age and evolution of the lower nw flank of the hecates tholus volcano mars based on crater size frequency distribution on ctx images abstract we present results of crater size frequency distribution sfd analysis of the lower nw flank of the hecates tholus volcano elysium volcanic province of mars by the use of images acquired by the context ctx instrument on board of mars reconnaissance orbiter 6 m pixel in resolution previous similar works were focused on the caldera complex of the volcano and some sectors of the lower nw flank in this study we analyzed the complete crater population of the main geomorphological units characterizing this sector of the volcano de pablo m a centeno j d 2012 journal of maps 8 3 208 2014 discarding areas with possible clustering to avoid erroneous results in total 16 areas corresponding to 10 geomorphological units were measured and absolute model ages were derived for them the ages correspond to ages of origin as well as of the end of resurfacing events depending on the analyzed sector resulting in some cases in more than one age per area our results are in general in agreement with previous works and establish that the age of the origin of the hecates tholus volcano could be at least 3 8 ga with possible volcanic eruptions occurring until at least 335 ma glacial events were also dated at 90 ma 30 ma 16 ma and 6 ma although it is possible to recognize ages which could also be related to the recent ice ages of mars between 2 and 0 4 ma our results allowed us to determine that glacial processes could have been active as far back as 1 4 ga with possible events at intermediate ages we deduced from the resulting ages and our observations on ctx images and the available geomorphological map of the area that glacial related processes played an important role in sculpting this flank of the volcano and the possible level of the glacial sheet at the edge of the main depression of this flank was also deduced with altitudes ranging between 2035 m and 2490 m in agreement with the presence of smooth outcrops and roche moutonnees in the area finally a possible evolution of this region of the hecates tholus volcano is proposed and discussed establishing the sequence of the most important geological events which occurred in the area and their possible timings

boulder movement at high northern latitudes of mars 1 we examine a narrow latitudinal band 60 n 70 n on mars to place constraints on the seasonally averaged velocity q of boulder movements over patterned ground these latitudes comprise a region of the northern lowlands where patterned ground covers nearly every surface here boulders meters in diameter are consistently found to be concentrated at or near the cracks that define the polygonal networks indicating a mobilization process because impact craters are the source for many boulders we can use craters and their degradation to estimate the time scales for boulder movement we study and catalog 1018 degraded impact craters 100 m d 1 km in 55 high resolution imaging science experiment hirise images we find that crater degradation occurs on a time scale 1 ma which is too recent for melting related mechanisms in a past warmer epoch clustering of boulders occurs at a time scale of a few ma or shorter which means that boulders on 5 20 m diameter polygons move at seasonal velocities q 1 10 m yr or faster

north to south asymmetries in the water equivalent hydrogen distribution at high latitudes on mars 1 water content and burial depths derived from thermal and epithermal neutron currents measured by the mars odyssey neutron spectrometer are used to determine north to south asymmetries and intercorrelations at high latitudes on mars our goal is to contrast observed asymmetries with predictions based on current climate conditions and potential regolith thermophysical and chemophysical properties the average mass fraction of water equivalent hydrogen within the buried layer is higher on average in the south between 60 and 75 latitude and is strongly anticorrelated with burial depth in both hemispheres these results argue that the observed water content at high latitudes may require differing north to south thermophysical and or chemophysical properties of the regolith

on the icy edge at louth and korolev craters abstract the modern climate of mars has been well characterized from over a decade of orbiting spacecraft in situ measurements via landers rovers and theoretical advances in climate modeling nonetheless important questions remain unanswered including the present day mass balance of the north polar residual cap and its icy outliers exposed water ice mounds are found in craters and extend as far equatorward as 70 2 n due to their southerly location these ice mounds are likely more sensitive to ongoing changes in climate we analyze high resolution images of the louth crater ice mound and employ a coupled 1 d thermal and atmospheric model to estimate annual mass balance of both louth and korolev water ice we incorporate the effects of shallowly sloping surfaces and seasonally dependent water ice albedo no clear trend in the advance or retreat of louth crater water ice is observed in over 4 mars years of repeat high resolution images secular changes are either sufficiently small as to not be detected or the ice is in equilibrium modeled mass balance ranges from 6 to 2 mm of water ice per mars year at both sites with nominal cases being in near equilibrium

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

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

chaotic obliquity and the nature of the martian climate recent calculations of the martian obliquity suggest that it varies chaotically on timescales longer than about 107 years and varies between about 0 and 60 we examine the seasonal water behavior at obliquities between 40 and 60 up to several tens of centimeters of water may sublime from the polar caps each year and possibly move to the equator where it is more stable co2 frost and co2 h2o clathrate hydrate are stable in the polar deposits below a few tens of meters depth so that the polar cap could contain a significant co2 reservoir if co2 is present it could be left over from the early history of mars also it could be released into the atmosphere during periods of high obliquity causing occasional periods of more clement climate

thermal contraction crack polygons on mars a synthesis from hirise phoenix and terrestrial analog studies thermal contraction crack polygons are complex landforms that have begun to be deciphered on earth and mars by the combined investigative efforts of geomorphology environmental monitoring physical models paleoclimate reconstruction and geochemistry thermal contraction crack polygons are excellent indicators of the current or past presence of ground ice ranging in ice content from weakly cemented soils to debris covered massive ice relative to larger topographic features polygons may form rapidly and reflect climate conditions at the time of formation preserving climate information as relict landforms in the geological record polygon morphology and internal textural characteristics can be used to distinguish surfaces modified by the seasonal presence of a wet active layer or dry active layer and to delimit subsurface ice conditions analysis of martian polygon morphology and distribution indicates that geologically recent thermal contraction crack polygons on mars form predominantly in an ice rich latitude dependent mantle more likely composed of massive ice deposited by precipitation than by cyclical vapor diffusion into regolith regional and local heterogeneities in polygon morphology can be used to distinguish variations in ice content deposition and modification history and to assess microclimate variation on timescales of ka to ma analyses of martian polygon morphology guided by investigations of terrestrial analog thermal contraction crack polygons strongly suggest the importance of excess ice in the formation and development of many martian thermal contraction crack polygons implying the presence of an ice rich substrate that was fractured during and subsequent to obliquity driven depositional periods and continually modified by ongoing vapor equilibration processes

driven by excess climatic implications of new global mapping of near surface water equivalent hydrogen on mars abstract we present improved mars odyssey neutron spectrometer mons maps of near surface water equivalent hydrogen weh on mars that have intriguing implications for the global distribution of excess ice which occurs when the mass fraction of water ice exceeds the threshold amount needed to saturate the pore volume in normal soils we have refined the crossover technique of feldman et al 2011 by using spatial deconvolution and gaussian weighting to create the first globally self consistent map of weh at low latitudes our new maps indicate that weh exceeds 15 in several near equatorial regions such as arabia terra which has important implications for the types of hydrated minerals present at low latitudes at high latitudes we demonstrate that the disparate mons and phoenix robotic arm ra observations of near surface weh can be reconciled by a three layer model incorporating dry soil over fully saturated pore ice over pure excess ice such a three layer model can also potentially explain the strong anticorrelation of subsurface ice content and ice table depth observed at high latitudes at moderate latitudes we show that the distribution of recently formed impact craters is also consistent with our latest mons results as both the shallowest ice exposing crater and deepest non ice exposing crater at each impact site are in good agreement with our predictions of near surface weh overall we find that our new mapping is consistent with the widespread presence at mid to high martian latitudes of recently deposited shallow excess ice reservoirs that are not yet in equilibrium with the atmosphere

the mars water cycle at other epochs recent history of the polar caps and layered terrain abstract the martian polar caps and layered terrain presumably evolve by the deposition and removal of small amounts of water and dust each year the current attributes of the cap therefore represent the incremental transport during a single year as integrated over long periods of time we have investigated the role of condensation and sublimation of water ice in this process by examining the seasonal water cycle during the past 10 7 years in our model axial obliquity eccentricity and l s of perihelion vary according to dynamic models at each epoch we calculate the seasonal variations in temperature at the two poles keeping track of the seasonal co 2 cap and the summertime sublimation of water ice into the atmosphere net exchange of water between the two caps is calculated based on the difference in the summertime sublimation between the two caps or on the sublimation from the other cap if one is covered with co 2 frost all year despite the simple nature of our model and the tremendous complexity of the martian climate system our results suggest two significant conclusions 1 only a relatively small amount of the available water in the polar deposits actually cycles between the poles on orbital evolution time scales such that it is to some extent the same water molecules moving back and forth between the two caps 2 the difference in elevation between the two caps results in different seasonal behavior such that there is a net transport of water from south to north averaged over long time scales this transport would cause the north cap to grow at the expense of the south cap until the product of water sublimation rate and cap area was equal for the caps minimizing any subsequent net transport these results can help explain 1 the apparent inconsistency between the timescales inferred for layer formation and the much older crater retention age of the cap and 2 the difference in sizes of the two residual caps with the south cap being smaller than the north

volcanic terrain and the possible periglacial formation of excess ice at the mid latitudes of utopia planitia mars at the mid latitudes of utopia planitia up mars a suite of spatially associated landforms exhibit geomorphological traits that on earth would be consistent with periglacial processes and the possible freeze thaw cycling of water the suite comprises small sized polygonally patterned ground polygon junction and margin pits and scalloped rimless depressions typically the landforms incise a dark toned terrain that is thought to be ice rich here we investigate the dark toned terrain by using high resolution images from the hirise as well as near infrared spectral data from the omega and crism the terrain displays erosional characteristics consistent with a sedimentary nature and near infrared spectra characterised by a blue slope similar to that of weathered basaltic tephra we also describe volcanic terrain that is dark toned and periglacially modified in the kamchatka mountain range of eastern russia the terrain is characterised by weathered tephra inter bedded with snow ice wedge polygons and near surface excess ice the excess ice forms in the pore space of the tephra as the result of snow melt infiltration and subsequently in situ freezing based on this possible analogue we construct a three stage mechanism that explains the possible ice enrichment of a broad expanse of dark toned terrain at the mid latitudes of up 1 the dark toned terrain accumulates and forms via the regional deposition of sediments sourced from explosive volcanism 2 the volcanic sediments are blanketed by atmospherically precipitated h2o snow ice or an admixture of the two either concurrent with the volcanic events or between discrete events and 3 under the influence of high obliquity or explosive volcanism boundary conditions tolerant of thaw evolve and this in turn permits the migration cycling and eventual formation of excess ice in the volcanic sediments over time and through episodic iterations of this scenario excess ice forms to decametres of depth

maps of subsurface hydrogen from the high energy neutron detector mars odyssey after 55 days of mapping by the high energy neutron detector onboard mars odyssey we found deficits of high energy neutrons in the southern highlands and northern lowlands of mars these deficits indicate that hydrogen is concentrated in the subsurface modeling suggests that water ice rich layers that are tens of centimeters in thickness provide one possible fit to the data

recent high latitude icy mantle in the northern plains of mars characteristics and ages of emplacement 1 martian high latitude zones are covered with a smooth layered ice rich mantle containing characteristic polygonal patterns the mantle is especially uniform and homogeneous in the northern plains we performed a survey of decameter scale mantle textures and circular features including impact craters in the northern lowlands down to 50 n latitude strongly altered and mantled craters of impact and non impact origin form a population of subtle circular features below the mantle pits of non impact origin are numerous in some regions at lower latitudes impact craters superposed on the mantle are small and very sparse the inferred mean crater retention age of the mantle is 0 1 ma the spatial distribution of young craters suggests an age difference between the highest latitudes younger and some lower latitude regions older latitudinal trends in polygon textures agree with impact crater evidence for a latitudinal age progression of mantle properties

vertical distribution of hydrogen at high northern latitudes on mars the mars odyssey neutron spectrometer 1 neutron leakage currents measured using the mars odyssey neutron spectrometer are used to develop a two layer model of the distribution of hydrogen here parameterized as water equivalent hydrogen weh at high northern latitudes the weh abundance in the upper layer wup was found to range between 1 and about 5 the maximum value of the apparent thickness d of this upper layer peaks at about 60 latitude giving the appearance of zonal bands of enhanced d in both hemispheres this maximum is consistent with an expected transition from weh contained solely in hydrous minerals at lower latitudes to weh contained both in the forms of water ice and water of hydration at high latitudes a strong anti correlation between the weh concentration in the lower layer and apparent depth d at high latitudes is observed and may provide clues to the origin of these deposits

periglacial landforms at the phoenix landing site and the northern plains of mars 1 we examine potentially periglacial landforms in mars orbiter camera moc and high resolution imaging science experiment hirise images at the phoenix landing site and compare them with numerical models of permafrost processes to better understand the origin nature and history of the permafrost and the surface of the northern plains of mars small scale 3 6 m polygonal patterned ground is ubiquitous throughout the phoenix landing site and northern plains larger scale 20 25 m polygonal patterns and regularly spaced 20 35 m rubble piles localized collections of rocks and boulders are also common rubble piles were previously identified as basketball terrain in moc images the small polygon networks exhibit well developed and relatively undegraded morphology and they overlay all other landforms comparison of the small polygons with a numerical model shows that their size is consistent with a thermal contraction origin on current day mars and are likely active in addition the observed polygon size is consistent with a subsurface rheology of ice cemented soil on depth scales of about 10 m the size and morphology of the larger polygonal patterns and rubble piles indicate a past episode of polygon formation and rock sorting in thermal contraction polygons while the ice table was about twice as deep as it is presently the pervasive nature of small and large polygons and the extensive sorting of surface rocks indicates that widespread overturning of the surface layer to depths of many meters has occurred in the recent geologic past this periglacial reworking has had a significant influence on the landscape at the phoenix landing site and over the martian northern plains

widespread excess ice in arcadia planitia mars the distribution of subsurface water ice on mars is a key constraint on past climate while the volumetric concentration of buried ice pore filling versus excess provides information about the process that led to its deposition we investigate the subsurface of arcadia planitia by measuring the depth of terraces in simple impact craters and mapping a widespread subsurface reflection in radar sounding data assuming that the contrast in material strengths responsible for the terracing is the same dielectric interface that causes the radar reflection we can combine these data to estimate the dielectric constant of the overlying material we compare these results to a three component dielectric mixing model to constrain composition our results indicate a widespread decameters thick layer that is excess water ice 104 km3 in volume the accumulation and long term preservation of this ice is a challenge for current martian climate models

episodes of aqueous flooding and effusive volcanism associated with hrad vallis mars nasa planetary geology and geophysics program nasa planetary science division nnx13ar14g 80nssc17k0307 nasa earth and space sciences fellowship nessf program nnx16ap09h

modeling the development of martian sublimation thermokarst landforms abstract sublimation thermokarst landforms result from collapse of the surface when ice is lost from the subsurface on mars scalloped landforms with scales of decameters to kilometers are observed in the mid latitudes and considered likely thermokarst features we describe a landscape evolution model that couples diffusive mass movement and subsurface ice loss due to sublimation over periods of tens of thousands of mars years under conditions similar to the present the model produces scallop like features similar to those on the martian surface starting from much smaller initial disturbances the model also indicates crater expansion when impacts occur in surfaces underlain by excess ice to some depth with morphologies similar to observed landforms on the martian northern plains in order to produce these landforms by sublimation substantial quantities of excess ice are required at least comparable to the vertical extent of the landform and such ice must remain in adjacent terrain to support the non deflated surface we suggest that martian thermokarst features are consistent with formation by sublimation without melting and that significant thicknesses of very clean excess ice up to many tens of meters the depth of some scalloped depressions are locally present in the martian mid latitudes climate conditions leading to melting at significant depth are not required

transport of bottom water in the romanche fracture zone and the chain fracture zone abstract two moored arrays deployed in the romanche fracture zone and chain fracture zone in the equatorial atlantic ocean provide two year long time series of current and temperature in the lower north atlantic deep water and the antarctic bottom water total time averaged transport of antarctic bottom water potential temperature 1 9 c across the mid atlantic ridge amounts to 1 22 106 m3 s 1 eastward with a standard deviation of 0 25 106 m3 s 1 a time averaged transport of 0 36 0 23 106 m3 s 1 eastward is found for the lower north atlantic deep water in the 1 9 2 1 c temperature range but this may represent only a fraction of the total flow of this water mass across the ridge contributions of the romanche fracture zone and chain fracture zone to the antarctic bottom water transport are similar while the chain fracture zone has the greater share of lower north atlantic deep water transport semiannual and annual periods are detected in the transport time series and together expl

development of seasonal pack ice in the beaufort sea during the winter of 1991 1992 a view from below subsea sonars moored in the beaufort sea acquired a spatial section of draft across 941 km of sea ice during the winter of 1991 1992 these observations document the development of seasonal sea ice from an open sea surface in october to an average accumulation exceeding 2 5 m draft by early april initially level ice occupied 85 of the profile but continued ridging reduced this fraction to 50 in late winter three modes of level ice were tracked that of seasonal ice whose growth was initiated at freeze up and two others created during openings of the ice field in january and in march the growth of these modes can be closely matched by calculations based on a slab model of ice formation forced using surface meteorological data initially ridge keels were small and widely spaced by midwinter an exponential dependence of keel frequency on draft was obvious e folding scale 2 16 m and the frequency and mean draft of keels had stabilized the maximum keel draft was a modest 17 4 m the low incidence of deep keels at all times is a statistically significant departure from the exponential dependence valid at lesser drafts the truncation point of the exponential relation is related to the draft of the thinnest level ice present in late winter the formation of deeper keels from thick first year ice was apparently precluded by the presence of younger thinner ice which limited the force available for ridge building through calculation of the seaward transport of ice over the sonars the total production of ice in the coastal flaw lead during 1991 1992 was determined to be about 60 of earlier indirect estimates in general the observations revealed winter ice conditions significantly less severe than those found on the periphery of the polar pack only a few tens of kilometers to the north but more so than conditions in a marginal first year ice zone at the same latitude in davis strait

chemical information content of lunar thermal and epithermal neutrons simulations of equilibrium thermal and epithermal neutron flux spectra for the moon have been studied to determine their chemical information content most of this information resides in a single parameter the ratio of macroscopic absorption to energy loss cross sections although this parameter cannot specify the chemistry of lunar soils uniquely it provides an index that can be used to quantitatively separate anorthositic from mafic chemistries hydrogen abundances can best be derived from measurements of the epithermal neutron flux which is strongly related to its macroscopic energy loss cross section the ratio of thermal to epithermal neutron flux measured by lunar prospector is shown to agree quantitatively with simulations this agreement is used to show that the highlands terrane on the farside of the moon is anorthositic containing high percentages of plagioclase and possibly a range of mg suite minerals with a high mg mg fe atomic ratio our best estimate of the abundance of feo is 2 with an upper limit of 5

global permittivity mapping of the martian surface from sharad abstract sharad is a subsurface sounding radar aboard nasa s mars reconnaissance orbiter capable of detecting dielectric discontinuities in the subsurface caused by compositional and or structural changes echoes coming from the surface contain information on geometric properties at metre scale and on the permittivity of the upper layers of the martian crust a model has been developed to estimate the effect of surface roughness on echo power depending on statistical parameters such as rms height and topothesy such model is based on the assumption that topography can be characterized as a self affine fractal and its use allows the estimation of the dielectric properties of the first few metres of the martian soil a permittivity map of the surface of mars is obtained covering several large regions across the planet surface the most significant correspondence with geology is observed at the dichotomy boundary with high dielectric constant on the highlands side 7 to over 10 and lower on the lowlands side 3 to 7 other geological correlations are discussed

grid mapping the northern plains of mars a new overview of recent water and ice related landforms in acidalia planitia we used a grid mapping technique to analyze the distribution of thirteen water and ice related landforms in acidalia planitia as part of a joint effort to study the three main basins in the northern lowlands of mars i e acidalia utopia and arcadia planitiae the landforms were mapped at full ctx resolution along a 300 km wide strip from 20 n to 84 n we identified four landform assemblages 1 geologically recent polar cap massive ice which superposes the ldm la1 2 ice related landforms such as ldm textured terrain small scale polygons scalloped terrain large scale vff and gullies which have an overlapping distribution la2 3 surface features possibly related to water and subsurface sediment mobilization la3 km scale polygons lpm spm tpt and 4 irregularly shaped pits with raised rims on equator facing slopes pits are likely the result of an energetic release of volatiles h2o co2 ch4 rather than impact volcanism or wind related processes ldm occurs ubiquitously from 44 n to 78 n in acidalia planitia various observations suggest an origin of air fall deposition of ldm which contains less ice in the uppermost tens of meters in acidalia planitia than in arcadia and utopia planitiae however ldm may be thicker and more extended in the past in acidalia planitia the transition between ldm free terrain and ldm is situated further north than in utopia and arcadia planitiae suggesting different past and or present climatic conditions among the main basins in the northern lowlands

expanded secondary craters in the arcadia planitia region mars evidence for tens of myr old shallow subsurface ice abstract a range of observations indicates widespread subsurface ice throughout the mid and high latitudes of mars in the form of both pore filling and excess ice it is generally thought that this ice was recently emplaced and is not older than a hundred thousand to a few millions of years old based on ice stability and orbital induced climate change we analyze the distribution of subsurface ice in arcadia planitia located in the northern mid latitudes by mapping thermokarstically expanded secondary craters providing additional evidence for extensive excess ice down to fairly low latitudes less than 40 n we further infer the minimum age of this subsurface ice based on the ages of the four primary craters that are thought to be the source of a large portion of these secondaries which yields estimates on the order of tens of millions of years old much more ancient than anticipated this estimated ancient age suggests that ice can be preserved in the shallow subsurface for long periods of time at least in some parts of arcadia planitia where expanded secondary craters are especially abundant we estimate the amount of ice lost to sublimation during crater expansion based on measurements of expanded secondary craters in hirise digital terrain models the loss is equivalent to a volume of ice between 140 and 360 km 3 which would correspond to a global layer of 1 2 5 mm thick we further argue that much more ice at least 6000 km 3 is likely preserved beneath the un cratered regions of arcadia planitia since significant loss of this excess ice would have caused extensive terrain dissection and the removal of the expanded secondary craters both the loss of ice due to secondary crater expansion and the presence of this ice today have implications for the martian climate

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

preservation of midlatitude ice sheets on mars national science foundation nsf dge 1143953 nasa earth and space sciences fellowship nessf nnx16ap09h nasa mars data analysis program mdap award nnx15am62g

initiation and growth of martian ice lenses abstract water ice in the upper meters of the martian regolith is a major volatile reservoir although the geographic extent burial depth and thermal stability of this shallow ice are well understood its origin history and stratigraphy are not over the past decade a growing body of observational evidence has indicated that shallow ground ice exceeds the pore volume of its host soil over large regions of both martian hemispheres this is confounding given that 1 the physical theory that accurately predicts the location of ground ice also assumes that ice should be pore filling in the upper meter of regolith and 2 the phoenix spacecraft uncovered far more pore filling ice than excess ice at its landing site in the northern hemisphere the development of ice lenses by low temperature in situ segregation analogous to the processes that generate frost heave on earth has been hypothesized to explain shallow excess ice on mars we have developed a numerical model of ice lens initiation and growth in the martian environment and used it to test this hypothesis for the first time we carried out a large suite of numerical simulations in order to place quantitative constraints on the timing and location of ice lens initiation and on the magnitude of ice lens growth in a variety of host soils we find that ice lens initiation is a ubiquitous process in the martian high latitudes but the ultimate magnitude of lens growth or frost heave is sensitive to the properties of the host soil depending on the specific properties of martian soils in situ segregation may be a very slow process sufficient to explain the excess ice observed in the dodo goldilocks trench at the phoenix landing site but without regionally significant effects alternatively if clay sized particles or perchlorate salts are present in situ segregation may be a vigorous process that has significantly affected the stratigraphy of ground ice in the upper meter of regolith throughout the high latitudes

massive co2 ice deposits sequestered in the south polar layered deposits of mars shallow radar soundings from the mars reconnaissance orbiter reveal a buried deposit of carbon dioxide co2 ice within the south polar layered deposits of mars with a volume of 9500 to 12 500 cubic kilometers about 30 times that previously estimated for the south pole residual cap the deposit occurs within a stratigraphic unit that is uniquely marked by collapse features and other evidence of interior co2 volatile release if released into the atmosphere at times of high obliquity the co2 reservoir would increase the atmospheric mass by up to 80 leading to more frequent and intense dust storms and to more regions where liquid water could persist without boiling

on the orbital forcing of martian water and co2 cycles a general circulation model study with simplified volatile schemes 1 variations in the martian water and co2 cycles with changes in orbital and rotational parameters are examined using the geophysical fluid dynamics laboratory mars general circulation model the model allows for arbitrary specification of obliquity eccentricity and argument of perihelion as well as the position and thickness of surface ice exchange of co2 between the surface and atmosphere is modeled generating seasonal cycles of surface ice and surface pressure water is allowed to exchange between the surface and atmosphere cloud formation is treated and both cloud and vapor are transported by modeled winds and diffusion exchange of water and co2 with the subsurface is not allowed and radiative effects of water vapor and clouds are not treated the seasonal cycle of co2 is found to become more extreme at high obliquity as suggested by simple heat balance models maximum pressures remain largely the same but the minima decrease substantially as more co2 condenses in the more extensive polar night vapor and cloud abundances increase dramatically with obliquity the stable location for surface ice moves equatorward with increasing obliquity such that by 45 obliquity water ice is stable in the tropics only ice is not spatially uniform but rather found preferentially in regions of high thermal inertia or high topography eccentricity and argument of perihelion can provide a second order modification to the distribution of surface ice by altering the temporal distribution of insolation at the poles further model simulations reveal the robustness of these distributions for a variety of initial conditions our findings shed light on the nature of near surface ice rich deposits at midlatitudes and low latitudes on mars

characteristics of pack ice stress in the alaskan beaufort sea ice stresses in a multiyear floe were continuously monitored over 6 months in the fall winter spring of 1993 1994 stresses sensors were installed at sites near the edge and at the center of the floe which was located in the pack ice of the alaskan beaufort sea compressive stresses in the major principal stress component varied significantly among the measurement sites being of greater magnitude and exhibiting more high frequency variations at the edge than at the center of the floe maximum compressive stresses measured at a site 400 m from the edge of the floe ranged from 100 to 300 kpa tensile stresses maximum of 50 kpa and the minor principal stress component 50 kpa were relatively constant at all measurement sites a cross correlation analysis indicates that the minor principal stress is strongly correlated to changes in the ice temperature this result suggests that the minor principal stress component provides a good first order approximation of thermally induced stresses correlation between the major principal stress component and the ice temperature at the center site was also high but weakened near the edges of the floe where the ice motion induced stresses became more significant attempts to filter the major principal stress signal to separate the thermal and ice motion induced stresses were unsuccessful this result implies that the ice motion induced stresses distinguished by variations in magnitude of the order of hours also have a significant low frequency content similar to the thermal stresses these low frequency changes occur over a period of days seasonal variations in the characteristics of the stress were also evident and are likely to reflect the developing continuity of the pack as the winter season progresses

subsurface volatile content of martian double layer ejecta dle craters abstract excess ice is widespread throughout the martian mid latitudes particularly in arcadia planitia where double layer ejecta dle craters also tend to be abundant in this region we observe the presence of thermokarstically expanded secondary craters that likely form from impacts that destabilize a subsurface layer of excess ice which subsequently sublimates the presence of these expanded craters shows that excess ice is still preserved within the adjacent terrain here we focus on a 15 km dle crater that contains abundant superposed expanded craters in order to study the distribution of subsurface volatiles both at the time when the secondary craters formed and by extension remaining today to do this we measure the size distribution of the superposed expanded craters and use topographic data to calculate crater volumes as a proxy for the volumes of ice lost to sublimation during the expansion process the inner ejecta layer contains craters that appear to have undergone more expansion suggesting that excess ice was most abundant in that region however both of the ejecta layers had more expanded craters than the surrounding terrain we extrapolate that the total volume of ice remaining within the entire ejecta deposit is as much as 74 km 3 or more the variation in ice content between the ejecta layers could be the result of 1 volatile preservation from the formation of the dle crater 2 post impact deposition in the form of ice lenses or 3 preferential accumulation or preservation of subsequent snowfall we have ruled out 2 as the primary mode for ice deposition in this location based on inconsistencies with our observations though it may operate in concert with other processes although none of the existing dle formation hypotheses are completely consistent with our observations which may merit a new or modified mechanism we can conclude that dle craters contain a significant quantity of excess ice today

probing supraglacial debris on mars 1 sources thickness and stratigraphy abstract geomorphic and geophysical evidence supports a debris covered glacier origin for a suite of landforms at the mid latitudes of mars including lobate debris aprons lda lineated valley fill lvf and concentric crater fill ccf these large reservoirs of ice and their near surface structure provide a rich record for understanding the planet s climate and history of global volatile exchange over the past billion years lda lvf and ccf are also potential sites for future robotic and human missions but the accessibility of glacial ice for direct sampling and in situ resource utilization depends largely on the geotechnical properties of the surface debris supraglacial debris including its thickness grain sizes and density structure the physical properties of this supraglacial debris layer have been poorly constrained we use images of morphology digital elevation models thermal inertia data and radar sounding data to probe the near surface of lda lvf and ccf in deuteronilus mensae in order to place constraints on the sources grain sizes thickness and stratigraphy of supraglacial debris we find evidence for at least a two layer stratigraphy layered mantle consisting of atmospherically emplaced dust and ice superposes boulder rich sediment sourced by rockfalls glacially transported downslope high thermal inertia boulder rich termini and debris bands reminiscent of medial moraines are found throughout the study region supporting a rockfall origin for at least a fraction of the debris exposed at the surface this supraglacial debris layer would have thickened with time from sublimation of glacial ice and liberation of englacial sediment and dust at present the entire supraglacial debris package is a minimum of a few meters in thickness and is likely tens of meters in thickness in many locations possibly thinning regionally at lower latitudes and locally thinning toward the headwalls the lack of terracing or interior structures in craters formed within lda lvf and ccf and the absence of near surface reflectors in sharad radar data further suggest that no strong contrasts in permittivity or strength occur at the interface of the layers

the 3 5 mhz global reflectivity map of mars by marsis mars express implications for the current inventory of subsurface h2o abstract we extracted the surface echo power from 2 years of marsis measurements the retrieved values are calibrated to compensate for changes in the distance of the spacecraft to the surface and for the attenuation of the signal by the ionosphere the results are used to build the first global map of surface echo power at 3 5 mhz the surface echo power variations are primarily caused by kilometer scale surface roughness then we derive the values of dielectric constant of the shallow subsurface materials by normalizing the surface echo power map using a simulation of marsis signal from the mola topography as a result we obtain a map that characterizes the dielectric properties of the materials down to a few decameters below the surface dielectric properties vary with latitude with high values in mid latitudes belts 20 40 and lower values at both equatorial and high latitudes from the comparison of marsis reflectivity map to grs observations we conclude that the reflectivity decrease observed poleward of 50 60 corresponds to the onset of water ice occurrence within the regolith assuming homogenous ground composition and texture at the scale of the marsis resolution cell our inferred volume of ground water ice is of 106 km3 equivalent to a polar cap low reflectivity areas are also observed in equatorial regions from radar studies alone equatorial low dielectric constant values could have different interpretations but the correlation with grs hydrogen distribution rather points toward a water related explanation

mars nature and evolution of young latitude dependent water ice rich mantle 1 high resolution altimetry and imaging have revealed the presence of a meters thick sedimentary layer at middle to high northern and southern latitudes presently covering at least 23 of the planet the layer is interpreted to be water ice rich and to undergone degradation recently its activity very likely coincided with the last major obliquity excursion a few hundred thousand years ago the majority of the layer at higher latitudes however persisted for a much longer time in the late amazonian stratigraphic analysis suggests a complex history of successive episodes of deposition and removal repeated deposition and removal of the mantles are interpreted to be responsible for the unusual statistical properties of kilometer scale topography in the transitional mid latitude zones

possible precipitation of ice at low latitudes of mars during periods of high obliquity most of the old cratered highlands of mars are dissected by branching river valleys that appear to have been cut by running water1 2 yet liquid water is unstable everywhere on the martian surface in the equatorial region where most of the valleys are observed even ice is unstable3 4 it has been suggested therefore that mars had an early denser atmosphere with sufficient greenhouse warming to allow the existence of liquid water5 here we suggest instead that during periods of very high obliquities ice could accumulate at low latitudes as a result of sustained sublimation of ice from the poles and transport of the water vapour equatorwards at low latitudes the water vapour would saturate the atmosphere and condense onto the surface where it would accumulate until lower obliquities prevailed the mechanism is efficient only at the very high obliquities that occurred before formation of tharsis very early in the planet s history but limited equatorial ice accumulation could also have occurred at the highest obliquities during the rest of the planet s history partial melting of the ice could have provided runoff to form the channels or replenish the groundwater system

on the numerical simulation of the sea ice ridging process a two dimensional particle simulation model of the sea ice ridging process is developed in this model ridges are formed from a floating layer of rubble compressed between converging multiyear floes the energy consumed in ridge growth including dissipation is explicitly calculated a series of experiments are performed to establish the dependence of the energy consumed in ridging on the velocity of the multiyear floes and on the shape the friction coefficient and the inelasticity of the rubble blocks the experiments show that shape and friction between ice blocks are the most significant factors in determining the energy required to ridge ice in large scale sea ice modeling using a variable thickness approach it is convenient to parameterize total ridging work in terms of the increase of potential energy the results of the ridging simulations with block shaped rubble suggest that the total ridging work may be 4 5 times the increase in potential energy at the same time an analytical model of the ridging process is developed from classical mohr coulomb rankine theory for a cohesionless granular material the predictions of this model using values of porosity and the passive pressure coefficient derived from the ridge simulations are in fair agreement with the numerical experiments however several violations of the basic assumptions underlying the mohr coulomb rankine model are noted in the ridge simulations

modeling sublimation of ice exposed by new impacts in the martian mid latitudes abstract new impacts in the martian mid latitudes have exposed near surface ice this ice is observed to slowly fade over timescales of months in the present martian climate exposed surface ice is unstable during summer months in the mid latitudes and will sublimate we model the sublimation of ice at five new impact sites and examine the implications of its persistence even with generally conservative assumptions for most reasonable choices of parameters it is likely that over a millimeter of sublimation occurred in the period during which the ice was observed to fade the persistence of visible ice through such sublimation suggests that the ice is relatively pure rather than pore filling such ice could be analogous to the nearly pure ice observed by the phoenix lander in the dodo goldilocks trench and suggests that the high ice contents reported by the mars odyssey gamma ray spectrometer at high latitudes extend to the mid latitudes our observations are consistent with a model of the martian ice table in which a layer with high volumetric ice content overlies pore filling ice although other structures are possible

apparent thermal inertia and the surface heterogeneity of mars abstract thermal inertia derivation techniques generally assume that surface properties are uniform at horizontal scales below the footprint of the observing instrument and to depths of several decimeters consequently surfaces with horizontal or vertical heterogeneity may yield apparent thermal inertia which varies with time of day and season to investigate these temporal variations we processed three mars years of mars global surveyor thermal emission spectrometer observations and produced global nightside and dayside seasonal maps of apparent thermal inertia these maps show broad regions with diurnal and seasonal differences up to 200 j m 2 k 1 s 1 2 at mid latitudes 60 s to 60 n and 600 j m 2 k 1 s 1 2 or greater in the polar regions we compared the seasonal mapping results with modeled apparent thermal inertia and created new maps of surface heterogeneity at 5 resolution delineating regions that have thermal characteristics consistent with horizontal mixtures or layers of two materials the thermal behavior of most regions on mars appears to be dominated by layering with upper layers of higher thermal inertia e g duricrusts or desert pavements over fines prevailing in mid latitudes and upper layers of lower thermal inertia e g dust covered rock soils with an ice table at shallow depths prevailing in polar regions less common are regions dominated by horizontal mixtures such as those containing differing proportions of rocks sand dust and duricrust or surfaces with divergent local slopes other regions show thermal behavior that is more complex and not well represented by two component surface models these results have important implications for mars surface geology climate modeling landing site selection and other endeavors that employ thermal inertia as a tool for characterizing surface properties

hirise observations of new impact craters exposing martian ground ice twenty small new impact craters or clusters have been observed to excavate bright material inferred to be ice at mid latitudes and high latitudes on mars in the northern hemisphere the craters are widely distributed geographically and occur at latitudes as low as 39 n stability modeling suggests that this ice distribution requires a long term average atmospheric water vapor content around 25 precipitable micrometers more than double the present value which is consistent with the expected effect of recent orbital variations alternatively near surface humidity could be higher than expected for current column abundances if water vapor is not well mixed with atmospheric co2 or the vapor pressure at the ice table could be lower due to salts ice in and around the craters remains visibly bright for months to years indicating that it is clean ice rather than ice cemented regolith although some clean ice may be produced by the impact process it is likely that the original ground ice was excess ice exceeding dry soil pore space in many cases observations of the craters suggest small scale heterogeneities in this excess ice the origin of such ice is uncertain ice lens formation by migration of thin films of liquid is most consistent with local heterogeneity in ice content and common surface boulders but in some cases nearby thermokarst landforms suggest large amounts of excess ice that may be best explained by a degraded ice sheet

dynamic and isotopic evolution of ice reservoirs on mars abstract the layered polar caps of mars have long been thought to be related to variations in orbit and axial tilt we dynamically link mars s past climate variations with the stratigraphy and isotopic composition of its ice by modeling the exchange of h2o and hdo among three reservoirs the model shows that the interplay among equatorial mid latitude and north polar layered deposits npld induces significant isotopic changes in the cap the diffusive properties of the sublimation lags and dust content in our model result in a cap size consistent with current mars the layer thicknesses are mostly controlled by obliquity variations but the precession period of 50 kyr dominates the variations in the isotopic composition during epochs of relatively low and nearly constant obliquity such as at present isotopic sampling of the top 100 m may reveal climate oscillations unseen in the layer thicknesses and would thus probe recent precession driven climate cycles

mars odyssey neutron data 2 search for buried excess water ice deposits at nonpolar latitudes on mars 1 global maps of hydrogen abundance near the surface of mars interpreted as the mass percent of water equivalent hydrogen weh have been generated from measurements of neutron leakage fluxes from mars although these data provide an unambiguous indicator of the presence of weh quantitative details of its magnitude and burial depth depend on the model of the host regolith that is used to interpret the data previous models assumed a spatially uniform surface cover layer having a one to two mass percent of weh and thickness d covering a semi infinite ice rich deposit these assumptions allowed the derivation of the relative proportions of ice and regolith in the lower layer which had been used to create global maps of weh in the near surface in this paper we develop a new method that determines from the mars odyssey neutron spectrometer mons data a self consistent model of the weh content of both the upper and lower layers as well as the thickness d of the upper layer the results of our model suggest that large areas at nonpolar latitudes may contain water ice deposits that have abundances that are larger than can be held by normal pore volumes these deposits are buried less than about 1 m below the surface and may represent buried water ice or high concentrations of hydrous minerals intriguingly the most definitive mons evidence at intermediate latitudes for excess ground ice corresponds to a region of arcadia planitia within which high resolution imaging science experiment hirise has observed fresh icy craters

former extent of glacier like forms on mars abstract mars mid latitude glacier like forms glfs have undergone substantial mass loss and recession since a hypothesised last martian glacial maximum lmgm stand to date there is a lack of knowledge of the nature and timing of the lmgm the subsequent mass loss and whether this mass loss has been spatially variable here we present the results of a population scale inventory of recessional glfs derived from analysis of 1293 glfs 3 identified within context camera ctx imagery to assess the distribution and controls on glf recession a total of 436 glfs were identified showing strong evidence of recession 197 in the northern hemisphere and 239 in the southern hemisphere relative to their parent populations recessional glfs are over represented in the low latitude belts between 25 and 40 and in areas of high relief suggesting that these zones exert some control over glf sensitivity and response to forcing this analysis is complemented by the reconstruction of the maximum extent and morphology of a specific glf for which high resolution imaging science experiment hirise derived digital elevation data are available using nye s nye j f 1951 proc roy soc lond ser a mat phys sci 207 554 572 perfect plastic approximation of ice flow applied to multiple flow lines under an optimum yield strength of 22 kpa we calculate that the reconstructed glf has lost an area of 6 86 km 2 with a corresponding volume loss of 0 31 km 3 since the lmgm assuming the loss reconstructed at this glf occurred at all mid latitude glfs yields a total planetary ice loss from mars glfs of 135 km 3 similar to the current ice volume in the european alps on earth

history and anatomy of subsurface ice on mars abstract ice buried beneath a thin layer of soil has been revealed by neutron spectroscopy and explored by the phoenix mars lander it has also been exposed by recent impacts this subsurface ice is thought to lose and gain volume in response to orbital variations milankovitch cycles we use a powerful numerical model to follow the growth and retreat of near surface ice as a result of regolith atmosphere exchange continuously over millions of years if a thick layer of almost pure ice has been deposited recently it has not yet reached equilibrium with the atmospheric water vapor and may still remain as far equatorward as 43 n where ice has been revealed by recent impacts a potentially observable consequence is present day humidity output from the still retreating ice we also demonstrate that in a sublimation environment subsurface pore ice can accumulate in two ways the first mode widely known is the progressive filling of pores by ice over a range of depths the second mode occurs on top of an already impermeable ice layer subsequent ice accumulates in the form of pasted on horizontal layers such that beneath the ice table the pores are completely full with ice most or all of the pore ice on mars today may be of the second type at the phoenix landing site where such a layer is also expected to exist above an underlying ice sheet it may be extremely thin due to exceptionally small variations in ice stability over time

distribution of mid latitude ground ice on mars from new impact craters new impact craters at five sites in the martian mid latitudes excavated material from depths of decimeters that has a brightness and color indicative of water ice near infrared spectra of the largest example confirm this composition and repeated imaging showed fading over several months as expected for sublimating ice thermal models of one site show that millimeters of sublimation occurred during this fading period indicating clean ice rather than ice in soil pores our derived ice table depths are consistent with models using higher long term average atmospheric water vapor content than present values craters at most of these sites may have excavated completely through this clean ice probing the ice table to previously unsampled depths of meters and revealing substantial heterogeneity in the vertical distribution of the ice itself

amazonian northern mid latitude glaciation on mars a proposed climate scenario recent geological observations in the northern mid latitudes of mars show evidence for past glacial activity during the late amazonian similar to the integrated glacial landsystems in the dry valleys of antarctica the large accumulation of ice many hundreds of meters required to create the observed glacial deposits points to significant atmospheric precipitation snow and ice accumulation and glacial flow in order to understand the climate scenario required for these conditions we used the lmd laboratoire de meteorologie dynamique mars gcm general circulation model which is able to reproduce the present day water cycle and to predict past deposition of ice consistent with geological observations in many cases prior to this analysis however significant mid latitude glaciation had not been simulated by the model run under a range of parameters in this analysis we studied the response of the gcm to a wider range of orbital configurations and water ice reservoirs and show that during periods of moderate obliquity 25 35 and high dust opacity sdust 1 5 2 5 broad scale glaciation in the northern mid latitudes occurs if water ice deposited on the flanks of the tharsis volcanoes at higher obliquity is available for sublimation we find that high dust contents of the atmosphere increase its water vapor holding capacity thereby moving the saturation region to the northern mid latitudes precipitation events are then controlled by topographic forcing of stationary planetary waves and transient weather systems producing surface ice distribution and amounts that are consistent with the geological record ice accumulation rates of 10 mm yr

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

temperature response of mars to milankovitch cycles 1 on mars annual mean surface temperature near 60 latitude varies predominately with precession and is not closely related to annual mean insolation based on the last few million years of orbital history the precession cycle dominates in a narrow latitude range 54 65 in which the margins of the two ice rich permafrost layers in each hemisphere happen to lie while mean annual temperature at other latitudes is controlled by the obliquity cycle the phenomenon already exists on an airless uniform body in mars orbit where this latitude range shifts to 62 74 on both hemispheres and is closely related to temperature amplitude dependent reradiation into space

the distribution and behavior of martian ground ice during past and present epochs mars undergoes significant oscillations in its orbit which will have a pronounced effect on its climate and in particular on the behavior of subsurface water ice we explore and map the behavior of ice in the martian near surface regolith over the past 1 m y using a diffusion and condensation model presented in an earlier paper with two primary modifications to include orbitally induced variations in insolation and atmospheric water abundance we find that the past behavior of ground ice differs significantly from that at the present epoch primarily the result of high amplitude oscillations in obliquity presently 25 in midlatitude and equatorial regions ground ice will condense from atmospheric water during times of higher obliquity filling the top few meters of the regolith with significant amounts of ice at an obliquity of 32 ground ice becomes stable globally during times of lower obliquity ground ice will sublime and diffuse back into the atmosphere dessicating the regolith to a depth of about 1 to 2 m equatorward of 60 to 70 latitude in the high latitude regions these oscillations are considerably subdued below this depth of cyclic saturation and dessication a long term stability of ice exists in some geographic regions we present a map of the distribution of ice expected at the present epoch cyclic exchange of water between the global regolith and polar regions will have significant implications for surface geology and the polar layered deposits

recent ice rich deposits formed at high latitudes on mars by sublimation of unstable equatorial ice during low obliquity observations from the gamma ray spectrometer instrument suite on the mars odyssey spacecraft have been interpreted as indicating the presence of vast reservoirs of near surface ice in high latitudes of both martian hemispheres1 2 3 4 5 ice concentrations are estimated to range from 70 per cent at 60 latitude to 100 per cent near the poles possibly overlain by a few centimetres of ice free material in most places4 this result is supported by morphological evidence of metres thick layered deposits that are rich in water ice6 7 8 9 and periglacial like features10 11 found only at high latitudes diffusive exchange of water between the pore space of the regolith and the atmosphere has been proposed to explain this distribution12 but such a degree of concentration is difficult to accommodate with such processes9 13 14 alternatively there are suggestions that ice rich deposits form by transport of ice from polar reservoirs and direct redeposition in high latitudes during periods of higher obliquity9 13 but these results have been difficult to reproduce with other models here we propose instead that during periods of low obliquity less than 25 high latitude ice deposits form in both hemispheres by direct deposition of ice as a result of sublimation from an equatorial ice reservoir that formed earlier during a prolonged high obliquity excursion using the ice accumulation rates estimated from global climate model simulations we show that over the past ten million years large variations of mars obliquity have allowed the formation of such metres thick sedimentary layered deposits in high latitude and polar regions

recent ice ages on mars the role of radiatively active clouds and cloud microphysics global climate models gcms have been successfully employed to explain the origin of many glacial deposits on mars however the latitude dependent mantle ldm a dust ice mantling deposit that is thought to represent a recent ice age remains poorly explained by gcms we reexamine this question by considering the effect of radiatively active water ice clouds racs and cloud microphysics we find that when obliquity is set to 35 as often occurred in the past 2 million years warming of the atmosphere and polar caps by clouds modifies the water cycle and leads to the formation of a several centimeter thick ice mantle poleward of 30 in each hemisphere during winter this mantle can be preserved over the summer if increased atmospheric dust content obscures the surface and provides dust nuclei to low altitude clouds we outline a scenario for its deposition and preservation that compares favorably with the characteristics of the ldm

kilometer scale roughness of mars results from mola data analysis the mars orbiter laser altimeter mola data are used to characterize the kilometer scale surface roughness of mars the median absolute value of the differential slope at a given baseline is proposed as a data derived measure of the surface roughness at this scale study of the scale dependence of roughness for the smoothest terrains gives an independent estimate of 20 cm for mola ranging accuracy the baseline lengths from 0 6 to 20 km are used and kilometer scale roughness is mapped for the entire surface the maps show that different geological units have distinctive roughness characteristics scale dependence of roughness for a number of geological units is presented and discussed the southern polar cap is rougher than the northern at kilometer and subkilometer scale which suggests differences in the sublimation condensation balance the vastitas borealis formation has a distinctive 3 km scale background surface topography which suggests a nonvolcanic origin for its upper layer young volcanic plains in amazonis planitia and the eastern part of elysium planitia are very similar to each other in their roughness characteristics and differ from other volcanic plains on mars which suggests a distinctive eruption style there are systematic latitudinal variations of roughness in both the southern highlands and the northern lowlands terrains at high latitude are smoother at short baselines the characteristic vertical scale related to this difference is several meters processes that could be responsible for formation of this trend include creep of ice rich near surface material at high latitudes treatment of the surface with repetitive deposition and sublimation of seasonal frost climate controlled deposition and or cementation of dust at high latitudes and repetitive sublimation and accumulation of subsurface ice at low latitudes with climate variations all mechanisms of origin could operate more effectively under different climate conditions relevant morphological observations favor mechanisms involving deposition of smooth blankets at high latitudes

mars the regolith atmosphere cap system and climate change abstract a new model for predicting the behavior of the martian regolith atmosphere cap co 2 regime and describing its role in climate change is derived the model describes the time temperature histories of 90 regolith chunks on a latitude depth grid accounting for co 2 exchange by means of laboratory derived expressions relating temperature co 2 pressure p co 2 and adsorbed co 2 mass co 2 polar cap formation and sublimation is accounted for subject to the constraint of constant total co 2 in the atmosphere regolith cap system the influence of differences in regolith adsorption laws for basalt and clay and the influence of variations in regolith depth with latitude regolith thermal diffusivity and total exchangeable co 2 inventory on predicted variations in atmospheric pressure and cap mass are examined the following results are indicated 1 the atmosphere acts as a low capacity conduit through which flows between 10 and 100 times the current atmospheric mass of co 2 between two reservoirs a regolith ocean of adsorbed co 2 and a polar cap cryosphere 2 exchange between these reservoirs is driven by variations of obliquity with the polar cap the dominant co 2 sink at low and the regolith dominating at high atmospheric pressure ranges between 0 1 low and 15 mbar high pressures of up to 25 mbar could result from pre tharsis variations pressure up to 40 mbarare achieved only in models which also call for a huge quasi permanent present co 2 cap which is not apparent 3 at high the atmospheric pressure is buffered by the regolith and satisfies adsorption equilibrium for the 90 chunks as well as conservation of co 2 mass at low a potetially large co 2 cap appears and the atmospheric pressure is buffered by the cap not the regolith 4 the periodic reservoir flushing can account for the observation of simultaneous nonenrichment of 18 o and enrichment of 13 n 5 mars climate history may be divided into three parts a post tharsis formation history as described above b pre tharsis formation with qualitatively similar processes but larger oscillations between reservoirs and larger atmospheric pressure and cap mass variation and c the very early period of channel formation 6 the nature of the response of the three part regolith atmosphere polar cap martian climate system to surface insolation variations may be analogous to that of earth s ocean atmosphere cryosphere system

compositions of subsurface ices at the mars phoenix landing site 1 nasa s phoenix lander uncovered two types of ice at its 2008 landing site on the northern plains of mars a brighter slab like ice that broke during robotic arm operations and a darker icy deposit spectra from the phoenix surface stereo imager ssi are used to demonstrate that the brighter material consists of nearly pure water ice which probably formed by migration and freezing of liquid water the darker icy material consists of 30 20 wt ice with the remainder composed of fine grained soil indicating that it probably formed as pore ice these two types of ice represent two different emplacement mechanisms and periods of deposition

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

ice rich periglacial vs icy glacial depressions in the argyre region mars a proposed cold climate dichotomy of landforms on mars so called scalloped depressions are widely observed in utopia planitia up and malea planum mp typically they are rimless metres to decametres deep incised sharply tiered inwardly polygonised and sometimes pitted the depressions seemingly incise terrain that is icy and possibly thermokarstic i e produced by the thermal destabilisation of the icy terrain agewise the depressions are thought to be relatively youthful originating in the late amazonian epoch here we report the presence of similar depressions in the argyre region ar 30 60 s 290 355 e more importantly we separate and differentiate these landforms into two groups ice rich periglacial depressions type 1 and icy glacial depressions type 2a c this differentiation is presented to the mars community for the first time based on a suite of morphological and geological characteristics synonymous with ice complexes in the lena peninsula eastern russia and the tuktoyaktuk coastlands northwest territories canada we propose that the type 1 depressions are ice rich periglacial basins that have undergone volatile depletion largely by sublimation and as the result of thermal destabilisation in keeping with the terms and associated definitions derived of terrestrial periglacial geomorphology ice rich refers to permanently frozen ground in which ice lenses or segregation ice collectively referenced as excess ice have formed we suggest that the depressions are the product of a multi step cold climate geochronology 1 atmospheric precipitation and surface accumulation of an icy mantle during recent high obliquities 2 regional or local triple point conditions and thaw evaporation of the mantle either by exogenic forcing i e obliquity driven rises of aerial and sub aerial temperatures or endogenic forcing i e along argyre impact related basement structures 3 meltwater migration into the regolith at least to the full depth of the depressions 4 freeze thaw cycling and the formation of excess ice 5 sublimation of the excess ice and depression formation as high obliquity dissipates and near surface ice becomes unstable the type 2 depressions exhibit characteristics suggestive of supra glacial dead ice basins and snow ice suncups observed in high alpine landscapes on earth e g the swiss alps and the himalayas like the type 1 depressions the type 2 depressions could be the work of sublimation however the latter differ from the former in that they seem to develop within a glacial like icy mantle that blankets the surface rather than within an ice rich and periglacially revised regolith at near the surface interestingly the type 2 depressions overlie the type 1 depressions at some locations if the periglacial glacial morphological and stratigraphical dichotomy of depressions is valid then this points to recent glaciation at some locations within the ar being precursed by at least one episode of periglaciation this also suggests that periglaciation has a deeper history in the region than has been thought hitherto moreover if the hypothesised differences amongst the argyre based depressions are mirrored in utopia planitia and malea planum then perhaps this periglacial glacial dichotomy and its associated geochronology are as relevant to understanding late period landscape evolution in these two regions as it is in the ar

h layering in the top meter of mars we explore the capability of a method of mapping the depth distribution of a hydrogen rich layer in the top meter of mars from the neutron currents measured by the mars odyssey neutron spectrometer assuming the soil can be modeled by two layers of known composition having different hydrogen contents simulations allow an inversion of the neutron data into knowledge of depth and hydrogen content of the lower layer the determination of these variables is sensitive to the hypothesis of chemical composition of the soil we quantify this contribution to the uncertainty in the method first in terms of individual chemical elements and then in terms of macroscopic absorption cross sections to minimize this source of error an average composition was inferred from mars exploration rover data possible compositions having a wide range of macroscopic absorption cross sections were used to evaluate the uncertainty associated with our calculations we finally compare our results to ice table depth estimates predicted by two published theoretical models at locations where the composition is relatively well known the fit is excellent in the southern high latitudes but questionable in the northern high latitudes possible explanations of these differences include the high geographical variations of the neutron currents relative to the spatial width of the response function of the instrument and the overly simple model we of necessity used for surface layering

ground ice at the phoenix landing site stability state and origin 1 a primary objective of the phoenix mission was to examine the characteristics of high latitude ground ice on mars we report observations of ground ice its depth distribution and stability characteristics and examine its origins and history high latitude ground ice was explored through a dozen trench complexes and landing thruster pits over a range of polygon morphological provinces shallow ground ice was found to be abundant under a layer of relatively loose ice free soil with a mean depth of 4 6 cm which varied by more than 10x from trench to trench these variations can be attributed mainly to slope effects and thermal inertia variations in the overburden soil affecting ground temperatures the presence of ice at this depth is consistent with vapor diffusive equilibrium with respect to a mean atmospheric water content of 3 4 1019 m 3 consistent with the present day climate significant ice heterogeneity was observed with two major forms ice cemented soil and relatively pure light toned ice ice cemented soils which comprised about 90 of the icy material exposed by trenching are best explained as vapor deposited pore ice in a matrix supported porous soil light toned ice deposits represent a minority of the subsurface and are thought to consist of relatively thin near surface deposits the origin of these relatively pure ice deposits appears most consistent with the formation of excess ice by soil ice segregation such as would occur by thin film migration and the formation of ice lenses needle ice or similar ice structures

the periglacial landscape at the phoenix landing site 1 the mars scout mission phoenix landed in the northern high latitudes of mars in an area thought to be dominated by subsurface ground ice and has provided a unique detailed examination of periglacial morphology and topography that is not visible from orbit the landing site and surrounding terrain is dominated by polygonal patterned ground typical of the martian northern plains the polygons exhibit a gentle u shaped trough and rounded mound topography with an average trough depth of 17 cm and an average surface slopes of only 6 7 polygons an average 4 3 m across form a pattern superimposed on all other geologic landforms including larger 20 25 m polygons and kilometer long linear ridges the polygon morphology and the predominance of subsurface ice cemented soil are consistent with the formation of subsurface sand wedges in a permanently frozen arid climate small scale soil furrows and cracks into the ice cemented soil indicate that the thermal contraction process responsible for the formation of the polygons is active today rocks appear to be sorted within the polygon troughs indicating a process of cryoturbation within the permanently frozen polygons the complexity of the patterns crosscutting relations and rock distributions indicate advanced maturity of the polygon networks and shifting crack patterns possibly facilitated by crack and wedge annealing during times of low obliquity

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

four stages of pressure ridging the pressure ridging process is simulated using a two dimensional particle model blocks are broken from an intact sheet of relatively thin lead ice pushed against a thick multiyear floe at a constant speed the blocks of ice rubble accumulate to form the ridge sail and keel during the simulations the energy consumed in ridge growth including dissipation is explicitly calculated on the basis of the results of simulations performed with the model the ridging process can be divided into four distinct stages the first stage begins with an intact sheet of lead ice impacting a floe and ends when the sail reaches its maximum height in the second stage the ridge keel deepens and widens the stage ends when the maximum keel draft is reached in the third stage the direction of growth is leadward creating a rubble field of more or less uniform thickness the third stage ends when the supply of thin ice is exhausted in the fourth stage the rubble field is compressed between converging floes the results of simulations establish the dependence of ridging energetics in the first and second stages on the thickness of the ice sheet and the amount of ice pushed into the ridge the average profiles of the simulated ridges delineate the growth process in the first second and third stages the energetics and profiles of the fourth stage were described by hopkins et al 1991 lead ice extents of up to 1300 m are pushed into ridges to determine maximum sail heights keel drafts and ridging forces

global distribution of neutrons from mars results from mars odyssey global distributions of thermal epithermal and fast neutron fluxes have been mapped during late southern summer northern winter using the mars odyssey neutron spectrometer these fluxes are selectively sensitive to the vertical and lateral spatial distributions of h and co 2 in the uppermost meter of the martian surface poleward of 60 latitude is terrain rich in hydrogen probably h 2 o ice buried beneath tens of centimeter thick hydrogen poor soil the central portion of the north polar cap is covered by a thick co 2 layer as is the residual south polar cap portions of the low to middle latitudes indicate subsurface deposits of chemically and or physically bound h 2 o and or oh