a new look at the saturn system the voyager 2 images voyager 2 photography has complemented that of voyager i in revealing many additional characteristics of saturn and its satellites and rings saturn s atmosphere contains persistent oval cloud features reminiscent of features on jupiter smaller irregular features track out a pattern of zonal winds that is symmetric about saturn s equator and appears to extend to great depth winds are predominantly eastward and reach 500 meters per second at the equator titan has several haze layers with significantly varying optical properties and a northern polar collar that is dark at short wavelengths several satellites have been photographed at substantially improved resolution enceladus surface ranges from old densely cratered terrain to relatively young uncratered plains crossed by grooves and faults tethys has a crater 400 kilometers in diameter whose floor has domed to match tethys surface curvature and a deep trench that extends at least 270 around tethys circumference hyperion is cratered and irregular in shape iapetus bright trailing hemisphere includes several dark floored craters and phoebe has a very low albedo and rotates in the direction opposite to that of its orbital revolution with a period of 9 hours within saturn s rings the birth of a spoke has been observed and surprising azimuthal and time variability is found in the ringlet structure of the outer b ring these observations lead to speculations about saturn s internal structure and about the collisional and thermal history of the rings and satellites

long term surface temperature modeling of pluto abstract nasa s new horizons reconnaissance of the pluto system has revealed at high resolution the striking albedo contrasts from polar to equatorial latitudes on pluto as well as the sharpness of boundaries for longitudinal variations these contrasts suggest that pluto must undergo dynamic evolution that drives the redistribution of volatiles using the new horizons results as a template we explore the surface temperature variations driven seasonally on pluto considering multiple timescales these timescales include the current orbit 248 years as well as the timescales for obliquity precession peak to peak amplitude of 23 over 3 million years and regression of the orbital longitude of perihelion 3 7 million years these orbital variations create epochs of extreme seasons where one pole receives a short relatively warm summer and long winter while the other receives a much longer but less intense summer and short winter we use thermal modeling to build upon the long term insolation history model described by earle and binzel 2015 and investigate how these seasons couple with pluto s albedo contrasts to create temperature effects from this study we find that a bright region at the equator once established can become a site for net deposition we see the region informally known as sputnik planitia as an example of this and find it will be able to perpetuate itself as an always available cold trap thus having the potential to survive on million year or substantially longer timescales meanwhile darker low albedo regions near the equator will remain relative warm and generally not attract volatile deposition we argue that the equatorial region is a preservation zone for whatever albedo is seeded there this offers insight as to why the equatorial band of pluto displays the planet s greatest albedo contrasts

cassini finds molecular hydrogen in the enceladus plume evidence for hydrothermal processes saturn s moon enceladus has a subsurface ocean covered by a layer of ice some liquid escapes into space through cracks in the ice which is the source of one of saturn s rings in october 2015 the cassini spacecraft flew directly through the plume of escaping material and sampled its chemical composition waite et al found that the plume contains molecular hydrogen h2 a sign that the water in enceladus ocean is reacting with rocks through hydrothermal processes see the perspective by seewald this drives the ocean out of chemical equilibrium in a similar way to water around earth s hydrothermal vents potentially providing a source of chemical energy science this issue p 155 1 see also p 132 2 1 lookup doi 10 1126 science aai8703 2 lookup doi 10 1126 science aan0444

density porosity and magnetic susceptibility of carbonaceous chondrites abstract we report physical properties bulk and grain density magnetic susceptibility and porosity measured using nondestructive and noncontaminating methods for 195 stones from 63 carbonaceous chondrites grain densities over the whole population average 3 44 g cm 3 ranging from 2 42 g cm 3 ci1 orgueil to 5 66 g cm 3 cb bencubbin magnetic susceptibilities in log units of 10 9 m3 kg 1 averaged log 4 22 ranging from 3 23 cv3 axtell to 5 79 cb bencubbin porosities averaged 17 ranging from 0 for a number of meteorites to 41 for one stone of the co ornans notably we found significant differences in porosity between the oxidized and reduced cv subgroups with the porosities of cvo averaging approximately 20 and cvr porosities approximately 4 overall porosities of carbonaceous chondrite falls trend with petrographic type from type 1 ci near 35 type 2 cm cr averaging 23 type 3 cv co 21 to type 4 ck and some co averaging 15 there is also a significant decrease in porosity between meteorites of shock stage s1 and those of s2 indicative of shock compression

hydrogen generation from low temperature water rock reactions hydrogen is commonly produced during the high temperature hydration of mafic and ultramafic rocks laboratory experiments suggest that water rock reactions also generate hydrogen at lower temperatures potentially fuelling microbial life in ultramafic aquifers in oceanic and terrestrial crust

reorientation and faulting of pluto due to volatile loading within sputnik planitia the location of sputnik planitia on pluto is shown to result from volatiles sequestered within the basin forcing the reorientation of the dwarf planet as supported by the planet wide fault network james keane et al report that the location of sputnik planitia the approximately 1 000 kilometre diameter topographic basin that dominates the surface of pluto is a natural consequence of the infill of volatile ices within the basin and the resulting reorientation true polar wander of the dwarf planet as sputnik planitia slowly loaded with volatiles the pull of tidal torques from charon would have resulted in the eventual alignment of the basin with the pluto charon tidal axis sputnik planitia probably formed northwest of its present location and was loaded with volatiles over million year timescales as a result of volatile transport cycles this is one of four papers on the geology of sputnik planitia in this issue of nature in news views amy barr puts these latest contributions into context pluto is an astoundingly diverse geologically dynamic world the dominant feature is sputnik planitia a tear drop shaped topographic depression approximately 1 000 kilometres in diameter possibly representing an ancient impact basin1 2 the interior of sputnik planitia is characterized by a smooth craterless plain three to four kilometres beneath the surrounding rugged uplands and represents the surface of a massive unit of actively convecting volatile ices n2 ch4 and co several kilometres thick1 2 3 4 5 this large feature is very near the pluto charon tidal axis here we report that the location of sputnik planitia is the natural consequence of the sequestration of volatile ices within the basin and the resulting reorientation true polar wander of pluto loading of volatile ices within a basin the size of sputnik planitia can substantially alter pluto s inertia tensor resulting in a reorientation of the dwarf planet of around 60 degrees with respect to the rotational and tidal axes the combination of this reorientation loading and global expansion due to the freezing of a possible subsurface ocean generates stresses within the planet s lithosphere resulting in a global network of extensional faults that closely replicate the observed fault networks on pluto sputnik planitia probably formed northwest of its present location and was loaded with volatiles over million year timescales as a result of volatile transport cycles on pluto6 7 pluto s past present and future orientation is controlled by feedbacks between volatile sublimation and condensation changing insolation conditions and pluto s interior structure

planetary science enceladus hot springs the detection of silicon rich particles originating from saturn s moon enceladus suggests that water rock interactions are currently occurring inside it the first evidence of ongoing hydrothermal activity beyond earth see letter p 207 hsiang wen hsu et al have analysed the silicon rich nanometre sized dust stream particles in the saturnian system using the cosmic dust analyser cda onboard the cassini spacecraft with the help of experiments and modelling the particles are interpreted as silica grains that were initially embedded in the icy plume emitted from subsurface waters on enceladus and released by sputter erosion in saturn s e ring their properties indicate their formation and transport by high temperature hydrothermal reactions from the ocean floor and up into the plume of enceladus

metasomatic clathrate xenoliths as a possible source for the south polar plumes of enceladus abstract the composition and abundance of volatile gases observed in the jets emanating from fissures near the south pole of saturn s moon enceladus are strongly indicative of outgassing from clathrate hydrates which formed as a result of hydrothermal activity rather than nebula condensation i suggest that fluids must be able to permeate the ice shell extensively metasomatising the mantle by emplacement of clathrates along fractures and grain boundaries which subsequently are entrained in rising cryomagmas as xenoliths these are carried upwards to the point where they dissociate releasing their gas load into the magma and promoting the vigorous ice fountaining observed a direct analogue of terrestrial basaltic fire fountains caused by volatile exsolution this clathrate xenolith model can explain the measured volatile abundances eruption velocities the ice to vapour ratio in the plumes and the vent temperatures

light element geochemistry of the tagish lake ci2 chondrite comparison with ci1 and cm2 meteorites we have studied the carbon and nitrogen stable isotope geochemistry of a small pristine sample of the tagish lake carbonaceous chondrite by high resolution stepped combustion mass spectrometry and compared the results with data from the orgueil ci1 eet 83334 cm1 and murchison cm2 chondrites the small chip of tagish lake analysed herein had a higher carbon abundance 5 81 wt than any other chondrite and a nitrogen content 1220 ppm between that of ci1 and cm2 chondrites owing to the heterogeneous nature of the meteorite the measured carbon abundance might be artificially high the carbon inventory and whole rock carbon isotopic composition 13c 24 4 of the chip was dominated by 13c enriched carbon from the decomposition of carbonates between 1 29 wt and 2 69 wt 13c 67 and 18o 35 in the proportions 4 1 dolomite to calcite in addition to carbonates tagish lake contains organic carbon 2 6 wt 13c 9 1033 ppm n 15n 77 a level intermediate between ci and cm chondrites around 2 of the organic material is thermally labile and solvent soluble a further 18 of the organic species are liberated by acid hydrolysis tagish lake also contains a complement of presolar grains it has a higher nanodiamond abundance 3650 4330 ppm than other carbonaceous chondrites along with 8 ppm silicon carbide whilst carbon and nitrogen isotope geochemistry is not diagnostic the data are consistent with classification of tagish lake as a ci2 chondrite

prerequisites for explosive cryovolcanism on dwarf planet class kuiper belt objects explosive extrusion of cold material from the interior of icy bodies or cryovolcanism has been observed on enceladus and perhaps europa triton and ceres it may explain the observed evidence for a young surface on charon pluto s surface is masked by frosts here we evaluate prerequisites for cryovolcanism on dwarf planet class kuiper belt objects kbos we first review the likely spatial and temporal extent of subsurface liquid proposed mechanisms to overcome the negative buoyancy of liquid water in ice and the volatile inventory of kbos we then present a new geochemical equilibrium model for volatile exsolution and its ability to drive upward crack propagation this novel approach bridges geophysics and geochemistry and extends geochemical modeling to the seldom explored realm of liquid water at subzero temperatures we show that carbon monoxide co is a key volatile for gas driven fluid ascent whereas co 2 and sulfur gases only play a minor role n 2 ch 4 and h 2 exsolution may also drive explosive cryovolcanism if hydrothermal activity produces these species in large amounts a few percent with respect to water another important control on crack propagation is the internal structure a hydrated core makes explosive cryovolcanism easier but an undifferentiated crust does not we briefly discuss other controls on ascent such as fluid freezing on crack walls and outline theoretical advances necessary to better understand cryovolcanic processes finally we make testable predictions for the 2015 new horizons flyby of the pluto charon system

aqueous geochemistry and diagenesis in the eastern snake river plain aquifer system idaho water budget and isotopic analyses of water in the eastern snake river plain aquifer system confirm that most if not all of the water is local meteoric in origin solute mass balance arguments suggest that 5 10 9 moles of calcite and 2 6 10 9 moles of silica are precipitated annually in the aquifer isotopic evaluations of calcite and petrographic observation of silica support the low temperature origin of these deposits approximately 2 8 10 9 moles of chloride 4 5 10 9 moles of sodium 1 4 10 9 moles of sulfate and 2 10 9 moles of magnesium are removed annually from the aquifer framework by solution proposed weathering reactions are shown to be consistent with mass balance carbon isotopes observed mineralogy and chemical thermodynamics large quantities of sodium chloride and sulfate are being removed from the system relative to their abundances in the rock sedimentary interbeds which are estimated to compose 2 yr or less than half the average of the north american continent this contrasts with the rate for the eastern snake river basin 34 mg km 2 yr which is almost identical to the average for the north american continent identification and quantification of reactions controlling solute concentrations in ground water in the eastern plain indicate that the aquifer is not an inert bathtub that simply stores and transmits water and solutes but is undergoing active diagenesis and is both a source and sink for solutes

modeling aqueous alteration of cm carbonaceous chondrites results from an inorganic geochemical modeling study support a scenario in which low temperature aqueous alteration of an anhydrous cm asteroidal parent body and melt water from h20 and co ices produces the altered assemblage observed in cm carbonaceous chondrites chrysotile greenalite tochilinite cronstedtite and minor calcite and magnetite we consider a range of possible precursor mineral assemblages varying with respect to the fe oxidation state of the initial anhydrous phases the aqueous solutions produced by this alteration are generally strongly basic and reducing and a large quantity of h2 and possible ch4 gas can be released during aqueous alteration

convection in a volatile nitrogen ice rich layer drives pluto s geological vigour the volatile ice filled basin informally named sputnik planum is central to pluto s geological activity this ice layer is organized into cells or polygons and it is now shown that convective overturn in a several kilometre thick layer of solid nitrogen can explain both the presence of the cells and their great width nasa s new horizons spacecraft has revealed fascinating details of the surface of pluto including a vast ice filled basin known as sputnik planum which is central to pluto s geological activity much of the surface of sputnik planum consisting mostly of nitrogen ice is divided into irregular polygons that are tens of kilometres in diameter and whose centres rise tens of metres above their sides two papers in this issue of nature analyse new horizons images of this polygonal terrain both conclude that it is continually being resurfaced by convection but arrive at contrasting models for the process alexander trowbridge et al report a parameterized convection model in which the nitrogen ice is vigorously convecting ten or more kilometres thick and about a million years old william mckinnon et al from the new horizons team show that sluggish lid convective overturn in a several kilometre thick layer of solid nitrogen can explain both the presence of the cells and their great width the vast deep volatile ice filled basin informally named sputnik planum is central to pluto s vigorous geological activity1 2 composed of molecular nitrogen methane and carbon monoxide ices3 but dominated by nitrogen ice this layer is organized into cells or polygons typically about 10 to 40 kilometres across that resemble the surface manifestation of solid state convection1 2 here we report on the basis of available rheological measurements4 that solid layers of nitrogen ice with a thickness in excess of about one kilometre should undergo convection for estimated present day heat flow conditions on pluto more importantly we show numerically that convective overturn in a several kilometre thick layer of solid nitrogen can explain the great lateral width of the cells the temperature dependence of nitrogen ice viscosity implies that the ice layer convects in the so called sluggish lid regime5 a unique convective mode not previously definitively observed in the solar system average surface horizontal velocities of a few centimetres a year imply surface transport or renewal times of about 500 000 years well under the ten million year upper limit crater retention age for sputnik planum2 similar convective surface renewal may also occur on other dwarf planets in the kuiper belt which may help to explain the high albedos shown by some of these bodies

deep slab fluids fuel extremophilic archaea on a mariana forearc serpentinite mud volcano ocean drilling program leg 195 1 as the pacific plate subducts beneath the mariana forearc it releases water that hydrates the overlying mantle wedge converting it to serpentinite that protrudes to form mud volcanoes at the seafloor excess h2o ascends through these mud volcanoes and exits as cold springs at their summits the composition of this deep slab derived water has been determined by drilling on two of these seamounts it has a ph of 12 5 and relative to seawater is enriched in sulfate alkalinity na cl k rb b light hydrocarbons ammonia 18o and deuterium and depleted in chloride mg ca sr li si phosphate and 87sr within the upper 20 m below seafloor at south chamorro seamount a microbial community operating at ph 12 5 made up overwhelmingly of archaea is oxidizing methane from the ascending fluid to carbonate ion and organic carbon while reducing sulfate to bisulfide and probably dissolved nitrogen to ammonia

sublimation as a landform shaping process on pluto fields of pits both large and small in tombaugh regio sputnik planitia and the pitted uplands to the east and along the scarp of piri rupes are examples of landscapes on pluto where we conclude that sublimation drives their formation and evolution our heuristic modeling closely mimics the form spacing and arrangement of a variety of tombaugh regio s pits pluto s sublimation modified landforms appear to require a significant role for diffusive mass wasting as suggested by our modeling in our models the temporal evolution of pitted surfaces is such that initially lots of time passes with little happening then eventually very rapid development of relief and rapid sublimation small pits on sputnik planitia are consistent with their formation in n2 dominated materials as n2 ice readily flows some other stiffer volatile ice may play a role in supporting the relief of sublimation degraded landforms that exhibit several hundred meters of relief a strong candidate is ch4 which is spectroscopically observed to be associated with these features but the current state of rheological knowledge for ch4 ice at pluto conditions is insufficient for a firm assessment

soilscape evolution of west tien shan during the late pleistocene based on humus properties of the obi rakhmat archaeological site analysis of the pedogenic humus properties of sediments at the obi rakhmat archaeological site is the basis for reconstructing soil forming processes as records of climatic fluctuations in the region of west tien shan the stratigraphic section has 10 zones of pedogenesis that are distinguishable by pedogenic humus and other features and consequently by the character of ancient soil forming processes we found that most of the sediments accumulated in an environment where serozem soils form that is in an arid subtropical landscape desert steppe zone the scheme of the altitudinal landscape sequence and the structure of the soil cover also changed according to climatic changes and regular displacements of the altitude zones occurred when analogs of modern dark serozems dominated near the site the altitude sequence was characterized by the most complexity with humid as well as arid landscapes occupying areas of the slopes climatic change trends both to humidity and to aridity simplified the altitude scheme when climate was arid humid landscapes were ousted mountain brown forest soils occurred only on the slope tops in contrast when climate was humid arid landscapes disappeared from the altitude sequence and forest and meadow zones were dominant

pluto s global surface composition through pixel by pixel hapke modeling of new horizons ralph leisa data abstract on july 14th 2015 nasa s new horizons mission gave us an unprecedented detailed view of the pluto system the complex compositional diversity of pluto s encounter hemisphere was revealed by the ralph leisa infrared spectrometer on board of new horizons we present compositional maps of pluto defining the spatial distribution of the abundance and textural properties of the volatiles methane and nitrogen ices and non volatiles water ice and tholin these results are obtained by applying a pixel by pixel hapke radiative transfer model to the leisa scans our analysis focuses mainly on the large scale latitudinal variations of methane and nitrogen ices and aims at setting observational constraints to volatile transport models specifically we find three latitudinal bands the first enriched in methane extends from the pole to 55 n the second dominated by nitrogen continues south to 35 n and the third composed again mainly of methane reaches 20 n we demonstrate that the distribution of volatiles across these surface units can be explained by differences in insolation over the past few decades the latitudinal pattern is broken by sputnik planitia a large reservoir of volatiles with nitrogen playing the most important role the physical properties of methane and nitrogen in this region are suggestive of the presence of a cold trap or possible volatile stratification furthermore our modeling results point to a possible sublimation transport of nitrogen from the northwest edge of sputnik planitia toward the south

vigorous convection as the explanation for pluto s polygonal terrain a parameterized convection model and observations of the puzzling polygons of the sputnik planum region of pluto are used to compute the rayleigh number of its nitrogen ice and show that it is vigorously convecting kilometres thick and about a million years old nasa s new horizons spacecraft has revealed fascinating details of the surface of pluto including a vast ice filled basin known as sputnik planum which is central to pluto s geological activity much of the surface of sputnik planum consisting mostly of nitrogen ice is divided into irregular polygons that are tens of kilometres in diameter and whose centres rise tens of metres above their sides two papers in this issue of nature analyse new horizons images of this polygonal terrain both conclude that it is continually being resurfaced by convection but arrive at contrasting models for the process alexander trowbridge et al report a parameterized convection model in which the nitrogen ice is vigorously convecting ten or more kilometres thick and about a million years old william mckinnon et al from the new horizons team show that sluggish lid convective overturn in a several kilometre thick layer of solid nitrogen can explain both the presence of the cells and their great width pluto s surface is surprisingly young and geologically active1 one of its youngest terrains is the near equatorial region informally named sputnik planum which is a topographic basin filled by nitrogen n2 ice mixed with minor amounts of ch4 and co ices1 nearly the entire surface of the region is divided into irregular polygons about 20 30 kilometres in diameter whose centres rise tens of metres above their sides the edges of this region exhibit bulk flow features without polygons1 both thermal contraction and convection have been proposed to explain this terrain1 but polygons formed from thermal contraction analogous to ice wedges or mud crack networks 2 3 of n2 are inconsistent with the observations on pluto of non brittle deformation within the n2 ice sheet here we report a parameterized convection model to compute the rayleigh number of the n2 ice and show that it is vigorously convecting making rayleigh benard convection the most likely explanation for these polygons the diameter of sputnik planum s polygons and the dimensions of the floating mountains the hills of of water ice along the edges of the polygons suggest that its n2 ice is about ten kilometres thick the estimated convection velocity of 1 5 centimetres a year indicates a surface age of only around a million years

recent tectonic activity on pluto driven by phase changes in the ice shell the new horizons spacecraft has found evidence for geologic activity on the surface of pluto including extensional tectonic deformation of its water ice bedrock see moore et al 2016 one mechanism that could drive extensional tectonic activity is global surface expansion due to the partial freezing of an ocean we use updated physical properties for pluto and simulate its thermal evolution to understand the survival of a possible subsurface ocean for thermal conductivities of rock less than 3 w m 1 k 1 an ocean forms and at least partially freezes leading to recent extensional stresses in the ice shell in scenarios where the ocean freezes and the ice shell is thicker than 260 km ice ii forms and causes global volume contraction since there is no evidence for recent compressional tectonic features we argue that ice ii has not formed and that pluto s ocean has likely survived to present day

sarykul paleosol in southern urals sediments russia abstract sarykul paleosols in the southern urals russia with a stable position in geological sediments are considered the brunhes matuyama boundary was found in these paleosols and they were used as a source of information on the environment data were obtained during the study of the sarykul paleosols in four sections located in the mountain part of the southern urals on the miass river erosion accumulation terrace and at the eastern edge on the trans uralian peneplain saykul paleosols have a relatively thick and compact humic horizon with a tongued lower boundary the paleosols are dark grey with high toc content that is not usual for the early pleistocene paleosols the materials showed that sarykul paleosols formed on different parent rocks may have various characteristics of the mineral part texture ph magnetic susceptibility carbonate content ratio of exchangeable cations while their humic substances characteristics humic and fulvic acid ratio humic acid characteristics of elemental composition and structure are very similar climate conditions during sarykul paleosol formation changed from relatively warm and humid to less warm and more humid the study of southern urals sarykul paleosols has shown that they can serve as a reliable marker of the final early pleistocene due to their specific characteristics not analogous to the modern soils

pedohumic method in paleoenvironmental reconstructions abstract paleopedology can be an instrument to better understand problems in natural and humanitarian sciences a new pedohumic method involving diagnosis and reconstruction of paleoenvironments is suggested the reconstruction of the kazantsevo r w interglacial paleoenvironment in the chulymo yenisei depression middle siberia is considered as an example the trend of environmental conditions within the r w interglacial is similar to that of the current southern taiga steppe

26 al 26 mg and 207 pb 206 pb systematics of allende cais canonical solar initial 26 al 27 al ratio reinstated abstract the precise knowledge of the initial 26 al 27 al ratio 26 al 27 al 0 is crucial if we are to use the very first solid objects formed in our solar system calcium aluminum rich inclusions cais as the time zero age anchor and guide future work with other short lived radio chronometers in the early solar system as well as determining the inventory of heat budgets from radioactivities for early planetary differentiation new high precision multi collector inductively coupled plasma mass spectrometry mc icp ms measurements of 27 al 24 mg ratios and mg isotopic compositions of nine whole rock cais six mineralogically characterized fragments and three micro drilled inclusions from the cv carbonaceous chondrite allende yield a well defined 26 al 26 mg fossil isochron with an 26 al 27 al 0 of 5 23 0 13 10 5 internal mineral isochrons obtained for three of these cais a44a ajef and a43 are consistent with the whole rock cai isochron the mineral isochron of ajef with 26 al 27 al 0 4 96 0 25 10 5 anchored to our precisely determined absolute 207 pb 206 pb age of 4567 60 0 36 ma for the same mineral separates reinstate the canonical 26 al 27 al 0 of 5 10 5 for the early solar system the uncertainty in 26 al 27 al 0 corresponds to a maximum time span of 20 ka thousand years suggesting that the allende cai formation events were culminated within this time span although all allende cais studied experienced multistage formation history including melting and evaporation in the solar nebula and post crystallization alteration likely on the asteroidal parent body the 26 al 26 mg and u pb isotopic systematics of the mineral separates and bulk cais behaved largely as closed system since their formation our data do not support the supra canonical 26 al 27 al ratio of individual minerals or their mixtures in cv cais suggesting that the supra canonical 26 al 27 al ratio in the cv cais may have resulted from post crystallization inter mineral redistribution of mg isotopes within an individual inclusion this redistribution must be volumetrically minor in order to satisfy the mass balance of the precisely defined bulk cai and bulk mineral data obtained by mc icp ms the radiogenic 208 pb 206 pb ratio obtained as a by product from the pb pb age dating is used to estimate time integrated 232 th 238 u ratio value of cais limited variations among the minerals within a single cai contrasted by much larger variations among the bulk cais suggest th u fractionation occurred prior to crystallization of igneous cais if interpreted as primordial heterogeneity the value can be used to calculate the mean age of the interstellar dust from which the cais condensed

a microbial ecosystem beneath the west antarctic ice sheet liquid water has been known to occur beneath the antarctic ice sheet for more than 40 years but only recently have these subglacial aqueous environments been recognized as microbial ecosystems that may influence biogeochemical transformations on a global scale here we present the first geomicrobiological description of water and surficial sediments obtained from direct sampling of a subglacial antarctic lake subglacial lake whillans slw lies beneath approximately 800 m of ice on the lower portion of the whillans ice stream wis in west antarctica and is part of an extensive and evolving subglacial drainage network the water column of slw contained metabolically active microorganisms and was derived primarily from glacial ice melt with solute sources from lithogenic weathering and a minor seawater component heterotrophic and autotrophic production data together with small subunit ribosomal rna gene sequencing and biogeochemical data indicate that slw is a chemosynthetically driven ecosystem inhabited by a diverse assemblage of bacteria and archaea our results confirm that aquatic environments beneath the antarctic ice sheet support viable microbial ecosystems corroborating previous reports suggesting that they contain globally relevant pools of carbon and microbes that can mobilize elements from the lithosphere and influence southern ocean geochemical and biological systems

present and past glaciation on pluto abstract modern n2 ice glaciers flow from highlands to the east of the 750 1400 km2 lowland of sputnik planum sp and merge with the ices of similar composition on sp we explore the possibility that glaciation may be fed by n2 sublimation from sp followed by redeposition on the highlands the uplands to the northeast north and west of sp have been erosionally sculpted into a variety of dissected terrains that feature linear depressions valleys locally in dendritic networks we interpret these dissected terrains to have been carved by n2 glaciers formerly covering the uplands depositional glacial landforms moraines eskers outwash have not been identified however n2 glaciation would have a different erosional manifestation because the substrate porous water ice and ch4 rich mantles probably has lower density than n2 and also because of the lack of freeze thaw weathering if sufficiently thick 1 4 km n2 glaciers might have experienced basal melting past flow of n2 glaciers from the highlands into sp may have detached and transported the prominent mountainous water ice mountains along the western border of sp

compositional controls on hydrogen generation during serpentinization of ultramafic rocks abstract where ultramafic rocks are exposed to water at temperatures 2 formation are not well established we used thermodynamic computations to examine the equilibrium mineral assemblages mineral compositions and the chemistry of fluids during serpentinization of 21 different ultramafic rock compositions and 10 distinct compositions of olivine between 25 c and 400 c at 50 mpa our models predict some systematic differences between serpentinization of olivine dominated lithologies i e peridotite and of orthopyroxene dominated lithologies i e pyroxenite most notably it is predicted that serpentinization of peridotite causes the formation of serpentine having elevated fe 3 fe 3 fe 2 values fe bearing brucite at temperatures ca 320 c and magnetite at temperatures ca 200 c while serpentinization of pyroxenite does not produce magnetite but instead forms fe rich serpentine with relative low fe 3 fe 3 fe 2 values and fe poor talc the predicted activities of dissolved hydrogen a h 2 aq dissolved silica a sio 2 aq as well as the ph vary accordingly at temperatures ca 350 c fluids interacting with peridotite are more reducing have lower a sio 2 aq and higher ph than fluids interacting with pyroxenite a direct correlation between the iron content of olivine its stability relative to water temperature and a h 2 aq is apparent from our calculations in contrast to forsterite rich olivine fayalite rich olivine can be stable to temperatures as low as 180 c in the presence of water as a consequence the predicted ah 2 aq for serpentinization of fayalite is maximal at temperatures 180 c

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

a clathrate reservoir hypothesis for enceladus south polar plume we hypothesize that active tectonic processes in the south polar terrain of enceladus the 500 kilometer diameter moon of saturn are creating fractures that cause degassing of a clathrate reservoir to produce the plume documented by the instruments on the cassini spacecraft advection of gas and ice transports energy supplied at depth as latent heat of clathrate decomposition to shallower levels where it reappears as latent heat of condensation of ice the plume itself which has a discharge rate comparable to old faithful geyser in yellowstone national park probably represents small leaks from this massive advective system

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

the geology of pluto and charon through the eyes of new horizons nasa s new horizons spacecraft has revealed the complex geology of pluto and charon pluto s encounter hemisphere shows ongoing surface geological activity centered on a vast basin containing a thick layer of volatile ices that appears to be involved in convection and advection with a crater retention age no greater than 10 million years surrounding terrains show active glacial flow apparent transport and rotation of large buoyant water ice crustal blocks and pitting the latter likely caused by sublimation erosion and or collapse more enigmatic features include tall mounds with central depressions that are conceivably cryovolcanic and ridges with complex bladed textures pluto also has ancient cratered terrains up to 4 billion years old that are extensionally faulted and extensively mantled and perhaps eroded by glacial or other processes charon does not appear to be currently active but experienced major extensional tectonism and resurfacing probably cryovolcanic nearly 4 billion years ago impact crater populations on pluto and charon are not consistent with the steepest impactor size frequency distributions proposed for the kuiper belt

observed glacier and volatile distribution on pluto from atmosphere topography processes simulations of the levels of nitrogen methane and carbon monoxide over thousands of years confirm the existence of a nitrogen glacier in sputnik planitia pluto s deepest basin tanguy bertrand and francois forget have developed a model for volatile transport on pluto and use it to simulate the evolution of n2 ch4 and co on the dwarf plant over tens of thousands of earth years the model predicts n2 ice accumulation in the deepest low latitude basin and the threefold increase in atmospheric pressure that has been observed to occur since 1988 this points to atmospheric topographic processes as the origin of the prominent equatorial n2 glacier known as sputnik planitia formerly sputnik planum this is one of four papers on the geology of sputnik planitia in this issue of nature in news views amy barr puts these latest contributions into context pluto has a variety of surface frosts and landforms as well as a complex atmosphere1 there is ongoing geological activity related to the massive sputnik planitia glacier mostly made of nitrogen n2 ice mixed with solid carbon monoxide and methane2 covering the 4 kilometre deep 1 000 kilometre wide basin of sputnik planitia1 3 near the anti charon point the glacier has been suggested to arise from a source region connected to the deep interior or from a sink collecting the volatiles released planetwide1 thin deposits of n2 frost however were also detected at mid northern latitudes and methane ice was observed to cover most of pluto except for the darker frost free equatorial regions2 here we report numerical simulations of the evolution of n2 methane and carbon monoxide on pluto over thousands of years the model predicts n2 ice accumulation in the deepest low latitude basin and the threefold increase in atmospheric pressure that has been observed to occur since 19884 5 6 this points to atmospheric topographic processes as the origin of sputnik planitia s n2 glacier the same simulations also reproduce the observed quantities of volatiles in the atmosphere and show frosts of methane and sometimes n2 that seasonally cover the mid and high latitudes explaining the bright northern polar cap reported in the 1990s7 8 and the observed ice distribution in 20152 the model also predicts that most of these seasonal frosts should disappear in the next decade

correlations of radon and carbon isotopic measurements with petroleum and natural gas at cement oklahoma radon in soil gas and the carbon isotopic composition of carbon compounds in soil have been measured at 98 sites over the cement oklahoma oil and gas field strong correlations were observed between the density of oil and gas wells and storage tanks and soil 222rn field 222rn vertical gas flow and 13c gradients no meaningful correlation is seen with 13c if further study shows that these results are general the types of measurement done here could facilitate exploratory drilling

mechanisms of radon loss from zircon microstructural controls on emanation and diffusion abstract understanding how radon escapes from minerals is important for many fields in earth science yet few studies have focused on the mechanisms for radon escape we measured radon emanation rate and radon loss upon heating for crushed aliquots of three large zircon crystals from three localities mud tank australia bancroft canada and malawi africa our study in conjunction with published data shows that the room temperature radon emanation coefficient rec varies over 5 orders of magnitude in zircon for low u zircon mud tank there are variations in rec that appear to be related to annealing at different temperatures possibly due to annealing of fission tracks however all rec values for mud tank zircon are within error of one another bancroft and malawi zircons have higher u content and do not show any systematic relationship of rec to annealing temperature results from mud tank zircon suggest that partial annealing of fission tracks decreases rec but when all fission tracks are annealed rec reaches a maximum rec in zircons with high u content bancroft and malawi is slightly higher than in zircon with lower u although results are within error results of measurements of radon loss upon heating suggest that radon diffusion is slow 30 of the radon is lost during heating at 975 c for 48 h samples heated a second time yield less fractional radon loss 10 suggesting that diffusion parameters are changed during heating at temperatures 975 c which is likely the result of annealing of radiation damage diffusion parameters calculated from the fractional loss experiments reflect diffusion in highly radiation damaged or metamict zircons our results indicate that internal microstructures in zircon such as fission tracks and alpha radiation damage influence radon escape for diffusion and recoil mechanisms and hence if these effects can be further characterized measurements of 222rn escape have the potential to be useful for probing the internal structure of zircon and other u bearing minerals

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

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

pluto s ocean is capped and insulated by gas hydrates many icy solar system bodies possess subsurface oceans on pluto sputnik planitia s location near the equator suggests the presence of a subsurface ocean and a locally thinned ice shell to maintain an ocean pluto needs to retain heat inside on the other hand to maintain large variations in its thickness pluto s ice shell needs to be cold here we show by thermal evolution and viscous relaxation calculations that the presence of a thin layer of clathrate hydrates gas hydrates at the base of the ice shell can explain both the long term survival of the ocean and the maintenance of shell thickness contrasts clathrate hydrates act as a thermal insulator preventing the ocean from completely freezing while keeping the ice shell cold and immobile the most likely clathrate guest gas is methane derived from precursor bodies and or cracking of organic materials in the hot rocky core nitrogen molecules initially contained and or produced later in the core would probably not be trapped as clathrate hydrates instead supplying the nitrogen rich surface and atmosphere the formation of a thin clathrate hydrate layer cap to a subsurface ocean may be an important generic mechanism to maintain long lived subsurface oceans in relatively large but minimally heated icy satellites and kuiper belt objects pluto s subsurface ocean and thickness variation in its ice shell may be maintained by a layer of methane clathrates forming an insulating cap to the ocean according to calculations of thermal evolution and viscous relaxation

the formation of charon s red poles from seasonally cold trapped volatiles a unique feature of pluto s large satellite charon is its dark red northern polar cap similar colours on pluto s surface have been attributed to tholin like organic macromolecules produced by energetic radiation processing of hydrocarbons the polar location on charon implicates the temperature extremes that result from charon s high obliquity and long seasons in the production of this material the escape of pluto s atmosphere provides a potential feedstock for a complex chemistry gas from pluto that is transiently cold trapped and processed at charon s winter pole was proposed as an explanation for the dark coloration on the basis of an image of charon s northern hemisphere but not modelled quantitatively here we report images of the southern hemisphere illuminated by pluto shine and also images taken during the approach phase that show the northern polar cap over a range of longitudes we model the surface thermal environment on charon and the supply and temporary cold trapping of material escaping from pluto as well as the photolytic processing of this material into more complex and less volatile molecules while cold trapped the model results are consistent with the proposed mechanism for producing the observed colour pattern on charon

deuterium enrichments in chondritic macromolecular material implications for the origin and evolution of organics water and asteroids here we report the elemental and isotopic compositions of the insoluble organic material iom isolated from several previously unanalyzed meteorites as well as the reanalyses of h isotopic compositions of some previously measured samples alexander et al 2007 the iom in ordinary chondrites ocs has very large d enrichments that increase with increasing metamorphism and decreasing h c the most extreme d value measured being almost 12 000 we propose that such large isotopic fractionations could be produced in the oc parent bodies through the loss of isotopically very light h2 generated when fe was oxidized by water at low temperatures 200 c we suggest that similar isotopic fractionations were not generated in the iom of cv and co chondrites with similar metamorphic grades and iom h c ratios because proportionately less water was consumed during metamorphism and the remaining water buffered the h isotopic composition of the iom even a h was being lost from it hydrogen would also have been generated during the alteration of ci cm and cr carbonaceous chondrites the iom in these meteorites exhibit a considerable range in isotopic compositions but all are enriched in d as well as 15n relative to terrestrial values we explore whether these enrichments could also have been produced by the loss of h2 but conclude that the most isotopically anomalous iom compositions in meteorites from these groups are probably closest to their primordial values the less isotopically anomalous iom has probably been modified by parent body processes the response of iom to these processes was complex and varied presumably reflecting differences in conditions within and between parent bodies the d enrichments associated with h2 generation along with exchange between d rich iom and water in the parent bodies means that it is unlikely that any chondrites retain the primordial h isotopic composition of the water ice that they accreted the h isotopic compositions of the most water rich chondrites the cms and cis are probably the least modified and their compositions d 25 suggest that their water did not form at large radial distances from the sun where ice is predicted to be very d rich yet models to explain the o isotopic composition of inner solar system bodies require that large amounts of ice were transported from the outer to the inner solar system

a habitable fluvio lacustrine environment at yellowknife bay gale crater mars the curiosity rover discovered fine grained sedimentary rocks which are inferred to represent an ancient lake and preserve evidence of an environment that would have been suited to support a martian biosphere founded on chemolithoautotrophy this aqueous environment was characterized by neutral ph low salinity and variable redox states of both iron and sulfur species carbon hydrogen oxygen sulfur nitrogen and phosphorus were measured directly as key biogenic elements by inference phosphorus is assumed to have been available the environment probably had a minimum duration of hundreds to tens of thousands of years these results highlight the biological viability of fluvial lacustrine environments in the post noachian history of mars

impact jetting of water ice with application to the accretion of icy planetesimals and pluto jetting can occur during oblique impacts of water ice bodies at relative velocities at low as approximately 500 m s sup minus 1 because of the low hugoniot elastic limit and high compressibility of ice compared to rock in jetted ice incipient melting complete melting and incipient vaporization occur upon release to low pressure at impact velocities of 1 3 2 0 and 2 7 km s sup minus 1 respectively much less than the 3 4 4 4 and 5 3 km s sup minus 1 required in head on collisions uncertainties in the shock equation of state may allow complete melting during jetting at relative velocities as low as 1 2 km s sup minus 1 because jet speeds exceed impact speeds often by a factor of several during the accretion of icy bodies greater than a few 100 km in radius there any be a significant loss of icy material this is more true if the accreting body is large enough to differentiate so that its surface layers are closer to pure ice in composition and especially true if bodies of comparable size are involved which emphasizes the obliqueness of the collision the author suggests that it is jetting during a charon forming collision and not vaporization that may account for pluto charon s relatively large rock ice ratio shouldmore the c o ratio of the solar nebula turn out too low to sufficiently raise the rock ice ratio of outer solar nebula condensates by formation of non condensable co less

an oceanic composition on early and today s enceladus 1 the oceanic composition on saturn s moon enceladus is evaluated through calculations of thermochemical equilibria at hydrothermal and freezing settings conditions of rock alteration are constrained from assumptions and models for the moon s interior composition and thermal evolution and from the composition of enceladus plume results show that an early ocean was an alkaline na cl hco3 solution underlying altered rocks consisted of mg phyllosilicates magnetite fe and ni sulfides and carbonates subsequent freezing of oceanic water caused the deposition of a nacl hydrate na k and ca carbonates and the formation of a salt free ice shell if an aqueous phase exists on today s enceladus it could consist of eutectic na cl hco3 brine that at least locally decouples the ice shell and facilitates tidal heating a lack of firm detection of na and cl at enceladus is consistent with the accumulation of salts at the ice rock boundary and implies the plume formation via sublimation in the ice shell

hydrogen generation from mantle source rocks in oman hydrogen gas associated with ca2 oh rich alkaline groundwaters ph 10 12 is at present emanating from ultramafic rocks of the oman ophiolite isotopic and chemical evidence indicates that hydrogen is formed by low temperature redox reactions in a closed groundwater environment this is normally a cryptic process in the hydrosphere but is fortuitously revealed by the unusual hydrogeological conditions in oman where atmospheric oxygen is totally assimilated it is suggested that hydrogen generation in mantle source rocks at depth and in the early archaean surface environment may be more widespread than has hitherto been realised

past epochs of significantly higher pressure atmospheres on pluto abstract pluto is known to have undergone thousands of cycles of obliquity change and polar precession these variations have a large and corresponding impact on the total average solar insolation reaching various places on pluto s surface as a function of time such changes could produce dramatic increases in surface pressure and may explain certain features observed by new horizons on pluto s surface including some that indicate the possibility of surface paleo liquids this paper is the first to discuss multiple lines of geomorphological evidence consistent with higher pressure epochs in pluto s geologic past and it also the first to provide a mechanism for potentially producing the requisite high pressure conditions needed for an environment that could support liquids on pluto the presence of such liquids and such conditions if borne out by future work would fundamentally affect our view of pluto s past climate volatile transport and geological evolution this paper motivates future more detailed climate modeling and geologic interpretation efforts in this area

the rapid formation of sputnik planitia early in pluto s history modelling suggests that the icy region on pluto known as sputnik planitia formed shortly after charon did and has since been stable with its latitude corresponding to a minimum in annual solar illumination and its longitude determined by tidal forces from charon douglas hamilton et al present modelling data that imply that pluto s sputnik planitia basin may be an ice cap rather than the product of an impact their data suggest that the feature formed shortly after pluto s largest satellite charon did and has since been stable with its latitude corresponding to a minimum in annual solar illumination over its orbital precession period of about a million years and its longitude determined by tidal forces from charon this is one of four papers on the geology of sputnik planitia in this issue of nature in news views amy barr puts these latest contributions into context pluto s sputnik planitia is a bright roughly circular feature that resembles a polar ice cap it is approximately 1 000 kilometres across and is centred on a latitude of 25 degrees north and a longitude of 175 degrees almost directly opposite the side of pluto that always faces charon as a result of tidal locking1 one explanation for its location includes the formation of a basin in a giant impact with subsequent upwelling of a dense interior ocean2 once the basin was established ice would naturally have accumulated there3 then provided that the basin was a positive gravity anomaly with or without the ocean true polar wander could have moved the feature towards the pluto charon tidal axis on the far side of pluto from charon2 4 here we report modelling that shows that ice quickly accumulates on pluto near latitudes of 30 degrees north and south even in the absence of a basin because averaged over its orbital period those are pluto s coldest regions within a million years of charon s formation ice deposits on pluto concentrate into a single cap centred near a latitude of 30 degrees owing to the runaway albedo effect this accumulation of ice causes a positive gravity signature that locks as pluto s rotation slows to a longitude directly opposite charon once locked charon raises a permanent tidal bulge on pluto which greatly enhances the gravity signature of the ice cap meanwhile the weight of the ice in sputnik planitia causes the crust under it to slump creating its own basin as has happened on earth in greenland5 even if the feature is now a modest negative gravity anomaly it remains locked in place because of the permanent tidal bulge raised by charon any movement of the feature away from 30 degrees latitude is countered by the preferential recondensation of ices near the coldest extremities of the cap therefore our modelling suggests that sputnik planitia formed shortly after charon did and has been stable albeit gradually losing volume over the age of the solar system

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

ikaite precipitation by mixing of shoreline springs and lake water mono lake california usa abstract metastable ikaite caco3 6h2o forms abundantly during winter months along the south shoreline of mono lake where shoreline springs mix with lake water ikaite precipitates because of its decreased solubility at low temperature and because of orthophosphate ion inhibition of calcite and aragonite during the spring some of the ikaite is transformed to anhydrous caco3 and is incorporated into tufa but most is dispersed by wave action into the lake where it reacts to form gaylussite na2ca co3 2 5h2o spring waters have low ph values are dominantly ca na hco3 have low radiocarbon activities and are mixtures of deep seated geothermal and cold groundwaters chemical modeling reveals that precipitation of caco3 can occur over a broad range of mixtures of spring and lake water with a maximum production occurring at 96 spring water and 4 lake water under these conditions all the ca and a significant fraction of the co3 of the precipitate is spring supplied a radiocarbon age of 19 580 years obtained on a natural ikaite sample supports this conclusion with the springs supplying a large and probably variable portion of the carbonate and with apparent 14c age of the carbonate varying from spring to spring tufa of similar actual antiquity may yield significantly different 14c dates making tufa at this location unsuitable for absolute age dating by the radiocarbon method

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

localized sources of water vapour on the dwarf planet 1 ceres the largest asteroid of the solar system 1 ceres has been thought to have an icy surface here it is observed to be emitting water vapour the presence of hydrated minerals on the surface of ceres the largest body in the solar system s main asteroid belt suggested that there may be water there too now infrared spectra obtained by esa s herschel space observatory provide unambiguous evidence that there is water ice at or near the surface of ceres water vapour is issuing at a rate of at least 1026 molecules per second from sources on ceres localized to mid latitude regions the water evaporation could be due to comet like sublimation or to cryo volcanism in which volcanoes erupt volatiles such as water instead of molten rocks this finding supports models that propose that the icy bodies such as comets may have migrated into the asteroid belt from beyond the notional snowline dividing the early solar system into a dry inner and icy outer regions the snowline conventionally divides solar system objects into dry bodies ranging out to the main asteroid belt and icy bodies beyond the belt models suggest that some of the icy bodies may have migrated into the asteroid belt1 recent observations indicate the presence of water ice on the surface of some asteroids2 3 4 with sublimation5 a potential reason for the dust activity observed on others hydrated minerals have been found6 7 8 on the surface of the largest object in the asteroid belt the dwarf planet 1 ceres which is thought to be differentiated into a silicate core with an icy mantle9 10 11 the presence of water vapour around ceres was suggested by a marginal detection of the photodissociation product of water hydroxyl ref 12 but could not be confirmed by later more sensitive observations13 here we report the detection of water vapour around ceres with at least 1026 molecules being produced per second originating from localized sources that seem to be linked to mid latitude regions on the surface14 15 the water evaporation could be due to comet like sublimation or to cryo volcanism in which volcanoes erupt volatiles such as water instead of molten rocks

tidally induced melting events as the origin of south pole activity on enceladus abstract the intense activity at the south pole of enceladus hints at an internal water reservoir however there is no direct evidence of liquid water at present and its long term stability in the interior remains problematic by modeling heat production and transfer in the ice shell in a spherical geometry we show that tidal heating naturally leads to a concentration of convective hot upwellings in the south polar region favoring the preservation of liquid water at depth we show that large volumes of water are produced within the ice shell at the south pole during periods of elevated orbital eccentricity 3 5 times the present day value strong lateral variations in the melt production and crystallization rates result in stress concentration in the south polar region thus providing an explanation for the tectonic activity observed today we predict that an internal ocean may be sustained over the long term as the consequence of repeated periods with elevated orbital eccentricity leading to episodic melting and resurfacing events

carbonate abundances and isotopic compositions in chondrites we report the bulk c abundances and c and o isotopic compositions of carbonates in 64 cm chondrites 14 cr chondrites 2 ci chondrites lew 85332 c2 kaba cv3 and semarkona ll3 0 for the unheated cms the total ranges of carbonate isotopic compositions are 13c 25 75 and 18o 15 35 and bulk carbonate c contents range from 0 03 to 0 60 wt there is no simple correlation between carbonate abundance and isotopic composition or between either of these parameters and the extent of alteration unless accretion was very heterogeneous the uncorrelated variations in extent of alteration and carbonate abundance suggests that there was a period of open system behavior in the cm parent body probably prior to or at the start of aqueous alteration most of the ranges in cm carbonate isotopic compositions can be explained by their formation at different temperatures 0 130 c from a single fluid in which the carbonate o isotopes were controlled by equilibrium with water 18o 5 and the c isotopes were controlled by equilibrium with co and or ch4 13c 33 or 20 for co or ch4 dominated systems respectively however carbonate formation would have to have been inefficient otherwise carbonate compositions would have resembled those of the starting fluid a quite similar fluid composition 18o 5 5 and 13c 31 or 17 for co or ch4 dominated systems respectively can explain the carbonate compositions of the cis although the formation temperatures would have been lower 10 40 c and the relative abundances of calcite and dolomite may play a more important role in determining bulk carbonate compositions than in the cms the cr carbonates exhibit a similar range of o isotopes but an almost bimodal distribution of c isotopes between more 13c 65 80 and less altered samples 13c 30 40 this bimodality can still be explained by precipitation from fluids with the same isotopic composition 18o 9 25 and 13c 21 or 8 for co or ch4 dominated systems respectively if the less altered crs had higher mole fractions of co2 in their fluids semarkona and kaba carbonates have some of the lightest c isotopic compositions of the meteorites studied here probably because they formed at higher temperatures and or from more co2 rich fluids the fluids responsible for the alteration of chondrites and from which the carbonates formed were almost certainly accreted as ices by analogy with cometary ices co2 and or co would have dominated the trapped volatile species in the ices the chondrites studied are too oxidized for co dominated fluids to have formed in their parent bodies if ch4 was the dominant c species in the fluids during carbonate formation it would have to have been generated in the parent bodies from co and or co2 when oxidation of metal by water created high partial pressures of h2 the fact that the chondrite carbonate c h2o mole ratios are of the order predicted for co co2 h2o ices that experienced temperatures of 50 100 k suggests that the chondrites formed at radial distances of 4 15 au

occultation evidence for an atmosphere on pluto on 9 june 1988 pluto occulted a 12th magnitude star1 several observations of the occultation were obtained from australia new zealand and the south pacific2 and indicated that the initial decline in stellar flux was gradual as would be expected if the starlight was defocused by an extended atmosphere around the planet here we interpret data obtained from the 1 telescope at the university of tasmania hobart in terms of a theory for occultation by an atmosphere whose thickness is comparable to the planetary radius the data can be satisfactorily fitted with a methane atmosphere at plausible pressures and temperatures the surface pressures inferred from this single chord are uncertain by an order of magnitude but are consistent with spectroscopic constraints

origin of the pluto charon system constraints from the new horizons flyby abstract new horizon s accurate determination of the sizes and densities of pluto and charon now permit precise internal models of both bodies to be constructed assuming differentiated rock ice structures we find that pluto is close to 2 3 solar composition anhydrous rock by mass and charon 3 5 solar composition anhydrous rock by mass pluto and charon are closer to each other in density than to other large 1000 km diameter kuiper belt bodies despite this we show that neither the possible presence of an ocean under pluto s water ice shell and no ocean within charon nor enhanced porosity at depth in charon s icy crust compared with that of pluto are sufficient to make pluto and charon s rock mass fractions match all four small satellites styx nix kerberos hydra appear much icier in comparison with either pluto or charon in terms of a giant impact origin both these inferences are most consistent with the relatively slow collision of partly differentiated precursor bodies canup astrophys j 141 35 2011 this is in turn consistent with dynamical conditions in the ancestral kuiper belt but implies that the impact precursors themselves accreted relatively late and slowly to limit 26 al and accretional heating the iciness of the small satellites is not consistent with direct formation of the pluto charon system from a streaming instability in the solar nebula followed by prompt collapse of gravitationally bound pebble piles a proposed formation mechanism for kuiper belt binaries nesvorn et al astron j 140 785 793 2010 growth of pluto scale bodies by accretion of pebbles in the ancestral kuiper belt is not ruled out however and may be needed to prevent the precursor bodies from fully differentiating due to buried accretional heat prior to the charon forming impact

the pluto system initial results from its exploration by new horizons the pluto system was recently explored by nasa s new horizons spacecraft making closest approach on 14 july 2015 pluto s surface displays diverse landforms terrain ages albedos colors and composition gradients evidence is found for a water ice crust geologically young surface units surface ice convection wind streaks volatile transport and glacial flow pluto s atmosphere is highly extended with trace hydrocarbons a global haze layer and a surface pressure near 10 microbars pluto s diverse surface geology and long term activity raise fundamental questions about how small planets remain active many billions of years after formation pluto s large moon charon displays tectonics and evidence for a heterogeneous crustal composition its north pole displays puzzling dark terrain small satellites hydra and nix have higher albedos than expected

reorientation of sputnik planitia implies a subsurface ocean on pluto to explain the position of the sputnik planitia basin on pluto the feature would need to have formed via impact and pluto would need to have a subsurface ocean the present location of sputnik planitia the prominent deep icy basin on pluto is close to one of the longitudes of the dwarf planet s tidal axis by analogy with other large basins in the solar system it is thought to be an impact feature although reorientation arising from tidal and rotational torques can explain the present day location of the basin it requires the feature to be a positive gravity anomaly despite its negative topography francis nimmo et al argue that if sputnik planitia formed via impact and if pluto possesses a subsurface ocean a positive gravity anomaly would naturally result because of shell thinning and ocean uplift followed by later modest nitrogen deposition this is one of four papers on the geology of sputnik planitia in this issue of nature in news views amy barr puts these latest contributions into context the deep nitrogen covered basin on pluto informally named sputnik planitia is located very close to the longitude of pluto s tidal axis1 and may be an impact feature2 by analogy with other large basins in the solar system3 4 reorientation5 6 7 of sputnik planitia arising from tidal and rotational torques can explain the basin s present day location but requires the feature to be a positive gravity anomaly7 despite its negative topography here we argue that if sputnik planitia did indeed form as a result of an impact and if pluto possesses a subsurface ocean the required positive gravity anomaly would naturally result because of shell thinning and ocean uplift followed by later modest nitrogen deposition without a subsurface ocean a positive gravity anomaly requires an implausibly thick nitrogen layer exceeding 40 kilometres to prolong the lifetime of such a subsurface ocean to the present day8 and to maintain ocean uplift a rigid conductive water ice shell is required because nitrogen deposition is latitude dependent9 nitrogen loading and reorientation may have exhibited complex feedbacks7

geological mapping of sputnik planitia on pluto abstract the geology and stratigraphy of the feature on pluto informally named sputnik planitia is documented through geologic mapping at 1 2 000 000 scale all units that have been mapped are presently being affected to some degree by the action of flowing n2 ice the n2 ice plains of sputnik planitia display no impact craters and are undergoing constant resurfacing via convection glacial flow and sublimation condensation of atmospheric n2 onto the surface to form a bright mantle has occurred across broad swathes of sputnik planitia and appears to be partly controlled by pluto s obliquity cycles the action of n2 ice has been instrumental in affecting uplands terrain surrounding sputnik planitia and has played a key role in the disruption of sputnik planitia s western margin to form chains of blocky mountain ranges as well in the extensive erosion by glacial flow of the uplands to the east of sputnik planitia

radon emanation coefficients of several minerals how they vary with physical and mineralogical properties the escape rates of radon gas from rocks and minerals are of great relevance to many branches of geosciences and it is thus important to understand the physical and mineralogical properties that control radon emanation rates mechanisms of radon loss from minerals have direct bearing on the reliability of u pb and u th he geochronology fourteen minerals from three different mineral groups and with localities spanning three continents were selected for this study the radon emanation coefficients rec for each mineral were measured as a function of grain size temperature 238 u and 232 th activities total absorbed dose density and mineral melting temperature the measured 238 u and 232 th activities ranged from 0 01 to 6487 bq g and from below detection limit to 776 bq g respectively the rec values for unheated pulverized samples ranged from 0 083 to 7 0 which is comparable to previously reported ranges except for zircon an inverse correlation between grain size and rec was observed full annealing of fission tracks resulted in an overall decrease in rec values suggesting that nuclear tracks could possibly act as conduits for radon release while activity dose density and melting temperatures are not strongly correlated with rec values it was observed that minerals with high melting points 1400 c have lower rec values most likely due to inhibition of radon release by compact crystal lattice structures this is the first attempt to our knowledge to correlate rec values with melting temperature and this study reports six minerals for which no rec values have been previously reported

coupled organic synthesis and mineral alteration on meteorite parent bodies the hypothesis that the soluble fraction of the organic compounds present in carbonaceous chondrite meteorites was formed during aqueous alteration of the parent body was tested with masstransfer reaction path calculations in these calculations we start with likely compositions of the original parent body and asteroidal fluids that are far from thermodynamic equilibrium and metastable and stable equilibrium constraints are imposed as the total gibbs free energy of the parent body environment is minimized the results of these calculations suggest that the classes of soluble organic compounds present in carbonaceous chondrite meteorites could have formed during relatively low temperature aqueous alteration of the meteorite parent body or bodies the main controls on the potential for synthesis and transformation of organic compounds were the oxidation state of the rock fluid system the bulk composition of that system and the temperatures that were achieved during the alteration event or events it also appears that the alteration mineral assemblages were influenced by the presence of soluble organic compounds and reaction among them

enceladus south polar sea recent observations of the south pole of saturn s moon enceladus by the cassini spacecraft have revealed an active world powered by internal heat in this paper we propose that localized subsurface melting on enceladus has produced an internal south polar sea evidence for this localized sea comes from the shape of enceladus which does not match a differentiated body at its current orbital position we show that melting induced by the observed heat flow at the south pole produces a large enough pit to match the shape of enceladus with a differentiated rock and ice interior numerical modeling of melting and ice flow shows that the sea produced beneath the south pole is stable against inflow of ductile ice from its surroundings for the duration of the heating the shape modification due to melting also produces a negative degree two gravity anomaly which can reorient the spin axis of enceladus in order to place the sea at the pole

shestakovo site of western siberia russia pedogenic features humic substances and paleoenvironment reconstructions for last 20 25 ka abstract new data characterizing sediments of the shestakovo iii section located in the southern part of the west siberian plain have been obtained the section reveals 9 m of strata in which a number of paleosols and pedogenic zones are identified on the basis of cumulative features of pedogenesis paleosols and pedogenic features reflect the pedogenic transformation of sediments in different environments during the late karghinsk interval w 2 sartan glaciation w 3 and holocene period the lower part of the sediments at a depth of 7 5 8 5 m has radiocarbon dates from 25 to 18 000 years the obtained characteristics of the composition structure and properties of humic substances as well as comparison with data obtained earlier by other methods of environmental reconstruction enable recognition of the environment at the southern margin of the west siberia plain during the last 20 25 ka in more detail

association of subsurface radon changes in alaska and the northeastern united states with earthquakes abstract changes of radon concentration in the ground have been reported to correlate with seismic activity in many places over widely varying distances from the earthquake epicenters sometimes over 100 s and occasionally over 1000 s of km depending on the magnitude m of the earthquakes for proper use of such correlations in forecasting the location and size of impending earthquakes it would be useful to establish a relation between m and the maximum distance x m at which radon can be significantly altered by preseismic effects we have monitored radon in the ground continuously at blue mountain lake ny starting dec 3 1975 and at three locations in alaska icy bay yakataga and sand point starting nov 12 1979 march 5 1980 and june 29 1980 respectively sample correlations from visual examination of the recent radon record and tentative use of a proposed scaling relation show a number of possible earthquake related signals at these locations the data are compatible with scaling relations that were derived from two separate models of premonitory elastic strains in this work x m 10 0 48 m where x m is in units of km and m 3 since tilt and strain signals correlate similarly with magnitude and distance it is likely that most earthquake related radon signals are mechanically induced

icemole a maneuverable probe for clean in situ analysis and sampling of subsurface ice and subglacial aquatic ecosystems there is significant interest in sampling subglacial environments for geobiological studies but they are difficult to access existing ice drilling technologies make it cumbersome to maintain microbiologically clean access for sample acquisition and environmental stewardship of potentially fragile subglacial aquatic ecosystems the icemole is a maneuverable subsurface ice probe for clean in situ analysis and sampling of glacial ice and subglacial materials the design is based on the novel concept of combining melting and mechanical propulsion it can change melting direction by differential heating of the melting head and optional side wall heaters the first two prototypes were successfully tested between 2010 and 2012 on glaciers in switzerland and iceland they demonstrated downward horizontal and upward melting as well as curve driving and dirt layer penetration a more advanced probe is currently under development as part of the enceladus explorer enex project it offers systems for obstacle avoidance target detection and navigation in ice for the enex icemole we will pay particular attention to clean protocols for the sampling of subglacial materials for biogeochemical analysis we plan to use this probe for clean access into a unique subglacial aquatic environment at blood falls antarctica with return of a subglacial brine sample

radio occultation measurements of pluto s neutral atmosphere with new horizons abstract on 14 july 2015 new horizons performed a radio occultation ro that sounded pluto s atmosphere down to the surface the sensitivity of the measurements was enhanced by a unique configuration of ground equipment and spacecraft instrumentation signals were transmitted simultaneously by four antennas of the nasa deep space network each radiating 20 kw at a wavelength of 4 2 cm the polarization was right circular for one pair of signals and left circular for the other pair new horizons received the four signals and separated them by polarization for processing by two independent receivers each referenced to a different ultra stable oscillator the two data streams were digitized filtered and stored on the spacecraft for later transmission to earth the results reported here are the first to utilize the complete set of observations we calibrated each signal to remove effects not associated with pluto s atmosphere including the limb diffraction pattern we then applied a specialized method of analysis to retrieve profiles of number density pressure and temperature from the combined phase measurements occultation entry sounded the atmosphere at sunset at 193 5 e 17 0 s on the southeast margin of an ice filled basin known informally as sputnik planitia sp occultation exit occurred at sunrise at 15 7 e 15 1 n near the center of the charon facing hemisphere above 1215 km radius 25 km altitude there is no discernible difference between the measurements at entry and exit and the ro profiles are consistent with results derived from ground based stellar occultation measurements at lower altitudes the ro measurements reveal horizontal variations in atmospheric structure that had not been observed previously and they are the first to reach the ground the entry profile has a strong temperature inversion that ends 3 5 km above the surface and the temperature in the cold boundary layer beneath the inversion is nearly constant 38 9 2 1 k and close to the saturation temperature of n 2 the exit profile has a much weaker inversion that extends all the way to the ground where the air temperature is 51 6 3 8 k three factors appear to be responsible for the presence of a cold boundary layer in the entry profile forget et al 2017 a substantial diurnal cycle of sublimation and condensation of n 2 ice in sp the local time of the ro observation and confinement within sp by the surrounding topography and katabatic winds we have also determined the surface pressure and the local radius at both entry and exit the best pressure reference is the mean value 11 5 0 7 microbar at 1189 9 0 2 km

stable asymmetric ice belts in an energy balance model of pluto abstract in this paper we analyze a latitude dependent energy balance model with two dynamic ice lines between the north and south poles and consider results for a range of parameter values of which some may pertain to pluto our analysis shows that for any albedo contrast there exist stable ice line equilibria where the northern and southern edges are not symmetric about the equator in particular stable asymmetric ice belts can be found within the latitude ranges defined by sputnik planitia on pluto however we find that an ice belt with northern and southern edges defined by the northern and southern boundaries of sputnik planitia would be flowing to a symmetrical configuration for the parameter values used in this study