a 1 d evolutionary model for icy satellites applied to enceladus abstract we develop a long term 1 d evolution model for icy satellites that couples multiple processes water migration and differentiation geochemical reactions and silicate phase transitions compaction by self gravity and ablation the model further considers the following energy sources and sinks tidal heating radiogenic heating geochemical energy released by serpentinization or absorbed by mineral dehydration gravitational energy and insolation and heat transport by conduction convection and advection we apply the model to enceladus by guessing the initial conditions that would render a structure compatible with present day observations assuming the initial structure to have been homogeneous assuming the satellite has been losing water continually along its evolution we postulate that it was formed as a more massive more icy and more porous satellite and gradually transformed into its present day state due to sustained long term tidal heating we consider several initial compositions and evolution scenarios and follow the evolution for the age of the solar system testing the present day model results against the available observational constraints our model shows the present configuration to be differentiated into a pure icy mantle several tens of km thick overlying a rocky core composed of dehydrated rock at the center and hydrated rock in the outer part for enceladus it predicts a higher rock ice mass ratio than previously assumed and a thinner ice mantle compatible with recent estimates based on gravity field measurements although obviously the model cannot be used to explain local phenomena it sheds light on the internal structure invoked in explanations of localized features and activities

the temperature and width of an active fissure on enceladus measured with cassini vims during the 14 april 2012 south pole flyover abstract the width and temperature of the active fissures on saturn s satellite enceladus provide key observable constraints on physical models of these geyser like eruptions we analyze a sequence of high spatial resolution near infrared spectra acquired with vims at 0 025 s intervals during a 74 km altitude flyover of the south pole of enceladus by the cassini spacecraft on 14 april 2012 utc a thermal emission spectrum covering 3 to 5 m wavelengths was detected as the field of view crossed one of the four major fissures baghdad sulcus within 1 km of 82 36s latitude and 28 24w longitude we interpret this spectrum as thermal emission from a linear fissure with temperature 197 20 k and width 9 m at the above wavelengths the spectrum is dominated by the warmest temperature component looking downward into the fissure at only 13 from the vertical we conclude that our results measure the temperature of the interior fissure walls and the h 2 o vapor at depths within 40 m of the surface

cassini finds molecular hydrogen in the enceladus plume evidence for hydrothermal processes saturn s moon enceladus has a subsurface ocean covered by a layer of ice some liquid escapes into space through cracks in the ice which is the source of one of saturn s rings in october 2015 the cassini spacecraft flew directly through the plume of escaping material and sampled its chemical composition waite et al found that the plume contains molecular hydrogen h2 a sign that the water in enceladus ocean is reacting with rocks through hydrothermal processes see the perspective by seewald this drives the ocean out of chemical equilibrium in a similar way to water around earth s hydrothermal vents potentially providing a source of chemical energy science this issue p 155 1 see also p 132 2 1 lookup doi 10 1126 science aai8703 2 lookup doi 10 1126 science aan0444

limits of enceladus s ice shell thickness from tidally driven tiger stripe shear failure 1 enceladus s south polar thermal anomaly and water rich plumes suggest the existence of a subsurface ocean which is overlain by an ice shell of uncertain thickness our objective is to constrain enceladus s ice shell thickness through assessment of tidally driven coulomb failure of enceladus s tiger stripe faults we find that thin to moderate ice shell thicknesses 40 km support shear failure along the tiger stripes assuming low ice coefficients of friction 0 1 0 3 and shallow fault depths 3 km these results are marginally consistent with the minimum ice shell thickness which can permit convection within enceladus s ice shell a plausible scenario is one in which the heat loss and tectonic style of enceladus has changed through time with convection initiating in a thick ice shell and tiger stripe activity commencing as the ice shell thinned

cryoclastic origin of particles on the surface of enceladus analogous to volcanic deposits on earth we can infer eruption characteristics on enceladus from the relationship between particle size and distance from the vent we develop a model in which ice particles feeding plumes are accelerated by the gas we consider two cases drag limited and collision limited acceleration which link particle size to exit velocity after being ejected at the vent particles follow ballistic trajectories we fit the model to observations of particle size on the surface inferred from modeled vims data collected by the cassini spacecraft we obtain a relationship between gas temperature and characteristic acceleration length whereby lower gas temperatures require longer acceleration lengths the model shows that the large size of particles on the surface is consistent with the size of particles observed with the cda and vims instruments at heights of cassini flybys and the size of particles that reach escape velocity and are found in saturn s e ring

researching the earth and a few of its neighbors during my career our knowledge of erupting geysers and volcanoes in the solar system has exploded in this prefatory i tell how i became fascinated with high speed processes through studying meteorite impact dynamics and then how my initial idea of studying old faithful geyser as a volcanic analog led me to work not only on the dynamics of eruption of mount st helens in 1980 but also on geysers erupting on io a fiery satellite of jupiter triton a frigid satellite of neptune and enceladus an active satellite of saturn unforeseeably the study of these events also led to work on mineral thermodynamics and the hydraulics and geomorphic evolution of rapids in the grand canyon this is a narrative not a formal review article but the reader can find references in the related resources section to explore topics in more detail

solid tidal friction above a liquid water reservoir as the origin of the south pole hotspot on enceladus abstract earth jupiter s moon io and saturn s tiny moon enceladus are the only solid objects in the solar system to be sufficiently geologically active for their internal heat to be detected by remote sensing interestingly the endogenic activity on enceladus is only located on a specific region at the south pole from which jets of water vapor and ice particles have been observed spencer j r and 9 colleagues 2006 science 311 1401 1405 porco c c and 24 colleagues 2006 science 311 1393 1401 the current polar location of the thermal anomaly can possibly be explained by diapir induced reorientation of the satellite nimmo f pappalardo r t 2006 nature 441 614 616 but the thermal anomaly triggering and the heat power required to sustain it over geological timescales remain problematic using a three dimensional viscoelastic numerical model simulating the response of enceladus to tidal forcing we explore the effect of a low viscosity anomaly in the ice shell localized to the south polar region on the tidal dissipation patterns we demonstrate that only interior models with a liquid water layer at depth can explain the observed magnitude of dissipation rate and its particular location at the south pole moreover we show that tidally induced heat must be generated over a relatively broad region in the southern hemisphere and it is then transferred toward the south pole where it is episodically released during relatively short resurfacing events as large tidal dissipation and internal melting cannot be induced in the south polar region in the absence of a pre existing liquid decoupling layer we propose that liquid water must have been present in the interior for a very long period of time and possibly since the satellite formation owing to the orbital equilibrium requirement meyer j wisdom j 2007 icarus 188 535 539 sustaining some liquid water at depth is impossible if heat is continuously emitted at a rate of 4 8 gw at the south pole based on that requirement we propose that the current thermal emission is not in equilibrium with the heat production and that the thermal emission rate is abnormally high at present time alternatively continuous dissipation at a rate of 1 2 gw in the ice shell at the south pole should be sufficient to induce internal melting and it could sustain a layer of liquid water at depth over geologic timescales

geophysical evolution of saturn s satellite phoebe a large planetesimal in the outer solar system abstract saturn s satellite phoebe is the best characterized representative of large outer solar system planetesimals thanks to the close flyby by the cassini spacecraft in june 2004 we explore the information contained in phoebe s physical properties density and shape which are significantly different from those of other icy objects in its size range phoebe s higher density has been interpreted as evidence that it was captured probably from the proto kuiper belt first we demonstrate that phoebe s shape is globally relaxed and consistent with a spheroid in hydrostatic equilibrium with its rotation period this distinguishes the satellite from rubble piles that are thought to result from the disruption of larger proto satellites we numerically model the geophysical evolution of phoebe accounting for the feedback between porosity and thermal state we compare thermal evolution models for different assumptions on the formation of phoebe in particular the state of its water amorphous or crystalline we track the evolution of porosity and thermal conductivity as well as the destabilization of amorphous ice or clathrate hydrates while rubble piles may never reach temperatures suitable for porous ice to creep and relax we argue that phoebe s shape could have relaxed due to heat from the decay of 26al provided that this object formed less than 3 myr after the production of the calcium aluminum inclusions this is consistent with the idea that phoebe could be an exemplar of planetesimals that formed in the transneptunian region and later accreted onto outer planet satellites either during the satellite s formation stage or still later during the late heavy bombardment

efficiency of neutrino induced radio measurements to inspect local areas of enceladus abstract the cassini probe observed a young and smooth surface around the south pole of enceladus while around the north pole the surface was found to be relatively old and inactive porco c c et al 2006 science 311 1393 1401 this heterogeneous surface implies that the ice thickness of enceladus is not uniform between the north and south polar regions determining the thickness of the icy layer is important to confirm the existence of an internal ocean as well as to reveal the heating mechanism of enceladus we show that the measurement of radio waves induced by cosmic neutrinos can be an effective method to constrain the ice thickness of a localized area where conventional gravity or electromagnetic field measurements cannot be used this method could be used to constrain the thickness of the icy layer on enceladus even if the ice is a few tens of kilometers thick measuring over a period of several years which greatly exceeds the ability of radar sounding and hence could be used in future orbiter missions

bright carbonate surfaces on ceres as remnants of salt rich water fountains abstract vinalia and cerealia faculae are bright and salt rich localized areas in occator crater on ceres the predominance of the near infrared signature of sodium carbonate on these surfaces suggests their original material was a brine here we analyze dawn framing camera s images and characterize the surfaces as composed of a central structure either a possible depression vinalia or a central dome cerealia and a discontinuous mantling we consider three materials enabling the ascent and formation of the faculae ice ascent with sublimation and carbonate particle lofting pure gas emission entraining carbonate particles and brine extrusion we find that a mechanism explaining the entire range of morphologies topographies as well as the common composition of the deposits is brine fountaining this process consists of briny liquid extrusion followed by flash freezing of carbonate and ice particles particle fallback and sublimation subsequent increase in briny liquid viscosity leads to doming dawn observations did not detect currently active water plumes indicating the frequency of such extrusions is longer than years

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

enceladus an active ice world in the saturn system enceladus one of the mid sized icy moons of saturn has an importance to planetary science far greater than its modest 504 km diameter would suggest intensive exploration of enceladus by the cassini saturn orbiter has revealed that it is the only known icy world in the solar system with ongoing deep seated geological activity active tectonic fractures at enceladus s south pole dubbed tiger stripes warmed by internal tidally generated heat spew supersonic jets of water vapor other gases and ice particles into circum saturnian space a subsurface saltwater sea probably exists under the south pole between the ice shell and the silicate core because of evidence that liquid water is probably present at the jet sources enceladus is also of great astrobiological interest as a potential habitat for life

a clathrate reservoir hypothesis for enceladus south polar plume we hypothesize that active tectonic processes in the south polar terrain of enceladus the 500 kilometer diameter moon of saturn are creating fractures that cause degassing of a clathrate reservoir to produce the plume documented by the instruments on the cassini spacecraft advection of gas and ice transports energy supplied at depth as latent heat of clathrate decomposition to shallower levels where it reappears as latent heat of condensation of ice the plume itself which has a discharge rate comparable to old faithful geyser in yellowstone national park probably represents small leaks from this massive advective system

a possible brine reservoir beneath occator crater thermal and compositional evolution and formation of the cerealia dome and vinalia faculae abstract the dawn spacecraft has imaged several putative cryovolcanic features on ceres and several lines of evidence point to past cryovolcanic activity at occator crater it is therefore possible that cryovolcanism played a key role in delivering sodium carbonate and chloride enriched brines to ceres surface in recent geological times the detection of a 200 km 200 km negative bouguer anomaly beneath occator suggests the presence of a low density region beneath the crater if this region is a residual partially crystallized cryomagma chamber excess pressures caused by its gradual freezing or stresses produced by the occator forming impact could have facilitated the delivery of cryolavas to the surface in the geologically recent past here the progressive solidification of a cryomagma chamber beneath occator and implications for the delivery of cryolavas to the surface has been explored models for the behavior of cryolavas at ceres surface and for the formation of the cerealia dome and vinalia faculae are also presented minimal crystallization of a subsurface fluid reservoir located at the crust mantle boundary could have driven cryolavas enriched in chloride salts and nh3 to ceres surface however cryolavas enriched in sodium carbonates would have had to have existed at shallower levels in the crust in order to be delivered to the surface via pressure driven ascent depending on the size of the reservoir cryolavas could have been driven to ceres surface for tens to hundreds of millions of years after cooling of the cryomagma chamber commenced the mineralogy at occator is suggestive of subsurface cryomagma reservoirs enriched in sodium carbonate and chloride salts aqueous solutions enriched in chloride salts and or ammonia would have arrived at the surface at warm enough temperatures to erupt if transported in propagating fractures that traveled at least 10 5 m s additionally if the cerealia dome was formed from viscous cryolava extrusions bulk kinematic lava viscosities may have been between 106 108 m2 s at the onset of relaxation plausible relaxation times to form the dome which are linked to bulk cryolava rheology are found to have ranged from 2 5 to 273 days moreover the low volatile content necessary to drive explosive eruptions on ceres supports the possibility that cerealia and vinalia faculae were emplaced as a consequence of ballistic eruptions the enigmatic geology of occator crater is consistent with a diversity of exchange processes operating on ceres in the geologically recent past further the processes that have occurred at occator could shed light on the changing geology associated with a relic ocean world future studies of occator and ceres should be undertaken with these results in mind

the impact of a weak south pole on thermal convection in enceladus ice shell abstract enceladus exhibits a strong hemispheric dichotomy of tectonism and heat flux with geologically young heavily tectonized terrains and a high heat flux in the south polar terrain spt and relatively ancient terrains with presumably lower heat fluxes over the rest of the satellite to understand the convective pattern and its relationship with surface tectonics we present three dimensional numerical models of convection in enceladus ice shell including basal heating and tidal heating our thermal boundary conditions exhibit no north south asymmetries but because the tectonism at the spt may weaken the ice there we impose a mechanically weak lithosphere within the spt the weakening is parameterized by adopting a reduced viscosity contrast within the spt without such a weak zone convection if any resides in stagnant lid mode and exhibits no hemispheric dichotomy in the presence of such an spt weak zone however we find vigorous convection in the ice underneath the spt with convective plumes rising close to the surface in contrast only stagnant lid convection or no convection at all occurs elsewhere over the satellite away from the spt the heat flux in our models is small 5 10 mw m 2 and the surface strains are small enough to imply surface ages 10 9 years within the spt however our models yield peak heat fluxes of 70 200 mw m 2 implying heat flows integrated across the spt of up to 5 gw similar to that inferred from cassini thermal observations the surface strains in our models are high enough near the south pole to cause intense tectonism and imply surface ages of 10 6 10 7 years consistent with age estimates of the spt

convection in enceladus ice shell conditions for initiation 1 observations of enceladus by the cassini spacecraft indicate that this tiny saturnian moon is geologically active with plumes of water vapor and ice particles erupting from its southern polar region this activity suggests that tidal dissipation has become spatially localized perhaps due to a compositional rheological and or thermal anomaly in its ice shell here we examine the role that solid state convection may have played in enceladus prolific activity by creating a suitable rheological and thermal anomaly we find convection can only initiate in the pure water ice i shell of a differentiated enceladus if the ice grain size is less than 0 3 mm which is quite small but may be realistic if non water ice impurities and or tidal stresses keep grains from growing this grain size restriction becomes more severe for lower basal ice temperatures which implies that any ammonia present has not become strongly concentrated in a thin basal ocean while convection occurs for a maximally thick pure ice shell and underlying ocean convective heat flows are 7 11 mw m 2 for ice grain sizes of 0 1 0 3 mm compared with the 100 mw m 2 measured for enceladus south polar terrain from cassini cirs observations thus whereas solid state convection may be a prerequisite for enceladus geological activity the observed heat flow requires strong tidal dissipation within the convecting region and possibly that convection reaches the surface

thermal evolution of kuiper belt objects with implications for cryovolcanism abstract we investigate the internal thermal evolution of kuiper belt objects kbos small radii 2500 kg m 3 bodies orbiting beyond neptune focusing on pluto s moon charon in particular our calculations are time dependent and account for differentiation we review evidence for ammonia hydrates in the ices of kbos and include their effects on the thermal evolution a key finding is that the production of the first melt at the melting point of ammonia dihydrate 176 k triggers differentiation of rock and ice the resulting structure comprises a rocky core surrounded by liquids and ice enclosed within a 100 km thick undifferentiated crust of rock and ice this structure is especially conducive to the retention of subsurface liquid and bodies the size of charon or larger radii 600 km are predicted to retain some subsurface liquid to the present day we discuss the possibility that this liquid can be brought to the surface rapidly via self propagating cracks we conclude that cryovolcanism is a viable process expected to affect the surfaces of large kbos including charon

joule heating of the south polar terrain on enceladus 1 we report that joule heating in enceladus resulting from the interaction of enceladus with saturn s magnetic field may account for 150 kw to 52 mw of power through enceladus electric currents passing through subsurface channels of low salinity and just a few kilometers in depth could supply a source of power to the south polar terrain providing a small but previously unaccounted for contribution to the observed heat flux and plume activity studies of the electrical heating of jupiter s moon europa have concluded that electricity is a negligible heating source since no connection between the conductive subsurface and alfven currents has been observed here we show that contrary to results for the jupiter system electrical heating may be a source of internal energy for enceladus contributing to localized heating production of water vapor and the persistence of the tiger stripes this contribution is of order 0 001 0 25 of the total observed heat flux and thus joule heating cannot explain the total south polar terrain heat anomaly the exclusion of salt ions during refreezing serves to enhance volumetric joule heating and could extend the lifetime of liquid water fractures in the south polar terrain

one hundred km scale basins on enceladus evidence for an active ice shell 1 stereo derived topographic mapping of 50 of enceladus reveals at least 6 large scale ovoid depressions basins 90 175 km across and 800 to 1500 m deep and uncorrelated with geologic boundaries in contrast the south polar depression is larger and apparently shallower and correlates with active resurfacing the shape and scale of the basins is inconsistent with impact geoid surface deflections or with dynamically supported topography isostatic thinning of enceladus ice shell associated with upwellings and tidally driven ice melting can plausibly account for these basins thinning implies upwarping of the base of the shell of 10 20 km beneath the depressions depending on total shell thickness loss of near surface porosity due to enhanced heat flow may also contribute to basin lows alternatively the basins may overly cold inactive and hence denser ice but thermal isostasy alone requires thermal expansion more consistent with clathrate hydrate than water ice

sodium chloride as a geophysical probe of a subsurface ocean on enceladus 1 recent data from the cassini spacecraft suggest that an ocean exists inside saturn s satellite enceladus here we show that the size of an ocean can be estimated if the nacl concentration of the ocean is known we find that concentrations of aqueous nacl reported by postberg et al 2009 imply a relatively large ocean comprising at least 17 by mass of volatiles on enceladus structural calculations indicate that this ocean would underlie more of enceladus surface than just the geologically active south polar region consistent with modeling of localized tidal dissipation conduction calculations suggest that a half global ocean can be maintained by steady state tidal heating provided that clathrate hydrate dominates enceladus ice shell we also find that rapid freezing of oceanic water could release large fluxes of stored tidal heat perhaps partly explaining the anomalous energy output of enceladus an alternative saltier ocean model is also examined

three dimensional modeling of turbid density currents in imha reservoir south korea abstractthe propagation dynamics of the turbid density currents of the imha reservoir is investigated using the flow 3d computational fluid dynamics code the renormalization group rng e turbulence scheme in a reynolds averaged navier stokes rans framework was applied for the field investigation a new particle dynamics algorithm was developed and coupled with the flow 3d model to simulate the settling of sediment particles and the model was tested with field measurements during typhoon ewiniar the coupled model correctly predicted the spatial and temporal evolution of intrusive density currents with plunging flows at a depth of 20 m and interflows propagating downstream at about 0 2 m s the simulation results with sediment settling demonstrated that the ratio of transported to initial sediment concentration c0 ci varies as a function of particle size ds and sediment concentration density currents can be classified into three regimes 1 a suspended regime ds 10 m where interflows will

modeling europa s dust plumes the discovery of jupiter s moon europa maintaining a probably sporadic water vapor plume constitutes a huge scientific opportunity for nasa s upcoming mission to this galilean moon measuring properties of material emerging from interior sources offers a unique chance to understand conditions at europa s subsurface ocean exploiting results obtained for the enceladus plume we simulate possible europa plume configurations analyze particle number density and surface deposition results and estimate the expected flux of ice grains on a spacecraft due to europa s high escape speed observing an active plume will require low altitude flybys preferably at altitudes of 5 100 km at higher altitudes a plume may escape detection our simulations provide an extensive library documenting the possible structure of europa dust plumes which can be quickly refined as more data on europa dust plumes are collected

eruptions arising from tidally controlled periodic openings of rifts on enceladus the cassini flyby of 14 july 2005 revealed plumes of water vapour and ice associated with the tiger stripe features on the surface of saturn s icy moon enceladus since then the challenge has been to explain the nature of the plumes and the forces driving them two papers this week offer an explanation that accounts for both the plume characteristics and the presence of hot spots without the need to assume the existence of near surface liquid water a requirement of some previous models nimmo et al identify tidally driven lateral fault motions near the tiger stripes as the most likely drivers of heat and vapour production and hurford et al show that as enceladus orbits saturn the parent planet s tides make the satellite s ice flex this may cause the tiger stripes to open and close periodically exposing volatile gases and allowing them to be released plumes of gas have been seen near the south polar region of enceladus a small icy satellite of saturn and observations revealed large rifts in the crust informally called tiger stripes hurford et al report that during each orbit every portion of each tiger stripe rift spends about half the time in tension which allows the rift to open exposing volatiles and allowing eruptions plume activity is expected to vary periodically in 2005 plumes were detected near the south polar region of enceladus1 a small icy satellite of saturn observations of the south pole revealed large rifts in the crust informally called tiger stripes which exhibit higher temperatures than the surrounding terrain and are probably sources of the observed eruptions2 models of the ultimate interior source for the eruptions are under consideration1 3 4 5 other models of an expanding plume6 require eruptions from discrete sources as well as less voluminous eruptions from a more extended source to match the observations no physical mechanism that matches the observations has been identified to control these eruptions here we report a mechanism in which temporal variations in tidal stress open and close the tiger stripe rifts governing the timing of eruptions during each orbit every portion of each tiger stripe rift spends about half the time in tension which allows the rift to open exposing volatiles and allowing eruptions in a complementary process periodic shear stress along the rifts also generates heat along their lengths7 8 9 which has the capacity to enhance eruptions plume activity is expected to vary periodically affecting the injection of material into saturn s e ring10 and its formation evolution and structure moreover the stresses controlling eruptions imply that enceladus icy shell behaves as a thin elastic layer perhaps only a few tens of kilometres thick

no sodium in the vapour plumes of enceladus the discovery of water vapour and ice particles erupting from saturn s moon enceladus fuelled speculation that an internal ocean was the source alternatively the source might be ice warmed melted or crushed by tectonic motions sodium chloride that is salt is expected to be present in a long lived ocean in contact with a rocky core here we report a ground based spectroscopic search for atomic sodium near enceladus that places an upper limit on the mixing ratio in the vapour plumes orders of magnitude below the expected ocean salinity the low sodium content of escaping vapour together with the small fraction of salt bearing particles argues against a situation in which a near surface geyser is fuelled by a salty ocean through cracks in the crust the lack of observable sodium in the vapour is consistent with a wide variety of alternative eruption sources including a deep ocean6 a freshwater reservoir or ice the existing data may be insufficient to distinguish between these hypotheses

an oceanic composition on early and today s enceladus 1 the oceanic composition on saturn s moon enceladus is evaluated through calculations of thermochemical equilibria at hydrothermal and freezing settings conditions of rock alteration are constrained from assumptions and models for the moon s interior composition and thermal evolution and from the composition of enceladus plume results show that an early ocean was an alkaline na cl hco3 solution underlying altered rocks consisted of mg phyllosilicates magnetite fe and ni sulfides and carbonates subsequent freezing of oceanic water caused the deposition of a nacl hydrate na k and ca carbonates and the formation of a salt free ice shell if an aqueous phase exists on today s enceladus it could consist of eutectic na cl hco3 brine that at least locally decouples the ice shell and facilitates tidal heating a lack of firm detection of na and cl at enceladus is consistent with the accumulation of salts at the ice rock boundary and implies the plume formation via sublimation in the ice shell

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

volcanism in the solar system the myriad bodies that occur in the solar system show a wide range of physical properties exploration by spacecraft during the past four decades has shown that volcanism a major mechanism by which internal heat is transported to the surface is common on many of these bodies

a fracture history on enceladus provides evidence for a global ocean 1 the region surrounding the south pole of saturn s moon enceladus shows a young pervasively fractured surface that emanates enough heat to be detected by the cassini spacecraft to explain the elevated heat and eruptive icy plumes originating from large cracks informally called tiger stripes in the surface many models implicitly assume a global liquid ocean beneath the surface here we show that the fracture patterns in the south polar terrain spt of enceladus are inconsistent with contemporary stress fields but instead formed in a temporally varying global stress field related to nonsynchronous rotation of a floating ice shell above a global liquid ocean this finding increase to at least three the number of outer planet satellites likely to possess a subsurface liquid water layer

2d models of gas flow and ice grain acceleration in enceladus vents using dsmc methods abstract the gas distribution of the enceladus water vapor plume and the terminal speeds of ejected ice grains are physically linked to its subsurface fissures and vents it is estimated that the gas exits the fissures with speeds of 300 1000 m s while the micron sized grains are ejected with speeds comparable to the escape speed schmidt j et al 2008 nature 451 685 688 we investigated the effects of isolated axisymmetric vent geometries on subsurface gas distributions and in turn the effects of gas drag on grain acceleration subsurface gas flows were modeled using a collision limiter direct simulation monte carlo dsmc technique in order to consider a broad range of flow regimes bird g 1994 molecular gas dynamics and the direct simulation of gas flows oxford university press oxford titov e v et al 2008 j propul power 24 2 311 321 the resulting dsmc gas distributions were used to determine the drag force for the integration of ice grain trajectories in a test particle model simulations were performed for diffuse flows in wide channels reynolds number 10 250 and dense flows in narrow tubular channels reynolds number 10 6 we compared gas properties like bulk speed and temperature and the terminal grain speeds obtained at the vent exit with inferred values for the plume from cassini data in the simulations of wide fissures with dimensions similar to that of the tiger stripes the resulting subsurface gas densities of 10 14 10 20 m 3 were not sufficient to accelerate even micron sized ice grains to the enceladus escape speed in the simulations of narrow tubular vents with radii of 10 m the much denser flows with number densities of 10 21 10 23 m 3 accelerated micron sized grains to bulk gas speed of 600 m s further investigations are required to understand the complex relationship between the vent geometry gas source rate and the sizes and speeds of ejected grains

the fascinating and complex dynamics of geyser eruptions geysers episodically erupt liquid and vapor despite two centuries of scientific study basic questions persist why do geysers exist what determines eruption intervals durations and heights what initiates eruptions through monitoring eruption intervals analyzing geophysical data taking measurements within geyser conduits performing numerical simulations and constructing laboratory models some of these questions have been addressed geysers are uncommon because they require a combination of abundant water recharge magmatism and rhyolite flows to supply heat and silica and large fractures and cavities overlain by low permeability materials to trap rising multiphase and multicomponent fluids eruptions are driven by the conversion of thermal to kinetic energy during decompression larger and deeper cavities permit larger eruptions and promote regularity by isolating water from weather variations the ejection velocity may be limited by the speed of sound of the liquid vapor mixture

pit chains on enceladus signal the recent tectonic dissection of the ancient cratered terrains abstract enceladus is the first outer solar system body on which pit chains have been positively identified we map the global distribution of pit chains and show that pit chains are among the youngest tectonic features on enceladus s surface concentrated in the cratered plains centered on enceladus s saturnian and anti saturnian hemispheres pit chains on enceladus are interpreted as the surface expressions of subsurface dilational fractures underlying a cover of unconsolidated material which we infer to be a geologically young cover of loose regolith that mantles the surface of enceladus a widespread layer of regolith may act to insulate the surface which has implications for the thermal state of enceladus s ice shell the widespread distribution of pit chains across the cratered plains indicates that this ancient surface has recently been tectonically active

is enceladus plume tidally controlled 1 explanations for the plume of gas water vapor and ice particles jetting from rifts in enceladus south polar region include boiling of liquid water and dissociation of clathrate hydrates in either case production of the plume may be quasi static or tidally controlled with implications for the interior structure and composition of enceladus previous quantification of the clathrate explanation assumed equilibrium dissociation and cannot be used to simulate a tidally generated plume we present a non equilibrium clathrate dissociation model which we use to reproduce past observations and predict the plume s properties during upcoming close encounters the total mass flux and water to gas mass ratio of a tidally generated plume are predicted to be lower than previous measurements in comparison for a quasi static plume these properties should have values close to previous measurements this provides an observational means of distinguishing quasi static from dynamic processes as the plume s source

enceladus near surface co 2 gas pockets and surface frost deposits abstract solid co2 surface deposits were reported in enceladus south polar region by brown et al 2006 they noted that such volatile deposits are temporary and posited ongoing replenishment we present a model for this replenishment by expanding on the matson et al 2012 model of subsurface heat and chemical transport in enceladus our model explains the distributions of both co2 frost and complexed co2 clathrate hydrate as seen in the cassini visual and infrared mapping spectrometer vims data we trace the journey of co2 from a subsurface ocean the ocean water circulation model of matson et al 2012 brings water up to near the surface where gas exsolves to form bubbles some of the co2 bubbles are trapped and form pockets of gas in recesses at the bottom of the uppermost ice layer when fissures break open these pockets the co2 gas is vented gas pocket venting is episodic compared to the more or less continuous eruptive plumes emanating from the tiger stripes that are supported by plume chambers two styles of gas pocket venting are considered 1 seeps and 2 blowouts the presence of co2 frost patches suggests that the pocket gas slowly seeped through fractured cold ice and when some of the gas reached the surface it was cold enough to condense i e t 70 to 119 k if the fissure opening is large a blowout occurs the rapid escape of gas and drop in pocket pressure causes water in the pocket to boil and create many small aerosol droplets of seawater these may be carried along by the erupting gas electrically charged droplets can couple to the magnetosphere and be dragged away from enceladus most of the co2 blowout gas escapes from enceladus and the remainder is distributed globally however co2 trapped in a clathrate structure does not escape it is much heavier and slower moving than the co2 gas its motion is ballistic and has an average range of about 17 km thus it contributes to deposits in the vicinity of the vent local heat flow indicates that gas pockets can be located as deep as several tens of meters below the surface gas pockets can be reused and we explore their life cycle

convection driven compaction as a possible origin of enceladus s long wavelength topography 1 the long wavelength surface topography of enceladus shows depressions about 1 km in depth and 102 km wide one possible cause of this topography is spatially variable amounts of compaction of an initially porous ice shell driven by spatial variations in heat flux here we show that the heat flux variations associated with convection in the shell can quantitatively match the observed features we develop a simple model of viscous compaction that includes the effect of porosity on thermal conductivity and find that an initial shell porosity of at least 20 25 is required to develop the observed topography over 1 ga this mechanism produces topographic depressions not rises above convective upwellings and does not generate detectable gravity anomalies unlike transient dynamic topography it can potentially leave a permanent record of ancient convective processes in the shallow lithospheres of icy satellites

constraining the enceladus plume using numerical simulation and cassini data abstract since its discovery the enceladus plume has been subjected to intense study due to the major effects that it has on the saturnian system and the window that it provides into the interior of enceladus however several questions remain and we attempt to answer some of them in this work in particular we aim to constrain the h2o production rate from the plume evaluate the relative importance of the jets and the distributed sources along the tiger stripes and make inferences about the source of the plume by accurately modeling the plume and constraining the model using the cassini inms and uvis data this is an extension of a previous work yeoh s k et al 2015 icarus 253 205 222 in which we only modeled the collisional part of the enceladus plume and studied its important physical processes in this work we propagate the plume farther into space where the flow has become free molecular and the cassini inms and uvis data were sampled then we fit this part of the plume to the inms h2o density distributions sampled along the e3 e5 and e7 trajectories and also compare some of the fit results with the uvis measurements of the plume optical depth collected during the solar occultation observation on 18 may 2010 we consider several vent conditions and source configurations for the plume by constraining our model using the inms and uvis data we estimate h2o production rates of several hundred kgs 1 400 500 kg s during the e3 and e7 flybys and 900 kg s during the e5 flyby these values agree with other estimates and are consistent with the observed temporal variability of the plume over the orbital period of enceladus hedman m m et al 2013 nature 500 182 184 in addition we determine that one of the tiger stripes cairo exhibits a local temporal variability consistent with the observed overall temporal variability of the plume we also find that the distributed sources along the tiger stripes are likely dominant while the jets provide a lesser contribution moreover our best fit solutions for the plume are sensitive to the vent conditions chosen the spreading angle of the jet produced is the main difference among the vent conditions and thus it appears to be an important parameter in fitting to these inms data sets in general we find that narrow jets produce better fits suggesting high mach numbers 5 at the vents this is supported by certain narrow features believed to be jets in both the inms and uvis data sets this tends to rule out sublimation from the surface but points to a deep underground source for the plume however the underground source can be either sublimation from an icy reservoir or evaporation from a liquid reservoir a high mach number at the vent also suggests subsurface channels with large variations in width and not fairly straight channels so that the gas can undergo sufficient expansion additionally the broad spreading angles inferred for the m sized grains ingersoll a p and ewald s p 2011 icarus 216 492 506 postberg f et al 2011 nature 474 620 622 cannot be due to spreading by the gas above the surface alone some other mechanism s must also be responsible perhaps occurring below the surface which further points to an underground source for the plume

endogenic heat from enceladus south polar fractures new observations and models of conductive surface heating linear features dubbed tiger stripes in the south polar region of enceladus have anomalously high heat fluxes and are the apparent source of the observed plume several explanations for the observed activity have been proposed including venting from a subsurface reservoir of liquid water sublimation of surface ice dissociation of clathrates and shear heating thermal modeling presented in this work coupled with observations from the cassini composite infrared spectrometer cirs instrument seeks to elucidate the underlying physical mechanism by constraining vent temperatures and thermal emission sources using a model in which the observed thermal signature results primarily from conductive heating of the surface by warm subsurface fractures the fractures feed surface vents which may themselves contribute to the observed thermal emission model variables include vent temperature presence of a surface insulating layer vent width time variable heat input and heat sources other than the central vent results indicate

determination of fracture inflow parameters with a borehole fluid conductivity logging method there is much current interest in determining the flow characteristics of fractures intersecting a well bore in order to provide data for use in estimating the hydrologic behavior of fractured rocks inflow rates from these fractures into the well bore are usually very low moreover in most cases only a few percent of the fractures identified by core inspection and geophysical logging actually conduct water the rest being closed clogged or isolated from the water flow system a new procedure is proposed and a corresponding method of analysis developed to locate water conducting fractures and obtain fracture inflow rates by means of a time sequence of electric conductivity logs of the borehole fluid the physical basis of the analysis method is discussed and the procedure is applied to an existing set of data which shows initiation and growth of nine conductivity peaks in a 900 m section of a 1690 m borehole corresponding to nine water conducting fractures intersecting the borehole by applying our analysis to these nine peaks the flow rates and the salinity of the water from these fractures are determined these results are used with other information to obtain transmissivities of the nine fractures which are validated against independent hydraulic measurements by packer tests the salinities measured in fluids from the fractures are also validated against salinity values obtained by chemical sampling of fluids from different depths of the borehole the applicability of this technique is discussed in the context of a borehole testing program