUTHOR]

The July 2015 encounter of the Pluto system by the NASA New Horizons spacecraft has facilitated the study of Pluto's origin, surface processes, volatile transport cycles, and the energetics and chemistry of its atmosphere in an unprecedented level of detail. Earle et al. (2018b) presented the highest spatial resolution composition maps of Pluto using data from the Ralph/MVIC instrument and provided a global interpretation of the maps. Here we build upon that work and leverage MVIC's high spatial resolution to study the volatile distribution in and around craters to better understand how small scale topography affects volatile transport. We find that the compositional morphology in and around craters in our study can be divided into four different latitudinal bands, where differences are found for distribution trends in nitrogen, methane, and organic signatures in crater floors, walls, and surrounding slopes. We summarize the compositional characteristics of a "typical" crater in each latitude band, provide some possible explanation for the distribution based on current volatile transport models, and highlight some questions to be addressed by ongoing models. • Use data from New Horizon's Ralph/MVIC instrument to study volatile distribution. • Leverage high spatial resolution to study how small-scale topography effects volatile transport. • Identify latitudinal trends in volatile distribution in and around craters. [ABSTRACT FROM AUTHOR]