simulation of historic glacier variations with a simple climate glacier model glacier variations during the last few centuries have shown a marked coherence over the globe characteristic features are the maximum stand somewhere in the middle of the nineteenth century and the steady retreat afterwards with some minor interrruptions depending on the particular region in many papers qualitative statements have been made about the causes of these fluctuations lower temperatures associated with solar variability and or volcanic activity are the most popular explanations in particular the statistical relation between glacier activity and major volcanic eruptions appears to be strong in this paper an attempt is made to simulate recent glacier fluctations with a physics based model a simple climate model calculating perturbations of surface radiation balance and air temperature not necessarily in phase is coupled to a schematic time dependent glacier model the climate model is forced by volcanic activity greenland acidity and or lamb s dust veil index and greenhouse warming solar variability was not considered because its effect on climate has still not been demonstrated in a convincing way the output is translated into variations in equilibrium line altitude driving the glacier model the simulated variations in glacier length show good agreement with the observed record but the amplitude is too small this is improved when mass balance gradients are assumed to be larger in warmer climates compared to recently published modelling studies of particular glaciers in which series of local parameters e g tree ring width and temperature were used as forcing the present simulation is better this suggests that the radiation balance is a decisive factor with regard to glacier variations on longer time scales the model experiments lend support to the results of porter 1986 who concluded from a more qualitative study that a strong relation exists between periods of increased volcanic activity and glacier advances a comparison of some selected runs shows that according to the present model the greenhouse warming would be responsible for about 50 of the glacier retreat observed over the last 100 years

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

albedo matters understanding runaway albedo variations on pluto abstract the data returned from nasa s new horizons reconnaissance of the pluto system show striking albedo variations from polar to equatorial latitudes as well as sharp longitudinal boundaries pluto has a high obliquity currently 119 that varies by 23 over a period of less than 3 million years this variation combined with its regressing longitude of perihelion 360 over 3 7 million years creates epochs of super seasons where one pole is pointed at the sun at perihelion thereby experiencing a short relatively warm summer followed by its longest possible period of winter darkness in contrast the other pole experiences a much longer less intense summer and a short winter season we use a simple volatile sublimation and deposition model to explore the relationship between albedo variations latitude and volatile sublimation and deposition for the current epoch as well as historical epochs during which pluto experienced these super seasons our investigation quantitatively shows that pluto s geometry creates the potential for runaway albedo and volatile variations particularly in the equatorial region which can sustain stark longitudinal contrasts like the ones we see between tombaugh regio and the informally named cthulhu regio

pluto pits and mantles on uplands north and east of sputnik planitia abstract the highlands region north and east of sputnik planitia can be subdivided into seven terrain types based on their physiographic expression the northern rough uplands are characterized by jagged uplands and broad troughs and it may contain a deeply eroded ancient mantle dissected terrain has been interpreted to have been eroded by paleo glaciation the smooth uplands and pits terrain contains broad rolling uplands surrounding complexes of pits some of which contain smooth floors the uplands are mantled by smooth surfaced deposits possibly derived from adjacent pits through low power explosive cryovolcanism or through slow vapor condensation the eroded smooth uplands appear to have originally been smooth uplands and pits terrain modified by small scale sublimation pitting the bright pitted uplands features intricate texturing by reticulate ridges that may have originated by sublimation erosion volatile condensation or both the bladed terrain is characterized by parallel ridges oriented north south and is discussed in a separate paper the dark uplands are mantled with reddish deposits that may be atmospherically deposited tholins their presence has affected long term landform evolution widespread pit complexes occur on most of the terrain units most appear to be associated with tectonic lineations some pits are floored by broad expanses of ices whereas most feature deep conical depressions a few pit complexes are enclosed by elevated rims of uncertain origin

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

bladed terrain on pluto possible origins and evolution abstract bladed terrain on pluto consists of deposits of massive ch 4 which are observed to occur within latitudes 30 of the equator and are found almost exclusively at the highest elevations 2 km above the mean radius our analysis indicates that these deposits of ch 4 preferentially precipitate at low latitudes where net annual solar energy input is lowest ch 4 and n 2 will both precipitate at low elevations however since there is much more n 2 in the atmosphere than ch 4 the n 2 ice will dominate at these low elevations at high elevations the atmosphere is too warm for n 2 to precipitate so only ch 4 can do so we conclude that following the time of massive ch 4 emplacement there have been sufficient excursions in pluto s climate to partially erode these deposits via sublimation into the blades we see today blades composed of massive ch 4 ice implies that the mechanical behavior of ch 4 can support at least several hundred meters of relief at pluto surface conditions bladed terrain deposits may be widespread in the low latitudes of the poorly seen sub charon hemisphere based on spectral observations if these locations are indeed bladed terrain deposits they may mark heretofore unrecognized regions of high elevation

the ch4 cycles on pluto over seasonal and astronomical timescales abstract pluto s surface is covered in numerous ch4 ice deposits that vary in texture and brightness as revealed by the new horizons spacecraft as it flew by pluto in july 2015 these observations suggest that ch4 on pluto has a complex history involving reservoirs of different composition thickness and stability controlled by volatile processes occurring on different timescales in order to interpret these observations we use a pluto volatile transport model able to simulate the cycles of n2 and ch4 ices over millions of years by assuming fixed solid mixing ratios we explore how changes in surface albedos emissivities and thermal inertias impact volatile transport this work is therefore a direct and natural continuation of the work by bertrand et al 2018 which only explored the n2 cycles results show that bright ch4 deposits can create cold traps for n2 ice outside sputnik planitia leading to a strong coupling between the n2 and ch4 cycles depending on the assumed albedo for ch4 ice the model predicts ch4 ice accumulation 1 at the same equatorial latitudes where the bladed terrain deposits are observed supporting the idea that these ch4 rich deposits are massive and perennial or 2 at mid latitudes 25 70 forming a thick mantle which is consistent with new horizons observations in our simulations both ch4 ice reservoirs are not in an equilibrium state and either one can dominate the other over long timescales depending on the assumptions made for the ch4 albedo this suggests that long term volatile transport exists between the observed reservoirs the model also reproduces the formation of n2 deposits at mid latitudes and in the equatorial depressions surrounding the bladed terrain deposits as observed by new horizons at the poles only seasonal ch4 and n2 deposits are obtained in pluto s current orbital configuration finally we show that pluto s atmosphere always contained over the last astronomical cycles enough gaseous ch4 to absorb most of the incoming lyman flux

a search for temporal changes on pluto and charon abstract a search for temporal changes on pluto and charon was motivated by 1 the discovery of young surfaces in the pluto system that imply ongoing or recent geologic activity 2 the detection of active plumes on triton during the voyager 2 flyby and 3 the abundant and detailed information that observing geologic processes in action provides about the processes a thorough search for temporal changes using new horizons images was completed images that covered the same region were blinked and manually inspected for any differences in appearance the search included full disk images such that all illuminated regions of both bodies were investigated and higher resolution images such that parts of the encounter hemispheres were investigated at finer spatial scales changes of appearance between different images were observed but in all cases were attributed to variability of the imaging parameters especially geometry or artifacts no differences of appearance that are strongly indicative of a temporal change were found on the surface or in the atmosphere of either pluto or charon limits on temporal changes as a function of spatial scale and temporal interval during the new horizons encounter are determined the longest time interval constraint is one pluto charon rotation period 6 4 earth days contrast reversal and high phase bright features that change in appearance with solar phase angle are identified the change of appearance of these features is most likely due to the change in phase angle rather than a temporal change had active plumes analogous to the plumes discovered on triton been present on the encounter hemispheres of either pluto or charon they would have been detected the absence of active plumes may be due to temporal variability i e plumes do occur but none were active on the encounter hemispheres during the epoch of the new horizons encounter or because plumes do not occur several dark streak features that may be deposits from past plumes are identified

sublimation waves geomorphic markers of interactions between icy planetary surfaces and winds abstract sublimation waves are periodic linear and transverse bedforms that grow by sublimation of icy substrates under turbulent winds they occur in different environments of the earth and other planets where the climate is favorable to sublimation their morphological and kinematic characteristics wavelength migration velocity characteristic time of formation depend on the environmental conditions in which they develop atmosphere viscosity wind speed sublimation rate to highlight these relations we designed a theoretical model for their formation based on models previously designed for dissolution bedforms from a linear stability analysis of the model we derived a dispersion relation and three scaling laws these are validated by comparison with measurements available for two natural terrestrial examples blue ice areas of the antarctic ice sheets and ice caves and with new measurements in a laboratory experiment they are applied to linear bedforms of hitherto unknown origin that we identified on the martian north polar cap we thus demonstrate that sublimation waves are convenient geomorphic markers to constrain surface compositions atmospheric properties climates and winds on terrestrial ice sheets and other icy planetary surfaces

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

methane distribution on pluto as mapped by the new horizons ralph mvic instrument abstract the data returned from nasa s new horizons spacecraft have given us an unprecedented detailed look at the pluto system new horizons ralph mvic multispectral visible imaging camera is composed of 7 independent ccd arrays on a single substrate among these are a red channel 540 700 nm near infrared channel 780 975 nm and narrow band methane channel 860 910 nm by comparing the relative reflectance of these channels we are able to produce high resolution methane equivalent width based on the 890 nm absorption band and spectral slope maps of pluto s surface from these maps we can then quantitatively study the relationships between methane distribution redness and other parameters like latitude and elevation we find pluto s surface to show a great diversity of terrains particularly in the equatorial region between 30 n and 30 s latitude methane equivalent width also shows some dependence on elevation while spectral slope shows very little

physical state and distribution of materials at the surface of pluto from new horizons leisa imaging spectrometer abstract from earth based observations pluto is known to be the host of n2 ch4 and co ices and also a dark red material very limited spatial distribution information is available from rotational visible and near infrared spectral curves obtained from hemispheric measurements in july 2015 the new horizons spacecraft reached pluto and its satellite system and recorded a large set of data the leisa spectro imager of the ralph instruments are dedicated to the study of the composition and physical state of the materials composing the surface in this paper we report a study of the distribution and physical state of the ices and non ice materials on pluto s illuminated surface and their mode and degree of mixing principal component analysis as well as various specific spectral indicators and correlation plots are used on the first set of 2 high resolution spectro images from the leisa instrument covering the whole illuminated face of pluto at the time of the new horizons encounter qualitative distribution maps have been obtained for the 4 main condensed molecules n2 ch4 co h2o as well as for the visible dark red material based on specific spectral indicators using either the strength or the position of absorption bands these 4 molecules are found to indicate the presence of 3 different types of ices n2 rich ch4 co ices ch4 rich co n2 ices and h2o ice the mixing lines between these ices and with the dark red material are studied using scatter plots between the various spectral indicators ch4 is mixed at the molecular level with n2 most probably also with co thus forming a ternary molecular mixture that follows its phase diagram with low solubility limits the occurrence of a n2 rich ch4 rich ices mixing line associated with a progressive decrease of the co ch4 ratio tells us that a fractionation sublimation sequence transforms one type of ice to the other forming either a n2 rich ch4 rich binary mixture at the surface or an upper ch4 rich ice crust that may hide the n2 rich ice below the strong ch4 rich h2o mixing line witnesses the subsequent sublimation of the ch4 rich ice lag left behind by the n2 co sublimation n spring summer or a direct condensation of ch4 ice on the cold h2o ice s autumn the weak mixing line between ch4 containing ices and the dark red material and the very sharp spatial transitions between these ices and this non volatile material are probably due to thermal incompatibility finally the occurrence of a h2o ice red material mixing line advocates for a spatial mixing of the red material covering h2o ice with possibly a small amount intimately mixed in water ice from this analysis of the different materials distribution and their relative mixing lines h2o ice appears to be the substratum on which other ices condense or non volatile organic material is deposited from the atmosphere n2 rich ices seem to evolve to ch4 dominated ices possibly still containing traces of co and n2 as n2 and co sublimate away the spatial distribution of these materials is very complex the high spatial definition of all these composition maps as well as those at even higher resolution that will be soon available will allow us to compare them with pluto s geologic features observed by lorri panchromatic and mvic multispectral imagers to better understand the geophysical processes in action at the surface of this astonishingly active frozen world

on the thermal regime of an arctic valley glacier a study of white glacier axel heiberg island n w t canada from 1974 to 1981 a total of 32 bore holes was drilled on white glacier and vertical ice temperature profiles measured the data obtained allowed the construction of three longitudinal and four transverse profiles of the two dimensional temperature distributions thus an extensive layer of temperate or near temperate ice was discovered close to the bedrock in the lowest part of the glacier tongue it was also found that the temperature distribution cannot be in a steady state since there is a temperature minimum 100 150 m below the glacier surface in the accumulation area a simple numerical model calculation shows that this minimum can be mostly explained by the general climatic warming since 1880 the 10 m temperatures show diffuse relations to climatic conditions and balance zones a simple scheme for extrapolating surface temperatures is discussed

basins fractures and volcanoes global cartography and topography of pluto from new horizons abstract the 2015 new horizons flyby has produced the first high resolution maps of morphology and topography of pluto and charon the most distant objects so mapped global integrated mosaics of pluto were produced using both lorri framing camera and mvic line scan camera data showing the best resolution data obtained for all areas of the illuminated surface 78 of the body a unique feature of the pluto imaging data set is the observation of terrains illuminated only by light scattered from atmospheric haze allowing us to map terrains in the southern hemisphere that would otherwise have been in darkness mvic 4 color data were combined with the panchromatic map to produce full color global maps digital elevation models dems over 42 of pluto were produced using combinations of mvic hemispheric scans and lorri mosaics from which slopes at scales of 1 km can be determined pluto can be divided into regions each with distinct topographic signatures corresponding with major physiographic terrain types large areas of pluto are comprised of low relief moderately cratered plains units deeply pitted and glaciated plains east of sputnik planitia are elevated 0 7 km the most dominant topographic feature on pluto is the 1200 by 2000 km wide depression enclosing the bright sputnik planitia ice sheet the surface of which is 2 5 to 3 5 km deep relative to the rim and 2 km deep relative to the mean radius the partial ring of steep sided massifs several of which are more than 5 km high along the western margins of sputnik planitia produce some of the locally highest and steepest relief on pluto with slopes of 40 50 the second major topographic feature is a complex eroded ridge trough system 300 400 km wide and at least 3200 km long extending north to south along the 155 meridian this enormous structure has several kilometers of relief it may predate the large impact event forming the basin though some post sputnik planitia deformation is evident the large depressed partially walled plain hyecho palus lies due southwest of sputnik planitia near the center of hyecho palus lie the circular constructional edifices wright and piccard montes wright mons rises 4 5 km above these plains with a central depression 4 5 km deep whereas piccard mons best observed in haze light rises 5 5 km above the plains but has a bowl shaped central depression 5 5 km below the plains for a total relief of up to 11 km the greatest observed on pluto both of these features are interpreted as constructional volcanic in nature additional prominent topographic features include a 2 3 km high and 600 km wide dome centered on the illuminated iau pole and the amoeboidal plateaus of bladed terrains in the equatorial region which rise 2 5 km above local terrains and are the highest standing geologic units on the encounter hemisphere the mean elevations in the integrated dem for the two radio occultation areas are consistent with the 5 6 km difference in elevation as determined independently by the radio experiment and a limb profile near the egress point confirms the presence of elevated bladed terrains in that area local relief of 3 5 km at massifs troughs and pits supports conclusions that the icy shell of pluto is relatively rigid numerous examples of topographic control of ice or frost deposition occur across pluto including the distinct coloration of the polar dome the elevated terrains of eastern tombaugh regio and along the ridge trough system where ridge tops and fossae rims are covered in different ices than at lower elevations the topographic hypsogram of pluto s encounter hemisphere is strongly bimodal due to the large sputnik planitia depression otherwise the topographic signature of pluto is controlled by deviations from the otherwise dominant low plains including elevated bladed terrain plateaus and the depressed volcanic province including wright and piccard montes

modeling cryogenic mud volcanism on pluto abstract subsurface ice cryofluids and ice interactions with ammonia for cryovolcanic materials give the potential ingredients for the formation of mud volcanoes on pluto in order to constrain the possible morphology from images acquired by the new horizons spacecraft we have modeled the formation of mud volcanoes isostatic layers of ice overlain by denser material from a series of possible solid liquid mud compositions methane and ammonia as well as accounting for the full range of eruption variables e g mud viscosity conduit diameter and eruption duration we categorize them into nine specific scenarios based on the composition of the top ice layer and mud composition from these scenarios the maximum height of the potential mud volcano can be calculated we find that ammonia mud sources produce smaller edifice heights and wider flow profiles compared to methane dominant mud cryovolcanoes assuming certain preliminary parameters we also propose the evolution and development of the edifice of wright mons in as little as 3 8 million years given a 10 wt ammonia subsurface mud composition if characterized on pluto s surface mud volcanoes would provide an interesting insight on the subsurface dynamics of solids and cryofluids on pluto

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

glacier and permafrost signals of 20th century warming currently available evidence of 20th century warming from glaciers and permafrost is briefly reviewed the signals are clear and strong warming of polar firn and permafrost and mass losses of glaciers at lower latitudes were most striking towards the middle of the century the easily observable length reduction of mountain glaciers confirms the global character of the evolution a probably intermittent reversal of the trend was observed in places after about 1950

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

the nitrogen cycles on pluto over seasonal and astronomical timescales abstract pluto s landscape is shaped by the endless condensation and sublimation cycles of the volatile ices covering its surface in particular the sputnik planitia ice sheet which is thought to be the main reservoir of nitrogen ice displays a large diversity of terrains with bright and dark plains small pits and troughs topographic depressions and evidences of recent and past glacial flows outside sputnik planitia new horizons also revealed numerous nitrogen ice deposits in the eastern side of tombaugh regio and at mid northern latitudes these observations suggest a complex history involving volatile and glacial processes occurring on different timescales we present numerical simulations of volatile transport on pluto performed with a model designed to simulate the nitrogen cycle over millions of years taking into account the changes of obliquity solar longitude of perihelion and eccentricity as experienced by pluto using this model we first explore how the volatile and glacial activity of nitrogen within sputnik planitia has been impacted by the diurnal seasonal and astronomical cycles of pluto results show that the obliquity dominates the n2 cycle and that over one obliquity cycle the latitudes of sputnik planitia between 25 s 30 n are dominated by n2 condensation while the northern regions between 30 n and 50 n are dominated by n2 sublimation we find that a net amount of 1 km of ice has sublimed at the northern edge of sputnik planitia during the last 2 millions of years it must have been compensated by a viscous flow of the thick ice sheet by comparing these results with the observed geology of sputnik planitia we can relate the formation of the small pits and the brightness of the ice at the center of sputnik planitia to the sublimation and condensation of ice occurring at the annual timescale while the glacial flows at its eastern edge and the erosion of the water ice mountains all around the ice sheet are instead related to the astronomical timescale we also perform simulations including a glacial flow scheme which shows that the sputnik planitia ice sheet is currently at its minimum extent at the northern and southern edges we also explore the stability of n2 ice deposits outside the latitudes and longitudes of the sputnik planitia basin results show that n2 ice is not stable at the poles but rather in the equatorial regions in particular in depressions where thick deposits may persist over tens of millions of years before being trapped in sputnik planitia finally another key result is that the minimum and maximum surface pressures obtained over the simulated millions of years remain in the range of milli pascals and pascals respectively this suggests that pluto never encountered conditions allowing liquid nitrogen to flow directly on its surface instead we suggest that the numerous geomorphological evidences of past liquid flow observed on pluto s surface are the result of liquid nitrogen that flowed at the base of thick ancient nitrogen glaciers which have since disappeared

glaciological investigations in the crete area central greenland a search for a new deep drilling site the results of the 1984 85 post gisp campaigns in central greenland are presented eight ice cores were obtained some spanning up to 360 years we present i geographical positions and elevations at the drill sites

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

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

palaeobiogeography of austral echinoid faunas a first quantitative approach few studies have been devoted to the palaeobiogeography of antarctic echinoids all of them analysing and discussing distribution patterns in a qualitative way the present work aims at exploring the evolution of palaeobiogeographic relationships of austral echinoid faunas through four time intervals from the maastrichtian to the present day using a quantitative approach the bootstrapped spanning network procedure analyses were successfully performed and improve our knowledge of biogeographic relationships between the different austral regions biogeographic maps were produced that can be easily and intuitively discussed our results mostly agree with palaeobiogeographic studies performed on other benthic invertebrates and are congruent with the palaeogeographic evolution of antarctica however two main points markedly contrast with other works there is no evidence of an austral provincialism at the end of the cretaceous and early cenozoic and echinoid data suggest isolation of southern argentina from other austral regions including antarctica in the early miocene

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

pluto s climate modeled with new observational constraints abstract pluto has a nitrogen atmosphere in vapor pressure equilibrium with surface ice n 2 is mobile and is transported seasonally even at pluto s cold temperatures in the outer solar system a thermal model developed by hansen and paige in 1996 to model pluto s climate has been re deployed in response to new data and in anticipation of the new horizons flyby of pluto in 2015 a number of stellar occultations have been observed in the last 11 years as pluto has crossed the galactic plane new hubble space telescope images show a variegated surface these recent observations allow us to model pluto s climate with much tighter constraints our findings suggest that pluto s atmosphere will not collapse prior to the arrival of new horizons although pressure will be dropping as n 2 condenses on the south polar cap this finding is in contrast to the olkin et al olkin et al 2013 arxiv1309 0841o prediction that permanent volatiles in the northern hemisphere maintain pluto s atmospheric pressure throughout its orbit the range of surface pressures predicted for 2015 for nine cases with very good matches to observables is 0 3 3 2 pa the best match predicts that new horizons will detect an atmospheric pressure of 2 4 pa

pluto s haze as a surface material pluto s atmospheric haze settles out rapidly compared with geological timescales it needs to be accounted for as a surface material distinct from pluto s icy bedrock and from the volatile ices that migrate via sublimation and condensation on seasonal timescales this paper explores how a steady supply of atmospheric haze might affect three distinct provinces on pluto we pose the question of why they each look so different from one another if the same haze material is settling out onto all of them cthulhu is a more ancient region with comparatively little present day geological activity where the haze appears to simply accumulate over time sputnik planitia is a very active region where glacial convection as well as sublimation and condensation rapidly refresh the surface hiding recently deposited haze from view lowell regio is a region of intermediate age featuring very distinct coloration from the rest of pluto using a simple model haze particle as a colorant we are not able to match the colors in both lowell regio and cthulhu to account for their distinct colors we propose that after arrival at pluto s surface haze particles may be less inert than might be supposed from the low surface temperatures they must either interact with local materials and environments to produce distinct products in different regions or else the supply of haze must be non uniform in time and or location such that different products are delivered to different places

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