a new look at the saturn system the voyager 2 images voyager 2 photography has complemented that of voyager i in revealing many additional characteristics of saturn and its satellites and rings saturn s atmosphere contains persistent oval cloud features reminiscent of features on jupiter smaller irregular features track out a pattern of zonal winds that is symmetric about saturn s equator and appears to extend to great depth winds are predominantly eastward and reach 500 meters per second at the equator titan has several haze layers with significantly varying optical properties and a northern polar collar that is dark at short wavelengths several satellites have been photographed at substantially improved resolution enceladus surface ranges from old densely cratered terrain to relatively young uncratered plains crossed by grooves and faults tethys has a crater 400 kilometers in diameter whose floor has domed to match tethys surface curvature and a deep trench that extends at least 270 around tethys circumference hyperion is cratered and irregular in shape iapetus bright trailing hemisphere includes several dark floored craters and phoebe has a very low albedo and rotates in the direction opposite to that of its orbital revolution with a period of 9 hours within saturn s rings the birth of a spoke has been observed and surprising azimuthal and time variability is found in the ringlet structure of the outer b ring these observations lead to speculations about saturn s internal structure and about the collisional and thermal history of the rings and satellites

apollo 16 regolith breccias characterization and evidence for early formation in the mega regolith all of the apollo 16 regolith breccias 8 specimens have been characterized in terms of their petrography grain size distribution porosity major and trace element composition noble gas contents and ferromagnetie resonance properties these breccias vary signkqcantly with respect to their density and porosity with the more dense breccias showing significant shock damage the regolith breccias resemble the soils in grain size distribution and in the relative proportions of major petrological components except agglutinates many of the breecias are compositionally different from the apollo 16 soils in that they lack an important marie component present in the soils although some groupings occur the petrologic and chemical compositions of the regolith breedas do not correlate with the station location of the samples all but one of the breceias show some evidence of irradiation at the lunar surface solar gases measurable fmr agglutinates and analyses made on grain size separates from two disaggregated breedas indicate that this irradiation occurred before compaction when the breccia material was finely disseminated on the surface however the concentrations of surface irradiation parameters solar gases fmr agglutinates for most breedas are far less than seen in any lunar soils or in regolith breccias from other apollo missions several breedas also contain unusually high trapped 4oar 36ar ratios of 8 12 and a significant fission xe component in excess of that expected from in situ production these observations suggest that the surface irradiation of these breedas occurred as early as 4 x 109 years ago we conclude that most of the apollo 16 regolith breedas were not formed from any known apollo 16 soil they appear to be well comminuted material that contains ancient regolith developed during the late stage heavy bombardment of the moon when large impacts were much more common relative to small impacts so that regoliths did not have time to significantly mature before being diluted by fresh ejecta and buffed this ancient megaregolith is significantly different from more recent lunar regolith but may be similar to asteroidal regoliths from which some brecciated meteorites have formed

cassini imaging science initial results on phoebe and iapetus the cassini imaging science subsystem acquired high resolution imaging data on the outer saturnian moon phoebe during cassini s close flyby on 11 june 2004 and on iapetus during a flyby on 31 december 2004 phoebe has a heavily cratered and ancient surface shows evidence of ice near the surface has distinct layering of different materials and has a mean density that is indicative of an ice rock mixture iapetus s dark leading side cassini regio is ancient heavily cratered terrain bisected by an equatorial ridge system that reaches 20 kilometers relief local albedo variations within and bordering cassini regio suggest mass wasting of ballistically deposited material the origin of which remains unknown

geochemistry of grain size fractions of luna 24 soil comments on the lunar regolith chemistry and petrology of luna 24 grain size fractions by j c laul o d rode s b simon and j j papike

compositional maps of saturn s moon phoebe from imaging spectroscopy the origin of phoebe which is the outermost large satellite of saturn is of particular interest because its inclined retrograde orbit suggests that it was gravitationally captured by saturn having accreted outside the region of the solar nebula in which saturn formed by contrast saturn s regular satellites with prograde low inclination circular orbits probably accreted within the sub nebula in which saturn itself formed here we report imaging spectroscopy of phoebe resulting from the cassini huygens spacecraft encounter on 11 june 2004 we mapped ferrous iron bearing minerals bound water trapped co2 probable phyllosilicates organics nitriles and cyanide compounds detection of these compounds on phoebe makes it one of the most compositionally diverse objects yet observed in our solar system it is likely that phoebe s surface contains primitive materials from the outer solar system indicating a surface of cometary origin

the geomorphology of rhea implications for geologic history and surface processes analyses of landforms on rhea are used to define three physiographic provinces cratered terrain 1 undifferentiated cratered terrain 1 lineated cratered terrain 2 for which stratigraphic relationships are derived and examined in relation to major impact basins and tectonic features the formation of multiringed basins may have caused or at least controlled the locations of major resurfacing and mantling events the diameters of central peaks relative to impact crater diameters are significantly larger than those within craters on the moon and mercury rim segments of polygonal craters have preferential orientations both crater and noncrater lineaments show regional orientations that do not fit current global or regional stress models superposition relationships of provinces and associated features imply the following postaccretional sequence for the geological evolution of rhea s surface cratered terrain 1 undifferentiated formed first then linear troughs and chains of coalescing pits developed extensively on cratered terrain 1 lineated a resurfacing event emplaced cratered terrain 2 on which small craters scarps and ridges formed small grooves on cratered terrain 1 undifferentiated are tentatively assigned a young age based on their susceptibility to impact erosion this geologic history is generally consistent with theoretical models for rhea s evolution

albedo and color maps of the saturnian satellites abstract maps of the normal reflectances and color ratios 0 58 0 41 m have been prepared from voyager images for the following saturian satellites mimas enceladus tethys dione and rhea albedo and color variegations on these objects are in general much less than those of the galilean satellites enceladus and mimas have no albedo or color variegations greater than 10 in the observed regions of their surfaces with the exception of a small high albedo area in the southern polar region of enceladus which may be similar to the bright wispy streaks linea on rhea and dione we find an albedo dichotomy of 20 between the leading bright and trailing sides of dione and confirm a similar dichotomy found by verbiscer and veverka icarus 1989 82 336 for rhea this dichotomy is not as marked in the color maps differences of 5 10 were found for the hemispheres of these two satellites unlike the galilean satellites there is little general correlation between color and albedo the only clear example we could find of the expected result that higher albedo surfaces are bluer is for the bright wispy streaks linea on the trailing sides of rhea and dione on tethys we see two lower albedo features the one on the trailing side is redder than the ambient terrain whereas the one on the leading side is bluer there is little correlation between mapped geologic units and features and the color albedo patterns rhea and the trailing side of dione are the only examples where correlations exist the higher albedo photometrically bland leading sides of tethys dione and rhea suggest enhanced erosion of this hemisphere by meteoritic and cometary impact in addition the optical properties of these satellites may be affected by two exogenic processes not considered extensively in previous studies alteration of the surfaces by ultraviolet radiation and accretion of particles from saturn s e ring

thermal properties of rhea s poles evidence for a meter deep unconsolidated subsurface layer abstract cassini s composite infrared spectrometer cirs observed both of rhea s polar regions during a close 2000 km flyby on 9th march 2013 during orbit 183 rhea s southern pole was again observed during a more distant 51 000 km flyby on 10th february 2015 during orbit 212 the results show rhea s southern winter pole is one of the coldest places directly observed in our solar system surface temperatures of 25 4 7 4 k and 24 7 6 8 k are inferred from orbit 183 and 212 data respectively the surface temperature of the northern summer pole inferred from orbit 183 data is warmer 66 6 0 6 k assuming the surface thermophysical properties of the two polar regions are comparable then these temperatures can be considered a summer and winter seasonal temperature constraint for the polar region orbit 183 will provide solar longitude ls coverage at 133 and 313 for the summer and winter poles respectively while orbit 212 provides an additional winter temperature constraint at ls 337 seasonal models with bolometric albedo values between 0 70 and 0 74 and thermal inertia values between 1 and 46 j m 2 k 1 s 1 2 otherwise known as mks units can provide adequate fits to these temperature constraints assuming the winter temperature is an upper limit both these albedo and thermal inertia values agree within the uncertainties with those previously observed on both rhea s leading and trailing hemispheres investigating the seasonal temperature change of rhea s surface is particularly important as the seasonal wave is sensitive to deeper surface temperatures tens of centimeters to meter depths than the more commonly reported diurnal wave typically less than a centimeter the exact depth difference dependent upon the assumed surface properties for example if a surface porosity of 0 5 and thermal inertia of 25 mks is assumed then the depth of the seasonal thermal wave is 76 cm which is much deeper than the 0 5 cm probed by diurnal studies of rhea howett et al 2010 the low thermal inertia derived here implies that rhea s polar surfaces are highly porous even at great depths analysis of a cirs focal plane 1 10 600 cm 1 stare observation taken during the orbit 183 encounter between 16 22 33 and 16 23 26 ut centered on 71 7 w 58 7 s provides the first analysis of a thermal emissivity spectrum on rhea the results show a flat emissivity spectrum with negligible emissivity features a few possible explanations exist for this flat emissivity spectrum but the most likely for rhea is that the surface is both highly porous and composed of small particles

three dimensional spectral analysis of compositional heterogeneity at arruntia crater on 4 vesta using dawn fc abstract we introduce an innovative three dimensional spectral approach three band parameter space with polyhedrons that can be used for both qualitative and quantitative analyzes improving the characterization of surface compositional heterogeneity of 4 vesta it is an advanced and more robust methodology compared to the standard two dimensional spectral approach two band parameter space the dawn framing camera fc color data obtained during high altitude mapping orbit resolution 60 m pixel is used the main focus is on the howardite eucrite diogenite hed lithologies containing carbonaceous chondritic material olivine and impact melt the archived spectra of heds and their mixtures from relab hoserlab and usgs databases as well as our laboratory measured spectra are used for this study three dimensional convex polyhedrons are defined using computed band parameter values of laboratory spectra polyhedrons based on the parameters of band tilt r0 92 m r0 96 m mid ratio r0 75 m r0 83 m r0 83 m r0 92 m and reflectance at 0 55 m r0 55 m are chosen for the present analysis an algorithm in idl programming language is employed to assign fc data points to the respective polyhedrons the arruntia region in the northern hemisphere of vesta is selected for a case study because of its geological and mineralogical importance we observe that this region is eucrite dominated howarditic in composition the extent of olivine rich exposures within an area of 2 5 crater radii is 12 larger than the previous finding thangjam g et al 2014 meteorit planet sci 49 1831 1850 lithologies of nearly pure cm2 chondrite olivine glass and diogenite are not found in this region although there are no unambiguous spectral features of impact melt the investigation of morphological features using fc clear filter data from low altitude mapping orbit resolution 18 m pixel suggests potential impact melt features inside and outside of the crater our spectral approach can be extended to the entire vestan surface to study the heterogeneous surface composition and its geology

the lunar regolith chemistry mineralogy and petrology the lunar regolith a several meter thick layer of unconsolidated debris forms the interface between the moon and its space environment the regolith forms from lithic sources by the destructional processes of comminution and the constructional processes of agglutinate formation in this manner a steady state soil can develop and will remain in a type of dynamic equilibrium until the system is disturbed by burial or mixing with new soil mixing takes place mainly on a local scale vertically through meters and horizontally over several kilometers lateral transport is a relatively inefficient process and therefore most of the lunar soil components were derived locally there is no evidence for preferential transport of the finer soil fractions relative to the coarser fractions the truly exotic derived at distances of tens of kilometers component is generally in low abundance 1 therefore remotely sensed data should provide a reasonably accurate picture of bedrock geology the chemical composition of the regolith varies with grain size the 10 m fraction is chemically fractionated from the bulk soil in most cases the 10 m fraction is enriched in al2o3 cao na2o k2o light rare earth elements and th and depleted in mgo feo mno and sc these systematics are largely a result of simple comminution with feldspar and friable mesostasis from local source rocks concentrating in the finest fraction there is evidence that agglutinate glass forms preferentially by fusion of the finest soil fractions therefore agglutinate glass like the 10 m soil fraction appears to be fractionated from bulk soil compositions highland soils are distinct from mare soils both chemically and petrologically soil samples collected near mare highland contacts are mixtures of the two lithologies mineral chemical systematics of monomineralic fragments in the lunar soil provide important clues to soil provenance they can in some cases sort out the highland mare contributions and in special cases can even further pinpoint a lithic source in theory lunar regolith cores can serve as solar probes recording the sun s activity over billions of years in practice this has generally not been the case the formation and evolution of most cores is still poorly understood for most we have not established how they formed for example how many depositional and erosional events were involved what the time span involved in the accretion of the sampled soil column was and how long that soil column has remained in situ without this information it is difficult if not impossible to read the sun s record more interdisciplinary studies on cores must be carried out before they can be used as solar probes

mineralogical analysis of quadrangle ac h 10 rongo on the dwarf planet ceres abstract quadrangle ac h 10 rongo lat 22 s to 22 n lon 288 360 e shows a fairly homogeneous topography with the presence of notable elevations such as ahuna mons liberalia mons and part of samhain and uhola catenae the deepest areas correspond to the rongo crater region the areas between samhain and uhola catenae and the region of the quadrangle south of ahuna mons a substantial variability in the 2 7 m band depth distribution is observed across the rongo quadrangle indicating an east west gradient in the abundance of mg phyllosilicates the nh4 phyllosilicates distribution appears quite homogeneous except some localized regions such as crater haulani s ejecta the flanks of ahuna mons and crater begbalel the two band depths at 2 7 and 3 1 m display an overall low correlation suggesting a variable degree of mixing between mg phyllosilicates and nh4 phyllosilicates at the local scale mineralogical phases other than phyllosilicates are observed quadrangle rongo includes sodium carbonate rich regions such as the flanks of ahuna mons the ejecta of xevioso crater located in the southern edge of liberalia mons and crater begbalel which often display a reduction in both the 2 7 and 3 1 m band depths associated with an increased band depth at 4 m related to the presence of na rich carbonate phases this suggests recent hydrothermal activity in this area due to several episodes of cryovolcanism or impacts that unveiled a peculiar composition in the shallow subsurface alternatively the crust in this region might show a variable degree of compactness such that the formation of na carbonates is favored only in specific locations de sanctis et al 2016 ruesch et al 2016 zambon et al 2017 from a geological standpoint quadrangle ac h 10 rongo shows a correlation between its two main geologic units platz et al 2017 and the distribution of mg phyllosilicates suggesting a link between geology and mineralogy in this area

spectrophotometry and organic matter on iapetus 2 models of interhemispheric asymmetry abstract the albedo asymmetry of iapetus is unique in the solar system many models have been proposed to explain why the leading hemisphere has a reflectance 10 20 times lower than the trailing hemisphere and the poles compositional and observational constraints appear to rule out many of these models little attempt has been made to explain why of all the moons in the solar system only iapetus displays such properties the photometric differences between phoebe and the dark material on iapetus and the expectation that accreted dust from phoebe would darken the poles more than the antapex of orbital motion on iapetus make the phoebe dust model inconsistent with observations other models that instead have iapetus accreting circumsaturnian material coming from either hyperion or iapetus itself are also beset by an inability to explain the bright poles the endogenous extrusion of dark organics by itself is ruled out since it is extremely unlikely that this model would produce elliptical albedo contours centered on the apex of orbital motion the modern impact flux does not deliver enough kinetic energy to iapetus s surface to vaporize significant quantities of water ice and produce a lag deposit also impact vaporization is expected to form a similar lag deposit on the trailing hemisphere our most optimistic estimate of the amount of organic material that accumulates on the surface from in situ radiation synthesis of solid organics from methane clathrate is more than sufficient to explain the albedo and spectrum this process however is more effective on the trailing than leading hemisphere so the reverse asymmetry is expected iapetus s asymmetry is best explained by a thick primordial low albedo subsurface layer of organics exhumed by impact erosion the layer may be the consequence of ancient thermochemistry in iapetus s interior processing methane and or hcn into dark organic matter which was then extruded over the entire surface the model requires a thin layer of nearly pure water ice either exogenous or endogenous deposited over the dark organics subsequent impacts would have preferentially eroded the ice on the leading hemisphere revealing the underlying dark material the uniqueness of iapetus s albedo asymmetry can be understood by its impact induced erosion rate size and formation distance from the sun and saturn a combination of parameters duplicated nowhere else in the solar system tests of these conclusions can be made by cassini

space time variability of low streamflows in river networks a low flow equation is derived from darcy s law and a mass balance equation for base flow from a hillside by assuming that groundwater recharge is constant over short time periods this low flow equation reduces to many of the existing mechanistic low flow equations but in its general form looks like a linear regression model and captures spatial variability in base flow among hillsides in a basin as a result it unifies the mechanics and statistics of low flows in river networks this equation is tested against low flow data from the flint river basin in georgia and the gasconade river basin in missouri both of which are approximately 7000 km2 in size

grain size evolution and fractionation trends in an experimental regolith the comminution of blocky planetary surfaces into fine grained regoliths was simulated by impacting a fragmental gabbro target 200 times with stainless steel projectiles diameter 6 35 mm mass 1 2g vi 1 35 km s initially the target fragments were 2 32 mm in size with a mean diameter of 15 2 mm which was reduced to 0 4 mm after 200 shots for the first 60 shots comminution was linear with cumulative kinetic energy and thus essentially linear with time the comminution efficiency however decreased at later stages this could be due to a change in fracture mechanism from predominantly intergranular to predominantly intragranular and or due to a change in partitioning of the projectile s kinetic energy from collisional fragmentation or large fragments at early times to cratering in a progressively finer grained medium at later stages mineral specific preferential comminution is abundantly observed in the modal make up of various grain size fractions plagioclase comminutes more readily than pyroxenes plagioclase initially present at 54 vol comprises typically 65 70 of the 125 250 m fraction pyroxenes initially at 33 are depleted to 20 25 this fractionation occurs in the earliest samples analyzed and is not a time dependent phenomenon bulk chemical analyses reveal a corresponding increase in al2o3 cao and na2o and a decrease in feo and mgo the finest grain sizes are generally the most severely affected by differential comminution similar if not exactly identical trends are abundantly documented for lunar soil samples these experimental findings illustrate that differential comminution is capable of producing fractionation in the finest grain sizes they diminish the need for prominent lateral and vertical transport of components otherwise foreign to a lunar soil sampling site as postulated by some workers on the basis of multivariate chemical mixing models

cassini vims observations of the galilean satellites including the vims calibration procedure the visual and infrared mapping spectrometer vims observed the galilean satellites during the cassini spacecraft s 2000 2001 flyby of jupiter providing compositional and thermal information about their surfaces the cassini spacecraft approached the jovian system no closer than about 126 jupiter radii about 9 million kilometers at a phase angle of 90 resulting in only sub pixel observations by vims of the galilean satellites nevertheless most of the spectral features discovered by the near infrared mapping spectrometer nims aboard the galileo spacecraft during more than four years of observations have been identified in the vims data analyzed so far including a possible 13c absorption in addition vims made observations in the visible part of the spectrum and at several new phase angles for all the galilean satellites and the calculated phase functions are presented in the process of analyzing these data the vims radiometric and spectral calibrations were better determined in preparation for entry into the saturn system treatment of these data is presented as an example of the vims data reduction calibration and analysis process and a detailed explanation is given of the calibration process applied to the jupiter data

thermal inertia and bolometric bond albedo values for mimas enceladus tethys dione rhea and iapetus as derived from cassini cirs measurements abstract spectra taken by cassini s composite infrared spectrometer cirs between 10 and 600 cm 1 17 1000 m of surface thermal emission of mimas enceladus tethys dione rhea and iapetus have been used to derive the thermal inertia and bolometric bond albedo values only an upper limit for the bolometric bond albedo of iapetus dark leading side could be determined due to the insensitivity of the thermal model to albedo when albedos are very low the thermal inertia in this region however is better constrained the cirs coverage of enceladus is extensive enough that the latitudinal variation in these values from 60 s to 70 n has been determined in 10 wide bins the bolometric bond albedos determined here are consistent with literature values which show the surface of the saturnian icy moons to be covered in ice contaminated to varying degrees the thermal inertia of the moons is shown to be in the range 9 20 j m 2 k 1 s 1 2 approximately 2 6 times lower than that of the galilean satellites implying a less well consolidated and more porous surface the thermal inertias of iapetus and phoebe are somewhat higher suggesting that the very low thermal inertias of satellites from rhea inwards may be related to their probable coating of e ring material latitudinal variations on the surface of enceladus show that the bolometric bond albedo and thermal inertia increase towards the active plume source at the south pole

dione s spectral and geological properties abstract we present a detailed analysis of the variations in spectral properties across the surface of saturn s satellite dione using cassini vims data and their relationships to geological and or morphological characteristics as seen in the cassini iss images this analysis focuses on a local region on dione s anti saturnian hemisphere that was observed by vims with high spatial resolution during orbit 16 in october 2005 the results are incorporated into a global context provided by vims data acquired within cassini s first 50 orbits our results show that dione s surface is dominated by at least one global process bombardment by magnetospheric particles is consistent with the concentration of dark material and enhanced co 2 absorption on the trailing hemisphere of dione independent of the geology local regions within this terrain indicate a special kind of resurfacing that probably is related to large scale impact process in contrast the enhanced ice signature on the leading side is associated with the extended ejecta of the fresh impact crater creusa 49 n 76 w although no geologically active regions could be identified dione s tectonized regions observed with high spatial resolution partly show some clean h 2 o ice implying that tectonic processes could have continued into more recent times

the small inner satellites of saturn shapes structures and some implications abstract properties of the small inner satellites of saturn are updated using final cassini image data the equatorial ridges on pan and atlas are morphologically structurally and gravitationally distinct from their cores and represent distinct additions to rather than modifications of the precursor bodies exposures of lineated substrates on pandora and epimetheus show a relationship between regolith grooves and structures in underlying bedrock structures exposed on epimetheus suggest formation at depth including filling or annealing of fractures these structures and sharp bedrock regolith boundaries indicate a history far more complex than simple rubble pile assembly these exposures of bedrock also indicate past removal of the expected regolith from large fractions of these object s surfaces late in their cratering records

nature distribution and origin of co2 on enceladus abstract we present the first map of co2 at the surface of enceladus using data obtained by the cassini visible infrared mapping spectrometer vims in order to measure the weak and narrow co2 absorption band depths around 4 26 m we improved 1 the calibration of vims spectra 2 the calculation of geographic coordinates and 3 the projection techniques we averaged multiple observations of a given area to obtain a signal to noise ratio high enough to map the co2 abundances co2 is reliably detected mostly in the south polar region this region includes active faults tiger stripes the highest observed surface temperatures and locations of active plume eruptions the occurrence here of co2 is consistent with an endogenic origin controlled by tectonics both pure co2 ice and complexed co2 are detected from the positions of absorption bands between 4 27 and 4 24 m the highest concentrations of co2 are between the main active faults of the south polar region where the surface temperature is low pure co2 ice deposits at the surface of enceladus are best modeled by the formation of gas pockets below the icy crust and above the surface of the internal ocean these pockets eventually release cold co2 gas 70 to 119 k at low velocity seeping between the tiger stripes matson et al 2018 icarus 302 18 26 co2 clathrate hydrates may form in the ocean and may be subsequently released when a co2 gas pocket blows out and erupts other mechanisms may contribute to reinforcing the anti correlation of the co2 distribution of any type with respect to the location of the tiger stripes such as successive sublimation of co2 and condensation on colder areas and partial frost cover by h2o releases from plume eruptions

saturn s icy satellites investigated by cassini vims ii results at the end of nominal mission abstract we report the detailed analysis of the spectrophotometric properties of saturn s icy satellites as derived by full disk observations obtained by visual and infrared mapping spectrometer vims experiment aboard cassini in this paper we have extended the coverage until the end of the cassini s nominal mission june 1st 2008 while a previous paper filacchione g and 28 colleagues 2007 icarus 186 259 290 hereby referred to as paper i reported the preliminary results of this study during the four years of nominal mission vims has observed the entire population of saturn s icy satellites allowing us to make a comparative analysis of the vis nir spectral properties of the major satellites mimas enceladus tethys dione rhea hyperion iapetus and irregular moons atlas prometheus pandora janus epimetheus telesto calypso phoebe the results we discuss here are derived from the entire dataset available at june 2008 which consists of 1417 full disk observations acquired from a variety of distances and inclinations from the equatorial plane with different phase angles and hemispheric coverage the most important spectrophotometric indicators as defined in paper i i f continua at 0 55 m 1 822 m and 3 547 m visible spectral slopes water and carbon dioxide bands depths and positions are calculated for each observation in order to investigate the disk integrated composition of the satellites the distribution of water ice respect to contaminants abundances and typical regolith grain properties these quantities vary from the almost pure water ice surfaces of enceladus and calypso to the organic and carbon dioxide rich hyperion iapetus and phoebe janus visible colors are intermediate between these two classes having a slightly positive spectral slope these results could help to decipher the origins and evolutionary history of the minor moons of the saturn s system we introduce a polar representation of the spectrophotometric parameters as function of the solar phase angle along radial distance and of the effective longitude interval illuminated by the sun and covered by vims during the observation in azimuth to better investigate the spatial distribution of the spectrophotometric quantities across the regular satellites hemispheres finally we report the observed spectral positions of the 4 26 m band of the carbon dioxide present in the surface material of three outermost moons hyperion iapetus and phoebe

a new look at the apollo 11 regolith and kreep although the apollo 11 mission landed in mare tranquillitatis 50 km from the nearest exposure of highlands small nonmare particles are conspicuous in the regolith the nonmare portion of the apollo 11 regolith is compositionally similar to the apollo 16 regolith at both sites most of the nonmare material is from the feldspathic highlands but some is mafic impact melt breccia with the chemical signature known as kreep for its high concentrations of k rare earth elements and p the composition of the apollo 11 regolith corresponds best to a mixture of 66 crystalline mare basalt 5 orange volcanic glass 20 material of the feldspathic highlands 8 kreep bearing impact melt breccia and 1 meteoritic material the volcanic glass and kreep bearing melt breccia components account for the high concentrations of mg and cr in the regolith the most kreep rich sample known from apollo 11 10085 1187 is an impact melt breccia that bears a strong textural and compositional similarity to a unique apollo 16 melt breccia 64815 although not of the maria such breccias are also not of the highlands provenance global data obtained from orbit show that kreep bearing materials are most common at low elevations in the imbrium procellarum region and are rare at high elevations thus as at apollo 16 the kreep bearing breccias of apollo 11 are probably ejecta from the imbrium impact into the low lying procellarum kreep terrane on the basis of these observation and others we suggest that the general acceptance of kreep as a material of the highlands is not supported by the data and results largely from historical accident

photometrically corrected global infrared mosaics of enceladus new implications for its spectral diversity and geological activity between 2004 and 2017 spectral observations have been gathered by the visual and infrared mapping spectrometer vims on board cassini brown et al 2004 during 23 enceladus close encounters in addition to more distant surveys the objective of the present study is to produce a global hyperspectral mosaic of the complete vims data set of enceladus in order to highlight spectral variations among the different geological units this requires the selection of the best observations in terms of spatial resolution and illumination conditions we have carried out a detailed investigation of the photometric behavior at several key wavelengths 1 35 1 5 1 65 1 8 2 0 2 25 2 55 and 3 6 m characteristics of the infrared spectra of water ice we propose a new photometric function based on the model of shkuratov et al 2011 when combined corrected mosaics at different wavelengths reveal heterogeneous areas in particular in the terrains surrounding the tiger stripes on the south pole and in the northern hemisphere around 30 n 90 w those areas appear mainly correlated to tectonized units indicating an endogenous origin potentially driven by seafloor hotspots

distribution of icy particles across enceladus surface as derived from cassini vims measurements abstract the surface of enceladus consists almost completely of water ice as the band depths of water ice absorptions are sensitive to the size of particles absorptions can be used to map variations of icy particles across the surface the visual and infrared mapping spectrometer vims observed enceladus with a high spatial resolution during three cassini flybys in 2005 orbits en 003 en 004 and en 011 based on these data we measured the band depths of water ice absorptions at 1 04 1 25 1 5 and 2 m these band depths were compared to water ice models that represent theoretically calculated reflectance spectra for a range of particle diameters between 2 m and 1 mm the agreement between the experimental vims and model values supports the assumption that pure water ice characterizes the surface of enceladus and therefore that variations in band depth correspond to variations in water ice particle diameters our measurements show that the particle diameter of water ice increases toward younger tectonically altered surface units with the largest particles exposed in relatively fresh surface material the smallest particles were generally found in old densely cratered terrains the largest particles 0 2 mm are concentrated in the so called tiger stripes at the south pole in general the particle diameters are strongly correlated with geologic features and surface ages indicating a stratigraphic evolution of the surface that is caused by cryovolcanic resurfacing and impact gardening

deciphering sub micron ice particles on enceladus surface 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 co2 nh3 ch4 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

cassini s geological and compositional view of tethys abstract the saturnian satellite tethys exhibits geological and spectral properties whose appearance nature and spatial distribution partly mirror those identified on the neighboring satellites dione and rhea or fit to the picture how spectral surface properties are expected to change from one satellite to the other within the inner saturnian system however we also identified spectral variations that are unique in the saturnian system whereas geologically young surface features are characterized by pure h2o ice composition with relatively large particles which match the particle sizes measured for fresh surface features also on dione and rhea geologically old weathered regions are dominated by submicron sized ice particles our investigations confirm that the odysseus impact event did not cause the formation of tethys extended graben system ithaca chasma on the contrary odysseus might be responsible for the n s trending icy bands that mark tethys surface in the center of its leading and trailing hemisphere

composition and evolution of the lunar crust in the descartes highlands apollo 16 samples from the north ray crater ejecta blanket apollo 16 were investigated by petrographic microscope electron microprobe instrumental neutron activation and xray fluorescence analyses and 40ar 39ar and rb sr dating techniques nine major groups of monomict and polymict breccias were defined on the basis of microscopic texture and these were further subdivided into chemical subgroups on the basis of characteristic elements such as al mg fe cr ree ni and co the polymict breccias fragmental breccias granulitic breccias and impact melt breccias are the result of multiple impact induced mechanical mixing and melting and of thermal and impact metamorphism of rock and mineral clasts derived from primordial igneous crustal rocks for calculations of mixing models it was found that end members consisting of the pristine igneous rock components present as discrete samples at the apollo 16 site and supplemented by kreep dunite and a meteoritic component yield the best fits for the composition of polymict breccias the end member rocks a re ferroan anorthosite various magnesian gabbronorites including sodic ferrogabbro and feldspathic lherzolite and spinei troctolite the following model is proposed for the composition and stratigraphy of the target for north ray crater the lower section of the stratigraphy is composed of a megabreccia with clasts of highly feldspathic polymict breccias kreep free old eastern highland rock suite interpreted as nectaris ejecta descartes formation the top section contains kreep bearing polymict breccias kreep bearing young western highland rock suite and appears to be similar to the lithologies found in the cayley plains this material interpreted as cayley formation may be a distant facies of imbrium basin ejecta deposits of the imbrium basin the petrographic differences between these two major selenographic units the descartes and the cayley formations in the apollo 16 area are more distinct than the chemical differences the petrographic and chemical composition of the primordial igneous upper crust in the regions of the nectaris and imbrium basins has been calculated by subtraction of the kreep and meteoritic components from the bulk composition of the descartes and cayley materials the nectaris crust which is better constrained consists of 86 87 a northosite 4 sodic ferrogabbro 0 5 1 3 feldspathic lherzolite 6 8 regular magnesian gabbronorite 1 8 2 8 dunite and 0 1 spinel troctolite a model for the evolution of the upper lunar crust in the descartes highlands is proposed on the basis of isotope ages and clast matrix relationships of polymict breccias essential features of this model in sequenial order are 1 development of multiple layers of kreep free early feldspathic fragmental megabreccias and impact melt sheets on the primordial crust in the time period from 4 4 aeons to the time of the nectaris impact which could have occurred as late as 3 85 aeons ago 2 excavation of these megabreccias by the nectaris event and deposition of a nectarian feldspathic fragmental megabreccia in the descartes area 3 introduction of kreep basaltic material into the upper crust mainly west and northwest of the descartes site and formation of kreepy impact melt sheets most probably from 4 05 to 3 80 aeons ago 4 imbrium impact at 3 8 aeons ago and deposition of kreep bearing imbrian feldspathic fragmental breccias at the descartes site which form the cayley formation and 5 redeposition mixing and melting of all preexisting breccias yielding kreep bearing and kreep poor post cayley fragmental breccias and melt ejecta glass bombs as the result of small impacts craters 1 5 km in diameter in the cayley plains and the descartes mountains respectively

the spectral parameter maps of ceres from nasa dawn vir data abstract this article presents the spectral parameter maps used in this surface composition of ceres special issue the definition and use of spectral parameters has always played a fundamental role in understanding the properties and composition of a planetary surface mapping proper spectral parameters shows the global mineralogical diversity across ceres in this work we discuss the production process of ceres spectral parameter maps derived by the data of the visible and infrared mapping spectrometer vir onboard nasa s dawn mission we describe the data processing of the vir spectra and the procedure to retrieve the geometries latitude longitude and illumination angles of the acquired data spectra and geometries are used to project and mosaic this data to produce geographic information system compatible spectral parameters maps of ceres an overview of the variability of the data across the quadrangles is given addressing the specific analysis to each quadrangle mapping paper included in this special issue

chemistry of the apollo 11 highland component chemical data 28 major minor and trace elements were obtained by instrumental neutron activation analysis inaa for 38 hand picked highland fragments 1 20 mg from coarse fines 10085 the apollo 11 highland chemical groups are represented by a range of petrographic types six major chemical highland groups are identified in the apollo 11 fragments these are 1 high k kreep 2 anorthosite e g 15415 60015 with 10 chondrite rare earth elements ree abundances a positive eu anomaly anorthosite with 30 chondrite abundances and a positive eu anomaly 3 anorthosite norite troctolite ant 67075 4 low k fra mauro lkfm 77135 5 anorthositic gabbro 68415 with no eu anomaly anorthositic gabbro 65055 67955 with a positive eu anomaly and anorthositic gabbro 68516 60015 with a negative eu anomaly and 6 apollo 11 dominant highland component 2 10 chondrite ree abundances with a positive 10 14 chondrite eu anomaly there are three newly recognized groups in the apollo 11 highland suite based on the ree patterns these are a ant with 5 chondrite la 22 chondrite abundances and a positive eu anomaly b 10 chondrite flat pattern with 14 chondrite positive eu anomaly and c 2 3 chondrite flat pattern with 10 chondrite positive eu anomaly the apollo 11 highland suite is very low in potassium non kreepy overall the apollo 11 highland suite is quite similar to the apollo 16 suite most previously recognized highland chemical groups are represented in the apollo 11 highland component

chemistry and petrology of apollo 12 drive tube 12027 modal and chemical data for 31 major minor and trace elements obtained by inaa for soils from four 5 cm depth intervals of drive tube 12027 show three compositional units within the core the upper 2 5 cm of 12027 represent part of the sharp crater rim crest deposit which has a total thickness of 23 cm chemical differences are attributed to addition of local mare rocks to the upper 2 cm and kreepy material to the lower stratigraphic layer 14 17 cm depth the coarser fractions 1000 90 90 20 and 20 10 pm are compositionally similar to each other but quite different from the 10 m fine fractions which are more feldspathic and enriched in incompatible lil elements correlation between fused soil contents and lil enrichments of the coarse fractions strongly suggests that agglutinates are derived from the fine fraction thus supporting the fusion of the finest fraction f3 model the trench soil 12033 from 15 cm depth is very similar to the 15 5 16 cm soil of core 12027 indicating that the apollo 12 regolith exhibits kreep enrichments at various depths and that exotic kreepy ejecta are wide spread at the apollo 12 site

mixing levels the apennine front soil component and compositional trends in the apollo 15 soils variations in concentrations of lithophile elements in samples of apollo 15 soil can be explained in terms of only four chemical components three components are represented by extrusive rock types found at the apollo 15 site mare basalt kreep basalt and the pyroclastic green glass associated with breccia 15426 the fourth component the highlands component can be represented by soil from the apennine front particularly the soil obtained from the 55 57 cm depth interval of station 2 core 15007 8 among samples of apennine front soil this one appears to be the least contaminated by mare materials and may be our most typical sample of the apennine front highlands although soil fron the apennine front is itself a complex mixture of many types of highlands rocks it behaves as a single component with respect to mixing with the other three rock type components the various subcomponents of the apennine front soil e g melt rock and anorthositic norite that have been used in some mixing models are not required as discrete components in order to explain the compositional variation among samples of apollo 15 soil most of this compositional variation results from mare highlands mixing i e apennine front soil with mare basalt kreep basalt which probably derives from local possibly unexposed sources is also a variable component of the soil and is most prevalent in the soil from stations lm 6 and 9

the dark side of iapetus abstract this paper presents new photometric and spectrophotometric observations of the dark leading hemisphere of saturn s satellite iapetus spectrophotometry from 0 3 1 0 um may 1979 shows the dark hemisphere to be very red similar to a few asteroids and the moon but with no spectral features attributable to olivine or pyroxene near infrared spectrophometry in the regions 1 4 2 5 um may 1981 and 3 0 3 8 um february 1981 reveals water ice absorption bands probably resulting from the polar caps intruding onto the dark hemisphere the reflectance of iapetus is unlike that of carbonaceous chondrites or c type asteroids and most closely resembles the reflectance and low albedo of carbonaceous organic residue from the murchison c2 carbonaceous chondrite the murchison material has the same red slope and a probable spectral feature near 0 6 um seen in iapetus data three hypotheses for the formation of the dark hemisphere are discussed in light of the observational data the favored hypothesis is that debris from phoebe or other unknown outer satellites of saturn impacts the dark hemisphere of iapetus as poynting robertson drag causes the debris to spiral toward saturn the high velocity impacts preferentially remove ice from the satellite s surface causing enrichment of included carbonaceous material intrinsic to iapetus the reflectance of phoebe itself is significantly different from that of iapetus suggesting that relatively little phoebe debris lies on the dark hemisphere there remains the possibility that the impacting debris originates from another body of composition similar to the murchison residue and that this material is exposed on the surface of iapetus

tethys lithospheric thickness and heat flux from flexurally supported topography at ithaca chasma 16 20 km surface heat fluxes are 18 30 mw m 2 for adopted strain rates of 10 17 10 14 s 1 these heat fluxes are more than 4 times higher than those calculated from thermal history models of tethys and indicate a strongly enhanced local heat flux associated with the formation of ithaca chasma we use crater size frequency counts and a lunar like impact chronology to fix the time of formation of ithaca chasma at 4 ga from present day ithaca chasma predates the odysseus basin and thus could not have been formed by this impact feature citation giese b r wagner g neukum p helfenstein and p c thomas 2007 tethys lithospheric thickness and heat flux from flexurally supported topography at ithaca chasma geophys res lett 34 l21203

baseflow recession and recharge as nonlinear storage processes discharge in many rivers is often fed by outflow from a shallow groundwater reservoir it is becoming clear that the outflow from this aquifer is not linearly proportional to storage as is commonly assumed in many algorithms numerical analysis of flow recession curves from about 100 river gauging stations instead reveals a nonlinear relationship between baseflow q and storage s for which the equation s aqb was adopted values of the exponent b are found by calibration to be between 0 and 1 but with a high concentration around 0 5 which is in accordance with the findings of other studies and theoretical approaches yielding b 0 5 for unconfined aquifers and relating the coefficient a to catchment properties primarily area and shape of basin pore volume and transmissivity this non linear reservoir function is proposed as a more realistic alternative to the linear reservoir function the relatively fast response of groundwater flow to rainfall is mainly a result of the increase of hydraulic head of the groundwater reservoir accelerating the exfiltration of old pre event water into the river bed as fissure and pore volumes communicate hydraulically it appears physically reasonable to model the system by one non linear reservoir for catchments or parts of them instead of applying independent parallel linear reservoirs the non linear reservoir algorithms are supported by an analytical derivation they are extended for the automatic separation of baseflow from a time series of daily discharge in rivers and the computation of storage and effective recharge of groundwater in river basins by inverse nonlinear reservoir routing the time series obtained allow the identification and quantification of long term changes to the water balance relationships between computed groundwater storage and observed groundwater level can also be established copyright 1999 john wiley sons ltd

spectral analysis of ahuna mons from dawn mission s visible infrared spectrometer ahuna mons is the highest mountain on ceres a unique complex in terms of size shape and morphology ahuna is bordered by flanks of the talus around its summit recent work by ruesch et al 2016 based on dawn s framing camera images shed light on the possible origin of ahuna mons according to ruesch et al 2016 ahuna mons is formed by a volcanic process involving the ascent of cryomagma and extrusion onto the surface followed by dome development and subsequent spreading here we analyzed in detail the composition of ahuna mons using data acquired by the visible and infrared spectrometer aboard dawn the spectral analysis reveals a relatively high abundance of carbonates and a non homogeneous variation in carbonates composition and abundance along ahuna s flanks associated with a lower amount of the ceres s ubiquitous nh4 phyllosilicates over a large portion of the flanks the grain size is coarser on the flanks than in the surrounding regions suggesting the presence of fresher material also compatible with a larger abundance of carbonates thermal variations are seen in ahuna supporting the evidence of different compactness of the surface regolith in specific locations results of the spectral analysis are consistent with a possible cryovolcanic origin which exposed fresher material that slid down on the flanks

mineralogical mapping of coniraya quadrangle of the dwarf planet ceres 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 m 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 m indicating the presence of na carbonates in the floor and ejecta ikapati gaue and other craters present smaller spectral features of nh4 and or oh stretching suggesting a volatile depletion process induced by the heating of the impact event

the mineralogy of ceres nawish quadrangle 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 nh4 phyllosilicates distribution the highlands in the eastern part of the quadrangle appear depleted in nh4 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 m 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 nh4 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

lunar regolith petrology of the 10 μm fraction it has been known for some time that the part of the lunar regolith smaller than 10 micrometers 10 m is chemically distinct from the bulk soil specifically it is enriched in al ca na k light rare earth elements and th and depleted in mg fe mn and sc three models have been proposed to explain those systematics the exotic component model holds that a fine grained kreepy exotic component was distributed on a global scale perhaps by the imbrian impact in the simple comminution model the 10 m chemical systematics are due to differential comminution processes with fine grained melt rock mesostasis and feldspar concentrating in this fraction the soil mixing model states that the chemical systematics are due to mixing of compositionally distinct soils that have different grain size distributions to determine which model is correct modal petrographic data were obtained by scanning transmission electron microscopy with energy dispersive x ray analysis for the 10 m fractions of four apollo soils 10084 14163 15271 and 64501 modal results are consistent with chemical data regarding feldspathic and kreep enrichments in the finest fraction soil glass contents crystalline silica and plagioclase mafic mineral ratios are greater in the 10 m fraction than in the coarser fractions for all soils grain size distributions are inconsistent with a fine grained exotic component derived from distant sources comminution of local lithologies vertical mixing and local lateral transport control the 10 m soil composition

particle deposition on the saturnian satellites from ephemeral cryovolcanism on enceladus the geologically active south pole of enceladus generates a plume of micron sized particles which likely form saturn s tenuous e ring extending from the orbit of mimas to titan interactions between these particles and satellites have been suggested though only as very thin surficial phenomena we scrutinize high resolution images with a newly developed numerical shape model of helene and find that the leading hemisphere of helene is covered by thick deposits of e ring particles which occasionally collapse to form gully like depressions the depths of the resultant gullies and near absence of small craters on the leading hemisphere indicate that the deposit is tens to hundreds of meters thick the ages of the deposits are less than several tens of my which coincides well with similar deposits found on telesto and calypso our findings as well as previous theoretical work collectively indicate that the cryovolcanic activity currently occurring on enceladus is ephemeral

the equatorial ridges of pan and atlas terminal accretionary ornaments in the outer regions of saturn s main rings strong tidal forces balance gravitational accretion processes thus unusual phenomena may be expected there the cassini spacecraft has recently revealed the strange flying saucer shape of two small satellites pan and atlas located in this region showing prominent equatorial ridges the accretion of ring particles onto the equatorial surfaces of already formed bodies embedded in the rings may explain the formation of the ridges this ridge formation process is in good agreement with detailed cassini images showing differences between rough polar and smooth equatorial terrains we propose that pan and atlas ridges are kilometers thick ring particle piles formed after the satellites themselves and after the flattening of the rings but before the complete depletion of ring material from their surroundings

spectroscopic classification of icy satellites of saturn ii identification of terrain units on rhea abstract dione is one of the largest and densest icy satellites of saturn its surface shows a marked asymmetry between its leading and trailing hemispheres the leading side being brighter than the trailing side which shows regions mantled by a dark veneer whose origin is likely exogenic in order to identify different terrain units we applied the spectral angle mapper sam classification technique to dione s hyperspectral images acquired by the visual and infrared mapping spectrometer vims onboard the cassini orbiter in the infrared range 0 88 5 12 m on a relatively limited portion of the surface of dione we first identified nine spectral endmembers corresponding to as many terrain units which mostly distinguish for water ice abundance and ice grain size we then used these endmembers in sam to achieve a comprehensive classification of the entire surface the analysis of the infrared spectra returned by vims shows that different regions of dione have variations in water ice bands depths in average ice grain size and in the concentration of contaminants such as co 2 and hydrocarbons which are clearly connected to morphological and geological structures generally the spectral units that classify optically dark terrains are those showing suppressed water ice bands a finer ice grain size and a higher concentration of carbon dioxide conversely spectral units labeling brighter regions have deeper water ice absorption bands higher albedo and a smaller concentration of contaminants we also considered vims cubes of the small satellite helene one of the two dione s trojan moons and we compared its infrared spectra to those of the spectral units found on dione we observe that the closest match between the spectra of the two satellites occurs for one of the youngest and freshest terrain units on dione the creusa crater region

cassini observes the active south pole of enceladus cassini has identified a geologically active province at the south pole of saturn s moon enceladus in images acquired by the imaging science subsystem iss this region is circumscribed by a chain of folded ridges and troughs at 55 s latitude the terrain southward of this boundary is distinguished by its albedo and color contrasts elevated temperatures extreme geologic youth and narrow tectonic rifts that exhibit coarse grained ice and coincide with the hottest temperatures measured in the region jets of fine icy particles that supply saturn s e ring emanate from this province carried aloft by water vapor probably venting from subsurface reservoirs of liquid water the shape of enceladus suggests a possible intense heating epoch in the past by capture into a 1 4 secondary spin orbit resonance

close cassini flybys of saturn s ring moons pan daphnis atlas pandora and epimetheus saturn s main ring system is associated with a set of small moons that are either embedded within it or interact with the rings to alter their shape and composition five close flybys of the moons pan daphnis atlas pandora and epimetheus were performed between december 2016 and april 2017 during the ring grazing orbits of the cassini mission data on the moons morphology structure particle environment and composition were returned along with images in the ultraviolet and thermal infrared the optical properties of the moons surfaces are determined by two competing processes contamination by a red material formed in saturn s main ring system and by accretion of bright icy particles or water vapor from volcanic plumes originating on the planet s moon enceladus

probing the regoliths of the classical uranian satellites are their surfaces mantled by a layer of tiny h2o ice grains abstract we investigate whether the surfaces of the classical moons of uranus are compositionally stratified with a thin veneer of mostly tiny h2o ice grains 2 m diameters mantling a lower layer composed of larger grains of h2o ice dark material and co2 ice 10 50 m diameters near infrared observations 1 2 5 m have determined that the h2o ice rich surfaces of these moons are overprinted by concentrated deposits of co2 ice found almost exclusively on their trailing hemispheres however best fit spectral models of longer wavelength datasets 3 5 m indicate that the spectral signature of co2 ice is largely absent and instead the exposed surfaces of these moons are composed primarily of tiny h2o ice grains to investigate possible compositional layering of these moons we have collected new data using the infrared array camera irac onboard the spitzer space telescope 3 5 m spectral modeling of these new data is consistent with prior analyses suggesting that the exposed surfaces of the uranian moons are primarily composed of tiny h2o ice grains furthermore analysis of these new data reveal that the trailing hemispheres of these moons are brighter than their leading hemispheres over the 3 to 5 m wavelength range except for miranda which displays no hemispherical asymmetries in its irac albedos our analyses also reveal that the surface of ariel displays five distinct regional scale albedo zones possibly consistent with the spatial distribution of co2 ice on this moon we discuss possible processes that could be enhancing the observed leading trailing albedo asymmetries exhibited by these moons as well as processes that could be driving the apparent compositional stratification of their near surfaces

the inner small satellites of saturn a variety of worlds more than a dozen small 150 km mean radius satellites occupy distinct dynamical positions extending from within saturn s classical rings to the orbit of dione the cassini mission has gradually accumulated image and spectral coverage of these objects to the point where some generalizations on surface morphology may be made objects in different dynamical niches have different surface morphologies satellites within the main rings display equatorial ridges the f ring shepherding satellites show structural forms and heavily cratered surfaces the co orbitals janus and epimetheus are the most lunar like of the small satellites satellites occupying libration zones trojan satellites have deep covering of debris subject to downslope transport small satellites embedded in ring arcs are distinctively smooth ellipsoids that are unique among small well observed solar system bodies and are probably relaxed effectively fluid equilibrium shapes indicative of mean densities of about 300 kg m 3

surface composition of hyperion hyperion saturn s eighth largest icy satellite is a body of irregular shape in a state of chaotic rotation the surface is segregated into two distinct units a spatially dominant high albedo unit having the strong signature of h2o ice contrasts with a unit that is about a factor of four lower in albedo and is found mostly in the bottoms of cup like craters here we report observations of hyperion s surface in the ultraviolet and near infrared spectral regions with two optical remote sensing instruments on the cassini spacecraft at closest approach during a fly by on 25 26 september 2005 the close fly by afforded us the opportunity to obtain separate reflectance spectra of the high and low albedo surface components the low albedo material has spectral similarities and compositional signatures that link it with the surface of phoebe and a hemisphere wide superficial coating on iapetus

saturn s icy satellites investigated by cassini vims iv daytime temperature maps abstract the spectral position of the 3 6 m continuum peak measured on cassini vims i f spectra is used as a marker to infer the temperature of the regolith particles covering the surfaces of saturn s icy satellites this feature is characterizing the crystalline water ice spectrum which is the dominant compositional endmember of the satellites surfaces laboratory measurements indicate that the position of the 3 6 m peak of pure water ice is temperature dependent shifting towards shorter wavelengths when the sample is cooled from about 3 65 m at t 123 k to about 3 55 m at t 88 k a similar method was already applied to vims saturn s rings mosaics to retrieve ring particles temperature filacchione g ciarniello m capaccioni f et al 2014 icarus 241 45 65 we report here about the daytime temperature variations observed on the icy satellites as derived from three different vims observation types a a sample of 240 disk integrated i f observations of saturn s regular satellites collected by vims during years 2004 2011 with solar phase in the 20 40 range corresponding to late morning early afternoon local times this dataset is suitable to exploit the temperature variations at hemispherical scale resulting in average temperature t t 88 k for enceladus t t 98 118 k for dione t 108 128 k for rhea t 118 128 k for hyperion t 128 148 and t 168 k for iapetus trailing and leading hemispheres respectively a typical 5 k uncertainty is associated to the temperature retrieval on tethys and dione for which observations on both leading and trailing hemispheres are available in average daytime temperatures higher of about 10 k on the trailing than on the leading hemisphere are inferred b satellites disk resolved observations taken at 20 40 km pixel 1 resolution are suitable to map daytime temperature variations across surfaces features such as enceladus tiger stripes and tethys equatorial dark lens these datasets allow to disentangle solar illumination conditions from temperature distribution when observing surface s features with strong thermal contrast c daytime average maps covering large regions of the surfaces are used to compare the inferred temperature with geomorphological features impact craters chasmatae equatorial radiation lenses and active areas and albedo variations temperature maps are built by mining the complete vims dataset collected in years 2004 2009 pre equinox and in 2009 2012 post equinox by selecting pixels with max 150 km pixel 1 resolution vims derived temperature maps allow to identify thermal anomalies across the equatorial lens of mimas and tethys a temperature t 115k is measured above enceladus damascus and alexandria sulci in the south pole region vims has the sensitivity to follow seasonal temperature changes on tethys dione and rhea higher temperature are measured above the south hemisphere during pre equinox and above the north hemisphere during post equinox epochs the measured temperature distribution appears correlated with surface albedo features in fact temperature increases on low albedo units located on tethys dione and rhea trailing hemispheres the thermal anomaly region on rhea s inktomi crater detected by cirs howett c j a spencer j r hurford t et al 2014 icarus 241 239 247 is confirmed by vims this area appears colder with respect to surrounding terrains when observed at the same local solar time

mimas photometric roughness and albedo map voyager imaging observations of mimas between 6 and 132 in phase angle provide sufficient data to model such surface characteristics as large scale roughness and directional scattering properties we have analyzed disk integrated and disk resolved voyager clear filter 0 48 m photometric data using a modified version of hapke s 1986 icarus 67 264 280 equation which accommodates anisotropic multiple scattering since near opposition observations are limited we assume mimas has a rhea like opposition surge with angular width h 0 066 and amplitude bo 0 55 we find a single scattering albedo o 0 951 0 002 a henyey greenstein asymmetry parameter g 0 213 0 005 and a macroscopic roughness parameter 30 1 the photometric roughness is greater than those derived in a similar manner from other bright icy satellite surfaces though comparable to the 30 determined for mimas by buratti 1985 icarus 61 208 217 who applied the hapke theory and the 30 25 found by mcewen 1987 personal communication who used fits to the minnaert k parameter to evaluate we find a geometric albedo pv 0 69 0 05 and phase integral q 0 78 0 05 corresponding to a spherical albedo a pvq 0 54 0 1 and a mean opposition magnitude vo 12 62 0 07 our photometric analysis is summarized in terms of an albedo map which reproduces the satellite s observed lightcurve and indicates that normal reflectance range from 0 64 on the leading hemisphere to 0 74 on the trailing one reflectances at extreme southern latitudes are a few percent higher than those at corresponding northern latitudes though in general the equatorial latitudes are brighter than the polar regions the photometric properties show no variation across the surface or relation to any particular terrain type

phoebe albedo map and photometric properties using clear filter images from voyager 2 effective wavelength 0 48 m we have constructed the first ever digital albedo map of saturn s moon phoebe most normal reflectances in this new map are between 0 07 and 0 11 the albedo histogram is largely bimodal suggesting that the satellite is covered predominantly by two different types of surface materials the highest albedos are confined to isolated quasi circular spots 40 to 100 km across including three spots of varying albedo in a band immediately south of the equator and one especially bright spot at latitude 60 n normal reflectance as high as 0 13 50 brighter than the average surface the bright northern spot and the brightest of the southern spots occur at approximately the same longitude an alignment that gives phoebe its significant rotational lightcurve the low resolution of the voyager images does not permit interpretation of the bright spots origin phoebe s global average photometric function was determined by combining the satellite s telescopic near opposition phase curve s kruseet al 1986 icarus68 168 175 with absolute disk resolved reflectances measured from the voyager images triaxial ellipsoid shape assumed with radii 115 110 and 105 km modeling of the telescopic observations supports the presence of a significant opposition surge although scatter in the data does not allow unambiguous determination of the surge s exact strength the derived photometric function is consistent with the idea that phoebe is a c type object probably a primitive captured body related to chiron pholus and the inhabitants of the kuiper belt the albedo map and photometric information will aid in the planning of high resolution cassini images of phoebe which will represent our first close look at this class of primitive outer solar system object

saturn s icy satellites and rings investigated by cassini vims iii radial compositional variability in the last few years cassini vims the visible and infrared mapping spectrometer returned to us a comprehensive view of the saturn s icy satellites and rings after having analyzed the satellites spectral properties filacchione g capaccioni f mccord t b coradini a cerroni p bellucci g tosi f d aversa e formisano v brown r h baines k h bibring j p buratti b j clark r n combes m cruikshank d p drossart p jaumann r langevin y matson d l mennella v nelson r m nicholson p d sicardy b sotin c hansen g hibbitts k showalter m newman s 2007 icarus 186 259 290 paper i and their distribution across the satellites hemispheres filacchione g capaccioni f clark r n cuzzi j n cruikshank d p coradini a cerroni p nicholson p d mccord t b brown r h buratti b j tosi f nelson r m jaumann r stephan k 2010 icarus 206 507 523 paper ii we proceed in this paper to investigate the radial variability of icy satellites principal and minor and main rings average spectral properties this analysis is done by using 2264 disk integrated observations of the satellites and a 12 700 pixels wide rings radial mosaic acquired with a spatial resolution of about 125 km pixel using different vis and ir spectral indicators e g spectral slopes and band depths we perform a comparative analysis of these data aimed to measure the distribution of water ice and red contaminant materials across saturn s system the average surface regolith grain sizes are estimated with different indicators through comparison with laboratory and synthetic spectra these measurements highlight very striking differences in the population here analyzed which vary from the almost uncontaminated and water ice rich surfaces of enceladus and calypso to the metal organic rich and red surfaces of iapetus leading hemisphere and phoebe rings spectra appear more red than the icy satellites in the visible range but show more intense 1 5 2 0 m band depths although their orbits are close to the f ring prometheus and pandora are different in surface composition prometheus in fact appears very water ice rich but at the same time very red at vis wavelengths these properties make it very similar to a b ring particles while pandora is bluer moving outwards we see the effects of e ring particles generated by enceladus plumes which contaminate satellites surfaces from mimas out to rhea we found some differences between tethys lagrangian moons calypso being much more water ice rich and bluer than telesto among outer satellites hyperion iapetus and phoebe we observe a linear trend in both water ice decrease and in reddening hyperion being the reddest object of the population the correlations among spectral slopes band depths visual albedo and phase permit us to cluster the saturnian population in different spectral classes which are detected not only among the principal satellites and rings but among co orbital minor moons as well these bodies are effectively the connection elements both in term of composition and evolution between the principal satellites and main rings finally we have applied hapke s theory to retrieve the best spectral fits to saturn s inner regular satellites from mimas to dione using the same methodology applied previously for rhea data discussed in ciarniello et al ciarniello m capaccioni f filacchione g clark r n cruikshank d p cerroni p coradini a brown r h buratti b j tosi f stephan k 2011 icarus 214 541 555

prediction of low flow indices in ungauged basins through physiographical space based interpolation low flow estimation is of great importance to assess the availability of water resources this study investigates the applicability of physiographical space based interpolation techniques for the prediction of low flow indices in ungauged basins basins for which discharge observations are sparse or unavailable the study considers 51 catchments located in a wide region of central italy for which several geomorphological and climatic descriptors are available the analysis applies both deterministic and geostatistical techniques for interpolating low flow indices in the physiographical space a jack knife cross validation procedure is applied in order to quantify the accuracy of each technique when it is applied to ungauged basins the results of the study show that physiographical space based interpolation is a viable approach for estimating low flow indices in ungauged basins and geostatistical techniques outperform deterministic techniques

iapetus surface variability revealed from statistical clustering of a vims mosaic the distribution of co2 abstract we present a detailed study of an iapetus mosaic of vims data with high spatial resolution 0 5 0 5 or 6 4 km pixel the spectra were taken in august 2007 and provide the highest vims spatial resolution data for this object during cassini s primary mission we analyze this set of data using a statistical clustering approach to reduce the analysis of a large number of data 10 4 spectra from 0 35 to 5 10 m to the study of seven representative groups accounting for 99 6 of the surface covered by the original sample we analyze the spectral absorption bands in the spectra of the different clusters indicative of different composition over the observed surface we find coherence between the distribution of the clusters and the geographical features on the surface we give special attention to the study of the water ice and co 2 bands we find that co 2 is widespread over the entire surface being studied including the bright and dark areas on iapetus surface and is probably trapped at the molecular level with other materials the strength of the co 2 band in the areas where both h 2 o and carbon bearing materials exist gives support to the hypothesis that this volatile is formed on the surface of iapetus as a product of irradiation of these two components finally we also compare the iapetus co 2 with that on other satellites confirming that there are evident differences on the center depth and width of the band on iapetus and phoebe where co 2 has been suggested to be endogenous