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 contribution of the precambrian continental lithosphere to global h 2 production the production of hydrogen gas from the precambrian continental lithosphere has been underestimated taking into account hydrogen from serpentinization and radiolysis may double estimates previously based on marine systems alone molecular hydrogen produced by interactions between water and rocks in the earth s subsurface and at deep ocean vents can sustain microbial ecosystems it was thought that global h2 production originates mainly from the marine lithosphere with a negligible contribution from precambrian rocks but here the authors present a global compilation of h2 concentration data that identifies the fracture waters in the precambrian continental subsurface as a domain of the terrestrial hydrosphere that produces h2 at a rate comparable to estimates from marine systems this finding revises our understanding of the production of reduced gases in the earth s subsurface and may aid in the exploration of life in deep habitat locations microbial ecosystems can be sustained by hydrogen gas h2 producing water rock interactions in the earth s subsurface and at deep ocean vents1 2 3 4 current estimates of global h2 production from the marine lithosphere by water rock reactions hydration are in the range of 1011 moles per year5 6 7 8 9 recent explorations of saline fracture waters in the precambrian continental subsurface have identified environments as rich in h2 as hydrothermal vents and seafloor spreading centres1 2 and have suggested a link between dissolved h2 and the radiolytic dissociation of water10 11 however extrapolation of a regional h2 flux based on the deep gold mines of the witwatersrand basin in south africa11 yields a contribution of the precambrian lithosphere to global h2 production that was thought to be negligible 0 009 1011 moles per year 6 here we present a global compilation of published and new h2 concentration data obtained from precambrian rocks and find that the h2 production potential of the precambrian continental lithosphere has been underestimated we suggest that this can be explained by a lack of consideration of additional h2 producing reactions such as serpentinization and the absence of appropriate scaling of h2 measurements from these environments to account for the fact that precambrian crust represents over 70 per cent of global continental crust surface area12 if h2 production via both radiolysis and hydration reactions is taken into account our estimate of h2 production rates from the precambrian continental lithosphere of 0 36 2 27 1011 moles per year is comparable to estimates from marine systems

superimposed brittle structures in the late orogenic extension of the northern apennine results from the carrara area alpi apuane nw tuscany this paper presents data on the geometric and kinematic features of brittle faults in the carrara area alpi apuane nw tuscany italy providing the first paleostress determination in a key region of the northern apennine meso and microfault analyses point out the presence of brittle structures formed during a polyphase deformation and characterized by an older stage ds1 with an interfering system of strike slip and normal faulting followed by the ds2 stage developing normal faults locally showing apenninic trend nw se as a whole the brittle structures are related to the late pliocene middle pleistocene evolution of the thyrrenian side of the northern apennine

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

spontaneous formation of geysers at only one pole on enceladus s ice shell the ice shell on enceladus an icy moon of saturn exhibits strong asymmetry between the northern and southern hemispheres with all known geysers concentrated over the south pole even though the expected pattern of tidal forced deformation should be symmetric between the north and south poles using an idealized ice evolution model we demonstrate that this asymmetry may form spontaneously without any noticeable a priori asymmetry such as a giant impact or a monopole structure of geological activity in contrast to previous studies infinitesimal asymmetry in the ice shell thickness due to random perturbations are found to be able to grow indefinitely ending up significantly thinning the ice shell at one of the poles thereby allowing fracture formation there necessary conditions to trigger this hemispheric symmetry breaking mechanism are found analytically a rule of thumb we find is that for galilean and saturnian icy moons the ice shell can undergo hemispheric symmetry breaking only if the mean shell thickness is around 10 to 30 km

modal mineralogy of cm2 chondrites by x ray diffraction psd xrd part 1 total phyllosilicate abundance and the degree of aqueous alteration abstract cm carbonaceous chondrites are samples of incompletely serpentinized primitive asteroids using position sensitive detector x ray diffraction psd xrd and a pattern stripping technique we quantify the modal mineralogy of cm2 chondrites mighei murray murchison nogoya and cold bokkeveld there is a narrow range in the combined modal volume vol of the most abundant phases mg serpentine 25 33 and fe cronstedtite 43 50 cold bokkeveld is anomalous in containing more mg serpentine 49 59 than fe cronstedtite 19 27 even including cold bokkeveld the range in modal total phyllosilicate is 73 79 average 75 total phyllosilicate abundance provides a non ambiguous measure of the degree of aqueous alteration and indicates that these meteorites have all experienced essentially the same degree of aqueous alteration this reflects pervasive hydration of matrix across cm2 samples apparent differences in the alteration of chondrules observed in petrographic studies represent various stages in the progression towards complete hydration of all components but are not manifest in significant differences in modal mineralogy for all samples there is a limited range in olivine 6 9 and pyroxene 5 abundances modal abundances of the remaining identified phases also show a limited range calcite 0 1 3 gypsum 0 1 6 magnetite 1 1 2 4 pentlandite 0 2 1 and pyrrhotite 1 3 8 as expected we observe a strong negative correlation in the modal abundance of anhydrous fe mg silicates olivine pyroxene and total phyllosilicate mg serpentine fe cronstedtite consistent with the idea that phyllosilicate is forming by aqueous alteration of the anhydrous components the negative correlation in the modal abundance between mg serpentine and fe cronstedtite indicates a mineralogic transformation of fe cronstedtite to mg serpentine by fluid driven recrystallisation or b that these meteorites had different initial abundances of olivine and pyroxene the observed positive correlation in the relative proportion of mg serpentine with increasing total phyllosilicate abundance reflects the evolution of increasingly mg rich phyllosilicate during aqueous alteration fe cronstedtite is the dominant phyllosilicate while cm chondrule olivines are forsteritic and will form mg serpentine during aqueous alteration this implies that matrix olivine was more fe rich than chondrule olivine prior to aqueous alteration

physical models of grooved terrain tectonics on ganymede grooved terrain on ganymede consists of distinct areas of parallel to subparallel ridges and troughs at a variety of spatial scales grooved terrain has been interpreted as the product of tectonism in the form of fault accommodated distributed lithospheric extension we use physical analog methods to test the formation of grooved terrain by imbricate normal faulting in response to distributed extension faults and fault systems produced in the models are geometrically and kinematically similar to patterns inferred for some grooved terrains on ganymede the high degree of similarity between model structures and those observed on ganymede indicates that rotational half graben brittle block faulting can explain at least some tectonic resurfacing on ganymede and that 20 extension is sufficient to form structures analogous to grooved terrain

experimental evidence for different strain regimes of crack populations in a clay model we report results from clay extension experiments used as a model for the evolution of fault populations due to stress interactions at yielding cracks begin to appear and the brittle strain due to them quickly reaches a rate matching the applied stretching rate the crack density number of cracks per unit area initially increases apace then reaches a maximum at a critical strain decreasing thereafter at low strains where the crack population is dilute a power law length distribution is observed which at high strain gradually transitions to an exponential this agrees with fault populations data observed in low and high strain settings these results indicate that fault populations ranging from power law to exponential size frequency distributions reflect the population evolution with increased strain

origin of ice diapirism true polar wander subsurface ocean and tiger stripes of enceladus driven by compositional convection abstract we consider the scenario in which the presence of ammonia in the bulk composition of enceladus plays a pivotal role in its thermochemical evolution because ammonia reduces the melting temperature of the ice shell by 100 k below that of pure water ice small amounts of tidal dissipation can power an ammonia feedback mechanism that leads to secondary differentiation of enceladus within the ice shell this leads to compositionally distinct zones at the base of the ice shell arranged such that a layer of lower density and compositionally buoyant pure water ice underlies the undifferentiated ammonia dihydrate ice layer above we then consider a large scale instability arising from the pure water ice layer and use a numerical model to explore the dynamics of compositional convection within the ice shell of enceladus the instability of the layer can easily account for a diapir that is hemispherical in scale as it rises to the surface it co advects the warm internal temperatures towards the outer layers of the satellite this advected heat facilitates the generation of a subsurface ocean within the ice shell of enceladus this scenario can simultaneously account for the origin of asymmetry in surface deformation observed on enceladus as well as two global features inferred to exist a large density anomaly within the interior and a subsurface ocean underneath the south polar region

abiotic methane formation during experimental serpentinization of olivine fluids circulating through actively serpentinizing systems are often highly enriched in methane ch4 in many cases the ch4 in these fluids is thought to derive from abiotic reduction of inorganic carbon but the conditions under which this process can occur in natural systems remain unclear in recent years several studies have reported abiotic formation of ch4 during experimental serpentinization of olivine at temperatures at or below 200 c however these results seem to contradict studies conducted at higher temperatures 300 c to 400 c where substantial kinetic barriers to ch4 synthesis have been observed here the potential for abiotic formation of ch4 from dissolved inorganic carbon during olivine serpentinization is reevaluated in a series of laboratory experiments conducted at 200 c to 320 c a 13c labeled inorganic carbon source was used to unambiguously determine the origin of ch4 generated in the experiments consistent with previous high temperature studies the results indicate that abiotic formation of ch4 from reduction of dissolved inorganic carbon during the experiments is extremely limited with nearly all of the observed ch4 derived from background sources the results indicate that the potential for abiotic synthesis of ch4 in low temperature serpentinizing environments may be much more limited than some recent studies have suggested however more extensive production of ch4 was observed in one experiment performed under conditions that allowed an h2 rich vapor phase to form suggesting that shallow serpentinization environments where a separate gas phase is present may be more favorable for abiotic synthesis of ch4

rock comminution as a source of hydrogen for subglacial ecosystems microbes live under glaciers that have persisted for millions of years without a clear energy supply analyses of crushed rocks suggest that interactions of glaciers with the rocks beneath can produce enough h2 to support methanogenic bacteria substantial parts of the beds of glaciers ice sheets and ice caps are at the pressure melting point1 the resulting water harbours diverse subglacial microbial ecosystems2 3 capable of affecting global biogeochemical cycles4 5 such subglacial habitats may have acted as refugia during neoproterozoic glaciations6 however it is unclear how life in subglacial environments could be supported during glaciations lasting millions of years because energy from overridden organic carbon would become increasingly depleted7 8 here we investigate the potential for abiogenic h2 produced during rock comminution to provide a continual source of energy to support subglacial life we collected a range of silicate rocks representative of subglacial environments in greenland canada norway and antarctica and crushed them with a sledgehammer and ball mill to varying surface areas under an inert atmosphere in the laboratory we added water and measured h2 production with time h2 was produced at 0 c in all silicate water experiments probably through the reaction of water with mineral surface silica radicals formed during rock comminution h2 production increased with increasing temperature or decreasing silicate rock grain size sufficient h2 was produced to support previously measured rates of methanogenesis under a greenland glacier we conclude that abiogenic h2 generation from glacial bedrock comminution could have supported life and biodiversity in subglacial refugia during past extended global glaciations

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

habitability of the marine serpentinite subsurface a case study of the lost city hydrothermal field the lost city hydrothermal field is a dramatic example of the biological potential of serpentinization microbial life is prevalent throughout the lost city chimneys powered by the hydrogen gas an

ongoing hydrothermal activities within enceladus analysis of silicon rich nanometre sized dust particles near saturn shows them to consist of silica which was initially embedded in icy grains emitted from enceladus subsurface waters and released by sputter erosion in saturn s e ring their properties indicate their ongoing formation and transport by high temperature hydrothermal reactions from the ocean floor and up into the plume of enceladus hsiang wen hsu et al have analysed the silicon rich nanometre sized dust stream particles in the saturnian system using the cosmic dust analyser cda onboard the cassini spacecraft with the help of experiments and modelling the particles are interpreted as silica grains that were initially embedded in the icy plume emitted from subsurface waters on enceladus and released by sputter erosion in saturn s e ring their properties indicate their formation and transport by high temperature hydrothermal reactions from the ocean floor and up into the plume of enceladus detection of sodium salt rich ice grains emitted from the plume of the saturnian moon enceladus suggests that the grains formed as frozen droplets from a liquid water reservoir that is or has been in contact with rock1 2 gravitational field measurements suggest a regional south polar subsurface ocean of about 10 kilometres thickness located beneath an ice crust 30 to 40 kilometres thick3 these findings imply rock water interactions in regions surrounding the core of enceladus the resulting chemical footprints are expected to be preserved in the liquid and subsequently transported upwards to the near surface plume sources where they eventually would be ejected and could be measured by a spacecraft4 here we report an analysis of silicon rich nanometre sized dust particles5 6 7 8 so called stream particles that stand out from the water ice dominated objects characteristic of saturn we interpret these grains as nanometre sized sio2 silica particles initially embedded in icy grains emitted from enceladus subsurface waters and released by sputter erosion in saturn s e ring the composition and the limited size range 2 to 8 nanometres in radius of stream particles indicate ongoing high temperature 90 c hydrothermal reactions associated with global scale geothermal activity that quickly transports hydrothermal products from the ocean floor at a depth of at least 40 kilometres up to the plume of enceladus

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

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

chemical and isotopic analyses of hydrocarbon bearing fluid inclusions in olivine rich rocks we examined the mineralogical chemical and isotopic compositions of secondary fluid inclusions in olivine rich rocks from two active serpentinization systems the von damm hydrothermal field mid

the ph of enceladus ocean abstract saturn s moon enceladus is a geologically active waterworld the prevailing paradigm is that there is a subsurface ocean that erupts to the surface which leads to the formation of a plume of vapor and ice above the south polar region the chemistry of the ocean is just beginning to be understood but is of profound geochemical and astrobiological interest here we determine the ph of the ocean using a thermodynamic model of carbonate speciation observational data from the cassini spacecraft are used to make a chemical model of ocean water on enceladus the model suggests that enceladus ocean is a na cl co3 solution with an alkaline ph of 11 12 the dominance of aqueous nacl is a feature that enceladus ocean shares with terrestrial seawater but the ubiquity of dissolved na2co3 suggests that soda lakes are more analogous to the enceladus ocean the high ph implies that the hydroxide ion should be relatively abundant while divalent metals should be present at low concentrations owing to buffering by carbonates and phyllosilicates on the ocean floor carboxyl groups in dissolved organic species would be negatively charged while amino groups would exist predominately in the neutral form knowledge of the ph improves our understanding of geochemical processes in enceladus ocean the high ph is interpreted to be a key consequence of serpentinization of chondritic rock as predicted by prior geochemical reaction path models although degassing of co2 from the ocean may also play a role depending on the efficiency of mixing processes in the ocean serpentinization leads to the generation of h2 a geochemical fuel that can support both abiotic and biological synthesis of organic molecules such as those that have been detected in enceladus plume serpentinization and h2 generation should have occurred on enceladus like on the parent bodies of aqueously altered meteorites but it is unknown whether these critical processes are still taking place or if enceladus rocky core has been completely altered by past hydrothermal activity the presence of native h2 in the plume would provide strong evidence for contemporary aqueous alteration that replenishes this source of energy for possible life the high ph also suggests that the delivery of strong oxidants from the surface to the ocean has not been significant otherwise sulfuric acid would be produced which would be consistent with geophysical models of episodic resurfacing activity on enceladus this paper represents an expansion of chemical oceanography to an ocean planet beyond earth

why aqueous alteration in asteroids was isochemical high porosity high permeability carbonaceous chondrite meteorites are the most compositionally primitive rocks in the solar system but the most chemically pristine ci1 and cm2 chondrites have experienced pervasive aqueous alteration apparently within asteroid parent bodies unfractionated soluble elements suggest very limited flow of liquid water indicting a closed system at scales large than 100 s m consistent with data from oxygen isotopes and meteorite petrography however numerical studies persistently predict large scale 10 s km water transport in model asteroids either in convecting cells or via exhalation flow an open system at scales up to 10 s km these models have tended to use permeabilites in the range 10 13 to 10 11 m2 we show that the permeability of plausible chondritic starting materials lies in the range 10 19 to 10 17 m2 0 1 10 d around six orders of magnitude lower than previously assumed this low permeability is largely a result of the extreme fine grain size of primitive chondritic materials applying these permeability estimates in numerical models we predict very limited liquid water flow distances of 100 s m at most even in a high porosity water saturated asteroid with a high thermal gradient over millions of years isochemical alteration with flow over minimal lengthscales is not a special circumstance it is inevitable once we consider the fundamental material properties of these rocks to achieve large scale flow it would require average matrix grain sizes in primitive materials of 10 s 100 s m orders of magnitude larger than observed finally in addition to reconciling numerical modelling with meteorite data our work explains several other features of these enigmatic rocks most particularly why the most chemically primitive meteorites are also the most altered

low temperature volatile production at the lost city hydrothermal field evidence from a hydrogen stable isotope geothermometer although commonly utilized in continental geothermal work the water hydrogen and methane hydrogen isotope geothermometers have been neglected in hydrothermal studies here we report d ch4 and d h2 values from high temperature black smoker type hydrothermal vents and low temperature carbonate hosted samples from the recently discovered lost city hydrothermal field methane deuterium content is uniform across the dataset at 120 12 hydrogen d values vary from 420 to 330 at high temperature vents to 700 to 600 at lost city the application of several geothermometer equations to a suite of hydrothermal vent volatile samples reveals that predicted temperatures are similar to measured vent temperatures at high temperature vents and 20 60 c higher than those measured at the lost city vents we conclude that the overestimation of temperature at lost city reflects 1 that methane and hydrogen are produced by serpentinization at n110 c and 2 that isotopic equilibrium at temperatures b70 c is mediated by microbial sulfate reduction the successful application of hydrogen isotope geothermometers to low temperature lost city hydrothermal samples encourages its employment with lowtemperature diffuse hydrothermal fluids 2005 elsevier b v all rights reserved

the origin and evolution of chondrites recorded in the elemental and isotopic compositions of their macromolecular organic matter extraterrestrial organic matter in meteorites potentially retains a unique record of synthesis and chemical thermal modification by parent body nebular and even presolar processes in a survey of the elemental and isotopic compositions of insoluble organic matter iom from 75 carbonaceous ordinary and enstatite chondrites we find dramatic variations within and between chondrite classes there is no evidence that these variations correlate with the time and or location of chondrite formation or with any primary petrologic or bulk compositional features that are associated with nebular processes e g chondrule and volatile trace element abundances nor is there evidence for the formation of the iom by fischer tropsch type synthesis in the nebula or in the parent bodies the elemental variations are consistent with thermal maturation and or oxidation of a common precursor for reasons that are unclear there are large variations in isotopic composition within and between chondrite classes that do not correlate in a simple way with elemental composition or petrologic type nevertheless because of the pattern of elemental variations with petrologic type and the lack of any correlation with the primary features of the chondrite classes at present the most likely explanation is that all iom compositional variations are the result of parent body processing of a common precursor if correct the range of isotopic compositions within and between chondrite classes implies that the iom is composed of several isotopically distinct components whose relative stability varied with parent body conditions the most primitive iom is found in the cr chondrites and bells cm2 isotopically the iom from these meteorites resembles the iom in interplanetary dust particles chemically their iom resembles the chon particles of comet halley despite the large isotopic anomalies in the iom from these meteorites it is uncertain whether the iom formed in the interstellar medium or the outer solar system although the former is preferred here

enceladus s internal ocean and ice shell constrained from cassini gravity shape and libration data the intense plume activity at the south pole of enceladus together with the recent detection of libration hints at an internal water ocean underneath the outer ice shell however the interpretation of gravity shape and libration data leads to contradicting results regarding the depth of ocean ice interface and the total volume of the ocean here we develop an interior structure model consisting of a rocky core an internal ocean and an ice shell which satisfies simultaneously the gravity shape and libration data we show that the data can be reconciled by considering isostatic compensation including the effect of a few hundred meter thick elastic lithosphere our model predicts that the core radius is 180 185 km the ocean density is at least 1030 kg m3 and the ice shell is 18 22 km thick on average the ice thicknesses are reduced at poles decreasing to less than 5 km in the south polar region

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

keeping enceladus warm abstract despite its small size enceladus emits considerable heat especially at its south pole even long after simple thermal models predict it should be frozen several sources of energy have been proposed as responsible for this heating such as tidal dissipative heating tdh convection and shearing in the ice shell and exothermic chemical reactions e g serpentine formation crater relaxation simulations suggest that episodic heating events have occurred over long stretches of enceladus history thermal history and hydrothermal simulations reported here show that a combination of steady plus episodic tdh heating could maintain at least a polar ocean to the present time hydrothermal circulation can play a significant role in mining enceladus internal heat facilitating the persistence of an ocean even to the present by focusing internal heat to the polar regions

primordial n2 provides a cosmochemical explanation for the existence of sputnik planitia pluto abstract the presence of n2 in the surface environment of pluto is critical in creating pluto s richness of features and processes here we propose that the nitrogen atoms in the n2 observed on pluto were accreted in that chemical form during the formation of pluto we use new horizons data and models to estimate the amounts of n2 in the following exterior reservoirs atmosphere escape photochemistry and surface the total exterior inventory is deduced to be dominated by a glacial sheet of n2 rich ices at sputnik planitia or by atmospheric escape if past rates of escape were much faster than at present pluto s atmosphere is a negligible reservoir of n2 and photochemical destruction of n2 may also be of little consequence estimates are made of the amount of n2 accreted by pluto based on cometary and solar compositions it is found that the cometary model can account for the amount of n2 in sputnik planitia while the solar model can provide a large initial inventory of n2 that would make prodigious atmospheric escape possible these consistencies can be considered preliminary evidence in support of a primordial origin of pluto s n2 however both models predict accreted ratios of co n2 that are much higher than that in pluto s atmosphere possible processes to explain missing co that are given quantitative support here are fractional crystallization from the atmosphere resulting in co burial at the surface and aqueous destruction reactions of co subject to metastable thermodynamic equilibrium in the subsurface the plausibility of primordial n2 as the primary source of pluto s nitrogen vs nh3 or organic n can be tested more rigorously using future constraints on the 14 n 15 n ratio in n2 and the 36ar n2 ratio

possible evidence for a methane source in enceladus ocean the internal ocean of enceladus can be expected to present conditions favorable to the trapping of volatiles in clathrates this process could influence the eventual composition of the ocean and therefore of the plumes emitted by the south polar region here we used a statistical thermodynamic model to assess which species detected in the plumes by the cassini ion and neutral mass spectrometer experiment are trapped in clathrates we treated enceladus internal ocean as a terrestrial subglacial lake with a mixture of dissolved volatiles indicated by plume gas measurements we find that the conditions for clathrate formation are met in this ocean except above 20 km or in hypothetical hot spots the formation of multiple guest clathrates depletes methane below plume levels suggesting that clathrates eventually dissociate releasing methane in the fissure that connects the ocean to the surface or that another mechanism such as hydrothermal reactions is compensating by adding methane into the ocean

geophysical controls of chemical disequilibria in europa the ocean in jupiter s moon europa may have redox balance similar to earth s on earth low temperature hydration of crustal olivine produces substantial hydrogen comparable to any potential flux from volcanic activity here we compare hydrogen and oxygen production rates of the earth system with fluxes to europa s ocean even without volcanic hydrothermal activity water rock alteration in europa causes hydrogen fluxes 10 times smaller than earth s europa s ocean may have become reducing for a brief epoch for example after a thermal orbital resonance 2 gyr after accretion estimated oxidant flux to europa s ocean is comparable to estimated hydrogen fluxes europa s ice delivers oxidants to its ocean at the upper end of these estimates if its ice is geologically active as evidence of geologic activity and subduction implies

tidal dissipation in enceladus uneven fractured ice shell abstract analysis of enceladus gravity topography and libration data suggests that the thickness of the ice crust significantly varies which may have important consequences for the heat transfer across and the tidal dissipation within the ice shell understanding these processes is a critical prerequisite for analyzing enceladus thermal evolution and assessing the long term stability of its subsurface ocean here we investigate the impact of ice shell thickness variations on the tidal deformation of the moon and the associated heat production using a finite element model that includes faults tiger stripes in the south polar region spr since the tidal deformation and the thermal structure of the ice shell are coupled through temperature and deviatoric stress we simultaneously solve the equations governing the anelastic deformation of ice and also equations which model conductive heat transfer in the ice shell we find that tidal heating is concentrated in a narrow low viscosity zone near the base of the ice shell and along faults outside the spr the thickness of this zone is about 1 10 of the local ice thickness and the associated volumetric heating is 1 0 6 w m 3 corresponding to less than 1 gw of dissipated power in the spr the tidal effects are enhanced by the combined action of faults and ice shell thinning although the volumetric heating in this relatively small region may be larger than 10 4 w m 3 the total heat production in this region does not exceed 1 1 gw our computations show that tidal heating in the ice shell can explain only a small fraction of enceladus heat production derived from astrometric observations implying that enceladus heat engine is powered by dissipation in the core or in the ocean

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

relict ooids off northwestern india inferences on their genesis and late quaternary sea level abstract relict carbonate sands dominated by ooids and faecal pellets are common on the continental shelf between 60 and 110 m off northwestern india the shiny tan white aragonitic ooids closely resemble modern bahamian ooids with cortex thicknesses varying from 23 ka bp and 18o values suggest that these relict ooids formed during cooler and drier post lgm conditions and later during the re intensified holocene monsoon climate an age vs depth plot suggests that most of the ooids formed at water depths between 10 and 40 m thereby calling into question whether relict shelf ooids are reliable indicators of past sea level

a serpentinite hosted ecosystem the lost city hydrothermal field the serpentinite hosted lost city hydrothermal field is a remarkable submarine ecosystem in which geological chemical and biological processes are intimately interlinked reactions between seawater and upper mantle peridotite produce methane and hydrogen rich fluids with temperatures ranging from 40 to 90 c at ph 9 to 11 and carbonate chimneys 30 to 60 meters tall a low diversity of microorganisms related to methane cycling archaea thrive in the warm porous interiors of the edifices macrofaunal communities show a degree of species diversity at least as high as that of black smoker vent sites along the mid atlantic ridge but they lack the high biomasses of chemosynthetic organisms that are typical of volcanically driven systems

effect of enceladus s rapid synchronous spin on interpretation of cassini gravity enceladus s degree 2 gravity determined by cassini is nominally nonhydrostatic to 3 j2 c22 3 38 3 63 as opposed to 10 3 iess et al 2014 interpret this in terms of a hydrostatic interior core and isostatic not hydrostatic floating ice shell enceladus s rapid 1 37 d synchronous spin and tide distorts its shape substantially though enough that the predicted hydrostatic j2 c22 is not 10 3 but closer to 3 25 this leads to the following revision to the internal picture of enceladus compared with iess et al 1 the satellite s core is somewhat smaller and slightly denser 190 km radius and 2450 kg m3 2 the compensation depth shell thickness of the global degree 2 ice shell is 50 km rather close to the base of the modeled ice water layer and 3 the compensation depth shell thickness beneath the south polar terrain from j3 remains shallower thinner at 30 km independent of but influenced by the degree 2 solution