diviner lunar radiometer observations of cold traps in the moon s south polar region diviner lunar radiometer experiment surface temperature maps reveal the existence of widespread surface and near surface cryogenic regions that extend beyond the boundaries of persistent shadow the lunar crater observation and sensing satellite lcross struck one of the coldest of these regions where subsurface temperatures are estimated to be 38 kelvin large areas of the lunar polar regions are currently cold enough to cold trap water ice as well as a range of both more volatile and less volatile species the diverse mixture of water and high volatility compounds detected in the lcross ejecta plume is strong evidence for the impact delivery and cold trapping of volatiles derived from primitive outer solar system bodies

high spatial resolution studies of epithermal neutron emission from the lunar poles constraints on hydrogen mobility 1 the data from the collimated sensors of the lend instrument are shown to be of exceptionally high quality counting uncertainties are about 0 3 relative and are shown to be the only significant source of random error thus conclusions based on small differences in count rates are valid by comparison with the topography of shoemaker crater the spatial resolution of the instrument is shown to be consistent with the design value of 5 km for the radius of the circle over which half the counts from the lunar surface would be determined the observed epithermal neutron suppression factor due to the hydrogen deposit in shoemaker crater of 0 25 0 04 cps is consistent with the collimated field of view rate of 1 7 cps estimated by mitrofanov et al 2010a the statistical significance of the neutron suppressed regions nsrs relative to the larger surrounding polar region is demonstrated and it is shown that they are not closely related to the permanently shadowed regions there is a significant increase in h content in the polar regions independent of the h content of the nsrs the non nsr h content increases directly with latitude and the rate of increase is virtually identical at both poles there is little or no increase with latitude outside the polar region various mechanisms to explain this steep increase in the non nsr polar h with latitude are investigated and it is suggested that thermal volatilization is responsible for the increase because it is minimized at the low surface temperatures close to the poles

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

reconstruction of the east asian summer monsoon rainfall distribution at centennial scale during the last glacial maximum abstract the last glacial maximum lgm defined as the period between 23 and 19 ka is considered a key climatic period with conditions in great contrast to the present study of this period may reveal aspects of global ice sheet sensitivity to regional and global climate change which is critical in understanding climate teleconnections and feedback mechanisms a stalagmite record from linglong cave central china in combination with other high resolution stalagmite records from southwest china and east china existing on the same moisture transport pathway allows a reconstruction of rainfall patterns during the lgm by making use of the 18o differences between stalagmite records the rainfall around both southwest and central east china show a prominent change centered at 24 ka corresponding to the h2 event one of the heinrich events related to north atlantic ice rafting also in central east china around the periods at 22 and 20 ka the rainfall is lower than the average during the whole lgm while around 23 21 and 19 ka the rainfall is higher than the average which is opposite to the rainfall variation in southwest china this apparent dipole rainfall pattern during the lgm is similar to the modern east asian summer monsoon easm rainfall distribution observed during weak monsoon periods suggesting a much weaker easm with its front moving less far north during the lgm than at present which may link to north atlantic climate and shifting of the intertropical convergence zone itcz power spectral analysis reveals that the rainfall variations in southwest china are mainly controlled by a cycle of 1000 yr while in central east china it is mainly controlled by cycles of 1800 yr and 1300 yr which are all possible solar activity cycles suggesting that the easm rainfall on long term scales is dominated by external forces

fast numerical method for growth and retreat of subsurface ice on mars abstract subsurface water ice on mars evolves due to exchange of vapor with the atmosphere in the form of loss of ice to the atmosphere or in the form of the growth of interstitial ice described here is an accelerated numerical method for the long term evolution of subsurface ice this accelerated method is five orders of magnitude faster than explicit vapor transport calculations enabling fundamentally new types of climate models its speed matches that of purely thermal models the speedup is achieved primarily by solving time averaged equations for vapor transport and ice volume change processes incorporated are growth of interstitial pore ice retreat of pore ice retreat of an ice sheet and retreat of pore ice due to geothermal heating from below two example applications illustrate this numerical method s capabilities near the permafrost margin at 55 latitude ice is periodically depleted and slowly recharged leading to a pore ice layer estimated to be currently no more than a few meters thick at the phoenix landing site it shows the formation of a three layered structure whereby the layer of pore ice can be very thin

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

effects of orbital evolution on lunar ice stability 1 many regions near the lunar poles are currently cold enough that surface water ice would be stable against sublimation losses for billions of years however most of these environments are currently too cold to efficiently drive ice downward by thermal diffusion leaving impact burial as the primary means of protection from surface loss processes in this respect most of the present near surface thermal environments on the moon may actually be quite poor traps for water ice this was not always the case long term orbital changes have dramatically altered the lunar polar thermal environment we develop a simple model of the evolution of the lunar orbit and spin axis to examine the thermal environments available for volatile deposition and retention in the past our calculations show that some early lunar polar environments were in the right temperature regime to have collected subsurface ice if a supply were available however a high obliquity period which occurred when the moon was at about half its present distance from the earth would either have driven this ice out into space or deep into the lunar subsurface since that time as the lunar obliquity has slowly decreased to its present value environments have undergone their own thermal evolution and each of the current cold traps experienced a period when they were most efficient at thermally burying ice we examine the thermal history of a lunar polar crater to provide a framework for examining other processes effecting volatiles in the moon s near surface cold traps

the tidal rotational shape of the moon and evidence for polar wander analysis of the moon s topography reveals that when its largest basins are removed the lunar shape is consistent with processes controlled by early earth tides and implies a reorientation of the moon s principal shape axes attempts to assess the various theories for the formation of the moon and to determine its true shape are complicated by the presence of several large basins on its surface that formed after the crust solidified here ian garrick bethell et al concentrate on the topography and gravity outside these basins and propose that the long wavelength shape of the moon has evolved through a combination of two early tidal processes first a crust building process controlled by early tidal heating throughout the moon and second the later development of a frozen tidal rotational bulge the authors also infer that an uneven distribution of internal density eventually reoriented the moon s polar axis by about 36 to the configuration that we see today the origin of the moon s large scale topography is important for understanding lunar geology1 lunar orbital evolution2 and the moon s orientation in the sky3 previous hypotheses for its origin have included late accretion events4 large impacts5 tidal effects6 and convection processes7 however testing these hypotheses and quantifying the moon s topography is complicated by the large basins that have formed since the crust crystallized here we estimate the large scale lunar topography and gravity spherical harmonics outside these basins and show that the bulk of the spherical harmonic degree 2 topography is consistent with a crust building process controlled by early tidal heating throughout the moon the remainder of the degree 2 topography is consistent with a frozen tidal rotational bulge that formed later at a semi major axis of about 32 earth radii the probability of the degree 2 shape having both tidal heating and frozen shape characteristics by chance is less than 1 we also infer that internal density contrasts eventually reoriented the moon s polar axis by 36 4 to the configuration we observe today together these results link the geology of the near and far sides and resolve long standing questions about the moon s large scale shape gravity and history of polar wander

mapping and characterization of non polar permanent shadows on the lunar surface abstract we present the first globally complete inventory of permanent shadows on the lunar surface that are detectable with the current global instrument datasets including discovery of regions with persistent shadows over geologic time periods as close to the equator as 58 of latitude these results were obtained through application of a ray tracing technique to the latest global topographic datasets from the lunar reconnaissance orbiter our analysis reveals that 13 361 km2 of surface in the northern hemisphere and 17 698 km2 in the southern hemisphere are permanently shadowed we present maps showing the locations of all the permanent shadows detectable using these datasets then turn our focus toward the permanent shadows farthest from the poles each permanent shadow on the equator side of 65 of latitude is shown in detail surface brightness temperature data derived from the diviner mid infrared radiometer on board the lunar reconnaissance orbiter have been analyzed for four of these locations and found to have mid day temperatures 75 120 k less than nearby comparison locations that experience direct daytime illumination in some cases the permanently shadowed locations have nighttime temperatures 10 25 k lower than surroundings the temperature results support our finding that these non polar craters are permanently shadowed the surface brightness temperature results also raise interesting questions about their ability to cold trap volatiles discovery of these non polar permanently shadowed regions increases possible locations of water resources and high priority exploration targets on the moon

evidence for water ice near the lunar poles improved versions of lunar prospector thermal and epithermal neutron data were studied to help discriminate between potential delivery and retention mechanisms for hydrogen on the moon improved spatial resolution at both poles shows that the largest concentrations of hydrogen overlay regions in permanent shade in the north these regions consist of a heavily cratered terrain containing many small less than 10 km diameter isolated craters these border circular areas of hydrogen abundance h that is only modestly enhanced above the average equatorial value but that falls within large flat bottomed and sunlit polar craters near the south pole h is enhanced within several 30 km scale craters that are in permanent shade but is only modestly enhanced within their sunlit neighbors we show that delivery by the solar wind cannot account for these observations because the diffusivity of hydrogen at the temperatures within both sunlit and permanently shaded craters near both poles is sufficiently low that a solar wind origin cannot explain their differences we conclude that a significant portion of the enhanced hydrogen near both poles is most likely in the form of water molecules

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

initial results for the north pole of the moon from mini sar chandrayaan 1 mission 1 we present new polarimetric radar data for the surface of the north pole of the moon acquired with the mini sar experiment onboard india s chandrayaan 1 spacecraft between mid february and mid april 2009 mini sar mapped more than 95 of the areas polewards of 80 latitude at a resolution of 150 meters the north polar region displays backscatter properties typical for the moon with circular polarization ratio cpr values in the range of 0 1 0 3 increasing to over 1 0 for young primary impact craters these higher cpr values likely reflect surface roughness associated with these fresh features in contrast some craters in this region show elevated cpr in their interiors but not exterior to their rims almost all of these features are in permanent sun shadow and correlate with proposed locations of polar ice modeled on the basis of lunar prospector neutron data these relations are consistent with deposits of water ice in these craters

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

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

high resolution radar imaging of mercury s north pole abstract the recently upgraded arecibo s band 12 6 cm radar was used to make delay doppler images of mercury s north polar region where earlier observations had shown strong echoes from putative ice deposits in craters the image resolution of 1 5 3 km is a substantial improvement over the 15 km resolution of the older arecibo images j k harmon et al 1994 nature 369 213 215 the new observations confirm all the original polar features and reveal many additional features including several at latitudes as low as 72 75 n and several from craters less than 10 km in diameter all of the new features located on the mariner imaged side of the planet can be matched with known craters or other shaded areas we find the north pole to be located 65 km from the original mariner based pole and 15 km from the new mariner based pole of m s robinson et al 1999 j geophys res 104 30 847 30 852 the improved resolution reveals fine structure in the radar features and their respective host craters including radar shadowing highlighting by central peaks and rim walls rim terracing and preferential concentration of radar bright deposits in shaded southern floor areas the radar features high brightness circular polarization inversion c 1 25 and confinement to regions permanently shaded from direct sunlight are all consistent with volume scattering from a cold trapped volatile such as clean water ice the sizes and locations of most of the features show good agreement with the thermal model of a r vasavada d a paige and s e wood 1999 icarus 141 179 193 for insulated buried water ice although the problems of explaining radar features in small craters and the rapid burial required at lower latitudes suggest that other factors may be suppressing ice loss after emplacement

radar mapping of mercury full disk images and polar anomalies a random code technique has been used at arecibo to obtain delay doppler radar images of the full disk of mercury anomalously bright features were found at the north and south poles the north polar feature is oblong 4 by 8 and offset from the pole the smaller south polar feature is mostly confined to the floor of the crater chao meng fu the polar locations and radar properties of these features indicate that they may be produced by volume scattering in ice the images also reveal a variety of more subdued reflectivity features ranging in size from hundreds to thousands of kilometers some of these appear to have an impact origin

lunar orbital evolution a synthesis of recent results the present rate of tidal dissipation in the earth moon system is known to be anomalously high in the sense that the implied age of the lunar orbit is only 1 5 109 years though other evidence suggests an age closer to 4 109 years to assess how long the anomalous dissipation has persisted we use published estimates of lunar orbital configurations derived from a fine grained sediments containing tidal laminations and b numerical ocean models averaged over varying ocean geometries the implied histories of the lunar semimajor axis are surprisingly consistent over the past 109 years the ocean models imply on average reduced dissipation in the past because of a spatial mismatch between tidal forcing and oceanic normal modes of higher frequencies webb s ocean model suggests that the anomalous oceanic dissipation began about 109 years ago and has been increasing since then

reconstruction of eolian bed forms and paleocurrents from cross bedded strata at victoria crater meridiani planum mars outcrop exposures imaged by the opportunity rover at victoria crater a 750 m diameter crater in meridiani planum are used to delineate sedimentary structures and further develop a dune interdune depositional model for the region the stratigraphy at victoria crater observed during opportunity s partial traverse of its rim includes the best examples of meter scale eolian cross bedding observed on mars to date the cape st mary promontory located at the southern end of the rim traverse is characterized by meter scale sets of trough cross bedding suggesting northward migrating sinuous crested bed forms cape st vincent which is located at the opposite end of the traverse shows tabular planar stratification indicative of climbing bed forms with meter to decameter scale dune heights migrating southward promontories located between cape st mary and cape st vincent contain superposed stratigraphic units with northward and southward dipping beds separated by outcrop scale bounding surfaces these bounding surfaces are interpreted to be either reactivation and or superposition surfaces in a complex erg sea any depositional model used to explain the bedding must conform to reversing northward and southward paleomigration directions and include multiple scales of bed forms in addition to stratified outcrop a bright diagenetic band is observed to overprint bedding and to lie on an equipotential parallel to the preimpact surface meter scale cross bedding at victoria crater is similar to terrestrial eolian deposits and is interpreted as a dry dune field comparable to jurassic age eolian deposits in the western united states

the procellarum kreep terrane implications for mare volcanism and lunar evolution geophysical remote sensing and sample data demonstrate that the procellarum and imbrium regions of the moon make up a unique geochemical crustal province here dubbed the procellarum kreep terrane geochemical studies of imbrium s ejecta and the crustal structure of the imbrium and serenitatis basins both suggest that a large portion of the lunar crust in this locale is composed of a material similar in composition to apollo 15 kreep basalt kreep basalt has about 300 times more uranium and thorium than chondrites so this implies that a large portion of moon s heat producing elements is located within this single crustal province the spatial distribution of mare volcanism closely parallels the confines of the procellarum kreep terrane and this suggests a causal relationship between the two phenomena we have modeled the moon s thermal evolution using a simple thermal conduction model and show that as a result of the high abundance of heat producing elements that are found in the procellarum kreep terrane partial melting of the underlying mantle is an inevitable outcome specifically by placing a 10 km kreep basalt layer at the base of the crust there our model predicts that mare volcanism should span most of the moon s history and that the depth of melting should increase with time to a maximum depth of about 600 km we suggest that the 500 km seismic discontinuity that is observed in the apollo seismic data may represent this maximum depth of melting our model also predicts that the kreep basalt layer should remain partially molten for a few billion years thus the imbrium impact event most likely excavated into a partially molten kreep basalt magma chamber we postulate that the kreep basalt composition is a by product of mixing urkreep with shallow partial melts of the underlying mantle since mg suite rocks are likely derived from crystallizing kreep basalt the provenance of these plutonic rocks is likely to be unique to this region of the moon

topography of the lunar poles from radar interferometry a survey of cold trap locations detailed topographic maps of the lunar poles have been obtained by earth based radar interferometry with the 3 5 centimeter wavelength goldstone solar system radar the interferometer provided maps 300 kilometers by 1000 kilometers of both polar regions at 150 meter spatial resolution and 50 meter height resolution using ray tracing these digital elevation models were used to locate regions that are in permanent shadow from solar illumination and may harbor ice deposits estimates of the total extent of shadowed areas poleward of 87 5 degrees latitude are 1030 and 2550 square kilometers for the north and south poles respectively

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

geology of shackleton crater and the south pole of the moon 1 using new smart 1 amie images and arecibo and goldstone high resolution radar images of the moon we investigate the geological relations of the south pole including the 20 km diameter crater shackleton the south pole is located inside the topographic rim of the south pole aitken spa basin the largest and oldest impact crater on the moon and shackleton is located on the edge of an interior basin massif the crater shackleton is found to be older than the mare surface of the apollo 15 landing site 3 3 ga but younger than the apollo 14 landing site 3 85 ga these results suggest that shackleton may have collected extra lunar volatile elements for at least the last 2 billion years and is an attractive site for permanent human presence on the moon

subsurface migration of h2o at lunar cold traps 1 permanently shaded areas near the poles of the moon and mercury may harbor water ice we develop a physical model for migration of water molecules in the regolith and discover two pathways that can lead to accumulation of h2o in the subsurface a small fraction of water molecules delivered either continuously or abruptly to permanently cold areas diffuses into the regolith and can remain there longer than on the surface higher temperatures lead to deeper burial at constant temperature this diffusive migration produces less than one molecular layer of volatile h2o on grains because it is driven by differences in surface concentrations the water is therefore expected to be in adsorbed form and the amount stored in this fashion could be at most a few hundred ppm of h2o a second pathway is pumping by diurnal temperature oscillations from a transient ice cover that may have formed during a large comet impact it can lead to high ground ice densities but the ground ice layer lasts not long beyond the disappearance of the ice cover both types of subsurface charging mechanism work best for temperatures typical of permanently shaded areas with sunlit surfaces in their field of view

no evidence for thick deposits of ice at the lunar south pole the rim of the shackleton crater at the lunar south pole is a candidate crash site for nasa s lcross probe lunar crater observation and sensing satellite due to launch in 2008 the plume of debris kicked up by the crash is to be analysed in the hope that it will reveal the water thought to be there suggestions of lunar ice date from 1996 when data from the clementine spacecraft gave some indications of the presence of ice on crater walls at the south pole now using high resolution radar imagery the radar scattering parameter thought indicative of thick ice deposits has been found also to match radar echoes from the rock strewn walls and ejecta of young impact craters at all lunar latitudes there is no evidence for thick ice though there could be grains of water ice spread more thinly through the lunar soil shackleton crater at the moon s south pole has been suggested as a possible site of concentrated deposits of water ice on the basis of modelling of bi static radar polarization properties and interpretations of earlier earth based radar images1 2 this suggestion and parallel assumptions about other topographic cold traps is a significant element in planning for future lunar landings hydrogen enhancements have been identified in the polar regions3 but these data do not identify the host species or its local distribution the earlier earth based radar data lack the resolution and coverage for detailed studies of the relationship between radar scattering properties cold traps in permanently shadowed areas and local terrain features such as the walls and ejecta of small craters here we present new 20 m resolution 13 cm wavelength radar images that show no evidence for concentrated deposits of water ice in shackleton crater or elsewhere at the south pole the polarization properties normally associated with reflections from icy surfaces in the solar system4 5 6 were found at all the observed latitudes and are strongly correlated with the rock strewn walls and ejecta of young craters including the inner wall of shackleton there is no correlation between the polarization properties and the degree of solar illumination if the hydrogen enhancement observed by the lunar prospector orbiter3 indicates the presence of water ice then our data are consistent with the ice being present only as disseminated grains in the lunar regolith

burial rate of mercury s polar volatile deposits 1 delay doppler images of mercury s polar regions showing enhanced radar backscatter have been interpreted as evidence for water ice in the polar craters and are consistent with pure water ice covered by about 20 cm of regolith in this paper we assume that the volatile at the hermean poles is water ice and that it was initially deposited at one time in a clean layer we constrain the time of such an impact by determining the rate of regolith emplacement the rate of burial of ice deposits in polar craters on mercury is estimated to be 0 43 cm myr if the ice deposits in hermean polar craters are both clean and buried by 20 cm of regolith they must be relatively recently emplaced 50 myr ago the predicted h concentration in the uppermost meter of regolith is calculated as a function of both time since emplacement of the ice and initial thickness of the ice layer the combination of neutron data and radar data can provide additional insight into the size and age of ice deposits at mercury

lack of exposed ice inside lunar south pole shackleton crater the inside of shackleton crater at the lunar south pole is permanently shadowed it has been inferred to hold water ice deposits the terrain camera tc a 10 meter resolution stereo camera onboard the selenological and engineering explorer selene spacecraft succeeded in imaging the inside of the crater which was faintly lit by sunlight scattered from the upper inner wall near the rim the estimated temperature of the crater floor based on the crater shape model derived from the tc data is less than 90 kelvin cold enough to hold water ice however at the tc s spatial resolution the derived albedo indicates that exposed relatively pure water ice deposits are not on the crater floor water ice may be disseminated and mixed with soil over a small percentage of the area or may not exist at all

space weathering effects on lunar cold trap deposits 1 both steady and episodic sources have been proposed as sources of hydrogen observed by lunar prospector in association with the regions of permanent shadow at the poles of the moon either source could supply significant quantities of water to the poles however space weathering processes affect the retention of water in the cold traps we investigate those effects by simulating the evolution of a column of regolith in the region of permanent shadow over time we determine the hydrogen concentration as a function of depth using a monte carlo model of discrete impacts and of delivery from the solar wind we treat the delivery sublimation sputtering and very small scale impacts as continual processes comparing the amount of water delivered to the poles to the amount remaining after space weathering we find a retention efficiency of 5 6 the retention efficiency of the polar cold traps is adequate for preserving volatile deposits over long periods of time the average hydrogen concentration in the regolith column is 4100 ppm in the top meter after 1 gyr this is a saturation level in the regolith increasing the amount of time deepens the enriched layer but does not lead to increased concentrations in 1 gyr about 1 6 m of the regolith is gardened therefore the top meter which is probed by the neutron spectroscopy technique has reached steady state in the simulations the 4100 ppm saturation level is about half of the amount of hydrogen inferred from the lunar prospector neutron data

radar mapping of mercury s polar anomalies ground based radar observations of mercury have revealed unusually strong highly depolarized echoes from the north1 2 and south2 poles these anomalous echoes have been cited as evidence of polar ice deposits1 5 thermal studies3 5 suggest that the permanently shaded floors of large polar craters are cold enough to preserve water ice in a stable state over aeons in spite of mercury s proximity to the sun here we present high resolution radar maps of mercury s polar regions derived from delay doppler measurements we have resolved the north and south polar anomalies into numerous crater sized features and we have been able to identify the source craters for many of these features after making small corrections to the pole positions on the mariner 10 images the coincidence with crater locations together with other properties of the radar features are consistent with the polar ice hypothesis

arecibo radar mapping of the lunar poles a search for ice deposits the arecibo 12 6 centimeter wavelength radar system was used to image the polar regions of the moon at a resolution of 125 meters in a search for ice deposits in areas of possible permanent shadow from the sun no areas greater than 1 square kilometer were found with high radar backscatter cross sections and high circular polarization ratios properties suggestive of the presence of ice a number of areas smaller than 1 square kilometer were found with these properties but optical images from spacecraft missions have shown some of these features to be in sunlight arecibo radar images of sinus iridum at latitude 47 n also showed a number of small features with similar properties the coincidence of some of these features with the radar facing slopes of craters and their presence in sunlit areas suggests that very rough surfaces rather than ice deposits are responsible for their unusual radar properties