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

crustal structure seismic stratigraphy and rift processes of the continental margin off eastern canada ocean bottom seismic refraction results off nova scotia two crustal seismic refraction profiles were obtained on the continental margin of eastern canada these lines were located on the upper continental rise and on the outer continental shelf off nova

serpentinization of oceanic peridotites 2 kinetics and processes of san carlos olivine hydrothermal alteration 1 the kinetics of the reaction mg fe olivine h 2 o serpentine magnetite brucite h 2 were investigated at 500 bars in the 250 350 c range using natural olivine san carlos fo 91 with grain sizes between 1 and 150 mm and for run durations up to 514 d the amount of magnetite produced which directly relates to reaction progress was accurately monitored using up to 24 time resolved magnetic measurements per experiment eighty percent of serpentinization was achieved after 60 d for olivine grain sizes of 5 15 mm and after 500 d for grain sizes of 50 63 mm serpentinization kinetics were found to be inversely proportional to the geometrical surface area of the starting olivine grains they were one or two orders of magnitude slower than serpentinization kinetics commonly used for modeling serpentinization related processes the nature of the serpentine mineral product depended on the initial olivine grain size igs for igs in the 5 150 mm range lizardite formed and olivine dissolution was the rate limiting process at igs below 5 mm chrysotile crystallized instead of lizardite and the relationship between olivine surface area and reaction kinetics no longer held we infer that for such small olivine grain sizes dissolution is no longer the rate limiting process serpentinization in our experiments was associated with the creation of new reactive surface area according to two cooperative processes etch pits formation associated with dissolution and grain fracturing for igs above 20 mm interestingly fractures and etch pits with similar geometry and sizes were also observed for residual olivine with a typical grain size of 50 mm in serpentinized peridotite samples from the southwest indian ridge this suggests that the processes governing olivine serpentinization kinetics in our experiments are similar to those prevailing in natural systems we therefore suggest that the new kinetic data set that we present here which encompasses a range of olivine grain sizes and reaction temperatures is relevant to the serpentinization of olivine in the oceanic crust insofar as water is available

planetary science enceladus hot springs the detection of silicon rich particles originating from saturn s moon enceladus suggests that water rock interactions are currently occurring inside it the first evidence of ongoing hydrothermal activity beyond earth see letter p 207 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

consequences of large impacts on enceladus core shape the intense activity on enceladus suggests a differentiated interior consisting of a rocky core an internal ocean and an icy mantle however topography and gravity data suggests large heterogeneity in the interior possibly including significant core topography in the present study we investigated the consequences of collisions with large impactors on the core shape we performed impact simulations using the code isale2d considering large differentiated impactors with radius ranging between 25 and 100 km and impact velocities ranging between 0 24 and 2 4 km s our simulations showed that the main controlling parameters for the post impact shape of enceladus rock core are the impactor radius and velocity and to a lesser extent the presence of an internal water ocean and the porosity and strength of the rock core for low energy impacts the impactors do not pass completely through the icy mantle subsequent sinking and spreading of the impactor rock core lead to a positive core topographic anomaly for moderately energetic impacts the impactors completely penetrate through the icy mantle inducing a negative core topography surrounded by a positive anomaly of smaller amplitude the depth and lateral extent of the excavated area is mostly determined by the impactor radius and velocity for highly energetic impacts the rocky core is strongly deformed and the full body is likely to be disrupted explaining the long wavelength irregular shape of enceladus core by impacts would imply multiple low velocity 2 4 km s collisions with deca kilometric differentiated impactors which is possible only after the lhb period

growth and evolution of small porous icy bodies with an adaptive grid thermal evolution code i application to kuiper belt objects and enceladus abstract we present a new 1 dimensional thermal evolution code suited for small icy bodies of the solar system based on modern adaptive grid numerical techniques and suited for multiphase flow through a porous medium the code is used for evolutionary calculations spanning 4 6 10 9 yr of a growing body made of ice and rock starting with a 10 km radius seed and ending with an object 250 km in radius initial conditions are chosen to match two different classes of objects a kuiper belt object and saturn s moon enceladus heating by the decay of 26al as well as long lived radionuclides is taken into account several values of the thermal conductivity and accretion laws are tested we find that in all cases the melting point of ice is reached in a central core evaporation and flow of water and vapor gradually remove the water from the core and the final present structure is differentiated with a rocky highly porous core of 80 km radius and up to 160 km for very low conductivities outside the core due to refreezing of water and vapor a compact ice rich layer forms a few tens of km thick except in the case of very high conductivity if the ice is initially amorphous as expected in the kuiper belt the amorphous ice is preserved in an outer layer about 20 km thick we conclude by suggesting various ways in which the code may be extended

the flat tops volcanic field 1 lower miocene open system multisource magmatism at flander trappers lake the lower miocene lavas 23 20 ma of the flat tops volcanic field nw colorado are one of the earliest and most voluminous phases of magmatic activity associated with the development of the rio grande rift flow by flow collections of the lavas at flander trappers lake provide evidence for complex open system magma chamber processes geochemically the lavas range from basalts to shoshonites and have concentrations of major and compatible trace elements that are buffered at higher levels than expected for simple fractional crystallisation cyclic repetitions at least five in the geochemical stratigraphy of the flander lavas suggest that they are the result of replenishment fractional crystallization rfc variations in some incompatible trace element ratios such as ta yb and lan ybn and radiogenic isotopes 87sr 86sr 0 70458 0 70607 143nd 144nd 0 51226 0 51241 suggest that the lavas have also been contaminated by approximately 10 of proterozoic 87sr rich upper crust in addition anomalously k rich lava flows with low 87sr 86sr occur close to the base and at the top of the succession it is argued that these are the products of mixing between magmas within the flat tops reservoir system and an influx of strongly potassic melt from lithospheric mantle without subsequent geochemical overprint by the effects of crustal contamination and rfc all of the lavas have incompatible trace element ratios that mostly resemble those of calc alkaline basalts e g their chondrite normalized patterns have troughs at nb and ta these features could result from several alternative processes such as melting within convecting mantle above a low angle subducted slab reaction between various asthenospheric melts and overlying lithospheric mantle and fusion of metasomatized lithospheric mantle as a result of decompression during regional extension

modeling serpentinization applied to the early evolution of enceladus and mimas abstract serpentinization is an exothermic reaction which involves the metamorphic transition of ultramafic rocks and liquid water into hydrated serpentine minerals it has been suggested that serpentinization may be a fundamental process in the development of icy planetary objects prompting a reaction runaway in which heat from serpentinization in a localized region of the body could result in principle in the melting of ice throughout the body we use a 1 dimensional adaptive grid thermal evolution code suited for small and medium sized icy bodies of the solar system which we apply to enceladus and mimas the satellites of saturn the code is used to investigate the multiphase flow of water through a porous rocky medium thus giving us a detailed look on the internal distribution of mass and energy we consider heating by serpentinization reactions accounting for the phase transition of the chemically altered rock and the water lost in the process short lived and long lived radionuclides gravitational potential energy and the introduction of ammonia to modify the thermodynamical properties of water ammonia solution we test several cases with different initial compositions our results show that in a short term radioactive heating scenario enceladus will fully differentiate into a rocky inner core topped by a very thin icy crust considering only long term radioactive heating in the absence of any short term radionuclides serpentinization in enceladus can be triggered providing ammonia is present in the water however long term triggered serpentinization is confined only to the inner core we conclude that serpentinization may have been triggered in enceladus during its early evolution and not in mimas leading to the dichotomy between them based on the assumptions that went into our model we may conclude that the formation time of saturn s satellites was around 3 myr after the formation of calcium aluminum inclusions

interior thermal state of enceladus inferred from the viscoelastic state of the ice shell abstract recent geodetic measurements for enceladus suggest a global subsurface ocean that is thicker beneath the south pole in order to maintain such an ocean viscous relaxation of topography at the base of the ice shell and melting of ice need to be balanced in this study we investigate the interior thermal state that can lead to the relaxation timescale being comparable to the melting timescale our results indicate that a basal heat flux about ten times higher than that due to radiogenic heating or an ice shell tidal heating rate about ten times higher than the conventional estimate of 1 1 gw is necessary if the ice shell is in thermal equilibrium these requirements are concordant with recent astrometric studies

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

seafloor hydrothermal systems driven by the serpentinization of peridotite 1 heat balance models predict that heat released upon serpentinization of peridotites can result in a wide range of hydrothermal venting temperatures temperatures ranging from a few to a few tens of c are likely temperatures 300 c may be possible in conjunction with significant heat input from below low fluid flow rate 10 kg s a high rate of serpentinization 100 kg s or some combination of these factors the volume of fresh lithosphere accessible to serpentinization may limit the duration of an episode of hydrothermal venting when the serpentinization rate exceeds 10 kg s hydrothermal venting driven by high rates of serpentinization may occur episodically as new reaction surfaces are made available by tectonic activity or crack propagation given the uncertainty of several parameters the current episode of venting at the lost city vent field on the mid atlantic ridge may range from 102 to 104 years

low temperature alteration of serpentinized ultramafic rock and implications for microbial life abstract alteration serpentinization of ultramafic rocks is known to generate hydrogen through oxidation of ferrous iron in olivine or pyroxene and reduction of water hydrogen oxidation can act as a primary source for chemolithotrophic microbial communities and it is suggested that hydrogen availability is essential for the existence of a deep subsurface biosphere in this study we focus on ongoing low temperature water rock processes in partially serpentinized dunite from the leka ophiolite complex mid norway we aim to determine whether these reactions release reduced compounds and nutrients that can be utilized by the associated microbial communities the study is based on the chemical and physical alteration features of a 51 m deep rock core as well as the chemical composition of groundwater from the core s borehole the borehole intersects three main fracture zones observations during drilling indicated that water infiltration largely takes place along the deepest zone the rock in the fracture zones is nearly completely altered to serpentine brucite magnetite and minor calcite an increase in ph and decrease in mg si and alkalinity of the groundwater along the borehole from the deepest to the outermost fracture zone reflect ongoing water rock reactions where dissolution of brucite serpentine and calcite and precipitation of chrysotile hydromagnesite and iron hydroxide are most likely to occur detection of both h 2 and o 2 in the groundwater influenced by the outermost fracture zone suggests that the local development of highly reducing conditions in the narrow fractures is due to low water rock ratios and to dissolution of fe ii containing brucite and serpentine resulting in the formation and successive diffusion of h 2 into the oxic borehole oxidation of h 2 reduced fe and mn nh 4 and ch 4 are all potential energy yielding reactions that could be utilized by chemolithotrophic microorganisms using dissolved organic or inorganic carbon as possible carbon sources methane could result from microbial oxidation of h 2 and reduction of co 2 or from the degradation of organic matter the results demonstrate that low temperature water rock reactions in serpentinized ultramafic rock lead to production of reduced chemical species that could support primary producers in diverse microbial communities

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

have olivine will gas serpentinization and the abiogenic production of methane on mars 1 spatial variability of methane ch4 on mars suggests the presence of localized subsurface sources here we show that olivine hydration in the martian regolith and crust may be a major ch4 source which contributed significantly to the warming of early mars methane production is kinetically and thermodynamically favored during low t aqueous alteration of olivine rich rocks sustained release of ch4 on present day mars may come through the breakdown of ancient ch4 hydrates and from springs driven by geothermal heat

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

tidal heating and the long term stability of a subsurface ocean on enceladus abstract tidal dissipation has been suggested as the heat source for the south polar thermal anomaly on enceladus we find that under present day conditions and assuming maxwellian behavior tidal dissipation is negligible in the silicate core dissipation may be significant in the ice shell if the shell is decoupled from the silicate core by a subsurface ocean we have run a series of self consistent convection and conduction models in 2d axisymmetric and 3d spherical geometry in which we include the spatially variable tidal heat production we find that in all cases the shell removes more heat from the interior than can be produced in the core by radioactive decay resulting in cooling of the interior and the freezing of any ocean under likely conditions a 40 km thick ocean made of pure water would freeze solid on a 30 ma timescale an ocean containing other chemical components will have a lower freezing point but even a water ammonia eutectic composition will only prolong the freezing not prevent it if the eccentricity of enceladus were higher e 0 015 in the past the increased dissipation in the ice shell may have been sufficient to maintain a liquid layer we cannot therefore rule out the presence of a transient ocean as a relic of an earlier era of greater heating if the eccentricity is periodically pumped up the ocean may have thickened and thinned on a similar timescale as the orbital evolution provided the ocean never froze completely we conclude that the current heat flux of enceladus and any possible subsurface ocean is not in steady state and is the remnant of an epoch of higher eccentricity and tidal dissipation

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

rate of serpentinization in seafloor environments the permeability of partially serpentinized peridotites has been measured near room temperature and found to be in the range of 10 11 to 10 12 darcys or 10 7 to 10 8 cm2 sec 1 comparable to shaley materials serpentinites act as semipermeable membranes to salt ions in ocean crust and deep groundwater environments serpentinization must be a continuous process controlled only by water access to ultramafic rocks through their cover given this it will generate high local strains and stresses with episodic cracking the serpentinization process may also contribute to heat flow and ocean floor topography

modeling kuiper belt objects charon orcus and salacia by means of a new equation of state for porous icy bodies abstract we use a one dimensional adaptive grid thermal evolution code to model kuiper belt objects charon orcus and salacia and compare their measured bulk densities with those resulting from evolutionary calculations at the end of 4 6 gyr our model assumes an initial homogeneous composition of mixed ice and rock and follows the multiphase flow of water through the porous rocky medium consequent differentiation and aqueous chemical alterations in the rock heating sources include long lived radionuclides serpentinization reactions release of gravitational potential energy due to compaction and crystallization of amorphous ice the density profile is calculated by assuming hydrostatic equilibrium to be maintained through changes in composition pressure and temperature to this purpose we construct an equation of state suitable for porous icy bodies with radii of a few hundred km based on the best available empirical studies of ice and rock compaction and on comparisons with rock porosities in earth analog and solar system silicates we show that the observed bulk densities can be reproduced by assuming the same set of initial and physical parameters including the same rock ice mass ratio for all three bodies we conclude that the mass of the object uniquely determines the evolution of porosity and thus explains the observed differences in bulk density the final structure of all three objects is differentiated with an inner rocky core and outer ice enriched mantle the degree of differentiation too is determined by the object s mass