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

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

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

space time variability of polar cap patches direct evidence for internal plasma structuring 1 coordinated observations of ionospheric variability near the geomagnetic pole using the resolute bay incoherent scatter radar risr n super dual auroral radar network superdarn high frequency hf radars and all sky imagers have clarified the relative contribution of structuring mechanisms operating on polar plasma patches from the multipoint risr n observations a three dimensional image can be constructed of the plasma parameters the colocated coherent echoes from the superdarn radars provide information on field aligned irregularities and from all sky imagers located in resolute bay canada and qaanaaq greenland information is obtained on the emission brightness at different wavelengths a good correlation is found between the location of the coherent incoherent and optical signals of patches from the superdarn radar data it is evident that plasma irregularities seem to be present throughout the region of enhanced electron density the patches are observed to be formed in the cusp region due to bursty flux transfer events and are then transported across the polar cap during the time period of about 10 minutes when a patch drifted through the risr n field of view the patch seemed to undergo significant deformation in all three spatial dimensions with density fluctuations of about 10 and spatial variations leading to stretching and tilting of the patch the findings show that plasma structuring can likely occur within polar cap patches which support previous suggestions that a patch is highly variable as it drifts across the polar cap with a faster spread of irregularities throughout the patch as a result

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

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

hf radar signatures of the cusp and low latitude boundary layer continuous ground based observations of ionospheric and magnetospheric regions are critical to the geospace environment modeling gem program it is therefore important to establish clear intercalibrations between different ground based instruments and satellites in order to clearly place the ground based observations in context with the corresponding in situ satellite measurements hf radars operating at high latitudes are capable of observing very large spatial regions of the ionosphere on a nearly continuous basis in this paper we report on an intercalibration study made using the polar anglo american conjugate radar experiment radars located at goose bay labrador and halley station antarctica and the defense meteorological satellite program dmsp satellites the dmsp satellite data are used to provide clear identifications of the ionospheric cusp and the low latitude boundary layer llbl the radar data for eight cusp events and eight llbl events have been examined in order to determine a radar signature of these ionospheric regions this intercalibration indicates that the cusp is always characterized by wide complex doppler power spectra whereas the llbl is usually found to have spectra dominated by a single component the distribution of spectral widths in the cusp is of a generally gaussian form with a peak at about 220 m s the distribution of spectral widths in the llbl is more like an exponential distribution with the peak of the distribution occurring at about 50 m s there are a few cases in the llbl where the doppler power spectra are strikingly similar to those observed in the cusp

interhemispheric study of polar cap patch occurrence based on swarm in situ data the swarm satellites offer an unprecedented opportunity for improving our knowledge about polar cap patches which are regarded as the main space weather issue in the polar caps we present a new robust algorithm that automatically detects polar cap patches using in situ plasma density data from swarm for both hemispheres we compute the spatial and seasonal distributions of the patches identified separately by swarm a and swarm b between december 2013 and august 2016 we show a clear seasonal dependency of patch occurrence in the northern hemisphere nh patches are essentially a winter phenomenon as their occurrence rate is enhanced during local winter and very low during local summer although not as pronounced as in the nh the same pattern is seen for the southern hemisphere sh furthermore the rate of polar cap patch detection is generally higher in the sh than in the nh especially on the dayside at about 77 magnetic latitude additionally we show that in the nh the number of patches is higher in the postnoon and prenoon sectors for interplanetary magnetic field imf by 0 respectively and that this trend is mirrored in the sh consistent with the ionospheric flow convection overall our results confirm previous studies in the nh shed more light regarding the sh and provide further insight into polar cap patch climatology along with this algorithm we provide a large data set of patches automatically detected with in situ measurements which opens new horizons in studies of polar cap phenomena

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

scintillation and irregularities from the nightside part of a sun aligned polar cap arc in this paper we study the presence of irregularities and scintillation in relation to the nightside part of a long lived sun aligned transpolar arc on 15 january 2015 the arc was observed in dmsp uv and particle data and lasted at least 3 h between 1700 and 2000 ut the arc was more intense than the main oval during this time from all sky imagers on svalbard we were able to study the evolution of the arc which drifted slowly westward toward the dusk cell the intensity of the arc as observed from ground was 10 17 kr in 557 7 nm and 2 3 5 kr in 630 0 nm i e significant emissions in both green and red emission lines we have used high resolution raw data from global navigation satellite systems gnss receivers and backscatter from super dual auroral radar network superdarn radars to study irregularities and scintillation in relation to the polar cap arc even though the literature has suggested that polar cap arcs are potential sources for irregularities our results indicate only very weak irregularities this may be due to the background density in the northward imf polar cap being too low for significant irregularities to be created

gps scintillation and irregularities at the front of an ionization tongue in the nightside polar ionosphere in this paper we study a tongue of ionization toi on 31 october 2011 which stretched across the polar cap from the canadian dayside sector to svalbard in the nightside ionosphere the toi front arrived over svalbard around 1930 ut we have investigated gps scintillation and irregularities in relation to this toi front this is the first study presenting such detailed multi instrument data of scintillation and irregularities in relation to a toi front combining data from an all sky imager the european incoherent scatter svalbard radar the super dual auroral radar network hankasalmi radar and three gps scintillation and total electron content tec monitors in longyearbyen and ny alesund we observe bursts of phase scintillation and no amplitude scintillation in relation to the leading gradient of the toi spectrograms of 50hz phase measurements show highly localized and variable structuring of the toi leading gradient with no structuring or scintillation within the toi or ahead of the toi

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

in situ measurement of a newly created polar cap patch 1 the investigation of cusp irregularities 2 sounding rocket was launched 5 december 2008 at 1035 ut we present an overview of the associated solar wind and auroral conditions and we look in detail at the relationship between poleward moving auroral forms pmafs and the creation of polar cap patches using ground based optical and radar data as well as in situ data from the rocket payload the solar wind was found to be dominated by a stable interplanetary magnetic field imf bz 0 situation the aurora was characterized by a series of pmafs throughout the period of interest associated with each pmaf were polar cap patches seen to emerge from the most poleward location of the pmafs on the basis of the available data we present a conceptual model explaining the creation of the polar cap patches under the given solar wind and ionospheric conditions

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

first in situ measurements of hf radar echoing targets 1 the sounding rocket investigation of cusp irregularities 2 ici 2 was launched into the cusp ionosphere over svalbard to investigate the production of decameter scale irregularities in the electron plasma associated with hf radar backscatter the main mission objective was to obtain high resolution measurements of decameter scale electron plasma irregularities and to quantify the growth rate for the gradient drift instability gdi at the 5 7 khz sampling rate of the absolute density measurements ici 2 has provided the first documentation in terms of absolute electron density measurements of how 10 m structures are located on km scale electron density gradients ici 2 traversed a cusp electron density structure created by ongoing soft precipitation 10 m scale irregularities were generated at km scale density gradients the estimated growth time for the gdi process was 10 50 seconds

observation of polar cap patches and calculation of gradient drift instability growth times a swarm case study the swarm mission represents a strong new tool to survey polar cap patches and plasma structuring inside the polar cap in the early commissioning phase the three swarm satellites were operated in

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

resolute bay incoherent scatter radar observations of plasma structures in the vicinity of polar holes the resolute bay incoherent scatter radar north risr n data collected between january 2012 and june 2013 are employed to identify and analyze 14 events with significant plasma density depressions ne 150 km with no apparent differences between structure shapes outside and inside low density regions the structure propagation velocity is perpendicular to its elongation direction and consistent with that of the large scale plasma convection the observations indicate that large scale density depressions can form under a variety of convection conditions and that plasma structuring processes outside the depressions may be responsible for their partial filling

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

planar microstructures in zircon from paleo seismic zones pseudotachylytes resulted from frictional melts associated with ultramylonites in high grade metapelitic rocks from the ivrea verbano zone in the southern alps northern italy were studied with focus on the deformation microstructures in zircon the aims were to investigate the characteristics of zircon deformation in seismic zones and to recognize specific microstructures generated in zircon during earthquakes which could be useful for mineral dating of paleo seismic events helps to understand how seismic energy is released at depth and interacts with metamorphic processes the interior of polished zircon grains ranging from 30 to 150 m in length were investigated with optical microscope and scanning electron microscope sem techniques including secondary electron se backscattered electron bse forward scattered electron fse cathodoluminescence cl imaging and crystallographic orientation mapping by electron backscatter diffraction analysis ebsd grains were studied in situ and as separated fractions embedded in epoxy disks among different cataclastic and crystal plastic deformation microstructures in zircon we identified characteristic planar deformation bands pdbs planar fractures pfs and curviplanar fractures cfs planar deformation bands in zircon are crystallographically controlled planar lattice volumes with misorientation from the host grain which varies from 0 4 to 2 7 pdbs are usually parallel to 100 crystallographic planes have width from 0 3 to 1 m and average spacing of 5 m in 2d sections planar deformation bands appear as contrast lamellae in orientation contrast images and in ebsd maps and in rare cases can be observed with the optical microscope pdbs form in specifically oriented grains due to high differential stresses high temperatures and high strain rates generated in seismically active environment and or due to shearing in the vicinity of frictional melts discovered structures represent a result of crystal plastic deformation of zircon grains with operating dislocations having 010 glide system and misorientation axis therefore they can be classified as a new type 4 lattice distortion pattern according to the existing classification for zircon piazolo et al 2012 kovaleva et al 2014 we have demonstrated that formation of planar fractures in zircon takes place not only during impacts but also in seismically active zones we observe at least two cases of formation of pfs with 100 orientation 1 as a result of evolution of pdbs and 2 as micro cleavage this study demonstrates that planar microstructures in terrestrial zircon do not exclusively form during impact events but also as a result of seismic events at depth due to unusually high differential stress strain rate and temperature according to the new findings pdbs in zircon from the deep crust are supposed to represent newly recognized evidence of seismicity

simultaneous ground based optical and hf radar observations of the ionospheric footprint of the open closed field line boundary along the geomagnetic meridian previous studies have confirmed that the equatorward boundaries of oi 630 0 nm auroral emissions and broad doppler spectral widths in super dual auroral radar network superdarn data the so called spectral width boundary swb are good empirical proxies for the dayside open closed field line boundary ocb in the ionosphere however both observational techniques are associated with mapping errors superdarn uses a virtual height model for mapping but it is not well known how the mapping error responds to a changing background ionosphere or transient reconnection events optical instruments such as the meridian scanning photometers have high spatial resolution near zenith where the mapping error due to the assumed oi 630 0 nm auroral emission height becomes small by comparison in this work an adjusted method is introduced to identify the swb which does not require temporal smoothing across several scans the difference in latitude between the swb as identified using this method and the simultaneously observed oi 630 0 nm auroral emission boundary along a common line of sight is compared utilizing the oi 630 0 nm boundary as a reference location we present two case studies observed at different levels of solar activity in both instances the latitude offset of swb from the reference location is discussed in relation to the background ionospheric electron density the compared results indicate that the intake of high density solar extreme ultraviolet ionized plasma from subauroral latitudes causes a refraction of the hf radar beam path which results in an overestimation of range mapping the adjusted method would thus be a useful tool for identifying the ocb under changing ionospheric conditions in the cusp region

on the generation of cusp hf backscatter irregularities 1 hf radar observations 630 0 nm cusp auroral emission and an ionospheric tomography scan are compared to investigate the mechanism by which radar cusp echoes are generated a collocation is reported between the equatorward boundaries of broad spectral width hf radar backscatter and 630 0 nm cusp auroral precipitation in addition the radio tomographic image reveals spatial structures in ionospheric electron density that map closely to the precipitation however the large scale horizontal gradient appears to be insufficiently steep to account alone for the rapid growth of irregularities by the gradient drift mechanism it is proposed that the initial source of the decameter scale features responsible for the backscatter may result from fine structure within the precipitation itself or alternatively from the cascade down of unstable intermediate scale gradients created in the plasma convecting poleward from the source region the latter process may explain the ongoing backscatter found poleward of the auroral band

scintillation and loss of signal lock from poleward moving auroral forms in the cusp ionosphere we present two examples from the cusp ionosphere over svalbard where poleward moving auroral forms pmafs are causing significant phase scintillation in signals from navigation satellites the data were obtained using a combination of ground based optical instruments and a newly installed multiconstellation navigation signal receiver at longyearbyen both events affected signals from gps and global navigation satellite system glonass when one intense pmaf appeared the signal from one gps spacecraft also experienced a temporary loss of signal lock although several polar cap patches were also observed in the area as enhancements in total electron content the most severe scintillation and loss of signal lock appear to be attributed to very intense pmaf activity this shows that pmafs are locations of strong ionospheric irregularities which at times may cause more severe disturbances in the cusp ionosphere for navigation signals than polar cap patches

large scale imaging of high latitude convection with super dual auroral radar network hf radar observations the hf radars of the super dual auroral radar network superdarn provide measurements of the e b drift of ionospheric plasma over extended regions of the high latitude ionosphere with the recent augmentation of the northern hemisphere component to six radars a sizable fraction of the entire convection zone approximately one third can be imaged nearly instantaneously 2 min to date the two dimensional convection velocity has been mapped by combining line of sight velocity measurements obtained from pairs of radars within common volume areas we describe a new method of deriving large scale convection maps based on all the available velocity data the measurements are used to determine a solution for the distribution of electrostatic potential expressed as a series expansion in spherical harmonics the addition of data from a statistical model constrains the solution in regions of no data coverage for low order expansions the results provide a gross characterization of the global convection we discuss the processing of the radar velocity data the factors that condition the fitting and the reliability of the results we present examples of imaging that demonstrate the response of the global convection to variations in the interplanetary magnetic field imf in the case of a sudden polarity change from northward to southward imf the convection is seen to reconfigure globally on very short 6 min timescales

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