south polar residual cap of mars features stratigraphy and changes abstract the south residual polar cap of mars rich in co2 ice is compositionally distinct from the north residual cap which is dominantly h2o ice the south cap is also morphologically distinct displaying a bewildering variety of depressions formed in thin layered deposits which have been observed to change by scarp retreat over an interval of one mars year malin et al 2001 science 294 2146 2148 the climatically sensitive locale of the residual caps suggests that their behavior may help in the interpretation of recent fluctuations or repeatability of the mars climate we have used mars global surveyor mars orbiter camera moc images obtained in three southern summers to map the variety of features in the south residual cap and to evaluate changes over two mars years mars y the images show that there are two distinct layered units which were deposited at different times separated by a period of degradation the older unit 10 m thick has layers approximately 2 m thick the younger unit has variable numbers of layers each 1 m thick the older unit is eroding by scarp retreat averaging 3 6 m mars y a rate greater than the retreat of 2 2 m mars y observed for the younger unit the rates of scarp retreat and sizes of the different types of depressions indicate that the history of the residual cap has been short periods of deposition interspersed with longer erosional periods erosion of the older unit probably occupied 100 150 mars y one layer may have been deposited after the mariner 9 observations in 1972 residual cap layers appear to differ from normal annual winter deposits by having a higher albedo and perhaps by having higher porosities these properties might be produced by differences in the depositional meteorology that affect the fraction of high porosity snow included in the winter deposition

effects of soil heterogeneity on martian ground ice stability and orbital estimates of ice table depth abstract data from the mars odyssey gamma ray spectrometer grs instrument suite and results from numerical simulations of subsurface ground ice stability have been used to estimate the depth of martian ground ice geographic correlation between these estimates is remarkable the relative ice table depth distributions also agree well however grs based estimates of ice table depth are generally deeper than predictions based on ground ice stability simulations this discrepancy may be related to heterogeneities in the martian surface such as rocks dust and albedo variations we develop a multi dimensional numerical model of ground ice stability in a heterogeneous martian subsurface and use it to place the first quantitative constraints on the response of the ice table to meter scale heterogeneities we find that heterogeneities produce significant undulations topography in the ice table at horizontal length scales of a few meters decimeter scale rocks create localized areas of deep ice producing a vertical depression of 10 60 cm in the ice table over a horizontal range of 1 2 rock radii decimeter scale dust lenses produce locally shallow ice however the magnitude of the vertical deflection of the ice table is small 1 4 cm the effects of decimeter scale albedo variations on the ice table are nearly negligible although albedo very weakly enhances the effects of dark rocks and bright dust on the ice table additionally we investigate the role played by rocks in estimates of ice table depth based on orbital data surface rocks can account for more than half of the discrepancy between ice table depths inferred from grs data and those predicted by theoretical ice stability simulations that utilize thermophysical observations our results have considerable relevance to the up coming mars scout mission phoenix because they indicate that the uncertainty in the ice table depth of a given region is greater than differences between current depth estimates likewise small scale depth variability due to heterogeneities at the eventual landing site is potentially greater than differences between current depth estimates

concentric crater fill in utopia planitia history and interaction between glacial brain terrain and periglacial mantle processes abstract at martian mid to high latitudes the surfaces of potentially ice rich features including concentric crater fill lobate debris aprons and lineated valley fill typically display a complex texture known as brain terrain due to its resemblance to the complex patterns on brain surfaces in order to determine the structure and developmental history of concentric crater fill and overlying latitude dependent mantle ldm material brain terrain and polygonally patterned ldm surfaces are analyzed using hirise images from four craters in utopia planitia containing concentric crater fill brain terrain and mantle surface textures are classified based on morphological characteristics 1 closed cell brain terrain 2 open cell brain terrain 3 high center mantle polygons and 4 low center mantle polygons a combined glacial and thermal contraction cracking model is proposed for the formation and modification of the brain terrain texture of concentric crater fill a similar model related to thermal contraction cracking and differential sublimation of underlying ice is proposed for the formation and development of polygonally patterned mantle material both models require atmospheric deposition of ice likely during periods of high obliquity but do not require wet active layer processes crater dating of brain terrain and mantled surfaces suggests a transition at martian mid latitudes from peak glacial conditions occurring within the past 10 100 my to a quiescent period followed by a cold desert periglacial period during the past 1 2 my

mercury radar imaging evidence for polar ice the first unambiguous full disk radar mapping of mercury at 3 5 centimeter wavelength with the goldstone 70 meter antenna transmitting and 26 antennas of the very large array receiving has provided evidence for the presence of polar ice the radar experiments conducted on 8 and 23 august 1991 were designed to image the half of mercury not photographed by mariner 10 the orbital geometry allowed viewing beyond the north pole of mercury a highly reflective region was clearly visible on the north pole during both experiments this polar region has areas in which the circular polarization ratio pt was 1 0 to 1 4 values 0 1 are typical for terrestrial planets such high values of have hitherto been observed in radar observations only from icy regions of mars and icy outer planet satellites

influence of calcite decarbonation on the frictional behavior of carbonate bearing gouge implications for the instability of volcanic flanks and fault slip abstract the impact of heat readily provided by magma circulating hot fluids or rapid fault slip on carbonate substrata is an important factor in determining the flank stability of volcanoes and the mechanical behavior of faults in areas where carbonate lithologies are prevalent the mineralogy and mechanical properties of carbonate rocks are demonstrably altered by thermally induced decarbonation while previous studies have considered the role of decarbonation in bulk strength loss at subvolcanic conditions and dynamic weakening during coseismic fault slip little is known about the effects of decarbonation on the frictional properties of carbonate rocks during both the nucleation and inter seismic phases here we present results from experiments performed on a portlandite rich material a typical hydrous product of the decarbonation reaction to evaluate frictional strength stability and healing at shallow crustal conditions we sheared gouge layers of this material under saturated conditions at room temperature and at velocities comparable to those involved in earthquake nucleation our data indicate that the reaction of calcite to portlandite results in a distinct change in the mechanical behavior of the gouge decarbonated shear zones are 1 frictionally weaker at higher normal stresses 2 more frictionally unstable and 3 likely to regain their frictional strength more quickly than unaltered calcite rich zones the occurrence of portlandite could be key for interpreting the stability of volcanic flanks that root into carbonate substrata and for seismogenic normal faults located within thick sedimentary sequences and thus provide a better understanding of the hazards they pose

dynamics of ice ages on mars mars experiences much greater fluctuations in exposure to sunlight than the earth does because of larger variations in astronomical factors such as the tilt of its axis relative to the orbital plane climate change is accordingly more intense on mars than on earth norbert schorghofer has now developed a climate model that accounts for the advance and retreat of the subsurface martian ice sheets over forty major ice ages and five million years this explains the present distribution of subsurface ice on mars in addition lessons learned from the long and relatively simple martian ice age stratigraphy should help when it comes to interpreting the more complicated events here on earth numerical simulation and modelling of the retreat and growth of ground ice on mars demonstrates how the subsurface ice sheets could have evolved and ended up in the state we see them today and also reveals that 40 major ice ages occurred on mars over the past 5 million years unlike earth where astronomical climate forcing is comparatively small mars experiences dramatic changes in incident sunlight that are capable of redistributing ice on a global scale1 2 3 4 5 6 the geographic extent of the subsurface ice found poleward of approximately 60 latitude on both hemispheres of mars7 8 9 coincides with the areas where ice is stable7 10 11 however the tilt of mars rotation axis obliquity changed considerably in the past several million years earlier work3 12 has shown that regions of ice stability which are defined by temperature and atmospheric humidity differed in the recent past from today s and subsurface ice is expected to retreat quickly when unstable11 12 13 here i explain how the subsurface ice sheets could have evolved to the state in which we see them today simulations of the retreat and growth of ground ice as a result of sublimation loss and recharge reveal forty major ice ages over the past five million years today this gives rise to pore ice at mid latitudes and a three layered depth distribution in the high latitudes of from top to bottom a dry layer pore ice and a massive ice sheet combined these layers provide enough ice to be compatible with existing neutron and gamma ray measurements7 8 9

mass movement and landform degradation on the icy galilean satellites results of the galileo nominal mission the galileo mission has revealed remarkable evidence of mass movement and landform degradation on the icy galilean satellites of jupiter weakening of surface materials coupled with mass movement reduces the topographic relief of landforms by moving surface materials down slope throughout the galileo orbiter nominal mission we have studied all known forms of mass movement and landform degradation of the icy galilean satellites of which callisto by far displays the most degraded surface callisto exhibits discrete mass movements that are larger and apparently more common than seen elsewhere most degradation on ganymede appears consistent with sliding or slumping impact erosion and regolith evolution sliding or slumping is also observed at very small 100 m scale on europa sputter ablation while probably playing some role in the evolution of ganymede s and callisto s debris layers appears to be less important than other processes sputter ablation might play a significant role on europa only if that satellite s surface is significantly older than 108 years far older than crater statistics indicate impact erosion and regolith formation on europa are probably minimal as implied by the low density of small craters there impact erosion and regolith formation may be important on the dark terrains of ganymede though some surfaces on this satellite may be modified by sublimation degradation while impact erosion and regolith formation are expected to operate with the same vigor on callisto as on ganymede most of the areas examined at high resolution on callisto have an appearance that implies that some additional process is at work most likely sublimation driven landform modification and mass wasting the extent of surface degradation ascribed to sublimation on the outer two galilean satellites implies that an ice more volatile than h2o is probably involved

preservation of miocene glacier ice in east antarctica antarctic climate during the pliocene has been the subject of considerable debate one view holds that during part of the pliocene east antarctica was largely free of glacier ice and that vegetation survived on the coastal mountains1a 4 an alternative viewpoint argues for the development of a stable polar ice sheet by the middle miocene which has persisted since then5a 10 here we report the discovery of buried glacier ice in beacon valley east antarctica which appears to have survived for at least 8 1 million years we have dated the ice by 40ar 39ar analysis of volcanic ash in the thin overlying glacial till which we argue has undergone little if any reworking isotope and crystal fabric analyses of the ice show that it was derived from an ice sheet we suggest that stable polar conditions must have persisted in this region for at least 8 1 million years for this ice to have avoided sublimation

stability of polar frosts in spherical bowl shaped craters on the moon mercury and mars following svitek martian water frost control of global distribution by small scale processes ph d thesis california institute of technology 1992 analytic solutions are presented for the effective albedo the effective emissivity and the radiative equilibrium temperature in the shadowed portions of a spherical bowl shaped crater the model assumes that the surface is a lambert scatterer with visual albedo and infrared emissivity each independent of wavelength across their respective spectral ranges absorption emission and multiple scattering from the walls of the crater are treated rigorously to all orders for airless bodies whose surfaces are in radiative equilibrium all shadowed portions of any individual crater have the same temperature whose value depends on four quantities the insolation product of the solar constant and the sine of the solar elevation angle the depth diameter ratio of the crater the visual albedo and the infrared emissivity as long as the crater is deep enough to have shadows the lowest temperatures are for the shallowest crater those with the smallest depth diameter ratio the model is applied first to the moon and mercury using a depth diameter ratio of 0 2 which is typical of the lunar highlands according to pike geophys res lett 1 291 294 1974 in impact and explosion cratering roddy et al eds pp 489 509 pergamon new york 1977 for mercury and the moon temperatures in shadows in polar craters are below 102 k so the sublimation rate of water ice calculated according to the model of watson et al j geophys res 66 3033 3015 1961 is less than 1 cm per byr the latitudinal extent of the cold zone on the moon is greater than that on mercury although temperatures at the poles of the two planets are similar the other application is to polar frosts on mars illuminated water frosts in radiative equilibrium grow rougher because the average temperature of a depression is greater than that of flat ground subliming co 2 frosts which are always at the same temperature grow rougher at low solar elevation angles because the heat flux absorbed by a depression is greater than that for a flat surface at high insolation rates high sun near perihelion the average heat flux to a depression is less than for a flat surface the latter evaporates faster which makes the average surface smoother and leads to a high average albedo this behavior helps explain the fact that the south co 2 cap which receives its greatest insolation near perihelion has a higher effective albedo and therefore can survive the summer whereas the north co 2 cap has a lower effective albedo and disappears each year around summer solstice

ice sublimation and rheology implications for the martian polar layered deposits it has been suggested that the martian polar layered deposits are composed largely of water ice if true then sublimation and deformation creep of the ice are important processes simple models indicate that sublimation will occur at a rate inconsistent with current estimates of the deposit s age and viking observations of the atmospheric water abundance suggesting that when considering the formation evolution and structure of the deposits one must include a mechanism by which sublimation is inhibited a surface layer of dust seems the most likely possibility additionally over the age of the deposits flows of at least 1 km are expected at viking resolution 150 m no obvious flow features are observed assuming that martian features would be similar to those that occur on the earth this limits the maximum flow rates possible and suggest the deposits need to be more than 90 ice or less than about 40 ice by volume the mars observer spacecraft will be able to constrain the ice abundance further by both searching for flow features and clarifying the nature of the deposit s surface and near surface

moc observations of four mars year variations in the south polar residual cap of mars abstract the residual south polar cap of mars rspc is distinct from the residual north polar cap both in composition and in morphology co 2 frost in the rspc is stabilized by its high albedo during southern spring and summer despite the relatively large insolation during that period the morphology of the rspc in summer displays a bewildering variety of depressions that are formed in relatively thin layers of co 2 the increase of the size of these depressions between each of the first three years of mars global surveyor mgs observations may possibly signal some sort of climate change on the planet for example the erosion of the bright plateaus might reduce the rspc albedo and affect the energy balance the mars orbiter cameras moc on mgs observed mars for four consecutive martian years before contact with the spacecraft was lost in late 2006 during this period coverage of the polar regions was particularly dense because mgs flew over them on every orbit in this paper we report on the four year behavior of the morphological features in the rspc and on the large scale variability in rspc albedo over the period the changes in the size of the surface features in the rspc due to backwasting that were first observed between mars years my 24 and 25 and subsequently between my25 and m26 was observed to continue at the same rate through my 27 the results indicate that on average thicker layers in the rspc retreat faster than thinner ones roughly in proportion to their thickness we argue that a simple difference in porosity between the a and b layers can explain this difference although other factors could be involved the large scale albedo of the rspc decreases as the depressions are uncovered by sublimation of seasonal co 2 however any interannual differences in albedo due to the backwasting process are masked by interannual differences in the summer dust opacity in the rspc region

sorted stone circles in elysium planitia mars implications for recent martian climate we have found sorted stone circles and polygons near the equator of mars using new 25 cm pixel nasa hirise high resolution imaging science experiment images the sorted circles occur in geologically recent catastrophic flood deposits in the equatorial elysium planitia region and are diagnostic of periglacial processes sorted polygons do not form from volcanic activity as has been suggested for non sorted polygons in this region these landforms indicate that i a long lived geologically recent active cryoturbation layer of ground ice was present in the regolith ii there was some degree of freeze thaw and thus iii there were sustained period s likely within the last 10 ma in which the martian climate was 40 to 60 k warmer than current models predict

fluxes of fast and epithermal neutrons from lunar prospector evidence for water ice at the lunar poles maps of epithermal and fast neutron fluxes measured by lunar prospector were used to search for deposits enriched in hydrogen at both lunar poles depressions in epithermal fluxes were observed close to permanently shaded areas at both poles the peak depression at the north pole is 4 6 percent below the average epithermal flux intensity at lower latitudes and that at the south pole is 3 0 percent below the low latitude average no measurable depression in fast neutrons is seen at either pole these data are consistent with deposits of hydrogen in the form of water ice that are covered by as much as 40 centimeters of desiccated regolith within permanently shaded craters near both poles

ice sublimation as a geomorphic process a planetary perspective abstract sublimation plays a role in the shaping of landforms of planetary surfaces where ice is present as frost as polar caps or in the subsurface this review is focused primarily on the geomorphologic consequences of sublimation a summary of the suite of landforms that have been observed on the surface of various planetary bodies and whose formation is attributed to sublimation is presented this includes the sublimation of a range of different ices that are found on planetary bodies water ice carbonic ice etc at least four groups of landforms are distinguishable independent of the planetary body i residual lags that are depleted in ice which form after sublimation loss such residual lags isolate deeper ice from sublimation and thus can have an important impact on planetary volatile cycles ii landforms due to differential sublimation resulting from enhanced sublimation in low albedo warmer areas of the planet and preservation of ice in the high albedo regions iii landforms due to differential sublimation initiated by fractures or ground heterogeneities for example sublimation enhanced polygonal cracks iv pitted terrains that occur in a relatively homogeneous ice bearing subsurface or as an effect of local ice enrichment or segregation in the ground

mass wasting and ground collapse in terrains of volatile rich deposits as a solar system wide geological process the pre galileo view the polar terrains of mars are covered in many places with irregular pits and retreating scarps as are some of the surfaces of the outer planet satellites these features are interpreted by us as diagnostic of exogenic degradation due to the loss of a volatile rock forming matrix or cement in this study we propose that sublimation degradation is a plausible solar system wide geological process candidate examples have been identified on mars io and triton and possibly europa and ganymede we envision this process as having two end member expressions pits and scarps for which we hypothesize two end member mechanisms massive localized lenses and areally extensive basal layers in this study we focus on the role this process may play on the surfaces of the galilean satellites our principle modeling results are that for these satellites h2s co2 and nh3are the only viable candidate volatiles for sublimation degradation of landforms in light of galilean satellite cosmochemistry for io s polar regions only h2s and then only from slopes that face the sun and have thin lags is volatile enough to cause the observed sublimation induced erosion at those latitudes so2is not a viable candidate as an agent of erosion especially for these polar landforms in the case of europa only co2and h2s are viable candidates given surface age constraints both species could be efficient eroders in nonpolar regions h2s could generate erosion within the polar regions if the deposition and erosion conditions were essentially identical as those we invoked for io s polar regions for ganymede and callisto nh3might be an agent of erosion in equatorial terrains of great age the sublimation of co2and h2s is much more robust than nh3 the much slower rate of sublimation degradation from nh3might be detectable by galileo and used as a compositional indicator

the clementine bistatic radar experiment during the clementine 1 mission a bistatic radar experiment measured the magnitude and polarization of the radar echo versus bistatic angle beta for selected lunar areas observations of the lunar south pole yield a same sense polarization enhancement around beta 0 analysis shows that the observed enhancement is localized to the permanently shadowed regions of the lunar south pole radar observations of periodically solar illuminated lunar surfaces including the north pole yielded no such enhancement a probable explanation for these differences is the presence of low loss volume scatterers such as water ice in the permanently shadowed region at the south pole

geomorphic analysis of lobate debris aprons on mars at mars orbiter camera scale evidence for ice sublimation initiated by fractures 1 lobate debris aprons known to be geomorphic landform indicators of the presence of ground ice are of special interest for future missions devoted to the research of water on mars lobate debris aprons in fretted terrains of deuteronilus and protonilus mensae 35 50 n show typical convex shapes interpreted to be the result of viscous deformation at the scale of mars orbiter camera moc high resolution images the surface of these debris aprons shows complex patterns with small pits and buttes these patterns can be explained by the mantling of dust the accumulation of interstitial ice and the subsequent removal of ice by sublimation the sublimation of the ground ice is especially initiated and accelerated by subsurface heterogeneities like fractures theoretical quantification of sublimation rates therefore minimizes sublimation which is not a homogeneous process at least over the landforms studied crater counts show that the sublimation occurred in the last tens of millions of years up to the recent past in the point of view of future searching of subsurface ice only surface layers are submitted to sublimation favoring the conservation of ground ice in deeper layers since the formation of the landform the geophysical survey of lobate debris aprons would give interesting insights into the subsurface distribution of ice and its seasonal variations especially in order to measure current sublimation of ground ice

the lakes of titan the surface of saturn s haze shrouded moon titan has long been proposed to have oceans or lakes on the basis of the stability of liquid methane at the surface1 2 initial visible3 and radar4 5 imaging failed to find any evidence of an ocean although abundant evidence was found that flowing liquids have existed on the surface5 6 here we provide definitive evidence for the presence of lakes on the surface of titan obtained during the cassini radar flyby of titan on 22 july 2006 t16 the radar imaging polewards of 70 north shows more than 75 circular to irregular radar dark patches in a region where liquid methane and ethane are expected to be abundant and stable on the surface2 7 the radar dark patches are interpreted as lakes on the basis of their very low radar reflectivity and morphological similarities to lakes including associated channels and location in topographic depressions some of the lakes do not completely fill the depressions in which they lie and apparently dry depressions are present we interpret this to indicate that lakes are present in a number of states including partly dry and liquid filled these northern hemisphere lakes constitute the strongest evidence yet that a condensable liquid hydrological cycle is active in titan s surface and atmosphere in which the lakes are filled through rainfall and or intersection with the subsurface liquid methane table

the thermal stability of water ice at the poles of mercury recent radar observations of mercury have revealed the presence of anomalous radar reflectivity and polarization features near its north and south poles thermal model calculations show that despite mercury s proximity to the sun the temperatures of flat low reflectivity surfaces at mercury s poles are not expected to exceed 167 kelvin the locations of the anomalous polar radar features appear to be correlated with the locations of large high latitude impact craters maximum surface temperatures in the permanently shadowed regions of these craters are expected to be significantly colder as low as 60 kelvin in the largest craters these results are consistent with the presence of water ice because at temperatures lower than 112 kelvin water ice should be stable to evaporation over time scales of billions of years

geology and activity around volcanoes on io from the analysis of nims spectral images abstract the last two successful flybys of io by galileo in 2001 orbits i31 i32 allowed the near infrared mapping spectrometer to enrich its collection of ir spectral image cubes of the satellite these data cover hemispheric portions of io several volcanic centers as well as their surroundings with a spatial resolution ranging from 2 to 93 km pixel 1 they map thermal emission from the hot spots and the distribution of solid so 2 in the 1 0 4 7 m spectral range we obtain maps of so 2 abundance and granularity from the nims data using the method of doute et al 2002 icarus 158 460 482 the maps are correlated to distinguish four different physical units that indicate zones of so 2 condensation metamorphism and sublimation we relate these information with visible images from galileo s solid state imaging system and with detailed mapping of the thermal emission produced by io s surface our principal goal is to understand the mechanisms controlling how lava pyroclastics and gas are emitted by different types of volcanoes and how these products evolve the 800 km diameter white ring of fallout created by a violent pillanian eruption during summer of 2001 is at least partly composed of solid so 2 and has enriched preexisting regional deposits orange materials have been recently or are currently emplaced 240 km south from the main eruption site possibly as sulfur flows a similar event may have taken place in the past at ababinili patera 12 5 n 142 w carefull study of so 2 maps covering the emakong region also suggests that sulfur forms the bright channel fed flow emerging from the south eastern side of the caldera within the main caldera of tvashtar catena completely cooled patches of crust exist elsewhere the caldera is still cooling from previous episodes of flooding we confirm that amirani emits constantly large amount of so 2 gas by interaction of fresh lava with the volatiles of the underlying plains nevertheless so 2 frost is not the major component of the bright white ring seen in the ssi images over the whole gish bar region so 2 frost seems barely stable and is constantly regenerated the stability increases along gray filamentary structures which could be faults filled with materials having peculiar thermal properties northwest of gish bar patera a localized bright deposit shows an unusual spectral signature potentially indicative of h 2 o molecules forming ice crystals or being trapped in a nonidentified matrix the chaac region may present a thickened old crust reducing the geothermal flux to levels lower than 0 5 w m 2 and thus creating a cold trap for so 2 looking at the abundance and degree of metamorphose of so 2 we establish the relative age of different flows and ejecta for the sobo fluctus finally the assumption that the white patches in visible images indicate so 2 rich deposits is once again challenged in the camaxtli region we identify a topographically controlled compact white deposit showing only moderate so 2 abundance in contrast we detect two spots of quite pure so 2 ice on the gray flanks of emakong furthermore the close association of fumarolic so 2 and red s 2 already noted for several volcanic centers is observed at tupan

superficial simplicity of the 2010 el mayor cucapah earthquake of baja california in mexico the geometry of faults is usually thought to be more complicated at the surface than at depth and to control the initiation propagation and arrest of seismic ruptures the fault system that runs from southern california into mexico is a simple strike slip boundary the west side of california and mexico moves northwards with respect to the east however the m w 7 2 2010 el mayor cucapah earthquake on this fault system produced a pattern of seismic waves that indicates a far more complex source than slip on a planar strike slip fault here we use geodetic remote sensing and seismological data to reconstruct the fault geometry and history of slip during this earthquake we find that the earthquake produced a straight 120 km long fault trace that cut through the cucapah mountain range and across the colorado river delta however at depth the fault is made up of two different segments connected by a small extensional fault both segments strike n130 e but dip in opposite directions the earthquake was initiated on the connecting extensional fault and 15 s later ruptured the two main segments with dominantly strike slip motion we show that complexities in the fault geometry at depth explain well the complex pattern of radiated seismic waves we conclude that the location and detailed characteristics of the earthquake could not have been anticipated on the basis of observations of surface geology alone

perennial water ice identified in the south polar cap of mars the inventory of water and carbon dioxide reservoirs on mars are important clues for understanding the geological climatic and potentially exobiological evolution of the planet1 from the early mapping observation of the permanent ice caps on the martian poles2 3 the northern cap was believed to be mainly composed of water ice whereas the southern cap was thought to be constituted of carbon dioxide ice however recent missions nasa missions mars global surveyor and odyssey have revealed surface structures4 altimetry profiles5 underlying buried hydrogen6 and temperatures of the south polar regions that are thermodynamically consistent with a mixture of surface water ice and carbon dioxide7 here we present the first direct identification and mapping of both carbon dioxide and water ice in the martian high southern latitudes at a resolution of 2 km during the local summer when the extent of the polar ice is at its minimum we observe that this south polar cap contains perennial water ice in extended areas as a small admixture to carbon dioxide in the bright regions associated with dust without carbon dioxide at the edges of this bright cap and unexpectedly in large areas tens of kilometres away from the bright cap

formation of iapetus extreme albedo dichotomy by exogenically triggered thermal ice migration the striking appearance of saturn s moon iapetus half black and half white has puzzled astronomers for over three centuries now spencer and denk p 432 1 published online 10 december present an explanation for this asymmetry a thermally controlled runaway migration of water ice triggered by exogenic deposition of dark material on the moon s leading darker side which faces the direction of motion of the moon in its orbit around saturn this mechanism is unique to iapetus because it rotates slowly enough to allow large temperature variations to arise it is small enough to allow long range migration of water and there is a source of dust to trigger the process in a related paper denk et al p 435 2 published online 10 december present data derived from the cassini imaging science subsystem that reveal that both dark and bright materials on the leading side of iapetus are redder than their trailing side counterparts this asymmetry results from the deposition of dust and debris from other moons in the saturnian system the very same process that initiates the thermal segregation proposed above 1 lookup doi 10 1126 science 1177132 2 lookup doi 10 1126 science 1177088

geographic variations in the thermal and diffusive stability of ground ice on mars to investigate the stability of ground ice within the top several meters of the martian regolith time dependent models of the thermal and diffusive behavior of the regolith have been developed the geographic distribution of thermal inertia and albedo as well as the latitudinal variation in insolation have been included in calculations of surface and subsurface temperatures between 60 latitude ground ice was found to be stable where the annual mean surface and subsurface temperatures were below the atmospheric frost point this generally occurs poleward of the mid latitudes the latitude poleward of which ground ice is stable varies by about 20 to 30 from one longitude to another geographic variations in thermal inertia and albedo are the primary factors controlling regional variations in ice stability calculations of temperatures at high and low obliquity suggest that ground ice would be stable globally at high obliquity and would not be stable between 60 latitude at low obliquity thermally driven diffusion of atmospheric water vapor within the regolith was modeled accounting for both ordinary molecular and knudsen transport and equilibrium between ice vapor and adsorbed phases atmospheric water vapor was found to be able to supply the top few meters of the regolith with ice in regions where the annual mean surface temperature was below the atmospheric frost point ice was found to begin condensing in as short as 1000 martian years rapid accumulation of ice in the pore space of the upper layers of the regolith acted to choke transport to lower layers and slow the diffusion process even so after 105 martian years in some cases as much as 30 to 40 of the available pore space accumulated ice the total amount of subsurface ice ranged from a few to more than 25 g cm2 within the top few meters in regions of stability ground ice was found to form below a depth where the annual average vapor pressure over ice was equal to the annual average atmospheric vapor pressure near the surface atmospheric vapor was not found to accumulate as ice below a depth where the seasonal temperature oscillations gave way to the geothermal gradient the time scales for condensation of ground ice were found to be comparable to that of orbital oscillations suggesting that the present geographic distribution of ground ice may depend on the orbital history of mars

sublimation of mars s southern seasonal co2 ice cap and the formation of spiders 1 in this paper we define and describe morphological features that have colloquially been termed spiders and map their distribution in the south polar region of mars we show that these features go through a distinct seasonal evolution exhibiting dark plumes and associated fan shaped deposits during the local defrosting of the seasonal cap we have documented the seasonal evolution of the cryptic region and have found that spiders only occur within this terrain these observations are consistent with a geyser like model for spider formation association with the transparent cryptic portion of the seasonal cap is consistent with basal sublimation and the resulting venting of co2 gas also consistent with such venting is the observation of dark fan shaped deposits apparently emanating from spider centers spiders are additionally confined to the polar layered deposits presumably due to the poorly consolidated and easily eroded nature of their upper surface

cold jets in the martian polar caps 1 mars seasonal polar caps display dark ice local darker spots aligned elongate patches and radially dendritic forms that reverse albedo contrast the unexpected variety and sequence of these features are explained on the basis of processes involving co2 dust sand and h2o these processes are largely related to the atmosphere being near its saturation temperature and they have few terrestrial analogies in the simplest case the 1 m thick seasonal cap initially dusty cleans itself and becomes translucent after sunrise and is impermeable over extensive regions except for local vents the slab ice sublimates at the base and is levitated on high pressure gas causing humidity exchange with deeper layers subslab gas converging toward the vents erodes channels in the soil and ejects this material in high velocity jets recent spectral observations indicate great variety in the details

geomorphic evidence for the distribution of ground ice on mars high resolution viking orbiter images show evidence for quasi viscous relaxation of topography the relaxation is believed to be due to creep deformation of ice in near surface materials the global distribution of the inferred ground ice shows a pronounced latitudinal dependence the equatorial regions of mars appear to be ice poor while the heavily cratered terrain poleward of 30 latitude appears to be ice rich the style of creep poleward of 30 varies with latitude possibly due to variations in ice rheology with temperature the distribution suggests that ice at low latitudes which is not in equilibrium with the present atmosphere has been lost via sublimation and diffusion through the regolith thereby causing a net poleward transport of ice over martian history

cryomagmatic mechanisms for the formation of rhadamanthys linea triple band margins and other low albedo features on europa we investigate cryomagmatic mechanisms for the formation of the diffuse low albedo margins of triple bands and haloes associated with elliptical lenticulae on europa one mechanism involves explosive venting of a gas particle spray derived from a subsurface body of volatile bearing water assuming the dark features represent cryoclastic deposits erupted from a medial or central vent modeling the dynamics of the eruptive plumes indicates that eruption velocities of 30 to 250 m s 1 and volatile contents of 0 1 to 20 wt are required to produce deposits having the observed dimensions calculated heights for ballistic plumes range from 1 to 25 km as an alternative mechanism we consider conductive heating of lithospheric ice by a subsurface heat source e g a warm ice diapir or cryomagmatic intrusion which promotes enhanced sublimation of surface ice producing local enrichment of nonice material an analytical model describing a constant temperature infinite heat source places lower bounds on the time scales required to produce a detectable feature a numerical treatment of more realistic geometries and boundary conditions allows cooling of the heat source to be modeled we find that the thermal model satisfactorily explains features with the dimensions of minor lineaments and lenticulae haloes a few kilometers over time intervals of 104 to 105 years the formation of a sublimation lag deposit proceeds rapidly once the ice temperature exceeds a threshold of 130 k however for triple bands measuring up to 25 km in width additional heat sources such as repeated or multiple intrusions are necessary to reproduce the observed dimensions this is consistent with the observation that well developed triple bands typically have multiple medial ridge sets each of which may represent a discrete tabular heat source although neither the volcanic nor intrusive thermal model can be ruled out at this stage the latter is a more satisfactory explanation for some characteristics of the low albedo features analyzed in this study

the topography of iapetus leading side abstract we have used cassini stereo images to study the topography of iapetus leading side a terrain model derived at resolutions of 4 8 km reveals that iapetus has substantial topography with heights in the range of 10 km to 13 km much more than observed on the other middle sized satellites of saturn so far most of the topography is older than 4 ga neukum g wagner r denk t porco c c 2005 lunar planet sci xxxvi abstract 2034 which implies that iapetus must have had a thick lithosphere early in its history to support this topography models of lithospheric deflection by topographic loads provide an estimate of the required elastic thickness in the range of 50 100 km iapetus prominent equatorial ridge porco c c and 34 colleagues 2005 science 307 1237 1242 reaches widths of 70 km and heights of up to 13 km from their base within the modeled area the morphology of the ridge suggests an endogenous origin rather than a formation by collisional accretion of a ring remnant ip w h 2006 geophys res lett 33 doi 10 1029 2005gl025386 l16203 the transition from simple to complex central peak craters on iapetus occurs at diameters of 11 3 km the central peaks have pronounced conical shapes with flanking slopes of typically 11 and heights that can rise above the surrounding plains crater depths seem to be systematically lower on iapetus than on similarly sized rhea which if true may be related to more pronounced crater wall slumping which widens the craters on iapetus than on rhea there are seven large impact basins with complex morphologies including central peak massifs and terraced walls the largest one reaches 800 km in diameter and has rim topography of up to 10 km generally no rings are observed with the basins consistent with a thick lithosphere but still thin enough to allow for viscous relaxation of the basin floors which is inferred from crater depth to diameter measurements in particular a 400 km basin shows up domed floor topography which is suggestive of viscous relaxation a model of complex crater formation with a viscoplastic bingham rheology melosh h j 1989 impact cratering oxford univ press new york of the impact shocked icy material provides an estimate of the effective cohesion viscosity at 0 04 0 01 mpa 0 6 0 2 gpa s the local distribution of bright and dark material on the surface of iapetus is largely controlled by topography and consistent with the dark material being a sublimation lag deposit originating from a bright icy substrate mixed with the dark components but frost deposits are possible as well

what we know about mars from its impact craters martian impact craters provide insights into formation ages of terrain units nearsurface properties and the planet s degradational history crater size frequency distribution analyses allow determination of terrain unit relative ages and extrapolation of the lunar crater chronology can provide estimates of absolute ages for these units such analyses indicate that mars has been geologically active throughout its history but it also retains extensive regions dating back to ca 4 ga higher cratering rates during the late heavy bombardment lhb helped to create the martian regolith and formation of large impact basins helped to erode the initially denser martian atmosphere and may have created the hemispheric dichotomy low global degradation rates since the end of lhb ca 3 8 ga resulted in well preserved impact crater morphologies the presence of layered ejecta blankets and central pits associated with fresh to moderately eroded craters suggests a volatile rich crust impact crater depth diameter relationships allow estimation of the vertical extent of crustal volatiles to depths greater than those probed by current spacecraft instrumentation temporal changes in subsurface ice reservoir depths are revealed by differences in layered ejecta onset diameter as a function of crater age an understanding of the morphology and morphometry of pristine impact craters facilitates efforts to determine the amount and types of degradation and the periods over which they operated impact craters therefore play a major role in unraveling the climatic and geologic history of mars

near surface temperatures on mercury and the moon and the stability of polar ice deposits abstract in order to assess the thermal stability of polar ice deposits we present model calculated temperatures of flat surfaces and surfaces within bowl shaped and flat floored polar impact craters on mercury and the moon our model includes appropriate insolation cycles realistic crater shapes multiple scattering of sunlight and infrared radiation and depth and temperature dependent regolith thermophysical properties unshaded water ice deposits on the surface of either body are rapidly lost to thermal sublimation a subsurface water ice deposit is stable within 2 latitude of the moon s poles meter thick water ice deposits require billions of years to sublime if located in the permanently shaded portions of flat floored craters within 10 latitude of the poles of mercury and 13 latitude of the poles of the moon results for craters associated with radar features on mercury are consistent with the presence of stable water ice deposits if a thin regolith layer thermally insulates deposits at lower latitudes and within smaller craters a regolith cover would also reduce losses from diffusion ion sputtering impact vaporization and h ly and is implied independently by the radar observations permanently shaded areas near the moon s poles are generally colder than those near mercury s poles but the moon s obliquity history its orbit through earth s magnetospheric tail and its radar opaque regolith may limit the volume and radar detectability of ice deposits there

martian perched craters and large ejecta volume evidence for episodes of deflation in the northern lowlands the northern lowland plains such as those found in acidalia and utopia planitia have high percentages of impact craters with fluidized ejecta in both regions the analysis of crater geometry from mars orbiter laser altimeter mola data has revealed large ejecta volumes some exceeding the volume of excavation moreover some of the crater cavities and fluidized ejecta blankets of these craters are topographically perched above the surrounding plains these perched craters are concentrated between 40 and 70 n in the northern plains the atypical high volumes of the ejecta and the perched craters suggest that the northern lowlands have experienced one or more episodes of resurfacing that involved deposition and erosion the removal of material most likely caused by the sublimation of ice in the materials and their subsequent erosion and transport by the wind is more rapid on the plains than on the ejecta blankets the thermal inertia difference between the ejecta and the surrounding plains suggests that ejecta characterized by a lower thermal inertia protect the underneath terrain from sublimation this results in a decreased elevation of the plains relative to the ejecta blankets sublimation and eolian erosion can be particularly high during periods of high obliquity

formation of glaciers on mars by atmospheric precipitation at high obliquity surface conditions on mars are currently cold and dry with water ice unstable on the surface except near the poles however geologically recent glacierlike landforms have been identified in the tropics and the midlatitudes of mars the ice has been proposed to originate from either a subsurface reservoir or the atmosphere we present high resolution climate simulations performed with a model designed to simulate the present day mars water cycle but assuming a 45 obliquity as experienced by mars a few million years ago the model predicts ice accumulation in regions where glacier landforms are observed on the western flanks of the great volcanoes and in the eastern hellas region this agreement points to an atmospheric origin for the ice and reveals how precipitation could have formed glaciers on mars

evidence for recent climate change on mars from the identification of youthful near surface ground ice ground ice in the crust and soil may be one of the largest reservoirs of water on mars1 2 3 near surface ground ice is predicted to be stable at latitudes higher than 40 ref 4 where a number of geomorphologic features indicative of viscous creep and hence ground ice have been observed5 mid latitude soils have also been implicated as a water ice reservoir6 the capacity of which is predicted to vary on a 100 000 year timescale owing to orbitally driven variations in climate7 it is uncertain however whether near surface ground ice currently exists at these latitudes and how it is changing with time here we report observational evidence for a mid latitude reservoir of near surface water ice occupying the pore space of soils the thickness of the ice occupied soil reservoir 1 10 m and its distribution in the 30 to 60 latitude bands indicate a reservoir of 1 5 6 0 104 km3 equivalent to a global layer of water 10 40 cm thick we infer that the reservoir was created during the last phase of high orbital obliquity less than 100 000 years ago and is now being diminished

north south geological differences between the residual polar caps on mars polar processes can be sensitive indicators of global climate and the geological features associated with polar ice caps can therefore indicate evolution of climate with time the polar regions on mars have distinctive morphologic and climatologic features thick layered deposits seasonal co 2 frost caps extending to mid latitudes and near polar residual frost deposits that survive the summer the relationship of the seasonal and residual frost caps to the layered deposits has been poorly constrained mainly by the limited spatial resolution of the available data in particular it has not been known if the residual caps represent simple thin frost cover or substantial geologic features here we show that the residual cap on the south pole is a distinct geologic unit with striking collapse and erosional topography this is very different from the residual cap on the north pole which grades into the underlying layered materials these findings indicate that the differences between the caps are substantial rather than reflecting short lived differences in frost cover and so support the idea of long term asymmetry in the polar climates of mars

the presence and stability of ground ice in the southern hemisphere of mars abstract we calculate new estimates of ground ice stability and the depth distribution of the ice table the depth boundary between ice free soil above and ice cemented soil below and compare these theoretical estimates of the distribution of ground ice with the observed distribution of leakage neutrons measured by the neutron spectrometer instrument of the mars odyssey spacecraft s gamma ray spectrometer instrument suite our calculated ground ice distribution contains improvements over previous work in that we include the effects of the high thermal conductivity of ice cemented soil at and below the ice table we include the surface elevation dependence of the near surface atmospheric humidity and we utilize new high resolution maps of thermal inertia albedo and elevation from mars global surveyor observations results indicate that ground ice should be about 5 times shallower than in previous predictions while results are dependent on the atmospheric humidity depths are generally between a few millimeters and a few meters with typical values of a few centimeters results are also geographically similar to previous predictions with differences due to the higher resolution of thermal inertia and the inclusion of elevation effects on humidity comparison with the measured epithermal neutron count rates in the southern hemisphere indicate that the geographic distribution of the count rate is best correlated with ground ice in equilibrium with 10 to 20 pr m precipitable micrometers column abundance of atmospheric water assuming a uniform distribution with co2 however given the uncertainties 5 to 30 pr m also may be viable this water abundance represents a longer term average over 100 to 1000 yr there is a high degree of correlation between the depth of the ice table and the epithermal count rate that agrees remarkably well with predicted count rates as a function of ice table depth these results indicate that ground ice in the upper meter of the martian soil is in diffusive equilibrium with the atmosphere since ground ice in this depth zone is expected to undergo saturation desiccation cycles with orbital variations this ice should be younger than about 500 kyr and was emplaced under similar cold and dry climate conditions of today remaining differences between the predicted depths of the ice table and those inferred from the neutron data are likely to be due to subpixel heterogeneity in the martian surface including the presence of rocks slopes and patches of soil with varying thermophysical properties