numerical modeling of endogenic thermal anomalies on europa abstract a variety of recent resurfacing features have been observed on europa which may produce thermal anomalies detectable by a future mission however the likelihood of such a detection depends on their size and lifetimes the results of this numerical study suggest that the lifetime of a thermal anomaly associated with the emplacement of 100 m of water onto the surface of europa is several hundred years and 10 years for 10 m of water if warm ice is emplaced on the surface instead of liquid water these lifetimes decrease by up to a factor of two exploration of model parameters indicates that a thin insulating surface layer can double thermal anomaly lifetimes anomalies emplaced at a latitude of 80 can remain detectable nearly a factor of two longer than those at equatorial latitudes and anomalies on the night side can remain detectable for up to 20 longer than those on the day side high temperatures are very short lived as the surface ice cools very rapidly to below 200 k due to sublimation cooling assuming steady state resurfacing the number of detectable thermal anomalies associated with the emplacement of 100 m of water would be on the order of 10 if the typical resurfacing area is 15 km 2 if recent resurfacing is dominated by chaos regions with typical areas of 100 to 1000 km 2 and lifetimes of 1000 to 4000 years the number of detectable thermal anomalies would be on the order of 1 to 10

resurfacing history of europa from pole to pole geological mapping abstract we produced geologic maps from two regional mosaics of galileo images across the leading and trailing hemispheres of europa in order to investigate the temporal distribution of units in the visible geologic record five principal terrain types were identified plains bands ridges chaos and crater materials which are interpreted to result from 1 tectonic fracturing and lineament building 2 cryovolcanic reworking of surface units with possible emplacement of sub surface materials and 3 impact cratering the geologic histories of both mapped areas are essentially similar and reflect some common trends tectonic resurfacing dominates the early geologic record with the formation of background plains by intricate superposition of lineaments the opening of wide bands with infilling of inter plate gaps and the buildup of ridges and ridge complexes along prominent fractures in the ice it also appears that lineaments are narrower and more widely spaced with time the lack of impact craters overprinted by lineaments indicate that the degree of tectonic resurfacing decreased rapidly after ridged plains formation in contrast the degree of cryovolcanic resurfacing appears to increase with time as chaos formation dominates the later parts of the geologic record these trends and the transition from tectonic to cryovolcanic dominated resurfacing could be attributed to the gradual thickening of europa s cryosphere during the visible geologic history that comprises the last 2 or 30 80 myr of europa s history an originally thin brittle ice shell could be pervasively fractured or melted through by tidal and endogenic processes the degree of fracturing and plate displacements decreased with time in a thickening shell and lineaments became narrower and more widely spaced formation of chaos regions could have occurred where the thickness threshold for solid state convection was exceeded and can be aided by preferential tidal heating of more ductile ice in a long term context it is not clear at this point whether this inferred thickening trend would reflect a drastic change in the thermal evolution of the satellite or cyclic or irregular episodes of tectonic and cryovolcanic activity

effects of plasticity on convection in an ice shell implications for europa abstract europa s surface exhibits numerous pits uplifts and disrupted chaos terrains that have been suggested to result from convection in the ice shell to test this hypothesis we present numerical simulations of convection in an ice shell including the effects of plasticity which provides a simple continuum representation for brittle or semibrittle deformation along discrete fractures plastic deformation occurs when stresses reach a specified yield stress at lower stresses the fluid flow follows a newtonian temperature dependent viscosity four distinct modes of behavior can occur for yield stresses exceeding 1 bar plastic effects are negligible and stagnant lid convection with no surface motion and minimal topography results at intermediate yield stresses a stagnant lid forms but deforms plastically leading to surface velocities up to several millimeters per year slightly smaller yield stresses allow episodic catastrophic overturns of the upper conductive lid with transient stagnant lids forming in between overturn events the smallest yield stresses allow continual recycling of the upper lid with simultaneous gradual ascent of warm ice to the surface and descent of cold near surface ice into the interior the exact yield stresses over which each regime occurs depend on the ice shell thickness melting temperature viscosity and activation energy for viscous creep to form hummocky matrix and translate chaos plates by several kilometers substantial surface strain must accompany chaos formation and the three plasticity dominated convection modes described here can provide such deformation our simulations suggest that if yield stresses of 0 2 1 bar are relevant to europa then convection in europa s ice shell can produce chaos like structures at the surface however our simulations have difficulty explaining europa s numerous pits and uplifts when plasticity forces the upper lid to participate in the convection dynamic topography of 50 100 m amplitude results but the topographic structures generally have diameters of 30 100 km an order of magnitude wider than typical pits and uplifts none of our simulations produced isolated pits or uplifts of any diameter

thermal and topographic tests of europa chaos formation models from galileo e15 observations stereo topography of an area near tyre impact crater europa reveals chaos regions characterised by marginal cliffs and domical topography rising to 100 200 m above the background plains the regions contain blocks which have both rotated and tilted we tested two models of chaos formation a hybrid diapir model in which chaos topography is caused by thermal or compositional buoyancy and block motion occurs due to the presence of near surface 1 3 km melt and a melt through model in which chaos regions are caused by melting and refreezing of the ice shell none of the hybrid diapir models tested generate any melt within 1 3 km of the surface owing to the low surface temperature a model of ocean refreezing following melt through gives effective elastic thicknesses and ice shell thicknesses of 0 1 0 3 and 0 5 2 km respectively however for such low shell thicknesses the refreezing model requires implausibly large lateral density contrasts 50 100 kg m 3 to explain the elevation of the centres of the chaos regions although a global equilibrium ice shell thickness of 2k m is possible if europa s mantle resembles that of io it is unclear whether local melt through events are energetically possible thus neither of the models tested here gives a completely satisfactory explanation for the formation of chaos regions we suggest that surface extrusion of warm ice may be an important component of chaos terrain formation and demonstrate that such extrusion is possible for likely ice parameters 2005 elsevier inc all rights reserved

persistence of thin ice regions in europa s ice crust 1 extensive data from planetary spacecraft as well as celestial mechanics models support the existence of a subsurface ocean on europa 100 km thick maintained by a tidal heat flux models in which the overlying ice crust is less than 20 km thick permit breaches in the ice due to impact events or thermal plumes from the tidally heated core we apply a two dimensional thermal model to the analysis of the refreezing of a hole in the ice crust following a breach event our model incorporates heat produced by tidal heating of europa in two ways a basal heat flux from europa s silicate and iron core together with volumetric heating of the ice shell we compare our refreezing timescales to those obtained from a model where viscous flow in the base of the ice crust fills the hole we find that catastrophic breaches in europa s ice crust may produce regions of relatively thin ice persisting up to 1 my these breaches are closed by viscous flow when radii are small 10 50 km and by conductive refreezing for larger radii especially if europa s crust has a high basal heat flow due to a hot core detection of the ice ocean interface by orbital detection of the temperature anomalies or radar sounding would be most probable in the vicinity of these events

rheological properties of water ice applications to satellites of the outer planets 1 abstract the icy moons of the outer solar system have not been quiescent bodies in part because many have a substantial water component and have experienced significant internal heating we can begin to understand the thermal evolution of the moons and the rate of viscous relaxation of surface topography because we now have good constraints on how ice in several of its polymorphic forms flows under deviatoric stress at planetary conditions details of laboratory derived flow laws for pure polycrystalline ice are reviewed in detail one of the more important questions at hand is the role of ice grain size grain size may be a dynamic quantity within the icy moons and it may or may not significantly affect rheology one recent beneficiary of revelations about grain size sensitive flow is the calculation of the rheological structure of europa s outer ice shell which may be no thicker than 20 km

heat transfer of ascending cryomagma on europa abstract jupiter s moon europa has a relatively young surface 60 90 myr on average which may be due in part to cryovolcanic processes current models for both effusive and explosive cryovolcanism on europa may be expanded and enhanced by linking the potential for cryovolcanism at the surface to subsurface cryomagmatism the success of cryomagma transport through europa s crust depends critically on the rate of ascent relative to the rate of solidification the final transport distance of cryomagma is thus governed by initial melt volume ascent rate overall ascent distance transport mechanism i e diapirism diking or ascent in cylindrical conduits and melt temperature and composition the last two factors are especially critical in determining the budget of expendable energy before complete solidification here we use these factors as constraints to explore conditions under which cryomagma may arrive at europa s surface to facilitate cryovolcanism we find that 1 5 km radius warm ice diapirs ascending from the base of a 10 km thick stagnant lid can reach the shallow subsurface in a partially molten state cryomagma transport may be further facilitated if diapirs travel along pre heated ascent paths under certain conditions cryolava transported from 10 km depths in tabular dikes or pipe like conduits may reach the surface at temperatures exceeding 250 k ascent rates for these geometries may be high enough that isothermal transport is approached cryomagmas containing significant amounts of low eutectic impurities can also be delivered to europa s surface by propagating dikes or pipe like conduits

the heat flow of europa the heat flow from europa has profound implications for ice shell thickness and structure as well as for the existence of an internal ocean which is strongly suggested by magnetic data the brittle ductile transition depth and the effective elastic thickness of the lithosphere are here used to perform heat flow estimations for europa results give preferred heat flow values for a typical geological strain rate of 10 15 s 1 of 70 110 mwm 2 for a brittle ductile transition 2 km deep the usually accepted upper limit for the brittle ductile transition depth in the ice shell of europa 24 35mwm 2 for an effective elastic thickness of 2 9 km supporting a plateau near the cilix impact crater and 130 mwm 2 for effective elastic thicknesses of 0 4 km proposed for the lithosphere loaded by ridges and domes these values are clearly higher than those produced by radiogenic heating thus implying an important role for tidal heating the 19 25 km thick ice shell proposed from the analysis of size and depth of impact structures suggests a heat flow of 30 45 mwm 2 reaching the ice shell base which in turn would imply an important contribution to the heat flow from tidal heating within the ice shell tidally heated convection in the ice shell ould be capable to supply 100 mwm 2 for superplastic flow and at the cilix crater region 35 50 mwm 2 for dislocation creep which suggests local variations in the dominant flow mechanism for convection the very high heat flows maybe related to ridges and domes could be originated by preferential heating at special settings

sedimentological and palaeoenvironmental study from waregi hill in the hiwegi formation early miocene on rusinga island lake victoria kenya

chaos on europa the characteristics of chaos regions on europa suggest they may be sites of melt through from below they are wide ranging in size location and age the largest are hundreds of kilometers across most are similar to conamara with a matrix reminiscent of frozen slush and often rafts of preexisting crust edges are of two types ramps perhaps the tapering of crustal thickness to zero or cliffs where rafts appear to have broken clear from the shore the small features called lenticulae generally appear to be small chaoses with textured matrix and occasional rafts and many domes may be small chaoses raised by isostatic compensation following refreezing of the crust the extent of chaoses often appears to be limited by ridge systems with the coastline parallel and set back by a distance comparable to the width of the ridge system preexisting ridges often survive as causeways or chains of rafts boundaries of chaoses are apparently not controlled by preexisting cracks consistent with formation by a thermal rather than mechanical process ridges may thicken the crust such that melt through is more likely but not always between ridge systems subsequent cracks and ridges form across preexisting chaoses ranging from fresh cases with few cracks or ridges across them with paths somewhat jagged as they meander among rafts to heavily dissected examples isolated tilted raft like blocks surrounded by densely ridged terrain may be relics of former chaotic terrain thus two fundamental resurfacing processes have alternated over europa s geological history melt through at various places and times forming chaos terrain and tectonic cracking and dilation building densely ridged and banded terrain mapping of chaos features based on morphology at 200 m shows that they correlate albeit imperfectly with dark regions in global 2 km resolution mosaics except dark regions due to ridge margins or craters extrapolating from our mapping of the 5 of europa covered by appropriate images at least 18 of the surface of europa is fresh appearing chaos an additional 4 is slightly modified chaos and much more older chaotic terrain has been overprinted by tectonic structures considerable area has been available globally to accommodate the expansion of crust that occurs along extensional ridges and bands chaos ubiquity suggests that europan geology has been dominated by the effects of having liquid water under a very thin ice shell with chaos regions being widespread indicators of occasional zero shell thickness

new oligocene early miocene microflora from the southwestern turkana basin palaeoenvironmental implications in the northern kenya rift we report five oligocene early miocene pollen assemblages from the loperot 1 exploration well drilled in the semi desert lokichar basin latitude 02 21 46 15 n longitude 35 52 23 47 e ground elevation 615 m above msl near lake turkana in northern kenya they represent the second oldest plant microfossils so far recovered from east africa and add significantly to the paleogene neogene tropical african fossil plant record the loperot pollen indicate a mosaic environment of semi deciduous forest and humid woodland whose floristic composition presents strong affinities with the vegetation occurring today in the guinea congolia zambezia phytogeographical transition zone with a rainfall more than 1000 mm year and a well defined dry season the weak representation of poaceae and herbaceous taxa characteristic of grassland dry bushland or savanna and the abundance of shade tolerant plants such as ferns all point to a vegetation composed to a variety of communities with closed forest formations predominant the lack of typical temperate mountains elements mainly podocarpus and juniperus today widespread on the east african highlands indicates that the geography of the region was different from that of today the plateaux or uplands adjacent to the lokichar basin were probably still not high enough during this period of early rifting in east africa to support the temperate coniferous forests characteristic of the plio pleistocene

ice melting and downward transport of meltwater by two phase flow in europa s ice shell with its young surface very few impact craters and the abundance of tectonic and cryovolcanic features europa has likely been subjected to relatively recent endogenic activity morphological analyses of chaos terrains and double ridges suggest the presence of liquid water within the ice shell a few kilometers below the surface which may result from enhanced tidal heating a major issue concerns the thermal gravitational stability of these water reservoirs here we investigate the conditions under which water can be generated and transported through europa s ice shell we address particularly the downward two phase flow by solving the equations for a two phase mixture of water ice and liquid water in one dimensional geometry in the case of purely temperate ice we show that water is transported downward very efficiently in the form of successive porosity waves the time needed to transport the water from the subsurface region to the underlying ocean varies between 1 and 100 kyr depending mostly on the ice permeability we further show that water produced in the head of tidally heated hot plumes never accumulates at shallow depths and is rapidly extracted from the ice shell within less than a few hundred kiloyears our calculations indicate that liquid water will be largely absent in the near subsurface with the possible exception of cold conductive regions subjected to strong tidal friction recently active double ridges subjected to large tidally driven strike slip motions are perhaps the most likely candidates for the detection of transient water lenses at shallow depths on europa

the micromorphology of gypsum and halite in reg soils the negev desert israel gypsum and halite are the most common salts in reg soils developed on alluvial parent material under extremely arid conditions in the negev desert israel the aim of this paper is to document the changes in the micromorphology of these salts at different stages of reg soil development on two alluvial fan chronosequences the micromorphological analyses included thin section observations and scanning electron microscope and electron microprobe analyses in this arid soil environment gypsum and halite possess a variety of crystal forms which may change with depth in a single profile and or between profiles of different ages the variety of crystal forms results from changes in the microenvironmental conditions that occur in desert reg soils over time poikilitic lenticular gypsum is found in all reg soils and is distributed throughout the profiles the conditions needed for such crystals to form are high ionic impurities and deposition in a void system where space is not limiting microcrystalline alabastrine gypsum is only found in mature reg soils and is crystallized when the profile has high amounts of fine material and a well developed desert pavement in a well developed reg soil profile indicators such as a well developed desert pavement and high amounts of fine earth limit the leaching depth and cause gypsum deposition from supersaturated soil solutions under high evaporation rates close to the surface prismatic and fibrous gypsum are less common low amounts of prismatic gypsum are found in young and mature soils while fibrous gypsum is found only in mature soils in re cemented shattered gravel the halite crystal form is mainly cubic with low amounts of host material incorporated into the crystal it occurs predominantly in mature reg soil profiles through the crystallization from supersaturated soil solutions at the depth of maximum water penetration although the alabastrine prismatic and fibrous gypsum and cubic halite are deposited in a displacive manner no correlation was found between their occurrence and the distribution of shattered gravel in the soil profile

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

dynamical investigation of a thickening ice shell implications for the icy moon europa abstract current astrobiological exploration of the outer solar system is largely driven by understanding planetary ice ocean systems such as those of europa and enceladus the ice shell thickness that affects the dynamics of the ice ocean system is determined by the balance between heat loss via convection and conduction and the heat production via tidal dissipation and radiogenic decay in this study we investigate how ice shells of such ocean moons grow and how convection inside them evolves as the system cools we perform geodynamical calculations to investigate the ice shell thickness and growth rate as the system cools from a warm initial condition we study both diffuse and localized end member modes of tidal dissipation within the ice shell we find that as the ice shell cools and thickens there is a reconfiguration of the convection patterns increasing the size of convection cells that leads to a relatively significant increase in the ice shell growth rate

tidal dissipation surface heat flow and figure of viscoelastic models of io abstract the distribution of hot spots on io s surface and io s figure constrain models of io s interior voyager observations indicate that most hot spots and volcanic plumes are close to the equator recently however it has been proposed that a large low albedo feature in the south polar region may be the source of 40 of the surface heat flow we calculate spatial distributions of the dissipation rate surface heat flow and the figures of three and four layer maxwell rheology models of io by using the correspondence principle the models are required to satisfy the observed surface heat flow constraint and are consistent with the composition of a dehydrated c2 chondrite they consist of an inviscid fe fes core and viscoelastic silicate mantle and lithosphere layers a comparison of the calculated equilibrium figure with the observed figure of io supports the chosen core radius of 980 km in addition the four layer model has a partially molten asthenosphere a few tens of kilometers thick the preferred three layer model has a mantle shear modulus of 10 10 pa and a viscosity of 2 10 16 pa s consistent with rock properties the tidal dissipation rate for this model is largest along the polar axis integration of the dissipation rate over radius gives a surface heat flow with maxima at the poles and minima near the sub jovian and anti jovian points in contrast the dissipation rate in a molten or partially molten incompressible asthenosphere has maxima near the equator and is close to zero at the poles the asthenosphere dissipation rate is mainly a function of asthenosphere viscosity and thickness the thinner the asthenosphere the smaller is the required viscosity a 50 km thick asthenosphere requires a viscosity of about 10 8 pa s a strong south polar hot spot if it can be confirmed by infrared observation favors dissipation in the mantle but does not exclude dissipation in a partially molten asthenosphere equatorial hot spots and the concentration of prometheus type plumes near the equator favor asthenosphere heating but do not rule out deep mantle dissipation both asthenosphere and deep mantle heating may contribute to io s surface heat flow the properties of magma transport through the lithosphere and the planform of mantle convection might exert a control on the surface expression of heating at greater depth

constraining the thickness of europa s water ice shell insights from tidal dissipation and conductive cooling abstract the time of crystallization of a 100 km thick ocean on europa is estimated using a stefan style solidification solution this solution is then extended to estimate the present thickness of the ice shell it is assumed that the shell is initially in a steady state conductive regime and the ocean is taken to be an infinite liquid half space cooling from above we find that in the absence of tidal heating and without the presence of low eutectic impurities to serve as anti freezes a 100 km thick ocean solidifies in about 64 myr conversely when considering the present thickness of europa s ice shell if tidal heating is included at a global dissipation rate of 1 tw the shell is found to be on average approximately 28 km thick however if this dissipative heating is solely restricted to the shell the local rate of heating may vary significantly due to crustal compositional heterogeneities and it is shown that this process may in turn produce thermal maxima in the crust which could lead to local melting and structural instabilities perhaps associated with the formation of chaos regions our approach is also extended to ganymede and callisto in order to estimate the time of solidification of their putative subsurface oceans and the current thicknesses of their ice i shells

active formation of chaos terrain over shallow subsurface water on europa the galileo spacecraft revealed a number of chaos regions on jupiter s moon europa where the surface terrain appears to have been disrupted from below in many places the surface contains sharp edged blocks or rafts of ice that have at some point been flipped or rotated some characteristics of these regions have been hard to explain such as the fact that the archetypal conamara chaos stands above its surroundings and contains matrix domes schmidt et al apply lessons learned from analogous processes within earth s subglacial volcanoes and ice shelves to an analysis of archival data that suggests chaos terrain forms above liquid water lenses that are perched only 3 kilometres deep within the ice shell the data suggest that ice water interactions and freeze out give rise to the varied morphology of chaos terrains implying that more water is involved than has been previously appreciated for instance the sunken topography of thera macula a large chaos area may indicate that europa is actively resurfacing over a lens comparable in volume to north america s great lakes europa the innermost icy satellite of jupiter has a tortured young surface1 2 3 4 and sustains a liquid water ocean1 2 3 4 5 6 below an ice shell of highly debated thickness1 2 3 4 5 7 8 9 10 quasi circular areas of ice disruption called chaos terrains are unique to europa and both their formation and the ice shell thickness depend on europa s thermal state1 2 3 4 5 7 8 9 10 11 12 13 14 15 16 17 no model so far has been able to explain why features such as conamara chaos stand above surrounding terrain and contain matrix domes10 18 melt through of a thin few kilometre shell3 7 8 is thermodynamically improbable and cannot raise the ice10 18 the buoyancy of material rising as either plumes of warm pure ice called diapirs1 9 10 11 12 13 14 15 or convective cells16 17 in a thick 10 kilometres shell is insufficient to produce the observed chaos heights and no single plume can create matrix domes10 18 here we report an analysis of archival data from europa guided by processes observed within earth s subglacial volcanoes and ice shelves the data suggest that chaos terrains form above liquid water lenses perched within the ice shell as shallow as 3 kilometres our results suggest that ice water interactions and freeze out give rise to the diverse morphologies and topography of chaos terrains the sunken topography of thera macula indicates that europa is actively resurfacing over a lens comparable in volume to the great lakes in north america

origin and evolution of castalia macula an anomalous young depression on europa europa s castalia macula region was comprehensively imaged by the galileo spacecraft on several orbits at both local and regional resolutions and with different illumination geometries using these datasets we have mapped and identified the different geological units within the castalia area and derived digital elevation models dems of the topography within most of the castalia macula region using these data sets in combination allows us to map the geology and topography of this area in greater detail than perhaps any other site on europa castalia macula consists of unusually dark and reddish material most of which is confined to a broad topographic depression 350 m deep located between two large uplifted domes 900 and 750 m high to the north and south respectively the preservation of topography at the bottom of castalia macula indicates that dark material initially filled the depression to a certain depth but was subsequently removed via drainage resulting in a dark stain up to the original equipotential surface superposition and topographic relationships suggest that the castalia macula plains deposit formed prior to uplift of both domes and at least two distinct episodes of chaos formation have occurred near and on top of the northern dome it appears that castalia macula is comparatively young and was active relatively recently therefore it could provide an ideal place to sample material that has recently been erupted from the subsurface and may have been in communication with europa s ocean these factors combine to make castalia macula a very attractive site for a future europa lander

heat flow lenticulae spacing and possibility of convection in the ice shell of europa abstract two opposing models to explain the geological features observed on europa s surface have been proposed the thin shell model states that the ice shell is only a few kilometers thick transfers heat by conduction only and can become locally thinner until it exposes an underlying ocean on the satellite s surface according to the thick shell model the ice shell may be several tens of kilometers thick and have a lower convective layer above which there is a cold stagnant lid that dissipates heat by conduction whichever the case from magnetic data there is strong support for the presence of a layer of salty liquid water under the ice the present study was performed to examine whether the possibility of convection is theoretically consistent with surface heat flows of 100 200 mw m 2 deduced from a thin brittle lithosphere and with the typical spacing of 15 23 km proposed for the features usually known as lenticulae it was obtained that under europa s ice shell conditions convection could occur and also account for high heat flows due to tidal heating of the convective nearly isothermal interior but only if the dominant water ice rheology is superplastic flow with activation energy of 49 kj mol 1 this is the rheology thought dominant in the warm interior of the ice shell in this case the ice shell would be 15 50 km thick furthermore in this scenario explaining the origin of the lenticulae related to convective processes requires ice grain size close to 1 mm and ice thickness around 15 20 km

near surface heating on enceladus and the south polar thermal anomaly 1 strike slip motion is predicted to be a consequence of diurnal tidal stresses in most satellites of the outer solar system such motion can lead to near surface heating through friction or viscous dissipation here we discuss the effect of near surface shear heating on convection in the underlying ice shells of icy satellites we present models of convection in spherical shells including tidal and shear heating and show that localized near surface heating enhances convective upwelling beneath it the near surface heating promotes regional melting of the ice shell which likely results in subsidence of the surface topography the long wavelength geoid resulting from the subsidence plume buoyancy and dynamic topography may lead to small 4 per ma amounts of true polar wander potentially contributing to the south polar location of the observed thermal anomaly however compositional effects are likely required in addition to thermal effects to generate larger degrees of reorientation

causes characteristics and consequences of convective diapirism on europa 1 we investigate the hypothesis that the 10 km diameter dome shaped features seen on europa s surface are caused by strongly temperature dependent convection in which upwellings form isolated diapirs or thermals we use the observed lower limit on dome diameter of 4 km to deduce that the conductive stagnant lid thickness must be 5 km such a lid thickness implies a minimum surface heat flux of 90 mwm 2 compatible with recent estimates of tidal heating we also use the mean observed dome diameter to infer a lower thermal boundary layer thickness of 1 km we find that the ice is probably deforming in the diffusion creep regime with a grain size in the range 0 02 0 06 mm the fraction of internal heating is 0 5 the ice viscosity 10 12 10 13 pa s and the crustal solidification rate 5km ma index terms 6218 planetology solar system objects jovian satellites 5430 planetology solid surface planets interiors 8147 5418 planetology solid surface planets heat flow 5455 planetology solid surface planets origin and evolution citation nimmo f and m manga causes characteristics and consequences of convective diapirism on europa geophys res lett 29 23 2109 doi 10 1029 2002gl015754 2002

evaluation of models for the formation of chaotic terrain on europa chaotic terrain on europa is interpreted to be the result of the breakup of brittle surface materials over a mobile substrate two end member models have been proposed for the mobile substrate a liquid water ocean or solid warm ductile ice direct contact between the brittle surface ice and an underlying ocean might be accomplished by melting through europa s ice shell but plausible sources of thermal energy are insufficient to locally melt through the ice shell we calculate that a liquid or partially liquid substrate is probably necessary for tilted blocks to be observed challenging a solid state model we propose that a model in which chaos areas on europa formed over bodies of melt or partial melt within the ice shell may be the best match to observational and thermal constraints such bodies of melt within the ice shell may be triggered by warm diapirs of relatively clean ice that partially melted an overlying layer of lower melting temperature such as ice contaminated with salts

europa s crust and ocean origin composition and the prospects for life abstract we have considered a wide array of scenarios for europa s chemical evolution in an attempt to explain the presence of ice and hydrated materials on its surface and to understand the physical and chemical nature of any ocean that may lie below we postulate that following formation of the jovian system the europan evolutionary sequence has as its major links a initial carbonaceous chondrite rock b global primordial aqueous differentiation and formation of an impure primordial hydrous crust c brine evolution and intracrustal differentiation d degassing of europa s mantle and gas venting e hydrothermal processes and f chemical surface alteration our models were developed in the context of constraints provided by galileo imaging near infrared reflectance spectroscopy and gravity and magnetometer data low temperature aqueous differentiation from a carbonaceous ci or cm chondrite precursor without further chemical processing would result in a crust ocean enriched in magnesium sulfate and sodium sulfate consistent with galileo spectroscopy within the bounds of this simple model a wide range of possible layered structures may result the final state depends on the details of intracrustal differentiation devolatilization of the rocky mantle and hydrothermal brine reactions could have produced very different ocean crust compositions e g an ocean crust of sodium carbonate or sulfuric acid or a crust containing abundant clathrate hydrates realistic chemical physical evolution scenarios differ greatly in detailed predictions but they generally call for a highly impure and chemically layered crust some of these models could lead also to lateral chemical heterogeneities by diapiric upwellings and or cryovolcanism we describe some plausible geological consequences of the physical chemical structures predicted from these scenarios these predicted consequences and observed aspects of europa s geology may serve as a basis for further analys is and discrimination among several alternative scenarios most chemical pathways could support viable ecosystems based on analogy with the metabolic and physiological versatility of terrestrial microorganisms

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

evidence for a weakly stratified europan ocean sustained by seafloor heat flux we interpret chaos type features on the surface of europa as melt through structures formed by rotationally confined steady and or episodic oceanic plumes that rise to the base of the ice shell from magmatically heated regions of the seafloor smaller lenticular features in the vicinity of chaos type regions might be formed by baroclinically unstable vortices that spin off the main convective plume or by persistent heating from localized hydrothermal venting sites the ocean is assumed to be weakly stratified because of turbulent convection generated by heating from below and cooling from above seafloor heating maintained by tidal dissipation in the rocky interior generates an estimated global heat flux of 8 7 1012 w and limits the mean ice thickness to 2 5 km for seafloor heat sources with radii r that are less than the ocean s deformation radius rd nd n is the brunt vaisala frequency d is the water depth and is the coriolis parameter the diameters of chaos type regions are expected to diminish from o 100 km within equatorial regions to o 10 km at high latitudes assuming spatially uniform water depth and density structure where r rd the scale of the source region determines the scale of the melt through features provided there is sufficient time before refreezing ice rafts in large melt through regions are imbedded in episodes of preferentially anticyclonic circulation corresponding to clockwise counterclockwise motions in the northern southern hemisphere we calculate that 1021 j were required to melt the ice in the 100 km diameter conamara chaos region and that for a steady localized heat flux f 1011 w 1 of the global heat flux it took 1000 years for the initial melt through to occur assuming that ice raft displacements in conamara chaos occurred during a major melt through event maximum current speeds in the region were o 10 cm s 1 and refreezing occurred within 20 hours a lack of well defined ice drift in other major melt through regions suggests that these regions formed through episodes of melting and refreezing that modified the existing structure but left little time for the establishment of organized advective motion

multistage evolution and variable motion history of agenor linea europa abstract europa the second galilean moon of jupiter is composed of a silicate mantle and an ice shell which overlies a supposed subsurface ocean the surface of europa is scarred with fractures varying in morphology dimensions and geometry we focus on agenor linea a 1500 km bright band that extends across europa s antijovian to trailing southern hemisphere agenor linea is morphologically a band like strike slip fault however it experienced at least three evolutionary growth phases marked by three zones of varying albedo each with a different geological history structures within the band material and kinematic indicators are consistent with formation through oblique left lateral dilation followed by normal dilation and right lateral strike slip movement or combinations thereof these motions produced a cumulative maximum right lateral offset of 29 5 km and a maximum band width of 34 km we interpret agenor linea to have formed primarily in response to the combined effects of nonsynchronous rotation stress and diurnal tidal flexing if so its orientation is optimal for right lateral oblique opening in the current global stress field consistent with its most recent kinematic behavior a small amount of offset of relatively young tension fractures that postdate cryospheric disruption by lenticulae suggest the possibility of ongoing activity along agenor in contrast to a previously published model in which strike slip duplexing was the primary process of band formation this study shows that initial dilation of three distinct morphological zones under disparate stress orientations preceded strike slip motion that resulted in both localized and distributed deformation features within the zones across the width of the band

cryovolcanic emplacement of domes on europa abstract here we explore the hypothesis that certain domes on europa may have been produced by the extrusion of viscous cryolavas a new mathematical method for the emplacement and relaxation of viscous lava domes is presented and applied to putative cryovolcanic domes on europa a similarity solution approach is applied to the governing equation for fluid flow in a cylindrical geometry and dome relaxation is explored assuming a volume of cryolava has been rapidly emplaced onto the surface nonphysical singularities inherent in previous models for dome relaxation have been eliminated and cryolava cooling is represented by a time variable viscosity we find that at the onset of relaxation bulk kinematic viscosities may lie in the range between 103 and 106 m2 s while the actual fluid lava viscosity may be much lower plausible relaxation times to form the domes which are linked to bulk cryolava rheology are found to range from 3 6 days to 7 5 years we find that cooling of the cryolava while dominated by conduction through an icy skin should not prevent fluids from advancing and relaxing to form domes within the timescales considered determining the range of emplacement conditions for putative cryolava domes will shed light on europa s resurfacing history in addition the rheologies and compositions of erupted cryolavas have implications for subsurface cryomagma ascent and local surface stress conditions on europa

numerical simulations of convection in europa s ice shell implications for surface features 1 europa s icy surface displays numerous small 5 to 30 km diameter pits spots and uplifts that have been suggested to result from convection in the ice shell to test this hypothesis we present numerical simulations of convection in europa s ice shell including temperature dependent viscosity and tidal heating ice shells 15 and 50 km thick are considered consistent with several estimates of the shell thickness on europa the convection produces deep pits consistent with some of the observed features when the lithospheric viscosity is 103 105 times greater than that of the underlying ice but greater viscosity contrasts lead to topography insufficient to explain the observed pits if ductile creep is the only deformation mechanism these results imply that convection cannot produce the observed pits and uplifts because in that case the predicted surface viscosity exceeds that of the warm underlying ice by at least a factor of 1010 however the strength of europa s surface may be low enough for plastic deformation to play a role in the convection opening the possibility that convection could produce some of europa s pits for plausible viscosities 1013 pa s at the melting temperature the pits are 100 300 m deep and 10 20 km in diameter greater or lesser viscosities lead to wider or narrower pits respectively none of our simulations produced isolated uplifts of any diameter however so these probably formed by another mechanism the convection can induce surface stresses 1 bar which exceeds the inferred strength of europa s crust and indicates the likelihood of surface disruption the maximum tidal heat fluxes that can be transported by convection at realistic ice viscosities are 0 05 0 07 w m 2

europa initial galileo geological observations abstract images of europa from the galileo spacecraft show a surface with a complex history involving tectonic deformation impact cratering and possible emplacement of ice rich materials and perhaps liquids on the surface differences in impact crater distributions suggest that some areas have been resurfaced more recently than others europa could experience current cryovolcanic and tectonic activity global scale patterns of tectonic features suggest deformation resulting from non synchronous rotation of europa around jupiter some regions of the lithosphere have been fractured with icy plates separated and rotated into new positions the dimensions of these plates suggest that the depth to liquid or mobile ice was only a few kilometers at the time of disruption some surfaces have also been upwarped possibly by diapirs cryomagmatic intrusions or convective upwelling in some places this deformation has led to the development of chaotic terrain in which surface material has collapsed and or been eroded

distribution of chaotic terrain on europa the locations of chaotic terrain are mapped over all regions of europa for which we have adequate resolution 200 m or better and appropriate lighting geometry sun angle 35 from the local horizontal comprising 9 of the total surface of the satellite nearly 30 of the mapped area is occupied by chaotic terrain recognizable at 200 m resolution and sampling at higher resolution suggests that at least 10 more may be covered by small chaos features the largest contiguous area of chaotic terrain is 1300 km across chaotic terrain displays variations in freshness of appearance probably because of aging by fine scale tectonics resurfacing of previous chaotic terrain by larger scale tectonics or disruption by newer chaos are common chaos formation is not necessarily recent relative to tectonics both types of process appear to have gone on diachronously the size distribution shows no dominant or characteristic size and appears to have been controlled by competition from tectonics which has created terrain that occupies more than half of the surface of europa

plate tectonic evolution of the southern margin of eurasia in the mesozoic and cenozoic abstract thirteen time interval maps were constructed which depict the triassic to neogene plate tectonic configuration paleogeography and general lithofacies of the southern margin of eurasia the aim of this paper is to provide an outline of the geodynamic evolution and position of the major tectonic elements of the area within a global framework the hercynian orogeny was completed by the collision of gondwana and laurussia whereas the tethys ocean formed the embayment between the eurasian and gondwanian branches of pangea during late triassic early jurassic times several microplates were sutured to the eurasian margin closing the paleotethys ocean a jurassic cretaceous north dipping subduction boundary was developed along this new continental margin south of the pontides transcaucasus and iranian plates the subduction zone trench pulling effect caused rifting creating the back arc basin of the greater caucasus proto south caspian sea which achieved its maximum width during the late cretaceous in the western tethys separation of eurasia from gondwana resulted in the formation of the ligurian penninic pieniny magura ocean alpine tethys as an extension of middle atlantic system and a part of the pangean breakup tectonic system during late jurassic early cretaceous times the outer carpathian rift developed the opening of the western black sea occurred by rifting and drifting of the western central pontides away from the moesian and scythian platforms of eurasia during the early cretaceous cenomanian the latest cretaceous paleogene was the time of the closure of the ligurian pieniny ocean adria alcapa terranes continued their northward movement during eocene early miocene times their oblique collision with the north european plate led to the development of the accretionary wedge of the outer carpathians and its foreland basin the formation of the west carpathian thrusts was completed by the miocene the thrust front was still propagating eastwards in the eastern carpathians during the late cretaceous the lesser caucasus sanandaj sirjan and makran plates were sutured to the iranian afghanistan plates in the caucasus caspian sea area a north dipping subduction zone jumped during paleogene to the scythian turan platform the shatski terrane moved northward closing the greater caucasus basin and opening the eastern black sea the south caspian underwent reorganization during oligocene neogene times the southwestern part of the south caspian basin was reopened while the northwestern part was gradually reduced in size the collision of india and the lut plate with eurasia caused the deformation of central asia and created a system of nw se wrench faults the remnants of jurassic cretaceous back arc systems oceanic and attenuated crust as well as tertiary oceanic and attenuated crust were locked between adjacent continental plates and orogenic systems

unraveling climatic changes from intraprofile variation in oxygen and hydrogen isotopic composition of goethite and kaolinite in laterites an integrated study from yaou french guiana an integrated study of o and h isotopes in the lateritic profile of yaou french guiana was undertaken to investigate the usefulness of stable isotopes as tracers of climatic changes in continental environments the studied profile is composed of a 27 m thick saprolite mostly developed in the past under wet and dry tropical climate in association with a duricrust overlain by a 3 m thick yellow latosol formed more recently under present equatorial hot and humid climate 18o d values determined for weathering goethite pseudomorphs after pyrite and kaolinite microcrystalline clay groundmass throughout the 30 m deep profile reflect formation temperatures consistent with present 25 c and realistic past climatic temperatures 20 c 30 c indicating that weathering minerals formed in isotopic equilibrium with their genetic environment and were not subjected to significant isotope exchange after formation a distinct shift downward 2 for 18o 15 for d from low to high 18o d values occurs around 20 m depth in the saprolite it is interpreted as recording the change from the past tropical to the present equatorial climate goethite and kaolinite in the 5 10 m thick saprolite interval immediately above the active basement weathering front are in isotopic equilibrium with modern water and must have formed under present equatorial humid conditions in contrast goethite and kaolinite found higher up in the saprolite and in the duricrust formed in the past under tropical wet and dry climate from waters distinctly depleted in 18o and d relative to modern water the marked depletion of paleo meteoric water at yaou most likely reflects a more contrasted or monsoonal character of the ancient tropical climate the present study shows that ancient weathering minerals in lateritic profiles preserve their 18o d values and carry a time signal the time signal is best expressed in minerals formed rapidly at the weathering front and not subjected to post formational remobilization such as the goethite pseudomorphs after pyrite occurring at yaou groundmass kaolinite is more susceptible to partial remobilization through successive dissolution precipitation reactions which may obliterate the paleoclimatic signal unraveling the climatic record carried by weathering minerals in old soil systems is greatly enhanced by studying both oxygen and hydrogen isotopic compositions

europa tidal heating of upwelling thermal plumes and the origin of lenticulae and chaos melting europa we show that tidal energy can be preferentially focused in rising plumes for viscosities in agreement with laboratory experiments when the plume cores reach the base of the outer cold brittle layer they spread laterally causing shallow melting disruption and formation of terrain similar to lenticulae and chaos we show that this mechanism can readily explain the major characteristics of chaos and lenticulae even if the average outer solid ice layer thickness is larger than 20 km

iapetus geophysics rotation rate shape and equatorial ridge iapetus has preserved evidence that constrains the modeling of its geophysical history from the time of its accretion until now the evidence is a its present 79 33 day rotation or spin rate b its shape that corresponds to the equilibrium figure for a hydrostatic body rotating with a period of 16 h and c its high equatorial ridge which is unique in the solar system this paper reports the results of an investigation into the coupling between iapetus thermal and orbital evolution for a wide range of conditions including the spatial distributions with time of composition porosity short lived radioactive isotopes slri and temperature the thermal model uses conductive heat transfer with temperature dependent conductivity only models with a thick lithosphere and an interior viscosity in the range of about the water ice melting point can explain the observed shape short lived radioactive isotopes provide the heat needed to decrease porosity in iapetus early history this increases thermal conductivity and allows the development of the strong lithosphere that is required to preserve the 16 h rotational shape and the high vertical relief of the topography long lived radioactive isotopes and slri raise internal temperatures high enough that significant tidal dissipation can start and despin iapetus to synchronous rotation this occurred several hundred million years after iapetus formed the models also constrain the time when iapetus formed because the successful models are critically dependent upon having just the right amount of heat added by slri decay in this early period the amount of heat available from short lived radioactivity is not a free parameter but is fixed by the time when iapetus accreted by the canonical concentration of 26al and to a lesser extent by the concentration of 60fe the needed amount of heat is available only if iapetus accreted between 2 5 and 5 0 myr after the formation of the calcium aluminum inclusions as found in meteorites models with these features allow us to explain iapetus present synchronous rotation its fossil 16 h shape and the context within which the equatorial ridge arose

a passive probe for subsurface oceans and liquid water in jupiter s icy moons abstract we describe an interferometric reflectometer method for passive detection of subsurface oceans and liquid water in jovian icy moons using jupiter s decametric radio emission dam the dam flux density exceeds 3000 times the galactic background in the neighborhood of the jovian icy moons providing a signal that could be used for passive radio sounding an instrument located between the icy moon and jupiter could sample the dam emission along with its echoes reflected in the ice layer of the target moon cross correlating the direct emission with the echoes would provide a measurement of the ice shell thickness along with its dielectric properties the interferometric reflectometer provides a simple solution to sub jovian radio sounding of ice shells that is complementary to ice penetrating radar measurements better suited to measurements in the anti jovian hemisphere that shadows jupiter s strong decametric emission the passive nature of this technique also serves as risk reduction in case of radar transmitter failure the interferometric reflectometer could operate with electrically short antennas thus extending ice depth measurements to lower frequencies and potentially providing a deeper view into the ice shells of jovian moons

ice diapirs on europa implications for liquid water early examinations of galileo images of europa revealed features that look like low topographic domes these small 5 10 km in radius domes have been interpreted as surface manifestations of diapirs as a way to probe the subsurface structure of europa we investigate the possibility that thermally driven ice diapirism created these surface features we use a previously developed analytic model for rising diapirs to estimate the initial radii of the diapirs their initial depth the temperature of the medium through which they rise and their formation timescales we assume that the diapirs originate at the boundary layer between solid ice and whatever underlies it whether it be liquid water or solid rock our results show that the diapirs originate at a depth of no more than a few tens of kilometers since the h2o layer on europa is substantially thicker than this our results support the view that liquid water recently existed beneath the ice on europa at this location at a depth of no more than a few tens of kilometers further the ice must have been warm 250 270 k and was therefore likely to have been convecting

effects of anisotropic viscosity and texture development on convection in ice mantles 1 convection may occur in the ice shells of satellites in the outer solar system the style of convection rate of heat transport and resulting surface features depend on the rheology of ice which in turn depends on temperature grain size stress and crystallographic preferred orientation cpo here we study the effect of cpo development and anisotropic viscosity on convection by coupling a model of polycrystalline ice deformation with a macroscopic flow model despite having a first order effect on velocities and heat transport in a convecting ice shell fabric development is unlikely to be observable either directly by spacecraft based radar or indirectly based on changes in the wavelength or amplitude of dynamic topography

geology and origin of europa s mitten feature murias chaos 1 the mitten provisionally named murias chaos by the international astronomical union is a region of elevated chaos like terrain in the leading hemisphere of europa its origin had been explained under the currently debated theories of melting through a thin lithosphere or convection within a thick one galileo observations reveal several characteristics that suggest that the mitten is distinct from typical chaos terrain and point to a different formational process photoclinometric elevation estimates suggest that the mitten is slightly elevated with respect to the surrounding terrain geologic relations indicate that it must have raised significantly from the plains in its past resembling disrupted domes on europa s trailing hemisphere moreover the mitten material appears to have extruded onto the plains and flowed for tens of kilometers the area subsequently subsided as a result of isostatic adjustment viscous relaxation and or plains loading using plate flexure models we estimated the elastic lithosphere in the area to be several kilometers thick we propose that the mitten originated by the ascent and extrusion of a large thermal diapir thermal mechanical modeling shows that a mitten sized plume would remain sufficiently warm and buoyant to pierce through the crust and flow unconfined on the surface such a diapir probably had an initial radius between 5 and 8 km and an initial depth of 20 40 km consistent with a thick lithosphere model in this scenario the mitten appears to represent the surface expression of the rare ascent of a large diapir in contrast to lenticulae and chaos terrain which may form by isolated and clustered small diapirs respectively

water generation and transport below europa s strike slip faults jupiter s moon europa has a very young surface with the abundance of unique terrains that indicate recent endogenic activity morphological models as well as spectral observations suggest that it might possess shallow lenses of liquid water within its outer ice shell here we investigate the generation and possible accumulation of liquid water below the tidally activated strike slip faults using a numerical model of two phase ice water mixture in two dimensional cartesian geometry our results suggest that generation of shallow partially molten regions underneath europa s active strike slip faults is possible but their lifetime is constrained by the formation of rayleigh taylor instabilities due to the negative buoyancy of the melt once formed typically within a few million years these instabilities efficiently transport the meltwater through the shell consequently the maximum water content in the partially molten regions never exceeds 10 which challenges their possible detection by future exploration mission

interior structure models and tidal love numbers of titan 1 interior models of a differentiated titan with an internal ammonia water ocean and chondritic radiogenic heat production in an undifferentiated rock iron core have been calculated we assume thermal and mechanical equilibrium and calculate the structure of the interior as a function of the thickness of an ice i layer on top of the ocean as well as the moment of inertia factor and the tidal love numbers for comparison with cassini gravity data the love numbers are linearly dependent on the thickness of the ice i shell at constant rheology parameters but decrease by one order of magnitude in the absence of an internal ocean ice shell thicknesses are between 90 and 105 km for models with 5 wt ammonia and for core densities between 3500 and 4500 kg m 3 for 15 wt ammonia the shell is 65 to 70 km thick we use a strongly temperature dependent viscosity parameterization of convective heat transport and find that the stagnant lid comprises most of the ice i shell tidal heating in the warm convective sublayer is of minor importance the internal ocean is several hundred kilometers thick and its thickness decreases with increasing thickness of the ice shell core sizes vary from 1500 to 1800 km radius with associated moment of inertia factors of 0 30 0 01

convective instability in europa s floating ice shell models of the tidally heated floating ice shell proposed for the jovian satellite europa generally find shell thicknesses less than 30 km past parameterized convection models indicated that such shells are stable against convective overturn which otherwise ostensibly leads to freezing of the ocean underneath here i apply the temperature dependent viscosity convection scaling developed by solomatov and coworkers to the europan ice shell the temperature dependent properties of ice are linearized about 260 k as any convective interior should be close to this temperature with the colder ice forming an essentially passive stagnant lid ice shells 10 km thick are found to be unstable to convection at their base for melting point viscosities of 1013 pa s as linearized by tidal stresses if the ice deforms by superplastic creep but such low viscosities require small grain sizes 1 mm this requirement may be met if grain sizes observed in terrestrial polar glaciers can be strain rate scaled to europa regardless convection at the base of the ice shell if initiated may not freeze the ocean because of tidal heating a stagnant lid regime ice shell is much more dissipative than a conductive shell of the same thickness such a shell should thin not thicken and the potential exists for further thermal instabilities and runaways

long period seismology on europa 1 physically consistent interior models 1 in order to examine the potential of seismology to determine the interior structure and properties of europa it is essential to calculate seismic velocities and attenuation for the range of plausible interiors we calculate a range of models for the physical structure of europa as constrained by the satellite s composition mass and moment of inertia we assume a water ice shell a pyrolitic or a chondritic mantle and a core composed of pure iron or iron plus 20 weight percent of sulfur we consider two extreme mantle thermal states hot and cold given a temperature and composition we determine density seismic velocities and attenuation using thermodynamical models while anelastic effects will be negligible in a cold mantle and the brittle part of the ice shell strong dispersion and dissipation are expected in a hot convective mantle and the bulk of the ice shell there is a strong relationship between different thermal structures and compositions the hot mantle may maintain temperatures consistent with a liquid core made of iron plus light elements for the cold scenarios the possibility of a solid iron core cannot be excluded and it may even be favored the depths of the ocean and core mantle boundary are determined with high precision 10 km and 40 km respectively once we assume a composition and thermal structure furthermore the depth of the ocean is relatively insensitive 4 km to the core composition used

on the origins of band topography europa we use stereo derived topography of extensional bands on europa to show that these features can be elevated by 100 150 m with respect to the surroundings and that the positive topography sometimes extends beyond the band margins lateral variations in shell thickness cannot maintain the observed topography for timescales greater than 0 1 myr lateral density variations can maintain the observed topography indefinitely mean density contrasts of 5 and 50 kg m 3 are required for shell thicknesses of 20 and 2 km respectively density variations caused by temperature contrasts require either present day heating or that bands are young features 1 myr old stratigraphic analyses suggest that these mechanisms are unlikely the observation that bands form from ridges may be explained by an episode of shear heating on ridges weakening the ridge area and leading to strain localization during extension fracture porosity is likely to persist over myr timescales in the top one third to one quarter of the conductive part of the ice shell lateral variations in this porosity of order 20 are the most likely mechanism for producing band topography if the ice shell is thin 2 km porosity variations of 2 or less are required if the shell is thicker 20 km if the ice shell is thick lateral variations in salt content are a more likely mechanism warm ice will tend to lose dense low melting temperature phases and be buoyant relative to colder salt rich ice thus lateral density variations will arise naturally if bands have been the sites of either localized heating or upwelling of warm ice during extension

formation of bands and ridges on europa by cyclic deformation insights from analogue wax experiments 1 we perform a set of analogue wax experiments aimed at understanding the processes and conditions that lead to lineament formation on europa we heat a layer of wax from below and cool it from above so that a solid layer of wax forms above a molten layer simulating either the liquid ocean or the actively convecting part of the ice shell the solid layer of wax is then deformed periodically simulating the cyclic strain caused by tides or by the satellite s nonsynchronous rotation we find that the formation and morphology of lineaments that develop in the solid wax layer are governed by two main dimensionless parameters the ratio of the cooling timescale for the solid layer to the deformation timescale and the dilation quotient which is defined as the magnitude of net extension during one cycle of deformation divided by the amplitude of the periodic deformation for 1 features form that qualitatively resemble bands and ridge complexes on europa we conclude that diurnal tides may be responsible for the formation of bands on europa if the conducting layer of ice is a few hundred meters thick and is underlain by a convecting layer of ice features resembling double ridges can form if the ice shell has a thickness of a few kilometers and periodic strains are caused by europa s nonsynchronous rotation

cyclic nature of lamination in the tithonian solnhofen plattenkalk of southern germany and its palaeoclimatic implications in the tithonian solnhofen plattenkalk malm 2 of southern germany layers of purely micritic limestone are rhythmically interbedded with ones of marly micritic limestone it appears that this alternation was formed under control of the tithonian orbital variations the fourier spectral analysis shows that on a decimetric to metric scale the long term cyclicities in the number of laminae per centimetre are in agreement with those found in the bed thickness series varying from 0 7 to 1 3 m cycles the number of laminae of the solnhofen formation ranges from about 5 800 to about 12 800 laminae per main cycle this indicates that under an assumption that the main cycle of the solnhofen formation corresponds to the tithonian precessional one a single lamina represents a multi year time interval particularly in the short term cyclic domain the laminated sequence contains clearly millimetric cycles consisting of about two to three cyclic components it implies that laminae formation may result from the composite effect of two or three distinct climatic processes

the origin of domes on europa the role of thermally induced compositional diapirism 1 the surface of jupiter s moon europa is peppered by topographic domes interpreted as sites of intrusion and extrusion diapirism is consistent with dome morphology but thermal buoyancy alone cannot produce sufficient driving pressures to create the observed dome elevations instead diapirs may initiate by thermal convection that induces compositional segregation exclusion of impurities from warm upwellings allows sufficient buoyancy for icy plumes to create the observed surface topography provided the ice shell has a small effective elastic thickness 0 2 to 0 5 km and contains low eutectic point impurities at the few percent level this model suggests that the ice shell may be depleted in impurities over time

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

comparison of the bedform distribution and dynamics of modern and ancient sandy ephemeral flood deposits in the southwestern karoo region south africa abstract during january 1981 unusually high rainfall patterns in the semi arid southwestern karoo region of south africa gave rise to catastrophic floods in the area the most devastating of which was the ephemeral flash flood that partially destroyed the town of laingsburg flood waters at laingsburg spread from a dry river bed rising to a depth of 12 m within 7 h washing away houses and burying the town with up to 3 5 m of sand and silt facies sequences and bedforms in the laingsburg flood deposits are related to specific subenvironments and flow conditions during the flood event two large scale sedimentary units in erosive contact with each other were deposited by two major discharge pulses within the same flood event vertical and lateral variations in the bedform distributions reflect fluctuations in flow velocity and turbulence comparison is drawn between the laingsburg flood deposits and fluvial sandstones of the permian lower beaufort in the southwestern karoo the multistoried sandstone bodies composed mainly of a horizontally laminated lithofacies are interpreted as the products of a complex series of ephemeral flooding events individual storey units in the palaeochannel sequences are generally envisaged as the deposits of different floods however evidence from the modern flood shows that separate pulses of a single flooding episode can also produce a sequence of storey units bounded by erosive scours spectacular palaeosurfaces in the lower beaufort also have modern analogues in the laingsburg overbank deposits discussion on the preservation potential of delicate sedimentary structures and biogenic traces on these surfaces emphasizes the necessity for pulsatory deposition of bedload and suspended load material over short intervals of time by comparing facies profiles and surface bedforms the ephemeral fluvial facies model for the lower beaufort is critically appraised

coupling mantle convection and tidal dissipation applications to enceladus and earth like planets 1 anelastic dissipation of tidal forces likely contributes to the thermal budget of several satellites of giant planets and earth like planets closely orbiting other stars in order to address how tidal heating influences the thermal evolution of such bodies we describe here a new numerical tool that solves simultaneously mantle convection and tidal dissipation in a three dimensional spherical geometry since the two processes occur at different timescales tidal dissipation averaged over a forcing period is included as a volumetric heat source for mantle dynamics for the long term flow a purely viscous material is considered whereas a maxwell like formalism is employed for the tidal viscoelastic problem due to the strongly temperature dependent rheological properties of both mechanisms the coupling is achieved via the temperature field the model is applied to two examples enceladus and an earth like planet for enceladus our new 3 d method shows that the tidal strain rates are strongly enhanced in hot upwellings when compared with classical methods moreover the heat flux at the base of enceladus ice shell is strongly reduced at the poles thus favoring the preservation of a liquid reservoir at depth for earth like planets tidal dissipation patterns are predicted for different orbital configuration thermal runaway is observed for orbital periods smaller than a critical value e g 30 days for an eccentricity of 0 2 and 3 2 resonance this is likely to promote large scale melting of the mantle and io like volcanism

formation of lenticulae on europa by saucer shaped sills abstract europa s surface contains numerous quasi elliptical features called pits domes spots and small chaos we propose that these features collectively referred to as lenticulae are the surface expression of saucer shaped sills of liquid water in europa s ice shell in particular the inclined sheets of water that surround a horizontal inner sill limit the lateral extent of intrusion setting the lateral dimension of lenticulae furthermore the inclined sheets disrupt the ice above the intrusion allowing the inner sill to thicken to produce the observed relief of lenticulae and to fracture the crust to form small chaos scaling relationships between sill depth and lateral extent imply that the hypothesized intrusions are or were 1 5 km below the surface liquid water is predicted to exist presently under pits and for a finite time under chaos and domes

cryomagma ascent on europa abstract europa s surface exhibits morphological features which associated with a low crater density might be interpreted to have formed as a result of recent cryovolcanic activity in particular the morphology of smooth deposits covering parts of the surface and their relationship to the surrounding terrains suggest that they result from liquid extrusions furthermore recent literature suggests that the emplacement of liquid related features such as double ridges lenticulae and chaos could result from the presence of liquid reservoirs beneath the surface we model the ascent of liquid water through a fracture or a pipe like conduit from a subsurface reservoir to europa s surface and calculate the eruption time scale and the total volume extruded during the eruption as a function of the reservoir volume and depth we also estimate the freezing time of a subsurface reservoir necessary to trigger an eruption our model is derived for pure liquid water and for a briny mixture outlined by kargel 1991 81 wt h2o 16 wt mgso4 3 wt na2so4 considering compositional data for salt impurities for europa we discuss the effect of mgso4 and na2so4 on the cryomagma freezing time scale and ascent for plausible reservoir volumes and depths in the range of 106 m3 v 1010 m3 and 1 km h 10 km respectively the total extruded cryolava volume ranges from 103 m3 to 108 m3 and the duration of the eruptions varies from few minutes to few tens of hours the freezing time scale of the cryomagma reservoirs varies with cryomagma composition and the temperature gradient in the ice shell from a few days to a thousand years for pure water cryomagma and from a few months to a 104 years for briny cryomagma

brine mobilization during lithospheric heating on europa implications for formation of chaos terrain lenticula texture and color variations the background lineated plains on europa are locally highly modified and destroyed in regions known as chaos and lenticulae produced there are 1 isolated fragments and polygons of background material which rotate and translate 2 matrix which fills in the areas between the fragments and polygons and 3 surface discolorations using observations and constraints from high resolution galileo images we find that a model for the formation of these terrains which involves mobilization and migration of brines and a possible percolation phase transition as the europan lithosphere is warmed can readily explain the vast majority of their characteristics in addition the presence of melt fractions of a few percent in the adjacent ice framework may enhance the creep rate and the accompanying deformation rates the characteristics and distribution of lenticulae suggest that among the strong candidates for heat sources for brine migration and ice mobilization processes is diapirism linked to solid state convection in a layer underlying a brittle lid and possibly overlying a liquid water layer

geometry and spatial distribution of lenticulae on europa the surface of europa contains several types of roughly elliptical features collectively called lenticulae lenticulae may have positive relief domes or negative relief pits may disrupt the crust chaos or discolor the surface spots some lenticulae have attributes of both domes and chaos dome chaos we map the location dimensions and shapes of all lenticulae and their interactions with other lenticulae and lineaments we find that 1 pits and domes have similar sizes 2 chaos are larger than the other lenticulae 3 pits are clustered within the trailing antijovian quadrant and the leading subjovian quadrant whereas domes dome chaos and chaos terrains are more uniformly distributed 4 the areal density for all lenticulae is not uniform 5 lenticulae do not divert the path of younger lineaments such as ridges taken together these observations are consistent with conceptual models in which lenticulae are created by intrusion of liquid water bodies or convection within the ice shell additionally the observations are consistent with the notion that each type of lenticula is a surface expression of dynamics within the ice shell at a different stage of lenticulae evolution the similar size and shape of pits and domes suggests that one may evolve into the other because domes are more numerous and more uniformly distributed than pits they are more likely to represent the end stage of this evolution assuming the end stage leaves a longer lasting surface expression models also predict that larger features are more likely to disrupt the crust which is consistent with dome chaos and chaos being larger than pits and domes we find no examples of lineaments offsetting pits but lineaments do cross some chaos pits also have a preferred northwest southeast elongation whereas domes dome chaos and chaos do not have a preferred orientation if lenticulae orientation is influenced by crustal stress then pits may have formed during a shorter time interval than the other features as a result pits may sample a shorter more recent time period than domes dome chaos and chaos consistent with pits being the earliest stage in the evolution of lenticulae we find no strong evidence that lineaments are deflected by lenticulae implying either that the stresses created by lenticulae are too small to influence lineaments or that the complete evolution of lenticulae occurs on a time scale that is short compared to the time between the formation of lineaments at a given location

mapping europa s microfeatures in regional mosaics new constraints on formation models abstract europa is an unusual world and its surface features provide clues as to how it has evolved we mapped characterized and analyzed small 100 km2 in area endogenic features on europa s surface in order to identify patterns among and within different types of features and provide observational tests for formation models to create a fully digitized and validated data set of these microfeatures we merged data sets obtained by previous mapping studies that focused on small chaos domes pits spots and hybrid features in moderate resolution 230 m pix images of europa including the four main regional map areas we expanded upon the definition of a recently identified feature definition type here called hybrids and suggest more quantitative metrics for describing pits spots domes and microchaos across all four regions mapped we find that microchaos are the most numerous followed by pits and domes respectively spots are the least common features and the smallest which might indicate an observational bias as they may contain disruptions smaller than what is visible at this scale microchaos features are on average larger and darker than all other microfeature types we compare our observations to the findings and predictions of previous numerical modeling studies and suggest that the observations are most consistent with cryovolcanism and liquid water sill models while no one model is able to explain all the observations there are elements of each that should be considered in future modeling studies

the contribution of termites to the microgranular structure of soils on the uasin gishu plateau kenya abstract the structure of many clay soils in tropical africa is composed of microaggregates that range in size from 0 03 to 1 mm these structural units are often very stable and known as pseudo sand or pseudo silt their presence is detected from the loamy feel of the soil this paper tests the hypothesis that termites contribute to a stable microgranular i e finely aggregated soil structure a termite mound was selected on pedologically unaffected clayey weathering material derived from phonolite the fate of microaggregates produced by termites has been followed through the various stages of mound building field evidence was supplemented with microscopic analysis development of the mound begins when lumps of soil are detached from the subsoil by termites and carried as microaggregates up to the surface in the next stage the microaggregates are cemented to form the nest breakdown begins when the nest is abandoned and disintegrates by splash and runoff producing colluvium or is demolished by ants in the final stage this material is integrated in the soil of the mound soil aggregates produced by splash ants and soil forming processes have different size characteristics but the original microaggregates produced by the termites are preserved in the matrix throughout it is assumed that they owe their stability to impregnation with saliva or other body fluid excreted by the termites termites produce also microaggregates in the form of fecal pellets but these appear to be unstable and are found only in the voids of the soil developed during the last stage

conamara chaos region europa reconstruction of mobile polygonal ice blocks new galileo images of europa reveal regions of chaotic terrain in otherwise highly lineated background plains examination of conamara chaos shows that 59 of the region is composed of fine textured matrix material lying at low elevations and formed by destruction of lineated plains while the remainder consists of 139 fragmented polygons of linear textured background plains using through trending linear features we reconstruct the original positions of chaos polygons and find that significant lateral translation and rotation have occurred 78 of the polygons have undergone horizontal translations with most moving between 1 and 5 km and 81 have rotated average rotation of 11 movement of polygons appears to be inward from the chaos margins and clockwise in the center while polygon rotation is evenly clockwise and counterclockwise chaos formation in this region thus involves destruction of over half of the pre existing terrain and mobilization translation and rotation of the remaining polygons implying elevated near surface temperatures and a highly mobile substrate over lateral scales of 100 km

thermal orbital evolution of io and europa coupled thermal orbital evolution models of europa and io are presented it is assumed that io europa and ganymede evolve in the laplace resonance and that tidal dissipation of orbital energy is an internal heat source for both io and europa while dissipation in io occurs in the mantle as in the mantle dissipation model of segatz et al 1988 icarus 75 187 two models for europa are considered in the first model dissipation occurs in the silicate mantle while in the second model dissipation occurs in the ice shell in the latter model ice shell melting and variations of the shell thickness above an ocean are explicitly included the rheology of both the ice and the rock is cast in terms of a viscoelastic maxwell rheology with viscosity and shear modulus depending on the average temperature of the dissipating layer heat transfer by convection is calculated using a parameterization for strongly temperature dependent viscosity convection both models are consistent with the present orbital elements of io europa and ganymede it is shown that there may be phases of quasi steady evolution with large or small dissipation rates in comparison with radiogenic heating phases with runaway heating or cooling and oscillatory phases during which the eccentricity and the tidal heating rate will oscillate europa s ice thickness varies between roughly 3 and 70 km dissipation in the silicate layer or 10 and 60 km dissipation in the ice layer suggesting that europa s ocean existed for geological timescales the variation in ice thickness including both convective and purely conductive phases may be reflected in the formation of different geological surface features on europa both models suggest that at present europa s ice thickness is several tens of km thick and is increasing while the eccentricity decreases implying that the satellites evolve out of resonance including lithospheric growth in the models makes it impossible to match the high heat flux constraint for io other heat transfer processes than conduction through the lithosphere must be important for the present io

eruption of lava flows on europa theory and application to thrace macula europa on the basis of its spectral characteristics and its apparently young surface age is likely to be at least partially resurfaced by liquid water volcanic processes however convincing evidence for lava flow morphology in voyager data has not previously been found and the lower density of liquid water relative to an overlying solid water ice crust suggests that extrusive volcanism could be uncommon we examine a candidate lava flow like feature thrace macula and compare its characteristics with theoretical predictions for the ascent and eruption of water magma on europa outlining a range of conditions under which water ice magma could plausibly be erupted to the surface thrace macula 45 s 171 w is a dark lobate feature extending nnw to sse its northern part is centered in a 140 km diameter arcuate to circular lineament and within this zone are radial and concentric lineaments and three dark lobes similar in appearance to flow lobes extending away from a central region for distances of 40 50 and 160 km the 160 km lobe appears to follow local topographic features producing lobate margins at subdued structures broadening locally parallel to structural trends and terminating against a gray band models for the present structure and state of the predominantly h2o exterior of europa range from solid water ice to a thin ice layer overlying a liquid water layer and these conditions may even vary as a function of space and time ascent and eruption of h2o magma through a less dense water ice crust means that sustained effusive eruptions are very difficult to produce if a globally continuous liquid water or salt water layer exists e g crawford and stevenson 1988 kargel 1991 for flows as extensive as the thrace macula feature we thus require magma source regions sufficiently localized that excess pressure can be built up in the source region given the elastic properties of ice at these source depths the most likely scenario is intrusion of silicate magma into the base of an ice crust and melting and mobilization of water magma with this range of magma source settings we model plausible surface vent geometries for a water lava flow interpretation of thrace macula modeling calculations show that flow lobes with the above geometries and thicknesses on the order of 10 m could be formed in water eruptions on europa involving discharge rates of 2 105 m3 s through dikes with widths in the range 5 10 m these discharge rates about 3 times larger than those of terrestrial flood basalts should not be unusual for water eruptions on europa under these conditions and suggest that water volcanic resurfacing could be common on the satellite if source regions meeting these criteria were readily available the lack of abundant similar dark flows could be due to brightening with time or might imply that conditions for their formation grounded or nearly solid ice crust only evolved in the latter part of europan history

pressurized oceans and the eruption of liquid water on europa and enceladus 1 it is difficult for liquid water to erupt onto the surface of icy satellites such as europa and enceladus because liquid water is more dense than ice if the ice shell thickens the volume expansion of ice upon freezing increases pressure in the subsurface ocean the excess pressure is determined by a balance between compression of ocean water and elastic expansion of the ice shell we show that on europa the freezing of 1 10 km of ice generates tangential stresses that exceed the tensile strength of ice excess pressure however is insufficient for liquid water to erupt to the surface within smaller icy satellites such as enceladus ocean pressure can become large enough to cause an eruption of large amounts of liquid water

flow strength of highly hydrated mg and na sulfate hydrate salts pure and in mixtures with water ice with application to europa 1 we selected two europan ice shell candidate highly hydrated sulfate salts for a laboratory survey of ductile flow properties mgso4 7h2o epsomite and na2so4 10h2o mirabilite called ms7 and ns10 respectively polycrystalline samples in pure form and in mixtures with water ice i were tested using our cryogenic high pressure creep apparatus at temperatures 232 t 294 k confining pressures p 50 and 100 mpa and strain rates 4 10 8 7 10 5 s 1 grain size of ns10 samples was 100 m the flow strength of pure ms7 was over 100 times that of polycrystalline ice i at comparable conditions that of pure ns10 over 20 times that of ice in terms of the creep law a n e q rt where r is the gas constant we determine parameter values of a 1012 1 mpa ns 1 n 5 4 and q 128 kj mol for pure ns10 composites of ice i and ns10 of volume fraction ns10 have flow strength c ns10 ns10j 1 ns10 iceij 1 j where j 0 5 making the effect on the flow of ice with low volume fractions of ns10 much like that of virtually undeformable hard rock inclusions being much stronger and denser than ice massive sulfate inclusions in the warmer ductile layer of the europan ice shell are less likely to be entrained in convective ice flow and more likely to be drawn to the base of the ice shell by gravitational forces and eventually expelled with only smaller dispersed sulfate inclusions at probable sulfate 0 2 the shell may be treated rheologically as pure polycrystalline ice with boundary conditions perhaps influenced by the high density and low thermal conductivity of the hydrated salts

the orbital thermal evolution and global expansion of ganymede article history the tectonically and cryovolcanically resurfaced terrains of ganymede attest to the satellite s turbulent geologic history yet the ultimate cause of its geologic violence remains unknown one plausible scenario suggests that the galilean satellites passed through one or more laplace like resonances before evolving into the current laplace resonance passage through such a resonance can excite ganymede s eccentricity leading to tidal dissipation within the ice shell to evaluate the effects of resonance passage on ganymede s thermal history we model the coupled orbital thermal evolution of ganymede both with and without passage through a laplace like resonance in the absence of tidal dissipation radiogenic heating alone is capable of creating large internal oceans within ganymede if the ice grain size is 1 mm or greater for larger grain sizes oceans will exist into the present epoch the inclusion of tidal dissipation significantly alters ganymede s thermal history and for some parameters e g ice grain size tidal q of jupiter a thin ice shell 5 to 20 km can be maintained throughout the period of resonance passage the pulse of tidal heating that accompanies laplace like resonance capture can cause up to 2 5 volumetric expansion of the satellite and contemporaneous formation of near surface partial melt the presence of a thin ice shell and high satellite orbital eccentricity would generate moderate diurnal tidal stresses in ganymede s ice shell larger stresses result if the ice shell rotates non synchronously the combined effects of satellite expansion its associated tensile stress rapid formation of near surface partial melt and tidal stress due to an eccentric orbit may be responsible for creating ganymede s unique surface features

tidally heated convection constraints on europa s ice shell thickness 1 the thickness of europa s ice shell is constrained with numerical experiments of thermal convection including heterogeneous tidal heating thermal convection occurs in the stagnant lid regime with most of the tidal heating located in the bottom half of the layer the addition of tidal heating mainly results in the increase of the temperature of the well mixed interior and in the decrease of the heat flux at the base of the ice layer in many simulations the ice in hot plumes is heated up to its melting point this induces episodic upwellings 0 5 ma of partially molten ice up to the base of the conductive lid with possible implications for the formation of lenticulae and chaos regions the thickness of the convective ice shell in equilibrium with the heat flow from the silicate core is estimated to be about 20 25 km tidal dissipation and surface temperature variations create lateral variations of the ice shell thickness of about 5 km with maxima near the equator at the jovian and anti jovian points and minima at midlatitudes surface heat flux is about 35 40 mw m 2 it is almost constant all over europa s surface even though the tidal dissipation rate is four times larger at the poles than at the equator

thermo compositional convection in europa s icy shell with salinity 1 we present two dimensional numerical simulations of thermo compositional convection to test the hypothesis that the combined buoyancy from both thermal and salinity contrasts in europa s ice shell can produce the numerous uplifts and pits on europa s surface our simulations show that uplifts and pits with amplitude of 100 500 m and diameters of 10 30 km similar to some of the observed features can be produced in a 10 30 km thick ice shell with 2 10 compositional density variations if the viscosity contrast due to temperature variation does not exceed 106 the pit and uplift formation time and lifetime are approximately proportional to the surface viscosity ranging from 104 years to 107 years for viscosity contrasts of 104 106 convection cannot produce substantial surface topography if the viscosity contrast exceeds 107 108 these results imply that thermo compositional convection can only produce europa s pits and uplifts if europa s surface is weak

formation of ridges on europa above crystallizing water bodies inside the ice shell abstract jupiter s second galilean satellite europa is a moon sized body with an icy shell and global ocean approximately 100 km thick surrounding a rocky interior its surface displays extensive tectonic activity in a geologically recent past europa s most ubiquitous surface features double ridges have a central trough flanked by two raised edifices double ridges can extend hundreds of kilometers and appear genetically related to cracks formed in the europan ice shell the origin of the raised flanks has been the center of much debate and many models have been proposed there are also ridges without a central trough single ridges these ridges are far less common than their double ridge counterparts however there are locations where along strike changes in ridge type appear to occur we explore an elastic model in which the ridges form in response to crystallization of a liquid water intrusion in our model liquid water fills tension cracks that open in the europan crust in response to tidal stress or perhaps overpressure of a subsurface ocean the crack would be long and essentially continuous similar to dikes on earth explaining the remarkable continuity and lack of segmentation of europan ridges the freezing of the water would cause a volume expansion compressing and buckling the adjacent crust we find that the geometry of the intruding water body controls the shape of the resulting ridges with single ridges forming above sill like intrusions and double ridges above dike like intrusions in order to match the ridge heights observed for double ridges we would need approximately 1 5 km2 of water intruded at a shallow depth in the ice shell potentially over the course of multiple events deeper intrusions result in a broader lower amplitude ridge than shallow intrusions

paleocene and eocene kaolinite distribution in the south atlantic and southern ocean antarctic climatic and paleoceanographic implications abstract clay mineral associations of paleocene and eocene age have been examined in six drilled sequences from the southern south atlantic and southern ocean these sites are located to provide three depth transects across intermediate water masses widespread abundance of pedogenic smectite at all locations suggests globally warm climates and alternating wet and dry seasons on the adjacent continental margins including antarctica as was the case during the late cretaceous remarkably kaolinite is observed only in paleocene eocene sediments at the highest latitudes of these sites and must have originated from antarctica the restriction of kaolinite to the antarctic region is inferred to have resulted from especially higher rainfall there during the paleocene eocene relative to the lower latitude areas examined this inferred high rainfall is considered to have resulted from globally warm temperatures that increased poleward latent heat transport compensating for a strong heat deficit in the antarctic region relative to the tropics kaolinite was not observed in the latest cretaceous maastrichtian sediments of maud rise antarctica kaolinite first appears in the clay mineralogical assemblages in the earliest paleocene 64 to 64 5 ma at a time of relatively cool intermediate waters and before a warming trend of surface waters currents at intermediate water depths transported fine terrigenous sediments from the antarctica during the latest paleocene and early eocene 59 to 52 ma at a time when the oxygen isotopic strongly in east antarctica during the latest paleocene and early eocene 59 to 59 ma at a time when the oxygen isotopic data indicate maximum warmth of surface and intermediate waters of the southern ocean these are interpreted to reflect a paleocene maximum of antarctic rainfall this development peaked at 57 3 m close to the paleocene eocene boundary a time of maximum warmth based on oxygen isotopic data increased illite content and associated chlorite and random mixed layer clays at the end of the middle eocene 41 ma suggest local development of poorly weathered soils on antarctica favored by a cooling of the southern ocean coeval extension of kaolinite into shallower water depths and similar clay mineral associations in shallower and deeper sites indicate the development of cooler conditions led to an increasing influence of antarctic environments upon intermediate water masses at high latitudes

does europa have a subsurface ocean evaluation of the geological evidence it has been proposed that jupiter s satellite europa currently possesses a global subsurface ocean of liquid water galileo gravity data verify that the satellite is differentiated into an outer h2o layer about 100 km thick but cannot determine the current physical state of this layer liquid or solid here we summarize the geological evidence regarding an extant subsurface ocean concentrating on galileo imaging data we describe and assess nine pertinent lines of geological evidence impact morphologies lenticulae cryovolcanic features pull apart bands chaos ridges surface frosts topography and global tectonics an internal ocean would be a simple and comprehensive explanation for a broad range of observations however we cannot rule out the possibility that all of the surface morphologies could be due to processes in warm soft ice with only localized or partial melting two different models of impact flux imply very different surface ages for europa the model favored here indicates an average age of 50 myr searches for evidence of current geological activity on europa such as plumes or surface changes have yielded negative results to date the current existence of a global subsurface ocean while attractive in explaining the observations remains inconclusive future geophysical measurements are essential to determine conclusively whether or not there is a liquid water ocean within europa today

diapir induced reorientation of saturn s moon enceladus the recent discovery of active water venting from the surface of saturn s icy moon enceladus has caused a ripple of excitement as it suggests the possibility of subsurface liquid water geologically enceladus poses problems one the reason why the hotspot of geological activity is centred precisely on the south pole has been tackled by francis nimmo and robert t pappalardo they identify reorientation of enceladus s rotation axis as the likely cause and an upwelling of low density material to the surface as the cause of that reorientation comparison of the distribution of impact craters on the leading and trailing hemispheres will be a good test of the reorientation part of the theory enceladus is a small icy satellite of saturn its south polar region consists of young tectonically deformed terrain and has an anomalously high heat flux1 2 this heat flux is probably due to localized tidal dissipation within either the ice shell3 or the underlying silicate core4 the surface deformation is plausibly due to upwelling of low density material diapirism5 as a result of this tidal heating here we show that the current polar location of the hotspot can be explained by reorientation of the satellite s rotation axis because of the presence of a low density diapir if the diapir is in the ice shell then the shell must be relatively thick and maintain significant rigidity elastic thickness greater than 0 5 km if the diapir is in the silicate core then enceladus cannot possess a global subsurface ocean because the core must be coupled to the overlying ice for reorientation to occur the reorientation generates large 10 mpa tectonic stress patterns6 that are compatible with the observed deformation of the south polar region2 we predict that the distribution of impact craters on the surface will not show the usual leading hemisphere trailing hemisphere asymmetry a low density diapir also yields a potentially observable negative gravity anomaly

europa s differentiated internal structure inferences from four galileo encounters radio doppler data from four encounters of the galileo spacecraft with the jovian moon europa have been used to refine models of europa s interior europa is most likely differentiated into a metallic core surrounded by a rock mantle and a water ice liquid outer shell but the data cannot eliminate the possibility of a uniform mixture of dense silicate and metal beneath the water ice liquid shell the size of a metallic core is uncertain because of its unknown composition but it could be as large as about 50 percent of europa s radius the thickness of europa s outer shell of water ice liquid must lie in the range of about 80 to 170 kilometers

domes pits and small chaos on europa produced by water sills pits domes and small chaos on europa s surface are quasi circular features a few to a few tens of kilometers in diameter we examine if injection of water sills into europa s ice shell and their subsequent evolution can induce successive surface deformations similar to the morphologies of these features we study the dynamics of water spreading within the elastic part of the ice shell and show that the mechanical properties of ice exert a strong control on the lateral extent of the sill at shallow depths water makes room for itself by lifting the overlying ice layer and water weight promotes lateral spreading of the sill in contrast a deep sill bends the underlying elastic layer and its weight does not affect its spreading in that case the sill lateral extent is limited by the fracture toughness of ice and the sill can thicken substantially after emplacement cooling of the sill warms the surrounding ice and thins the overlying elastic ice layer as a result preexisting stresses in the elastic part of the ice shell increase locally to the point that they may disrupt the ice above the sill small chaos disruption of the surface also allows for partial isostatic compensation of water weight leading to a topographic depression at the surface pit of the order of 10 2 m complete water solidification finally causes expansion of the initial sill volume and results in an uplifted topography dome of 10 2 m

a 17 my old whale constrains onset of uplift and climate change in east africa timing and magnitude of surface uplift are key to understanding the impact of crustal deformation and topographic growth on atmospheric circulation environmental conditions and surface processes uplift of the east african plateau is linked to mantle processes but paleoaltimetry data are too scarce to constrain plateau evolution and subsequent vertical motions associated with rifting here we assess the paleotopographic implications of a beaked whale fossil ziphiidae from the turkana region of kenya found 740 km inland from the present day coastline of the indian ocean at an elevation of 620 m the specimen is 17 my old and represents the oldest derived beaked whale known consistent with molecular estimates of the emergence of modern strap toothed whales mesoplodon the whale traveled from the indian ocean inland along an eastward directed drainage system controlled by the cretaceous anza graben and was stranded slightly above sea level surface uplift from near sea level coincides with paleoclimatic change from a humid environment to highly variable and much drier conditions which altered biotic communities and drove evolution in east africa including that of primates

cryovolcanic features on titan s surface as revealed by the cassini titan radar mapper abstract the cassini titan radar mapper obtained synthetic aperture radar images of titan s surface during four fly bys during the mission s first year these images show that titan s surface is very complex geologically showing evidence of major planetary geologic processes including cryovolcanism this paper discusses the variety of cryovolcanic features identified from sar images their possible origin and their geologic context the features which we identify as cryovolcanic in origin include a large 180 km diameter volcanic construct dome or shield several extensive flows and three calderas which appear to be the source of flows the composition of the cryomagma on titan is still unknown but constraints on rheological properties can be estimated using flow thickness rheological properties of one flow were estimated and appear inconsistent with ammonia water slurries and possibly more consistent with ammonia water methanol slurries the extent of cryovolcanism on titan is still not known as only a small fraction of the surface has been imaged at sufficient resolution energetic considerations suggest that cryovolcanism may have been a dominant process in the resurfacing of titan

material transport across europa s ice shell jupiter s moon europa exhibits a deformed icy surface with salt deposits concentrated along the varied geological features the topographic alignment of salt deposits has been speculated to indicate an endogenic sourcing of the material two way transport of salts from a liquid water ocean beneath the ice shell to the surface and vice versa has been speculated we present dynamical models that demonstrate the incorporation of newly frozen ice into convective plumes within the ice shell caused by convection within the ice shell that drives dynamic topography along the ice ocean boundary the new ice that forms at the freezing front can be transported by the rising ice plumes toward the surface until it is blocked by a high viscosity lid at the surface weakening of the lid by tidal or tectonic forces could then lead to the surface detection of ocean trace chemistry captured in the newly formed ice

a model for the temperature dependence of tidal dissipation in convective plumes on icy satellites implications for europa and enceladus abstract to explain the formation of surface features on europa enceladus and other satellites many authors have postulated the spatial localization of tidal heating within convective plumes however the concept that enhanced tidal heating can occur within a convective plume has not been rigorously tested most models of this phenomenon adopt a tidal heating with a temperature dependence derived for an incompressible homogeneous zero dimensional maxwell material but it is unclear whether this formulation is relevant to the heterogeneous situation of a warm plume surrounded by cold ice to determine whether concentrated dissipation can occur in convective plumes we develop a two dimensional model to compute the volumetric dissipation rate for an idealized vertically oriented isolated convective plume obeying a maxwellian viscoelastic compressible rheology we apply the model to the europa and enceladus ice shells and we investigate the consequences for partial melting and resurfacing processes on these bodies we find that the tidal heating is strongly temperature dependent in a convective ice plume and could produce elevated temperatures and local partial melting in the ice shells of europa and enceladus our calculation provides the first quantitative verification of the hypothesis by sotin et al sotin c head j w tobie g 2002 geophys res lett 29 74 1 and others that the tidal dissipation rate is a strong function of temperature inside a convective plume on europa such localized heating could help allow the formation of domes and chaos terrains by convection on enceladus localized tidal heating in a thermal plume could explain the concentrated activity at the south pole and its associated heat transport of 2 7 gw

a common origin for ridge and trough terrain on icy satellites by sluggish lid convection abstract ridge and trough terrain is a common landform on outer solar system icy satellites examples include ganymede s grooved terrain europa s gray bands miranda s coronae and several terrains on enceladus the conditions associated with the formation of each of these terrains are similar heat flows of order tens to a hundred milliwatts per meter squared and deformation rates of order 10 16 10 12 s 1 our prior work shows that the conditions associated with the formation of these terrains on ganymede and the south pole of enceladus are consistent with vigorous solid state ice convection in a shell with a weak surface we show that sluggish lid convection an intermediate regime between the isoviscous and stagnant lid regimes can create the heat flow and deformation rates appropriate for ridge and trough formation on a number of satellites regardless of the ice shell thickness for convection to deform their surfaces the ice shells must have yield stresses similar in magnitude to the daily tidal stresses tidal and convective stresses deform the surface and the spatial pattern of tidal cracking controls the locations of ridge and trough terrain