global multispectral mosaics of the icy galilean satellites multispectral mosaics of the three icy galilean satellites have been produced from low to moderate resolution voyager images the digital image data have been calibrated using preflight and in flight calibration data and reduced to normal albedos for four color band passes centered at 0 35 0 41 0 48 and 0 59 microns the individual images have been geometrically corrected mosaiked and presented in a normal cylindrical map projection at a uniform scale of 8 km pixel preliminary analysis of the normal albedo data shows that 1 the darkest terrains on the satellites are the dark regions on callisto 2 the brightest regions are bright plains regions on europa and bright fresh craters on ganymede 3 bright craters on ganymede and its dark cratered regions are both significantly brighter than comparable terrains on callisto and 4 europa exhibits several distinct spectral units with regions on the trailing hemisphere having lower relative ultraviolet spectral reflectance than areas on the leading hemisphere this is consistent with proposals that io related plasma impact on europa s trailing side has altered its optical properties

disk resolved photometric analysis of european terrains abstract using hapke s photometric model we examined the photometric textures of a representative subset of the geologic units on europa defined by lucchitta and soderblom 1982 satellites of jupiter pp 521 555 university of arizona press tucson the individual units studied possess the same small mean photometric slope angle as that found by domingue et al 1991 icarus 90 30 42 for the entire disk with one major exception the particles composing the surfaces of most of the units have similar scattering properties however the single particle scattering functions of the two bright plains regions examined are very different from each other and from the other units if the bright plains units are geologically younger than the other units an aging process that affects the single particle phase functions and albedos is inferred in our previous study we concluded that the disk integrated photometric properties of europa could not be explained adequately by ion bombardment however a new study on the effects of ion irradiation on the optical properties of materials sack et al 1991 j geophys res e 96 2 17535 17539 renders this conclusion invalid

layer formation in sedimentary fingering convection author s reali jf garaud p alsinan a meiburg e abstract when particles settle through a stable temperature or salinity gradient they can drive an instability known as sedimentary fingering convection this phenomenon is thought to occur beneath sediment rich river plumes in lakes and oceans in the context of marine snow where decaying organic materials serve as the suspended particles or in the atmosphere in the presence of aerosols or volcanic ash laboratory experiments of houk a green deep sea res vol 20 1973 pp 757 761 and green sedimentology vol 34 2 1987 pp 319 331 have shown sedimentary fingering convection to be similar to the more commonly known thermohaline fingering convection in many ways here we study the phenomenon using three dimensional direct numerical simulations we find evidence for layer formation in sedimentary fingering convection in regions of parameter space where it does not occur for non sedimentary systems this is due to two complementary effects sedimentation affects the turbulent fluxes and broadens the region of parameter space unstable to the unicode stix x1d6fe instability radko j fluid mech vol 497 2003 pp 365 380 to include systems at larger density ratios it also gives rise to a new layering instability that exists in unicode stix x1d6fe stable regimes the former is likely quite ubiquitous in geophysical systems for sufficiently large settling velocities while the latter probably grows too slowly to be relevant at least in the context of sediments in water

zonal motion and structure in jupiter s upper troposphere from voyager infrared and imaging observations abstract voyager infrared data are used to produce global cylindrical projection digital maps of temperature at the 270 and 150 mb pressure levels infrared cloud optical depths at 45 and 5 m wavelength and the ammonia abundance near the 680 mb level voyager imaging data are used to produce maps of orange reflectivity and violet reflectivity effective wavelengths of 0 58 and 0 41 m respectively the zonal motions of the dominant structures in each of the quantities are evaluated using cross correlation of the maps structures in the maps of cloud optical depths ammonia abundance and visible reflectivities show the same zonal motion at almost all latitudes the dominant upper tropospheric thermal structures move at a rate which is far different than the cloud indicators and they remain stationary with respect to the bulk rotation of the planet comparison of these motions with the zonally averaged thermal wind shear inthe upper troposphere indicates that the thermal structures move at a rate far different than the local fluid velocity we present a simple theory which suggests that these slowly moving thermal structures could represent the influence of a disturbance seated in a slowly moving region deep in jupiter s atmospheres although this explanation is not unique intercomparison of the motions and longitudinal alignment of the various cloud indicators with the thermal wind shear in the upper troposphere shows that the few latitudes at which differences exist correlate strikingly with latitudes of largest shear suggesting that the observed differences may reflect height differences in observed cloud features fourier analysis of the maps of temperature at 270 mb show a robust stationary feature at a zonal wavenumber of 9 near 15 n latitude the maps of cloud optical depth at 45 m show a feature at zonal wavenumber 11 near 20 n these periodicities may be related to similar structures recently detected in groundbased observations and their longevity and robustness may indicate preferred wavemodes of the atmosphere

mass transfer and problems of secondary porosity creation in deeply buried hydrocarbon reservoirs abstract secondary porosity created by the post depositional leaching of detrital grains and cements can be of great economic importance the term secondary porosity is only descriptive and does not give any information on whether the porosity of the rock has been enhanced in reality there are two end member volumetric outcomes to the leaching process firstly the mineral can be completely dissolved and its components transported out of the system in such an instance the porosity of the rock will be enhanced secondly it is possible that a mineral will decompose and by product minerals will be precipitated which will occupy approximately the same volume as the original mineral the latter case is more likely where the pore waters are close to equilibrium with the majority of the minerals of the rock this will occur at elevated temperatures and or where the pore waters have been in contact with the rock for a long time these conditions are commonly met during intermediate to deep burial many metastable minerals such as high temperature feldspars probably decompose in this way a consequence of the decomposition of such metastable minerals is that primary porosity will be swapped for secondary and that older and more deeply buried rocks will contain a higher proportion of secondary porosity the mass transport equation may be used to examine the physico chemical environment where enhanced porosities most likely occur during leaching by using a simple non equilibrium mass transport model based on the silica system it is possible to demonstrate the relative importance of flow rate reaction rates specific surfaces and temperature in controlling the areal extent of leaching wide leaching zones are related to high flow rates which in turn promote a high throughput of undersaturated fluid and dispersion leaching over a wide area is also favoured by low reaction rates which will occur at low temperatures although it is true to say that less of a given silicate mineral can be dissolved by an undersaturated pore water at low temperature than at high temperature it is probable that pore fluids from deeply buried sediments are more likely to be close to equilibrium with a given mineral than for instance meteoric water thus the most likely environment for the production of widespread enhanced porosity is in the shallow subsurface the lower flow rates and higher temperatures that are encountered during deep burial diagenesis will result in far narrower more intense leaching zones as a result providing sufficient reactive mineral is present any undersaturated pore water will approach equilibrium in a short distance in order to transport undersaturated pore waters appreciable distances in the deep subsurface it is necessary to minimize their interaction with the host rock this could occur if the pore fluid were to move through a fracture system where it would interact with a far smaller surface area of reactive mineral than if it moved through the pore network

europa s opposition surge in the near infrared interpreting disk integrated observations by cassini vims abstract near infrared observations of europa s disk integrated opposition surge by cassini vims first published in fig 4 of brown et al 2003 icarus 164 461 have now been modeled with the commonly used hapke photometric function the vims data set emphasizes observations at 16 solar phase angles from 0 4 to 0 6 the first time the 1 phase heart of europa s opposition surge has been observed this well in the near ir this data set also provides a unique opportunity to examine how the surge is affected by changes in wavelength and albedo at vims wavelengths of 0 91 1 73 and 2 25 m the geometric albedo of europa is 0 81 0 33 and 0 18 respectively despite this factor of four albedo range however the slope of europa s phase curve at 1 phase is similar at all three wavelengths to within the error bars and this common slope is similar to the phase coefficient seen in visible light observations of europa the two components of the opposition surge involving different models of the physical cause of the surge are the shadow hiding opposition effect shoe and the coherent backscatter opposition effect cboe because of sparse vims phase coverage it is not possible to constrain all the surge parameters at once in a hapke function that has both shoe and cboe accordingly we performed separate hapke fits for shoe only and cboe only surges at 2 25 m where vims data are somewhat noisy both types of surges can mimic the slope of the vims phase curve at 1 phase at 0 91 and 1 73 m however where vims data are cleaner cboe does a noticeably poorer job than shoe of matching the vims phase coefficient at 1 phase in particular the best cboe fit insists on having a steeper phase curve slope than the data this discrepancy suggests that europa s near ir opposition surge cannot be explained by cboe alone and must have a significant shoe component even at wavelengths where europa is bright

the importance of double diffusion to the settling of suspended material the vertical fingering motions which can occur when warm salty water overlies colder fresher water are important to the vertical flux of salt in the ocean an analogous and not uncommon situation is that where turbid water overlies clearer and denser water for the case of an originally sharp horizontal interface between the two water layers associated as an example with an interflow due to a warm muddy river entering a stratified lake the resulting downward sediment flux is compared with that occurring by way of gravitational settling rules are proposed to ascertain when the fingering effect could be important to sedimentation for example it seems that fingering could be of consequence in the situation where the sediment has a diameter of 2 m and the upper layer is about 1 c warmer than the clear lower layer when the upper layer concentration is 1 ppm the effect of fingering on the residence time of a gravitationally stable turbid layer is calculated such layers may be more short lived than commonly thought

the geology and geophysics of kuiper belt object 486958 arrokoth the cold classical kuiper belt a class of small bodies in undisturbed orbits beyond neptune is composed of primitive objects preserving information about solar system formation in january 2019 the new horizons spacecraft flew past one of these objects the 36 kilometer long contact binary 486958 arrokoth provisional designation 2014 mu69 images from the flyby show that arrokoth has no detectable rings and no satellites larger than 180 meters in diameter within a radius of 8000 kilometers arrokoth has a lightly cratered smooth surface with complex geological features unlike those on previously visited solar system bodies the density of impact craters indicates the surface dates from the formation of the solar system the two lobes of the contact binary have closely aligned poles and equators constraining their accretion mechanism

dark halo craters and the thickness of grooved terrain on ganymede dark halo craters in grooved terrain on ganymede represent potential probes of the subsurface geology these craters are surrounded by a broad diffuse low albedo annulus or halo halo radius is linearly proportional to crater radius indicating that the halo is related to the continuous ejecta deposit of the crater and is not removed by natural aging processes such as regolith development and exposure to the space environment the halos have orange violet albedo ratios that are intermediate between ratios associated with grooved terrain and cratered terrain we propose that halos result from the incorporation of cratered terrain material into crater ejecta in uruk sulcus only craters greater than 12 km in diameter have halos indicating that the cratered terrain material there forms a stratigraphic horizon buried at depth in the grooved terrain into which only larger craters can excavate this depth can be calculated from the transition diameter by reconstructing the transient crater we calculate a depth of excavation corresponding to the depth of burial of cratered terrain of 1 0 to 1 6 km this shallow burial is inconsistent with deep subsidence and burial stoping into the interior or lateral spreading apart of ancient cratered terrain units but is consistent with a filled graben model for grooved terrain where relatively clean ice has been emplaced over downdropped blocks of cratered terrain

albedo and color maps of the saturnian satellites abstract maps of the normal reflectances and color ratios 0 58 0 41 m have been prepared from voyager images for the following saturian satellites mimas enceladus tethys dione and rhea albedo and color variegations on these objects are in general much less than those of the galilean satellites enceladus and mimas have no albedo or color variegations greater than 10 in the observed regions of their surfaces with the exception of a small high albedo area in the southern polar region of enceladus which may be similar to the bright wispy streaks linea on rhea and dione we find an albedo dichotomy of 20 between the leading bright and trailing sides of dione and confirm a similar dichotomy found by verbiscer and veverka icarus 1989 82 336 for rhea this dichotomy is not as marked in the color maps differences of 5 10 were found for the hemispheres of these two satellites unlike the galilean satellites there is little general correlation between color and albedo the only clear example we could find of the expected result that higher albedo surfaces are bluer is for the bright wispy streaks linea on the trailing sides of rhea and dione on tethys we see two lower albedo features the one on the trailing side is redder than the ambient terrain whereas the one on the leading side is bluer there is little correlation between mapped geologic units and features and the color albedo patterns rhea and the trailing side of dione are the only examples where correlations exist the higher albedo photometrically bland leading sides of tethys dione and rhea suggest enhanced erosion of this hemisphere by meteoritic and cometary impact in addition the optical properties of these satellites may be affected by two exogenic processes not considered extensively in previous studies alteration of the surfaces by ultraviolet radiation and accretion of particles from saturn s e ring

crater relaxation as a probe of europa s interior viscous relaxation rates of craters are examined to discriminate among models of europa s interior it is shown that the presence of an insulating surface regolith is required for ice lithospheres that do not contain a liquid h2o layer without the presence of such an insulating regolith relaxation times for craters 100 km in diameter are excessively long 1 b y and thus inconsistent with the absence of such features in voyager images finite element calculations indicate that a thick insulating surface frost layer raising surface temperatures 40 k above the solar radiation ambient temperature of 92 k allows a 25 km thick surface viscous layer to relax 100 km diameter craters on the short timescales 100 m y required if the icy lithosphere is 100 km thick and without a liquid h2o layer but containing a subsolidus convecting region surface temperatures need to be raised 20 k by insulation to allow relaxation of craters in this size range to occur within the required time

the influence of diffusive convection on sedimentation from buoyant plumes abstract diffusive convection driven by the differential diffusion of density altering fluid properties may enhance the scavenging of particles from natural buoyant plumes for single phase fluid solute heat systems this phenomenon has been extensively studied because salt fingering generated at the oceanic thermocline is a major mechanism of salt transport in the oceans however the influence of this process on particle laden plumes for example fluvial plumes in lakes and estuaries volcanic clouds and seafloor hydrothermal plumes is largely unknown in this paper we present direct experimental measurements of the interfacial particle flux at the plume base which can be applied to predict particle scavenging from natural buoyant plumes particle flux is measured using a light attenuation technique employing a chain of photodiodes which average concentration over a large number of fingers the results are in good general agreement with earlier studies based on finger velocity flux measurements cover a wide range of conditions from those where diffusive convection dominates to those where settling and diffusive convection are of a similar magnitude for very small particles double diffusive salt finger theory is applicable to two component particulate systems as suggested by earlier studies green t 1987 the importance of double diffusion to the settling of suspended material sedimentology 34 319 331 two component diffusive convection theory is extended to three components in order to predict particle scavenging from marine fluvial plumes which involve the diffusion of sediment salt and heat for larger particles which settle significantly the flux can be approximated by adding the double diffusive and settling fluxes a theory to predict particle transport through the lower layer and sedimentation at the bed is developed based on the observation of strong convection below the plume application of our theory and experimental results indicates that while double diffusion may significantly influence the longitudinal distribution and vertical sorting of deposits from lacustrine plumes the diffusive convection process is generally insignificant in marine plumes observational evidence for lacustrine double diffusion based on water column measurements is presented

resolved spectrophotometric properties of the ceres surface from dawn framing camera images we present a global spectrophotometric characterization of the ceres surface using dawn framing camera fc images we identify the photometric model that yields the best results for photometrically correcting images corrected fc images acquired on approach to ceres were assembled into global maps of albedo and color generally albedo and color variations on ceres are muted the albedo map is dominated by a large circular feature in vendimia planitia known from hst images li et al 2006 and dotted by smaller bright features mostly associated with fresh looking craters the dominant color variation over the surface is represented by the presence of blue material in and around such craters which has a negative spectral slope over the visible wavelength range when compared to average terrain we also mapped variations of the phase curve by employing an exponential photometric model a technique previously applied to asteroid vesta schroder et al 2013b the surface of ceres scatters light differently from vesta in the sense that the ejecta of several fresh looking craters may be physically smooth rather than rough high albedo blue color and physical smoothness all appear to be indicators of youth the blue color may result from the desiccation of ejected material that is similar to the phyllosilicates water ice mixtures in the experiments of poch et al 2016 the physical smoothness of some blue terrains would be consistent with an initially liquid condition perhaps as a consequence of impact melting of subsurface water ice we find red terrain positive spectral slope near ernutet crater where de sanctis et al 2017 detected organic material the spectrophotometric properties of the large vendimia planitia feature suggest it is a palimpsest consistent with the marchi et al 2016 impact basin hypothesis the central bright area in occator crater cerealia facula is the brightest on ceres with an average visual normal albedo of about 0 6 at a resolution of 1 3 km per pixel six times ceres average the albedo of fresh bright material seen inside this area in the highest resolution images 35 m per pixel is probably around unity cerealia facula has an unusually steep phase function which may be due to unresolved topography high surface roughness or large average particle size it has a strongly red spectrum whereas the neighboring less bright vinalia faculae are neutral in color we find no evidence for a diurnal ground fog type haze in occator as described by nathues et al 2015 we can neither reproduce their findings using the same images nor confirm them using higher resolution images fc images have not yet offered direct evidence for present sublimation in occator

settling driven convection a mechanism of sedimentation from stratified fluids convection driven by sediment particles may play an important role in sedimentation from the base of buoyant hypopycnal plumes for example fluvial plumes in stratified estuaries and lakes black smokers on the ocean floor volcanic clouds and coastal currents in addition to the well known double diffusive convection mechanism another mode of convective instability development is by settling across the density interface we performed laboratory experiments to investigate this fingering convective instability mechanism and its effect on particle distribution in the water column and deposition at the bed a simple theoretical model of finger formation at a fluid density interface is developed based on an analogy with thermal plume formation at a flat heated plate this model which involves a thickening interface layer that becomes gravitationally unstable relative to the ambient fluid is in good agreement with measurements of finger size and instability wavelength from visualization experiments since fingering at the density interface drives larger scale convection in the fluid below a mass balance model of the lower layer assuming strong mixing i e uniform sediment concentration is successfully applied to predict sediment concentration in the water column and deposition at the bed strong mixing can be assumed since convective velocities are usually much greater than the particle fall velocities as convection proceeds the sediment concentrations in the two layers approach each other and convection will die out using the model equations we develop analytical expressions for the time when convection ceases and the portion of sediment remaining in the water column

particle sedimentation and diffusive convection in volcanic ash clouds 1 understanding the longevity of volcanic ash clouds generated by powerful explosive eruptions is a long standing problem for assessing volcanic hazards and the nature and time scale of volcanic forcings on climate change it is well known that the lateral spreading and longevity of these clouds is influenced by stratospheric winds particle settling and turbulent diffusion observations of the recent 2010 eyjafjallajokull and 2011 grimsvotn umbrella clouds as well as the structure of atmospheric aerosol clouds from the 1991 mt pinatubo event suggest that an additional key process governing the cloud dynamics is the production of internal layering here we use analog experiments on turbulent particle laden umbrella clouds to show that this layering occurs where natural convection driven by particle sedimentation and the differential diffusion of primarily heat and fine particles give rise to a large scale instability where umbrella clouds are particularly enriched in fine ash this particle diffusive convection strongly influences the cloud longevity more generally cloud residence time will depend on fluxes due to both individual settling and diffusive convection we develop a new sedimentation model that includes both sedimentation processes and which is found to capture real time measurements of the rate of change of particle concentration in the 1982 el chichon 1991 mt pinatubo and 1992 mt spurr ash clouds a key result is that these combined sedimentation processes enhance the fallout of fine particles relative to expectations from individual settling suggesting that particle aggregation is not the only mechanism required to explain volcanic umbrella longevity

hyperpycnal plume formation from riverine outflows with small sediment concentrations a series of laboratory experiments has been conducted in order to elucidate the sediment induced mixing processes accompanying riverine outflows specifically the discharge of a warm fresh particle laden fluid over a relatively dense cool brine in a parameter regime analogous to recently acquired field measurements hypopycnal surface plumes were subject to a convective instability driven by some combination of heat diffusing out of the warm fresh sediment laden plume and particle settling within it convection was robust in the presence or absence of intense turbulence at sediment concentrations as low as 1 kg m 3 and took the form of millimetre scale sediment laden fingers descending from the base of the surface plume a consequence of the convective instability of the original hypopycnal plume is the generation of a hyperpycnal bottom riding flow the experiments presented here indicate that natural river outflows may thus generate hyperpycnal plumes when sediment concentrations are 40 times less than those required to render the outflow heavy relative to the oceanic ambient the resulting hyperpycnal plumes may play an important role in transporting substantial quantities of sediment to the continental slope and beyond

global color and albedo variations on io abstract three multispectral mosaics of io have been produced from voyager imaging data a global mosaic from each of the voyager 1 and voyager 2 data sets and a high resolution mosaic of the region surrounding the volcano ra patera the mosaics are maps of normal albedo and color in accurate geometric map formats io s photometric behavior mapped with a two image technique is spatially variable especially in the bright white areas the disk integrated color and albedo of the satellite have been remarkably constant over recent decades despite the volcanic activity and the many differences between voyager 1 and 2 images acquired just 4 months apart this constancy is most likely due to the consistent occurrence of large pele type plumes with relatively dark red deposits in the region from long 240 to 360 a transient brightening southeast of pele during the voyager 1 encounter was probably due to real changes in surface and or atmospheric materials rather than to photometric behavior the intrinsic spectral variability of io as seen in a series of two dimensional histograms of the multispectral mosaics consists of continuous variation among three major spectral end members the data were mapped into five spectral units to compare them with laboratory measurements of candidate surface materials and to show the planimetric distributions unit 1 is best fit by the spectral reflectance of ordinary elemental sulfur and it is closely associated with the peletype plume deposits unit 2 is strongly confined to the polar caps above about latitude 50 but its composition is unknown unit 5 is probably so 2 with relatively minor contamination it is concentrated in the equatorial region and near the long lived prometheus type plumes units 3 and 4 are gradational between units 1 and 5 in addition to so 2 and elemental sulfur other plausible components of the surface are polysulfur oxides fecl 2 na 2 s and nahs

bolometric albedos and diurnal temperatures of the brightest regions on io abstract using voyager imaging data we have constructed simple cylindrical maps giving the locations and estimated bolometric or bond albedos of the brightest regions on the surface of io straightforward calculations that have previously indicated a bond albedo for io as a whole of 0 50 d p simonelli and j veverka 1984 icarus 59 406 425 lead to the following highest computed albedos ab 0 5 0 6 using the mean macroscopic surface roughness of io as a whole represented by 25 and ab 0 6 0 7 if one assumes a smoother surface 5 albedos are then rescaled to correct for 1 radiometric calibration uncertainties and 2 indications from infrared observations that ab for io as a whole is closer to 0 56 the highest surface albedos then become ab 0 6 0 7 25 or a b 0 7 0 8 for 5 in any case the highest albedos are only moderately larger than the bond albedo of io as a whole so that temperatures computed for the brightest parts of the satellite are not that much colder than typical ionian surface temperatures this may limit the efficiency of regional cold trapping of so2 frost the brightest regions on io include 1 two bright patches southeast of the active vents maui and amirani which contain the brightest point on the satellite latitude 22 longitude 110 a b 0 68 for 25 2 the largest field of high albedo material on io on the equator to the north northwest and west of emakong patera longitudes 115 135 and 3 a lone bright patch at high northern latitudes latitude 65 longitude 200 likely to be one of the coldest points on the satellite the latter region which also has a strong albedo contrast with surrounding dark material may perturb locally the global flow of so2 gas modeled by ingersoll et al 1985 icarus 64 375 390 our albedo map emphasizes that throughout longitudes 0 270 the distribution of albedos on io is strongly latitude dependent bolometric albedos averaged over these longitudes show a well defined falloff from equator to pole with polar albedos on the order of 60 as large as those near the equator

observational and laboratory insights into salt finger convection improving observational capabilities in the ocean are revealing a substantial body of evidence that the double diffusive instability known as salt fingers is widely present and plays a significant role in oceanic mixing this evidence includes unique fine and microstructure features in particular regions and distinct patterns in the temperature and salinity variations over large areas laboratory experiments have also advanced our understanding of salt fingers the insights gleaned from both laboratory and ocean are reviewed and related to large scale ocean structure and climate modeling

voyager photometry of europa abstract ninety voyager images ranging in phase angle from 3 to 143 and covering the spectral range from 0 34 to 0 58 m were analyzed to derive the photometric properties of europa at small phase angles the disk integrated phase curve is remarkable in that it shows little or no evidence of an opposition effect in agreement with earlier earth based observations by millis and thompson icarus 26 408 1975 the phase integral determined in the voyager clear filter centered near 0 47 m is 1 09 0 11 in good agreement with previous estimates based on radiometry the bolometric bond albedo is 0 62 0 14 the scattering properties of europa in general and of the two major terrain types bright plains and darker mottled terrain in particular cannot be represented by a lunar like photometric law however an equation which is a linear superposition of a lunar like scattering law and a lambert component provides an adequate simple representation of the scattering properties the plains are photometrically more homogeneous than the darker mottled terrain in the voyager clear filter the average normal reflectance is 0 71 for the plains on both the leading and trailing hemispheres for the darker mottled terrain the values are 0 60 on the leading hemisphere and 0 48 on the trailing one

convective instability in sedimentation linear stability analysis 1 convective sedimentation in a stably stratified saltwater is studied using the linear stability analysis convective sedimentation is known to occur due to the double diffusive mechanism and the settling driven mechanism in this study a semi empirical closure of sediment diffusivity based on the long range hydrodynamics effect is adopted the sediment phase can act as either the slow or fast diffusing agent in the double diffusive system for the given salt diffusivity moreover the settling driven effect is proportional to the square of the sediment diameter via stoke settling law we consider sediment concentration grain size in the upper freshwater layer to be in the range of 0 1 to 39 4 g l 2 to 60 m which is on top of a saltwater layer with salinity 35 ppt linear stability analysis allows us to identify the dominant mechanism that triggers the instability the growth rate and the resulting characteristic finger width model results suggest that for fine sediment with grain diameter smaller than 10 m settling velocity 0 09 mm s double diffusive mechanism controls the instability and the resulting sediment finger size is of millimeter scale for the given threshold of growth rate of o 0 01 s 1 the minimum sediment concentration is about 8 15 g l for grain size greater than or around 10 m the settling driven mechanism dominates and instabilities occur at sediment concentration as low as o 0 1 g l with centimeter scale fingers our findings may contribute to a better understanding on the observed rapid sediment removal in the plume of small mountainous rivers

numerical experiments on salt finger convection salt finger convection is now widely recognized as an important mechanism for mixing heat and salt both vertically and laterally in the ocean this article reviews numerical simulations of salt finger salt fingers were first produced in the laboratory in the mid 1960s when their structure and transport mechanisms were partially described however rapid diffusion of heat in the laboratory frustrates exact or conclusive understanding of many aspects of salt fingers numerical simulation of salt finger began in the 1980s the rapid development of computational technology has brought great improvements in our understanding of salt fingers however fully 3 d simulations that resolve all the scales present in salt fingering particularly in an oceanic environment where internal waves and turbulence are confounding influences pose many more challenges for the future

a review of oceanic salt fingering theory salt fingering is a potentially important mechanism for mixing different water masses in those parts of the ocean where warm salty waters overlie cooler fresher this review surveys advances in salt fingering theory as they pertain to ocean mixing basic equations are presented along with steady maximum buoyancy flux and fastest growing finger solutions attempts to quantify theoretically finger induced fluxes of heat salt and buoyancy and to understand staircase formation and maintenance are described also considered are the confounding influences of internal wave shear and strain and intermittent internal wave shear driven turbulence which are present in the ocean but in few theories finally outstanding theoretical questions about the role of salt fingers in the ocean are raised

application of a radiative transfer model to bright icy satellites a radiative transfer model derived largely from the work of b w hapke 1981 j geophys res 86 3039 3054 and j d goguen 1981 ph d thesis cornell university ithaca n y is fit to voyager imaging observations of europa mimas enceladus and rhea it is possible to place constraints on the single scattering albedo the porosity of the optically active upper regolith the single particle phase functions and in the cases of europa and mimas the mean slope angle of macroscopic surface features the texture of the surfaces of the saturnian satellites appears to be similar to the earth s moon however europa is found to have a distinctly more compact regolith and a more forward scattering single particle phase function

hydrated salt minerals on europa s surface from the galileo near infrared mapping spectrometer nims investigation we reported evidence of heavily hydrated salt minerals present over large areas of europa s surface from analysis of reflectance spectra returned by the galileo mission near infrared mapping spectrometer nims mccord et al 1997a b 1998a b here we elaborate on this earlier evidence present spatial distributions of these minerals examine alternate water ice interpretations expand on our hydrated salts interpretation consider salt mineral stability on europa and discuss the implications extensive well defined areas on europa show distinct asymmetric water related absorption bands in the 1 to 2 5 m region radiative transfer modeling of water ice involving different particle sizes and layers at europa temperatures does not reproduce the distinctive europa water bands however ice near its melting temperature such as in terrestrial environments does have some characteristics of the europa spectrum alternatively some classes of heavily hydrated minerals do exhibit such water bands among plausible materials heavily hydrated salt minerals such as magnesium and sodium sulfates sodium carbonate and their mixtures are preferred all europa spectral features are present in some salt minerals and a very good match to the europa spectrum can be achieved by mixing several salt spectra however no single or mix of salt mineral spectra from the limited library available has so far been found to perfectly match the europa spectrum in every detail the material is concentrated at the lineaments and in chaotic terrain which are technically disrupted areas on the trailing side since the spectrum of the material on europa is nearly the same everywhere so far studied the salt or salt mixture composition may be nearly uniform this suggests similar sources and processes over at least a near hemispheric scale this would suggest that an extensive subsurface ocean containing dissolved salts is the source and several possible mechanisms for deposit emplacement are considered the hydrogen bonds associated with hydration of these salts are similar or greater in strength and energy to those in pure water ice thus once on the surface the salt minerals should be as stable to disruption as water ice at the europa temperatures and mechanisms are suggested to enhance the stability of both materials spectra obtained of mgso4 6h2o at 77 k show only small differences from room temperature spectra the main difference is the appearance of the individual absorptions composing the broad composite water features and associated with the several different h2o sites in the salt hydrate molecule this suggests that the europa absorption bands are also composites thus higher spectral resolution may reveal these diagnostic features in europa s spectrum the specific salts present and their relative abundances would be indicators of the chemistry and conditions of an ocean environment and areas of fresh heavy concentration of these minerals should make ideal lander mission sampling sites

temporal and spatial variations of mercury lead zinc and copper in sediments of the saguenay fjord sediment profiles of 19 cores from the saguenay fjord quebec canada have been analyzed for mercury lead zinc and copper core dating of post 1940 sediments is possible with above background concentrations of mercury the results agree well with those obtained previously with 137cs the northern basin of the fjord is the site of a major accumulation of trace elements the chronological distribution of mercury follows the events related to the operation of a chlor alkali plant construction increased production control of losses and closing the effect of a major landslide in 1971 is clearly shown in many sediment profiles the western basin of the fjord contains sediments enriched in mercury lead and zinc mercury input in the fjord has diminished since 1970 but other trace element influxes keep increasing trace elements in the north basin correlate well with carbon atmospheric lead appears to be a major anthropogenic source in sediments of the western basin

sediment transport dynamics near a river inflow in a large alpine lake sediment dynamics were investigated in lake maggiore italy with field observations from october to mid december 2012 three moorings were deployed in pallanza bay a small embayment on the western side of the lake near the toce river inflow to measure temperature and currents throughout the water column and suspended sediment concentration ssc was estimated with acoustic instrumentation river intrusions are shown to dominate observed ssc although a small amount of sediment resuspension was observed at the site of the shallowest mooring during a large wind event that produced strong upwelling of the thermocline followed by downwelling although vertical turbulent sediment flux is typically assumed to indicate resuspension and the upward transport of sediment w c 0 downward turbulent sediment flux was observed w c 0 near the bed during the largest observed intrusion event the downward turbulent sediment flux significantly contributes to net deposition rates which are one order of magnitude larger than rates of erosion measured during the two major events observed horizontal transport of sediment occurs in vertically confined layers due to buoyancy driven intrusions beneath the intrusions sediment settles out of the water column at settling rates that appear to be constant with depth based on acoustic doppler current profiler backscatter measurements the effective settling velocities needed to produce the observed vertical transport of ssc during an inflow intrusion are one order of magnitude larger than those due to the stokes settling velocity ws alone particle flocculation and possible convective instabilities may play a role in generating the large observed effective settling rates

the roughness of the dark side of iapetus from the 2004 to 2005 flyby abstract the roughness of a planetary surface offers clues to its past geologic history we apply a surface roughness model developed by buratti and veverka buratti b j veverka j 1985 icarus 64 320 328 to cassini iss data from the january 1st 2005 flyby of iapetus this model uses the observed scattering behavior to provide a depth to radius factor q quantifying the size of idealized craters on the surface our findings indicate that the surface on the dark side is significantly smoother than the surfaces of other icy low albedo saturnian satellites we have found that the average depth to radius on the leading dark side is 0 084 corresponding to a hapke mean slope angle of 6 as compared to the 13 33 hapke mean slope angle of other icy satellites buratti b j and 10 colleagues 2008 icarus 193 309 322 our results present a clearly different picture for the leading surface of iapetus suggesting that the dark deposit contributes to the decrease in macroscopic surface roughness of the leading side attempts were made to obtain an average depth to radius value for the trailing bright side however the scans of the bright side from this flyby exhibited large variations in albedo resulting in results that were physically unrealistic

the scattering properties of natural terrestrial snows versus icy satellite surfaces abstract a j verbiscer and j veverka 1990 icarus 88 418 428 demonstrated that the single scattering properties of terrestrial snows are highly forward scattering in contrast to the single scattering properties of icy satellite surfaces which all have a backscattering component to their single scattering functions as modeled with b hapke s equations 1981 j geophys res 86 3039 3054 1984 icarus 59 41 59 1986 icarus 67 264 280 this study demonstrates to first order that the differences between the scattering properties of icy satellite regoliths and their terrestrial counterparts are due to differences in particle structure and textures we find that the particles of the regoliths of the icy satellites are composed of a complex mixture of grain textures and structures

europa s ridged plains and smooth low albedo plains distinctive compositions and compositional gradients at the leading side trailing side boundary abstract this investigation uses linear mixture modeling employing cryogenic laboratory reference spectra to estimate surface compositions and water ice grain sizes of europa s ridged plains and smooth low albedo plains near infrared spectra for 23 exposures of ridged plains materials are analyzed along with 11 spectra representing low albedo plains modeling indicates that these geologic units differ both in the relative abundance of non ice hydrated species and in the abundance and grain sizes of water ice the background ridged plains in our study area appear to consist predominantly of water ice 46 with approximately equal amounts on average of hydrated sulfuric acid 27 and hydrated salts 27 the solutions for the smooth low albedo plains are dominated by hydrated salts 62 with a relatively low mean abundance of water ice 10 and an abundance of hydrated sulfuric acid similar to that found in ridged plains 27 the model yields larger water ice grain sizes 100 m versus 50 75 m in the ridged plains the 1 5 m water ice absorption band minimum is found at shorter wavelengths in the low albedo plains deposits than in the ridged plains 1 498 003 m versus 1 504 001 m the 2 0 m band minimum in the low albedo plains exhibits a somewhat larger blueshift 1 964 006 m versus 1 983 006 m for the ridged plains the study area spans longitudes from 168 to 185 w which includes europa s leading side trailing side boundary a well defined spatial gradient of sulfuric acid hydrate abundance is found for both geologic units with concentrations increasing in the direction of the trailing side apex we associate this distribution with the exogenic effects of magnetospheric charged particle bombardment and associated chemical processing of surface materials the radiolytic sulfur cycle however one family of low albedo plains exposures exhibits sulfuric acid hydrate abundances up to 33 lower than found for adjacent exposures suggesting that these materials have undergone less processing thus implying that these deposits may have been emplaced more recently modeling identifies high abundances to 30 of magnesium sulfate brines in the low albedo plains exposures our investigation marks the first spectroscopic identification of mgso4 brine on europa we also find significantly higher abundances of sodium bearing species bloedite and mirabilite in the low albedo plains the results illuminate the role of radiolytic processes in modifying the surface composition of europa and may provide new constraints for models of the composition of europa s putative subsurface ocean

crater formation and modification on the icy satellites of uranus and saturn depth diameter and central peak occurrence depth diameters d d for fresh craters on the intermediate sized icy satellites of uranus and saturn have been determined using photoclinometry and shadow lengths and are compared with similar measurements on the terrestrial planets simple bowl shaped craters on icy satellites including those on miranda for which the highest resolution data are available are systematically 20 40 shallower than on the terrestrial planets this pronounced difference between crater depths on icy and rocky surfaces indicates that differences in impact velocity or surface gravity are not as important as the differences in mechanical properties between ice and rock in controlling simple crater morphology experimental impact studies indicate that differences in material properties such as angle of internal friction can control crater depth alternatively breccia lenses may be thicker in icy satellite simple craters complex craters on the icy satellites become significantly deeper with increasing crater diameters unlike complex craters on terrestrial planets which are nearly constant in depth central peaks and hence floor rebound are also volumetrically and morphologically more prominent than wall slumping rim collapse on the icy satellites the magnitude of viscous relaxation of very large craters e g herschel and odysseus on the icy satellites can be estimated from extrapolation of the d d fits at smaller crater diameters the transition diameter from simple to complex morphology is inversely correlated with gravity as it is on the terrestrial planets but at significantly smaller diameters than would be expected from a simple extrapolation of the terrestrial trend thus crater modification especially floor rebound is easier to initiate on icy satellites estimated effective cohesions for shocked icy material are lower by a factor of 10 20 relative to rock although estimated effective viscosities are similar the distinct systematic differences between crater morphology on icy and rocky worlds indicate that gross material property differences between rock and ices play a key role in crater formation and modification but gravity is still the primary driving force

variations spatiales et temporelles du cesium 137 et du carbone dans des sediments du fjord du saguenay the accumulation rate of sediments in the saguenay fjord quebec canada established from 137cs activity measured in 19 cores varies between 1 0 cm year upstream and 0 2 cm year downstream cesium 137 profiles in cores from the northern basin follow that of fallouts on the ground and reflect the impact of a sudden inflow of clay from a major mudslide however 137cs accumulation in the larger basin seems less sensitive to external influences carbon content and the c n ratio are higher upstream than downstream based on 137cs dating core sections show carbon contents that reflect changes caused by the forest industry over the years journal translation

convective instability in sedimentation 3 d numerical study to provide a probable explanation on the field observed rapid sedimentation process near river mouths we investigate the convective sedimentation in stably stratified saltwater using 3 d numerical simulations guided by the linear stability analysis this study focuses on the nonlinear interactions of several mechanisms which lead to various sediment finger patterns and the effective settling velocity for sediment ranging from clay single particle settling velocity v0 0 0036 and 0 0144 mm s or particle diameter d 2 and 4 m to silt v0 0 36 mm s or d 20 m for very fine sediment with v0 0 0036 mm s the convective instability is dominated by double diffusion characterized by millimeter scale fingers gravitational settling slightly increases the growth rate however it has notable effect on the downward development of vertical mixing shortly after the sediment interface migrates below the salt interface for sediment with v0 0 0144 mm s rayleigh taylor instabilities become dominant before double diffusive modes grow sufficiently large centimeter scale and highly asymmetric sediment fingers are obtained due to nonlinear interactions between different modes for sediment with v0 0 36 mm s rayleigh taylor mechanism dominates and the resulting centimeter scale sediment fingers show a plume like structure the flow pattern is similar to that without ambient salt stratification rapid sedimentation with effective settling velocity on the order of 1 cm s is likely driven by convective sedimentation for sediment with v0 greater than 0 1 mm s at concentration greater than 10 20 g l

enhanced diapycnal mixing by salt fingers in the thermocline of the tropical atlantic diapycnal mixing plays a significant role in the ocean s circulation and uptake of heat and carbon dioxide but has not been quantified in salt finger driven thermohaline staircases we recently performed a tracer release experiment in the western tropical atlantic staircase at approximately 400 m depth the observed dispersion implies an effective diapycnal diffusivity for tracer and salt of 0 8 to 0 9 x 10 4 m2 s temperature microstructure data interpreted in terms of a vertical production dissipation balance yields a smaller effective diffusivity for heat of 0 45 0 2 x 10 4 m2 s consistent with salt fingers and well above the mixing ascribable to mechanical turbulence

ice covered water volcanism on ganymede eruption of liquid h2o magmas along extensional fractures and graben bounding normal faults may have played a critical role in the development of ganymede s grooved terrain the resurfacing potential of a water magma is dependent on a variety of factors including the areal extent of the source region the rate of discharge the thickness of the flow and the time that it takes the flow to completely freeze to its base in this paper the thermal evolution of such a flow is considered in detail the minimum unfrozen lifetime of a 5 m flow is approximately 12 5 days while a 10 m flow would survive for at least 50 days heating resulting from factional head loss could reasonably extend these lifetimes by 50 or more with a discharge rate of the order of 1 10 km3 d 1 an individual volcanic water flow could flood an area of 104 km2 before freezing as the flow solidifies its volume will increase thus lifting and arching its protective ice cover extensional fractures may then develop in the ice subparallel to the graben walls these fractures could result in grooves directly given a sufficiently thick 1 km flow or they may simply act to concentrate various tectonic forces that could initiate groove producing faults

martian phase function modeling the visible to near infrared surface photometric function using hst wfpc2 data abstract images of mars in the visible to near infrared acquired from 1996 to 2005 using the hubble space telescope wfpc2 have been used to model the martian surface photometric function at 502 673 953 and 1042 nm these data range in spatial resolution from 12 to 70 km pixel at the sub earth point and in phase angle coverage from 0 34 to 40 5 the wfpc2 images have been calibrated to radiance factor or i f and projected to a cylindrical map for coregistration and comparison to similarly mapped spacecraft data sets of albedo topography thermal inertia composition and geology we modeled the observed i f as a function of phase angle using minnaert lambert lunar lambert and hapke photometric functions for numerous regions of interest binned into albedo units defined by viking and tes albedo maps and thermal inertia units defined by tes thermal inertia maps visibly opaque water ice clouds and data acquired under high dust opacity conditions were excluded from the analysis our modeling suggests that under average to low atmospheric dust opacity conditions and over this range of phase angles the photometric properties of the martian surface at 502 673 953 and 1042 nm are best modeled by lunar lambert functions with parameters derived for three surface units defined by low moderate and high tes bolometric albedos

voyager photometry of iapetus abstract voyager images of iapetus ranging in phase angle from 8 to 90 were used to define the satellite s photometric properties and construct an albedo map of its surface the images confirm that the albedo distribution has a roughly hemispheric asymmetry as had been inferred from earlier analyses of the disk integrated lightcurve on the darker leading hemisphere albedo contours are roughly elliptical in shape and centered at the apex of orbital motion flattened at the poles and elongated along the equator the reflectance within the darker material is lowest 0 02 0 03 at the apex and increases with increasing distance from the apex the albedo pattern on the brighter trailing hemisphere is more complex reflectance increases gradually with increasing distance from the interface with the darker material and reaches a maximum near the poles reflectances of 0 3 0 4 in the brighter material are common and the highest values probably reach 0 6 the transition in reflectance contours between the two materials is gradual rather than sharp and albedo histograms of images centered on the visually perceived boundary are weakly bimodal the dark material on iapetus is reddish the bright material somewhat less so

dynamics of fingering convection part 1 small scale fluxes and large scale instabilities received and in revised form double diffusive instabilities are often invoked to explain enhanced transport in stablystratified fluids the most studied natural manifestation of this process fingering convection commonly occurs in the ocean s thermocline and typically increases diapycnal mixing by two orders of magnitude over molecular diffusion fingering convection is also often associated with structures on much larger scales such as thermohaline intrusions gravity waves and thermohaline staircases in this paper we present an exhaustive study of the phenomenon from small to large scales we perform the first three dimensional simulations of the process at realistic values of the heat and salt diffusivities and provide accurate estimates of the induced turbulent transport our results are consistent with oceanic field measurements of diapycnal mixing in fingering regions we then develop a generalized mean field theory to study the stability of fingering systems to large scale perturbations using our calculated turbulent fluxes to parameterize small scale transport the theory recovers the intrusive instability the collective instability and the instability as limiting cases we find that the fastest growing large scale mode depends sensitively on the ratio of the background gradients of temperature and salinity the density ratio while only intrusive modes exist at high density ratios the collective and instabilities dominate the system at the low density ratios where staircases are typically observed we conclude by discussing our findings in the context of staircase formation theory

hubble space telescope observations of the 1990 equatorial disturbance on saturn zonal winds and central meridian albedos abstract two sets of hubble space telescope hst data obtained in august 1990 and november 1990 are compared with voyager 1 and 2 data acquired in 1980 and 1981 a rare disturbance developed in the equatorial region of saturn in late september 1990 due to the large equatorial wind shear this disturbance generated inhomogeneous bright cloud structures in the equatorial region that extended to 25 north latitude in november 1990 meridional albedo scans and wind measurements from the voyager northern spring equinox and the hst northern summer observations are compared differences in average zonal winds in the images obtained with the green f547m and the methane f889n filters are interpreted as evidence of vertical shear in the zonal winds longitudinal variations in the equatorial zonal winds are interpreted as evidence of interaction between the storm nucleus generated during the disturbance and the local wind field

evolution of lineaments on europa clues from galileo multispectral imaging observations abstract four distinct classes of lineaments can be described on the basis of galileo s improved spectral and spatial coverage of europa 1 incipient cracks are narrow the morphologies spectral properties and orientations of the lineaments vary systematically with age suggesting that these four classes represent different stages of development in an evolutionary sequence lineament formation appears to be the dominant resurfacing mechanism on europa and every landscape that has escaped erasure by heating from below is imprinted with generation after generation of intersecting ridges at various scales and orientations relatively recent fractures expose coarse grained clean ice in the shallow subsurface possibly accounting for the distinctive color of the satellite in comparison to the other icy moons of jupiter the process of lineament formation may be continuing today the bright band agenor linea is among the leading candidates for current activity

heat salt and momentum transport in a laboratory thermohaline staircase flow characteristics and fluxes in thermohaline staircases are measured in two tanks differing in aspect ratio a where a is the ratio of tank width to fluid depth in one tank the 1 x 1 tank which is 30 cm deep and 30 cm wide a staircase of one salt finger layer and one convecting layer develops for a certain setting of the control parameters the convecting layer has a 2 shadowgraphs show convecting plumes that appear disorganized and a large scale flow never develops instead the finger layer grows in height overtakes the convecting layer and within a few days becomes one finger layer the second tank the 1 x 5 tank is also 30 cm deep but is 150 cm wide for the same control parameter setting a similar staircase with a finger layer 20 cm deep and a convecting layer 10 cm deep develop the convecting layer with a 15 has quite a different character a large scale flow develops so that the convecting layer has one cell 10 cm deep and 150 cm wide in this flow are large plumes which are transient and tilted particle image velocimetry measurements of reynolds stresses show they help to maintain the large scale flow against viscous dissipation shadowgraphs show all the finger tips swept in the direction of the large scale flow adjacent to the finger layer measurements show that the large scale flow collects the salt delivered by the many fingers so that the accumulated negative buoyancy leads to deep convection this is a more stable arrangement with the configuration lasting to the order of 10 2 days

compaction and movement of interstitial water in bottom sediments of the saguenay fjord quebec canada abstract eight sediment cores were collected along the length of the saguenay fjord and baie des ha ha quebec canada profiles of the sediment water contents were determined for each core porosities were fitted to an exponential relation with core depth the relation was modified to account for variations in granulometry and in organic carbon contents of the sediments porosities were observed to be more sensitive to variations in organic content than to variations in granulometry and grain sorting appeared more important than grain size grain size distribution of the sediments is in agreement with a sedimentation model where most of the suspended load enters the fjord from the saguenay river and is deposited downstream with the surface current the coarse particles are mainly found close to the head of the fjord whereas the fine particles are carried farther downstream surface porosities were observed to be proportional to the sedimentation fluxes obtained from the literature whereas the compaction showed an inverse relationship the fractional decreases in porosity due to compaction along the fjord indicate some horizontal flow of the interstitial water at both ends of the sampled part of the fjord an average vertical interstitial pore water flow of 0 4 cm yr 1 with respect to the surface horizon is estimated from the data this is small compared with the diffusion of the major constituents of sea water through the sediment

multispectral terrain analysis of europa from galileo images abstract galileo s solid state imaging camera recorded six images at wavelengths from 0 41 to 0 99 m of europa s trailing hemisphere 1 6 km pixel resolution during the g1 orbit 1st orbit target ganymede of the nominal mission we have photometrically corrected these data and extracted spectra representing europa s diverse geologic terrains the goals of the analysis of these spectra are 1 to determine whether europa s geologic units differ spectrally from one another 2 to determine the number of color components necessary to explain europa s dark material spectral behavior and 3 to examine how europan dark materials may change in color with time our data indicate that europan dark spots lineaments and triple band side materials represent a single dark and reddish endmember component we see no evidence for more than one dark endmember however the dark endmember seen in these g1 data is probably not a pure exposure of europan dark material mottled terrains brighter lineaments and aging triple bands can be modeled by a mixture of bright plains materials and the dark component exposures of europan dark materials may thus be brightening with time eventually blending into the surrounding bright plains

galileo s first images of jupiter and the galilean satellites the first images of jupiter io europa and ganymede from the galileo spacecraft reveal new information about jupiter s great red spot grs and the surfaces of the galilean satellites features similar to clusters of thunderstorms were found in the grs nearby wave structures suggest that the grs may be a shallow atmospheric feature changes in surface color and plume distribution indicate differences in resurfacing processes near hot spots on io patchy emissions were seen while io was in eclipse by jupiter the outer margins of prominent linear markings triple bands on europa are diffuse suggesting that material has been vented from fractures numerous small circular craters indicate localized areas of relatively old surface pervasive brittle deformation of an ice layer appears to have formed grooves on ganymede dark terrain unexpectedly shows distinctive albedo variations to the limit of resolution

geologic implications of spectrophotometric measurements of europa abstract detailed spectrophotometric measurements of europa have been obtained from voyager images of the satellite photometric functions and reflectances in four colors ultraviolet violet blue and orange were derived for six mapped geologic terrains plains and mottled terrains three types of lineaments wedge shape triple and gray bands and the brown spots the geologic units fall into two clear colorimetric classes red spectra of the dark brown spots and wedge shaped bands and bluer spectra of the light plains classification by albedo also shows two end member classes and a group with intermediate albedos the mottled terrains and triple bands these results suggest that there are two fundamental types of material on europa relatively clean ice making up the plains and darker redder silicate rich material making up the brown spots and wedge shaped bands the pristine plains material has undergone progressive darkening by the infilling of fractures with the silicate rich material to form the mottled terrains profiles of reflectance across the wedge shaped bands and triple bands indicate that in some cases similar albedo and color changes occur for the two classes of bands implying similar types of structures for both features many wedge shaped bands may be triple bands whose bright central stripes are below the limit of resolution of the voyager images

central pit and dome craters exposing the interiors of ganymede and callisto central pit craters on the large icy satellites ganymede and callisto are an unusual crater class perhaps related to the unusual properties of water ice the detailed morphology and dimensions of pit crater features differ from those of smaller normal complex craters on these two satellites pit crater depths appear to be constant regardless of diameter rim collapse is also restricted relative to that in lunar craters or smaller ganymede craters the floors of pits in craters larger than 60 km are occupied by smooth bright domes pit to crater and dome to crater diameter ratios increase linearly with crater diameter and are indistinguishable on ganymede and callisto and with terrain type or surface longitude the floors and central structures of young bright rayed pit craters such as osiris are covered by a thin uniformly bright impact melt or frost deposit thus domes and pits form rapidly on the time scale of the impact itself rather than by long term postimpact intrusion or extrusion the bright domes in pit craters are most simply explained as the uplift and exposure of relatively ice rich material from depths of 3 5 to 5 km during impact this process is almost directly analogous to the uplift and exposure of anamolous deep seated material observed in terrestrial and lunar craters the unusual pit morphology on icy satellites may be the result of impact into crust that is mechanically much weaker at shallow depth than on rocky bodies such as the moon because crater morphology is strongly dependent on ice rock composition the similarity of pit and dome dimensions on ganymede and callisto indicates that the structure and rheology of the crusts of these bodies down to depths of 10 km are very similar and have been for several b y pit crater morphology indicates that the crusts of both satellites are probably ice rich and differentiated

surface textural properties of icy satellites a comparison between europa and rhea abstract solar phase curves for rhea are presented using new telescopic opposition data along with voyager imaging observations two viable solutions were found to hapke s model 1986 icarus 67 264 280 which was used to describe this phase curve the porosity derived from the model s opposition parameters show that the optically active portion of rhea s regolith has a porosity between 80 and 95 which is slightly lower than the porosity seen on europa and higher than the porosity measured for the moon using similar methods the macroscopic roughness is comparable to that measured by verbiscer and veverka 1989 icarus 82 336 353 for rhea the single particle scattering functions found in this study are predominantly forward scattering which contradicts the results of verbiscer and veverka 1989

the search for current geologic activity on europa observational evidence and theoretical arguments suggest that jupiter s satellite europa could be geologically active and possess an ocean of liquid water beneath its surface at the present time we have searched for evidence of current geologic activity on europa in the form of active plumes venting material above the surface and by comparison of voyager and galileo images to look for any changes on the surface so far we have observed no plumes and have detected no definitive changes the lack of observed activity allows us to estimate a maximum steady state surface alteration rate of 1 km2 y 1 in the regions analyzed assuming alterations will cover contiguous areas of at least 4 km2 over a period of 20 years assuming this as a constant globally uniform resurfacing rate leads to a minimum average surface age of 30 million years we also suggest that the lack of obvious circular albedo patterns on the surface due to plumes coupled with the presence of bright rayed craters such as pwyll and the predicted sputtering erosion rate implies that no large scale plume activity has taken place over at least the last few thousand years we thus conclude that if europa s surface is currently active any changes must be relatively small in spatial scale or episodic in nature rather than continuous to detect potential small scale surface changes we need high resolution comparisons between the galileo data and future europa orbiter images

photometry of triton 1992 2004 surface volatile transport and discovery of a remarkable opposition surge abstract triton the large satellite of neptune was imaged by the voyager 2 spacecraft in 1989 with dark plumes originating in its volatile rich south polar region southern summer solstice a time when seasonal volatile transport should be at a maximum occurred in 2001 ground based observations of triton s rotational light curve obtained from table mountain observatory in 2000 2004 reveal volatile transport on its surface when compared with a static frost model constructed from voyager images the light curve shows an increase in total amplitude an earlier light curve obtained in 1992 from mauna kea observatory is consistent with the static frost model this movement of volatiles on the surface agrees with recent imaging results from the hubble space telescope bauer j m buratti b j li j y mosher j a hicks m d schmidt b e goguen j d 2010 astrophys j 723 l49 l52 the changes in the light curve can be explained by the transport of nitrogen frost on the surface or by the uncovering of bedrock of less volatile methane we also find that triton exhibits a large opposition surge at solar phase angles less than 0 1 this surge cannot be entirely explained by the effects of coherent backscatter

global albedos of pluto and charon from lorri new horizons observations abstract the exploration of the pluto charon system by the new horizons spacecraft represents the first opportunity to understand the distribution of albedo and other photometric properties of the surfaces of objects in the solar system s third zone of distant ice rich bodies images of the entire illuminated surface of pluto and charon obtained by the long range reconnaissance imager lorri camera provide a global map of pluto that reveals surface albedo variegations larger than any other solar system world except for saturn s moon iapetus normal reflectances on pluto range from 0 08 1 0 and the low albedo areas of pluto are darker than any region of charon charon exhibits a much blander surface with normal reflectances ranging from 0 20 0 73 pluto s albedo features are well correlated with geologic features although some exogenous low albedo dust may be responsible for features seen to the west of the area informally named tombaugh regio the albedo patterns of both pluto and charon are latitudinally organized with the exception of tombaugh regio with darker regions concentrated at the pluto s equator and charon s northern pole the phase curve of pluto is similar to that of triton the large moon of neptune believed to be a captured kuiper belt object kbo while charon s is similar to that of the moon preliminary bond albedos are 0 25 0 03 for charon and 0 72 0 07 for pluto maps of an approximation to the bond albedo for both pluto and charon are presented for the first time our work shows a connection between very high albedo near unity and planetary activity a result that suggests the kbo eris may be currently active

coordinates of features on the galilean satellites control nets of the four galilean satellites have been established photogrammetrically from pictures taken by the two voyager spacecraft during their flybys of jupiter in 1979 coordinates of 504 points on io 112 points on europa 1547 points on ganymede and 439 points on callisto are listed selected points are identified on u s geological survey maps of the satellites measurements of these points were made on 234 pictures of io 115 pictures of europa 282 pictures of ganymede and 200 pictures of callisto the systems of longitude were defined by craters on europa ganymede and callisto preliminary solutions have been found for the directions of the axes of rotation of the galilean satellites new mean radii have been determined as 1815 5 km for io 1569 10 km for europa 2631 10 km for ganymede and 2400 10 km for callisto

exogenic and endogenic albedo and color patterns on europa new global and high resolution multispectral mosaics of europa have been produced from the voyager imaging data photometric normalizations are based on multiple image techniques that explicitly account for intrinsic albedo variations through pixel by pixel solutions the exogenic color and albedo pattern on europa is described by a second order function of the cosine of the angular distance from the apex of orbital motion on the basis of this second order function and of color trends that are different on the leading and trailing hemispheres the exogenic pattern is interpreted as being due to equilibrium between two dominant processes 1 impact gardening and 2 magnetospheric interactions including sulfur ion implantation and sputtering redistribution removal of the model exogenic pattern in the mosaics reveals the endogenic variations consisting of only two major units darker redder and bright materials therefore europa s visual spectral reflectivity is simple having one continuous exogenic pattern and two discrete endogenic units

small lightning flashes from shallow electrical storms on jupiter lightning flashes have been observed by a number of missions that visited or flew by jupiter over the past several decades imagery led to a flash rate estimate of about 4 10 3 flashes per square kilometre per year refs 1 2 the spatial extent of voyager flashes was estimated to be about 30 kilometres half width at half maximum intensity hwhm but the camera was unlikely to have detected the dim outer edges of the flashes given its weak response to the brightest spectral line of jovian lightning emission the 656 3 nanometre h line of atomic hydrogen1 3 6 the spatial resolution of some cameras allowed investigators to confirm 22 flashes with hwhm greater than 42 kilometres and to estimate one with an hwhm of 37 to 45 kilometres refs 1 7 9 these flashes with optical energies comparable to terrestrial superbolts of 0 02 1 6 1010 joules have been interpreted as tracers of moist convection originating near the 5 bar level of jupiter s atmosphere assuming photon scattering from points beneath the clouds 1 3 7 8 10 12 previous observations of lightning have been limited by camera sensitivity distance from jupiter and long exposures about 680 milliseconds to 85 seconds meaning that some measurements were probably superimposed flashes reported as one1 2 7 9 10 13 here we report optical observations of lightning flashes by the juno spacecraft with energies of approximately 105 108 joules flash durations as short as 5 4 milliseconds and inter flash separations of tens of milliseconds with typical terrestrial energies the flash rate is about 6 1 10 2 flashes per square kilometre per year more than an order of magnitude greater than hitherto seen several flashes are of such small spatial extent that they must originate above the 2 bar level where there is no liquid water14 15 this implies that multiple mechanisms for generating lightning on jupiter need to be considered for a full understanding of the planet s atmospheric convection and composition small lightning flashes detected on jupiter by juno have shallow origins above the 2 bar level of jupiter s atmosphere where temperatures are too low for liquid water to exist

radiometric performance of the voyager cameras the voyager imaging experiment provided high quality data of jupiter and the galilean satellites with the two flyby trajectories in march and july of 1979 moderately accurate radio metric measurements have been made using these data this paper evaluates the radiometric results and describes the inflight and ground geometric and radiometric correction factors the radiometric quantities of intensity i and geometric albedo i f are derived and scaling factors for each of the filters are tabulated for correcting the calibrated data from the image processing laboratory at jpl in addition the key characteristics of both voyager 1 and voyager 2 cameras are tabulated

implications of using broadband photometry for compositional remote sensing of icy objects water ice has such a low absorption coefficient at visual wavelengths 0 01 cm 1 that a very small amount of particulate material can significantly darken an icy surface a variety of ice plus particle mixtures were studied to show that particulate contaminations of 1 by weight even 0 1 or less in some cases in ice or frosts result in reflectance levels close to that of the contaminants in a very clear ice no bubbles it is plausible to have a reflectance 0 05 for particulate contaminations 10 7 by weight for submicron dark particles such as carbon lampblack scattering conditions compete for domination with contaminants for control of visual reflectance implying that the apparent reflectivity level and color of a surface is a poor indicator of ice content a dark surface e g albedo 0 05 does not necessarily imply that there us very little water ice present infrared jhk colors of water ice and other minerals including ice mineral mixtures show that some orthopyroxenes can have jhk colors very similar to fine grained water frosts in general it is possible that the jhk colors of an ice plus particulate mixture can fall anywhere in the classical j h versus h k diagram thus the diagram cannot be used to distinguish a predominately rock surface from one which is predominantely ice for one specific case an important exception is the case where both the j h and h k colors are 0 2 it appears that such colors indicate a relatively pure icy surface in some cases the diagram might be used as a statistical tool to distinguish between the compositions of surfaces within a class of objects but the validity of such comparisons decreases for different classes such as the main belt asteroids when compared to outer solar system satellites where water ice is more stable

abrupt climate transition of icy worlds from snowball to moist or runaway greenhouse ongoing and future space missions aim to identify potentially habitable planets in our solar system and beyond planetary habitability is determined not only by a planet s current stellar insolation and atmospheric properties but also by the evolutionary history of its climate it has been suggested that icy planets and moons become habitable after their initial ice shield melts as their host stars brighten here we show from global climate model simulations that a habitable state is not achieved in the climatic evolution of those icy planets and moons that possess an inactive carbonate silicate cycle and low concentrations of greenhouse gases examples for such planetary bodies are the icy moons europa and enceladus and certain icy exoplanets orbiting g and f stars we find that the stellar fluxes that are required to overcome a planet s initial snowball state are so large that they lead to significant water loss and preclude a habitable planet specifically they exceed the moist greenhouse limit at which water vapour accumulates at high altitudes where it can readily escape or the runaway greenhouse limit at which the strength of the greenhouse increases until the oceans boil away we suggest that some icy planetary bodies may transition directly to a moist or runaway greenhouse without passing through a habitable earth like state icy planets and moons could become habitable as their host stars brighten and their ice melts climate simulations instead show a rapid transition from a snowball to an inhospitable greenhouse climate with significant water loss

the stability and transport of carbon dioxide on iapetus abstract carbon dioxide has been detected associated with iapetus dark material by the cassini spacecraft this co2 may be primordial and or resulting from ongoing production by photolysis of water ice in the presence of carbonaceous material allamandola l j sandford s a valero g j 1988 icarus 76 225 252 although any primordial co2 would likely be complexed with the dark material and thus stable against thermal transport to iapetus poles buratti b j and 28 colleagues 2005 astrophys j 622 l149 l152 active production of co2 would result in some fraction of the co2 being mobile enough to allow the accumulation of co2 at iapetus poles we develop a computer model to simulate ballistic transport of co2 ice on iapetus accounting for iapetus gravitational binding energy and polar cold traps we find that the residence time of co2 ice outside the polar regions is very short a sheet of co2 ice near the equator of iapetus decreases in thickness at a rate of 50 mm year 1 the sublimated co2 will ballistically move around iapetus until it reaches the polar cold traps where it can be sequestered for up to 15 years if the total surface inventory of co2 exceeds 3 10 7 kg the polar ice cap will be permanent while co2 is moving around the surface a small percentage will eventually reach escape velocity and be lost from the system as such a seasonal polar cap is lost at rate of 12 every solar orbit as the co2 moves between the two polar cold traps

brine volcanism and the interior structures of asteroids and icy satellites abstract cryovolcanism is among the foremost processes responsible for modifying the surfaces of icy satellites volcanic brine petrogenesis in ammonia deficient satellites should mainly involve eutectic melting in relevant salt water systems carbonaceous chondrites provide useful insights into the compositions of salts and aqueously altered rock in icy satellites and asteroids c1 chondrites contain about one fifth by mass of salts in various states of hydration many aspects of the petrogenesis and physical volcanology of icy satellite brines should be well described in the system h2o mgso4 na2so4 minor components include sulfates of k ni mn and ca chondrites also contain abundant carbonates but these are probably not very important in brine magmatism due to their low solubilities under expected conditions chlorides are also unimportant under most circumstances because of the low cosmic abundance ratio of cl s soluble salts may have profound effects on the geology and structure of icy satellites and asteroids in some models late episodes of water volcanism are facilitated by high buoyant forces due to the relatively high densities of sulfate rich mantle and crustal layers in other models early hypersaline brine volcanism quickly yields to plutonic magmatism due to low crustal densities europa probably has a layered crust composed of anhydrous mg na sulfates near the base and a frozen or partially molten eutectic mixture of ice and hydrated mg and na sulfates near the surface ganymede may have a crust about 300 km thick composed of a 10 1 ratio of ice mirabilite and a mantle 500 km thick composed of 50 ice phases plus 50 hydrated mg and na sulfates

sediment laden fresh water above salt water nonlinear simulations when a layer of particle laden fresh water is placed above clear saline water both double diffusive and rayleigh taylor instabilities may arise the present investigation extends the linear stability analysis of burns meiburg j fluid mech vol 691 2012 pp 279 314 into the nonlinear regime by means of two and three dimensional direct numerical simulations dns the initial instability growth in the dns is seen to be consistent with the dominant modes predicted by the linear stability analysis the subsequent vigorous growth of individual fingers gives rise to a secondary instability and eventually to the formation of intense plumes that become detached from the interfacial region the simulations show that the presence of particles with a stokes settling velocity modifies the traditional double diffusive fingering by creating an unstable nose region in the horizontally averaged profiles located between the upward moving salinity and the downward moving sediment interface the effective thickness l s l c of the salinity sediment interface grows diffusively as does the height h of the nose region the ratio h l s initially grows and then plateaus at a value that is determined by the balance between the flux of sediment into the rose region from above the double diffusive rayleigh taylor flux out of the nose region below and the rate of sediment accumulation within the nose region for small values of h l s leqslant o 0 1 double diffusive fingering dominates while for larger values h l s geqslant o 0 1 the sediment and salinity interfaces become increasingly separated in space and the dominant instability mode becomes rayleigh taylor like a scaling analysis based on the results of a parametric study indicates that h l s is a linear function of a single dimensionless grouping that can be interpreted as the ratio of inflow and outflow of sediment into the nose region the simulation results furthermore indicate that double diffusive and rayleigh taylor instability mechanisms cause the effective settling velocity of the sediment to scale with the overall buoyancy velocity of the system which can be orders of magnitude larger than the stokes settling velocity while the power spectra of double diffusive and rayleigh taylor dominated flows are qualitatively similar the difference between flows dominated by fingering and leaking is clearly seen when analysing the spectral phase shift for leaking dominated flows a phase locking mechanism is observed which intensifies with time hence the leaking mode can be interpreted as a fingering mode which has become phase locked due to large scale overturning events in the nose region as a result of a rayleigh taylor instability

color and morphology of lava flows on io abstract analyses of color and morphologic changes in voyager images of lava flows on io were conducted to extend previous flow studies to additional volcanoes in preparation for comparison to galileo data blue and orange filter images of atar daedalus and ra paterae were examined to identify systematic downflow decreases in blue orange reflectivity suggested in earlier studies as diagnostic of color changes in cooled sulfur flows analyses of the color and morphology of 21 lava flows were conducted at these volcanoes with additional morphologic analysis of lava flows at agni masaaw mbali shoshu and talos paterae a total of 66 lava flows of up to 245 km in length were mapped to identify morphologic changes consistent with the rheologic changes expected to occur in sulfur flows although downflow color changes are observed the trends are not consistent even at the same edifice individual flows exhibit a statistically significant increase in blue orange ratio decrease in blue orange ratio or a lack of progressive downflow color variation color changes have similar magnitudes downflow and across flow and the color ranges observed are similar from volcano to volcano suggesting that similar processes are controlling color ratios at these edifices in addition using flow widening and branching as an indicator of the low viscosity exhibited by sulfur cooling from high temperatures these flows do not exhibit morphologic changes consistent with the systematic behavior expected from the simple progressive cooling of sulfur

the geology of callisto the geology of callisto is not boring although cratered terrain dominates callisto a key end member of the jovian satellite system a number of more interesting features are apparent cratered terrain is broken into irregular mappable bright and dark subunits that vary in albedo by a factor of 2 and several relatively smooth units are depleted of small craters some of these areas may have been volcanically resurfaced lineaments including parallel and radial sets may be evidence for early global tectonism frost deposition occurs in cold traps and impact scars have formed from tidally disrupted comets geologic evidence suggests that callisto does have a chemically differentiated crust central pit and central dome craters and palimpsests are common the preferred interpretation is that a relatively ice rich material at depths of 5 km or more has been mobilized during impact and exposed as domes or palimpsests the close similarity in crater morphologies and dimensions indicates that the outermost 10 km or so of callisto may be as differentiated as on ganymede the geology of cratered terrain on callisto is simpler than that of cratered terrain on ganymede however orbital evolution and tidal heating may provide the answer to the riddle of why callisto and ganymede are so different malhotra 1991 we should expect a few surprises and begin to answer some fundamental questions when callisto is observed by galileo in late 1996

temperatures on europa from galileo photopolarimeter radiometer nighttime thermal anomalies galileo observations of europa s thermal emission show low latitude diurnal brightness temperatures in the range of 86 to 132 kelvin nighttime temperatures form an unexpected pattern with high temperatures on the bright ejecta blanket of the crater pwyll and an equatorial minimum in temperatures after sunset uncorrelated with surface albedo or geology the nighttime anomalies may be due to regional thermal inertia variations of an unknown origin which are equivalent to a two to threefold variation in thermal conductivity or to endogenic heat fluxes locally reaching 1 watt per square meter endogenic heat flow at this high level although consistent with some geological evidence is theoretically unlikely