mars near infrared spectral reflectance of surface regions and compositional implications reflectance spectra 0 65 2 50 m are presented for 11 martian areas the spectral resolution is 1 and the spatial resolution is 1000 2000 km these are the first high quality spectrophotometric data at these wavelengths for regions on the surface spectral features previously observed are confirmed and better defined and a number of important spectral properties are characterized for the first time the spectra show water ice absorptions in the 1 5 and 2 0 m regions which if due to surface frost would imply the presence of 1 to 2 mg cm2 h2o however other studies have shown that the presence of an unprotected surface frost in late morning is unlikely water ice is stable at night even at the equator and might persist until late morning when the air is well undersaturated if it is intimately dispersed in weathering products especially if clays are present the dark region spectra indicate about 4 times less water ice than seen in bright regions since some bright material is present in dark regions there may be no water ice associated with the dark materials themselves this tends to confirm that weathering products thought to be more abundant in bright regions are involved in the mechanism that allows temporary persistance of unstable water ice the presence of weak 2 3 m features in many of the spectra are consistent with the presence of hydroxylated magnesium rich minerals such as sheet silicates serpentine talc and magnesian smectites or amphiboles anthophyllite the apparent absence of a 2 2 m absorption implies that montmorillonite may not be a major component of the martian regolith many of the spectra also show an apparent absorption at 1 9 m in the wing of the 2 0 m martian atmospheric co2 absorption which would indicate bound molecular water observed dark regions have distinctive near infrared spectral shapes previously not well determined which are characteristic of thin semi transparent alteration coatings overlying dark unaltered rock previously observed ferrous and ferric iron absorptions in the 1 m region are better defined by these new data clinopyroxene augite is definitely present but olivine is not spectrally apparent

an observational search for carbonates on mars a search for carbonates and other salts exposed on the surface of mars was undertaken by observing areas of the surface in the 2 6 m to 4 2 m spectral region using the university of hawaii 2 2 m telescope at the mauna kea observatory hawaii observations of four mars areas syrtis major hellas arabia and an area northeast of hellas were made on the night of september 19 1986 the reflectance spectra for two partially overlapping areas show a weak absorption band in the 3 8 m to 3 9 m region which is in the spectral region where carbonate absorptions appear 3 8 m to 4 0 m the mars area of overlap contains syrtis planum the spectral feature from about 3 76 m to 3 95 m is clearly shortward of and broader than the calcium carbonate band about 3 9 m to 4 0 m and is at a slightly shorter wavelength position than magnesium carbonate magnesite bands about 3 8 m to 3 96 m as measured in this study positive identification of this band cannot be made by us at this time measurements for two other mars areas show no evidence of carbonate or other bands if the band is due to absorptions in the mars surface material spectrum and if it is due to carbonates then the results imply about 3 to 5 wt of a carbonate such as magnesite on average in the upper few millimeters of the mars surface material over the two areas where the weak spectral feature appears we can place an upper limit of 3 to 5 wt calcium carbonate and about 5 wt magnesite for all areas observed the interpretations are based on laboratory measurements of the reflectance spectra of calcite and magnesite and their mixtures with palagonite effects of thermal emission on the detection of carbonates were also explored for a wide range of temperatures thermal effects are not sufficient to mask the presence of calcite in the 3 to 5 wt range theoretical reasoning strongly supporting the presence of carbonates as a component of the mars surface is reviewed these and earlier observations do not rule out carbonates below the surface in other locations as small outcrops or in concentrations of less than 3 to 5 of the areas observed

detection of carbonates in martian weathering profiles noachian surfaces on mars exhibit vertical assemblages of weathering horizons termed as weathering profiles this indicates that surface water caused alteration of the rocks that required a different warmer climate than today evidence of this early martian climate with co 2 vapor as the main component causing greenhouse warming has been challenged by the lack of carbonate in these profiles here we report the analysis of compact reconnaissance imaging spectrometer for mars l detector data leading to the detections of carbonates using a spectral signature exclusively attributed to them the carbonates are collocated with hydroxylated minerals in weathering profiles over the martian surface the origin of co 2 for the formation of carbonates could be the atmosphere the widespread distribution of weathering profiles with carbonates over the surface of the planet suggest global interactions between fluids containing carbonate bicarbonate ions with the surface of mars in the presence of atmospheric water until around 3 7 billion years ago plain language summary the oldest surface of mars witnessed an impact of dense and humid atmosphere leading to the formation of hydrated minerals the analysis of remote sensing data allows identifying carbonates mixed with the hydrated minerals these associations of carbonates and hydrated minerals are widespread on the surface of the planet this indicates a planetary scale process of formation involving the presence of fluids containing inorganic carbon this finding allows a better understanding of the environment of mars during the period suspected to be the most likely to have host habitable environment on the planet

dual frequency interferometric sar observations of a tropical rain forest repeat pass interferometric radar observations of tropical rain forest collected by the shuttle imaging radar c sir c in the state of rondonia brazil reveal signal coherence is destroyed at c band 5 6 cm in the forest whereas l band 24 cm radar signals remain strongly coherent over the entire landscape at l band the rms difference in inferred topographic height between the forest and adjacent clearings is 5 m equivalent to the height noise atmospheric delays are large however forming kilometer sized anomalies with a 1 2 cm rms one way radar interferometric studies of the humid tropics must therefore be conducted at long radar wavelengths with kilometric baselines or with two antennas operating simultaneously

estimated optical constants of the tagish lake meteorite the visible near infrared and mid infrared 0 325 m real and imaginary indices of refraction are derived from reflectance measurements of the tagish lake meteorite these are compared to some real and imaginary indices of refraction of the individual minerals composing the tagish lake meteorite from this comparison it is clear that the imaginary indices of several individual minerals contribute to the estimated imaginary index of this meteorite

detectability of martian carbonates from orbit using thermal neutrons numerical simulations of martian neutron leakage flux spectra are made in order to explore the detectability of magnesium and calcium carbonate deposits using neutron spectroscopic techniques from orbit the primary signature of such deposits is found to be an enhanced thermal amplitude although this enhancement is weakened by 1 partial burial beneath an aeolian regolith blanket 2 admixture with regolith on a microscopic centimeter or macroscopic tens of centimeters scale and 3 reduction in the areal size of the deposit near surface stratigraphies of carbonates hypothesized by some authors as possible on mars are still detectable by simple neutron sensors from orbit however the large variations in the magnitude of the thermal neutron enhancements caused by different carbonate deposit configurations found in this study require a combined gamma ray and neutron analysis for their unique specification

spectral evidence for the mineralogy of high albedo soils and dust on mars because of the lack of direct mineralogic data available for mars spectral remote sensing techniques and in particular earth based reflectance spectroscopy remain the primary source of this information presented here are laboratory observations which further constrain the mineralogy and origin of the high albedo soils and dust earth based observations show the reflectance spectra of classical bright regions to be fairly uniform with a strong fe3 o2 charge transfer absorption edge extending from the near uv through the visible this absorption is relatively smooth unlike those observed for crystalline ferric oxides which have superimposed fe3 crystal field bands dilution of ferric oxide with a spectrally more neutral medium montmorillonite weakens the charge transfer and crystal field absorptions together and does not serve to make the ferric oxide spectrum more mars like smoother nontronite ferric iron bearing smectite clay was also investigated for spectral agreement with telescopic observations pure nontronite has fe3 absorptions analogous to but different from ferric oxides as in the previous case the absorptions are very distinct and inappropriate for mars admixture of neither montmorillonite nor ferric oxide serves to improve the nontronite spectrum the conclusion is that nontronite is not a major component of martian soils although the presence of other iron poor clays cannot be totally excluded based on currently available observational data the best spectral analogs known for high albedo soil and dust are a specific type of palagonite from hawaii x ray amorphous weathering products of mafic volcanic glass the indication is therefore that ferric iron on mars is likely to occur in poorly defined crystallo graphic sites such as found in these amorphous materials these materials form slowly under semiarid conditions at ambient temperature even low temperature hydrothermal alteration of glass might provide enough ion mobility to favor some formation of crystalline clays over amorphous gels and may therefore not be the primary mechanism responsible for soil formation on mars the amorphous hawaiian soils exist metastably for thousands of years on earth similar materials on mars would be expected to survive considerably longer under the present cold and dry climatic conditions

hydrothermal formation of clay carbonate alteration assemblages in the nili fossae region of mars abstract the compact reconnaissance imaging spectrometer for mars crism has returned observations of the nili fossae region indicating the presence of mg carbonate in small

new martian paradigms several interrelated paradigms concerning the nature and the evolution of mars are discussed these include an impact origin of the northern lowland mars as a water rich planet former oceans in the northern lowlands a warm wet climate on early mars and the possibility of ancient life on mars locations on mars suggested for the search of possible ancient life include the heavily cratered terrain dissected by valley networks possible lacustrine deposits in valles marineris the oxidizing layer below the surface sites along the fringes of the hypothetical northern circumpolar ocean and in evaporite deposits

are there carbonate deposits in the valles marineris mars the thick sequences of layered deposits found in the valles marineris have recently been determined by s s nedell s w squyres and d w andersen 1987 icarus 70 409 441 to contain a minimum of 105 km3 of material we suggest that this material could be derived from the precipitation of 30 mbar of atmospheric co2 as carbonates in lakes as surface temperatures fell on mars the presence of an insulating ice cover would have allowed liquid water to exist fed by transitory surface melting atmospheric co2 would have accumulated in such lakes enhancing carbonate precipitation support for this hypothesis comes from processes that occur in the perennially frozen lakes in the dry valleys of antarctica where the mean temperature is 253 k and the lake water is supersaturated with atmospheric gases a search of the recently reissued mariner 6 7 infrared spectrometer data in the wavelength region between 2 and 6 m failed to confirm the presence of carbonates due to the fact that no spectral footprints appear to directly overlie the layered deposits and that deposits may be blanketed by an eolian mantle this negative result is inconclusive we feel that the canyon deposits are still a prime site for future searches for carbonates on mars

carbonates and martian climate the case for global climate change on mars is neither ambiguous nor arguable cold dry and dusty right now the surface of mars shows ancient fluvial valley networks catastrophic flood channels sediment filled basins and many other features that require stable liquid water at the planet s surface such observations from orbit 1 imply that ancient mars was substantially warmer than it is today the favored scenario to heat up a young mars is greenhouse warming driven by a thick primitive co2 rich atmosphere of the kind thought common to all the terrestrial planets 2 clearly the greenhouse phase didn t last long for mars as a result almost every model for martian climate history includes an appreciable drawdown of co2 by precipitation of carbonates however only a small fraction of the carbonates predicted by this theory have been detected on page 421 of this issue morris et al 3 report the detection of ample carbonates dispersed within the subsurface thereby strengthening arguments that co2 played a major role in the early martian climate system

cosmogenic and nucleogenic isotopic changes in mars their rates and implications to the evolutionary history of martian surface abstract we present calculations of rates of production of several nuclides in the martian atmosphere and in the regolith due to nuclear interactions of cosmic ray and radiogenic particles and consider their implications to the evolutionary history of mars nuclides selected are those which considering their chemical properties may be useful as tracers for delineating the past histories of the martian atmosphere and regolith calculations are presented for different assumed atmospheric pressures the regolith production rates for the present thin martian atmosphere 20 g cm 2 are expected to be fairly robust because they are based primarily on observed cosmogenic effects in the moon for which semiempirical estimates of nuclide production rates have been provided earlier by reedy 1981 uncertainties which arise in the calculations of nuclide production rates for an earlier hypothetical martian atmosphere of 300 500 g cm 2 thickness are discussed compared to cosmic ray production rates the nucleogenic production rates are smaller by several orders of magnitude however the nucleogenic production extends to much deeper levels whereas the cosmogenic production is essentially confined to the top 750 1000 g cm 2 depth important examples of nucleogenic production are discussed isotopes of neon and argon appear to be very promising for delineating relative magnitudes of a number of planetary processes related to the temporal changes in the thickness of the atmosphere as well as their release from the regolith however quantification of the processes would require higher precision isotopic data for the atmosphere and also direct measurements of isotopic ratios in the martian regolith along with supplementary information on changes in the isotopic compositions of hydrogen carbon and nitrogen which are affected by a variety of mechanisms of escape of gases from the atmosphere cosmogenic effects are minimal in these cases we show that although we can at present draw but limited inferences the planet mars presents a unique opportunity to use cosmogenic nuclides as tools to delineate the evolutionary history of the planet as a whole as well as its regolith and the atmosphere this arises because of two factors minimal degassing of the planet and a fairly intense chemical weathering history of the upper surface consequently an appreciable fraction of some of the isotopes of volatile elements is contributed by nuclear reactions

mars regolith versus snc meteorites possible evidence for abundant crustal carbonates abstract viking xrf analyses of the martian regolith are compared with typical igneous rocks of the earth the moon the eucrite parent asteroid and especially the shergottites nakhlites and chassigny snc meteorites which are suspected to be basalts and mafic cumulates from mars a striking feature of the martian regolith compared to igneous rocks with similar molar mg fe si ratios is its extraordinarily low ca si ratio the regolith s low ca si ratio is probably not a result of simple mixing isochemical weathering of snc like rocks with other igneous rocks unless the regolith contains a large component of rock with an improbable combination of extremely low ca si and mg fe si and yet low k 2 o and zr several other models might conceivably account for the low ca si ratio but i suggest that most of the missing ca was removed from the regolith as ca carbonate formation of a mass of carbonate equivalent to a global shell 20 m thick would suffice to remove 1000 mbar of co 2 from the martian atmosphere thus the peculiar ca si ratio of the martian regolith tends to support the hypothesis that the climate of mars was once far warmer and wetter than it is today

a geochemical model for the formation of hydrothermal carbonates on mars it is often argued that substantially more carbon dioxide and water were degassed from the martian interior than can be found at present in the atmosphere polar caps and regolith calculations have shown that atmospheric escape cannot account for all of the missing volatiles suggestions that carbon dioxide is stored as marine or lacustrine deposits are challenged by earth based and spacecraft remote sensing data moreover recent modelling of the martian atmosphere suggests that rainfall or open bodies of water are in any case unlikely to have persisted for extended periods of time hydrothermal carbonates therefore provide a possible solution to this dilemma using an accessible terrestrial system iceland as a guide to the underlying processes and a host rock composition inferred from the least altered martian meteorite we present a geochemical model for the formation of carbonates in possible martian hydrothermal systems our results suggest that an extensive reservoir of carbonate minerals equivalent to an atmospheric pressure of carbon dioxide of at least one bar could have been sequestered beneath the surface by widespread hydrothermal activity in the martian past

infrared stealthy surfaces why tes and themis may miss some substantial mineral deposits on mars and implications for remote sensing of planetary surfaces 1 infrared spectral observations have yielded many important insights into the nature of mars however spectral effects tied to surface roughness and particle size can make mineral deposits substantially more difficult to detect and identify than is generally known including for current investigations the effects hold for mars and other planets but here we focus on the impact on the exploration of mars laboratory spectra of pure smooth surfaced minerals have previously been used to conclude that the 1996 global surveyor thermal emission spectrometer tes and the 2001 mars odyssey thermal emission imaging system themis will detect a mineral deposit that covers 10 of a pixel those laboratory spectra have formed the foundation for modeling and interpretations of tes themis data and for development of the 2003 mars rover minites here for the first time we compare tes themis foundation data to laboratory field and unique airborne spectra of rough surfaces we demonstrate that substantial well crystalline regional mineral deposits including rock outcrops can be 100 exposed and remain undetected at the sensitivity of tes themis we then detail the physics which apply to all geologic materials previous studies have demonstrated the complicating physical effects for solids versus particulates for a range of minerals including oxides sulfates carbonates and each of the seven silicate classes we identify three cases of spectral behavior that can impact interpretations in case 1 physical effects cause a target to be undetectable by a given infrared instrument infrared stealthy in case 2 variations in spectral contrast mimic abundance variations which confounds abundance mapping in case 3 alteration of the spectral band shape impacts compositional interpretations optically smooth materials will be well represented in tes themis minites identifications conversely if a material forms an optically rough surface or sufficiently small particles on mars then it will be comparatively underrepresented or missed surface roughness occurs on three broad scales and roughness at the grain scale can be a primary variable in whether a mineral is detectable nondetection of certain key minerals e g carbonates can significantly impact geologic and climatic interpretations and landing site selection the tes themis detection threshold may be 10 coverage on the basis of specific laboratory samples but for field measurements that prediction represents an idealized lower bound interpretations built on nondetection should be revisited after defining the uncertainties in detection capabilities for specific instruments as applied to expected mineral surface textures on mars including at the grain scale the impact on future measurement strategies including minites should also be assessed

chemical composition of martian fines of the 21 samples acquired for the viking x ray fluorescence spectrometer 17 were analyzed to high precision compared to typical terrestrial continental soils and lunar mare fines the martian fines are lower in al higher in fe and much higher in s and cl concentrations protected fines at the two lander sites are almost indistinguishable but concentration of the element s is somewhat higher at utopia duricrust fragments successfully acquired only at the chryse site invariably contained about 50 higher s than fines no elements correlate positively with s except cl and possibly mg a sympathetic variation is found among the triad si al ca positive correlation occurs between ti and fe sample variabilities are as great within a few meters as between lander locations 4500 km apart implying the existence of a universal martian regolith component of constant average composition the nature of the source materials for the regolith fines must be mafic to ultramafic

evidence for mg rich carbonates on mars from a 3 9 μm absorption feature abstract the origin and nature of the early atmosphere of mars is still debated the discovery of sulfate deposits on the surface coupled with the evidence that there are not large abundances of carbonates detectable on mars in the optically accessible part of the regolith leaves open different paleoclimatic evolutionary pathways even if carbonates are responsible for the feature observed by tes and mini tes at 6 76 m alternative hypotheses suggest that it could be due to the presence of hydrated iron sulfates his carbonates can be discerned from his by investigating the spectral region in which a strong overtone carbonate band is present the planetary fourier spectrometer on board the mars express spacecraft has acquired several thousand martian spectra in the range 1 2 45 m since january 2004 most of which show a weak absorption feature between 3 8 and 4 m a similar feature was observed previously from the earth but its origin could not be straightforwardly ascribed to surface materials and specifically to carbonates here we show the surficial nature of this band that can be ascribed to carbonate mixed with the martian soil materials the materials that best reproduce the detected feature are mg rich carbonates huntite camg3 co3 4 and or magnesite mgco3 the presence of carbonates is demonstrated in both bright and dark martian regions an evaluation of the likeliest abundance gives an upper limit of 10 wt the widespread distribution of carbonates supports scenarios that suggest carbonate formation occurred not by precipitation in a water rich environment but by weathering processes

possible mars brines equilibrium and kinetic considerations we calculate the fate of postulated near surface brines on mars no stable brine system can exist on mars today the integrated h2o flux from a subsurface h2o reservoir is greater than zero at all latitudes where the highest recurring temperature exceeds the eutectic of chemically reasonable brines nonequilibrium brine systems or brine systems in dynamic equilibrium are possible we calculate the rate of h2o mass loss from subsurface brines as a function of latitude depth regolith porosity eutectic temperature and pore size some brines may exist in the near equatorial subsurface of mars for periods on the order of 107 years seasonally variable radar reflectivity of the martian surface has been interpreted as indicative of melting of subsurface brines zisk and mouginis mark 1980 we present a model for a chemically reasonable brine that could reproduce radar results and estimate the escape rate of h2o molecules from such a brine the presence of a low permeability duricrust may be required to preserve such a brine for reasonable periods and to prevent detection of an areally extensive subsurface system by the viking mawd instrument a porosity no lower than 20 30 should suffice to reduce h2o escape fluxes to the required rates

hydrous carbonates on mars evidence from mariner 6 7 infrared spectrometer and ground based telescopic spectra absorption features at 2 28 and 5 4 m identified in mariner 6 7 infrared spectrometer and terrestrial telescopic spectra are consistent with the spectra of hydrous magnesium carbonates such as hydromagnesite and artinite spectral characteristics of these hydrous carbonates are different from those of the anhydrous carbonates as the former do not have the strong spectral features typically associated with anhydrous carbonates such as calcite and siderite theoretical mixing indicates that depending on the type of hydrous carbonate 10 20 wt can be incorporated into the regolith without contradicting the spectral observations or the viking x ray fluorescence chemical analysis hydrous carbonates form as weathering products of mafic minerals in the presence of h2o and co2 even in the antarctic their formation as evaporite minerals from either original magmas or hydrothermally altered rocks is consistent with the martian environment provided liquid water is or has been at least transiently present on earth formation of hydrous mg carbonates is associated with the production of amorphous iron oxides which is consistent with both the environment and the inferred surface mineralogy of mars these minerals are about 60 wt h2o co3 and oh if they are abundant everywhere at the 10 level then about 6 of the surface weight could be volatiles bound in this type of mineral although the stability of hydrous carbonates in a martian environment is uncertain there may be kinetic factors inhibiting the dehydration of these minerals which may persist metastably in the current environment although the spectroscopic evidence for anhydrous carbonates is scant the possible presence of hydrous carbonates provides an appealing mechanism for the existence of carbonates on mars

presence and detection of carbonates on the martian surface the messages we receive from mars about the presence of carbonates are quite contradictory on the one hand images of the planet clearly show the signatures of past bodies of standing water where the accumulation of sedimentary deposits should have occurred on the other hand the apparent absence of carbonates in the homogeneous fines covering the martian surface raises the question where could carbonates hide now in this paper we discuss the subject and demonstrate that a proposed destruction mechanism the photodecomposition caused by uv radiation cannot account alone for the missing carbonates by means of simulations we show that the difficulties in detecting the carbonates can be ascribed to the low temperatures of the emitting zones observed up to now finally we derive the minimum amount of such minerals that could possibly be detected in future observations of mars and we compare the results of simulations with observed spectra

search for signs of ancient life on mars expectations from hydromagnesite microbialites salda lake turkey the 9white rock9 constituting a portion of what may be a lacustrine sedimentary sequence near the margin of a crater c 90 km across in sabaea terra mars measures 18 15 km 180 540 m high it is re interpreted as a lens of magnesium carbonate precipitated where ground waters seeped into an ancient evaporating crater lake were life to have emerged on mars as seems feasible then the 9white rock9 might be expected to comprise a complex of stromatolitic mounds salda golu lake in turkey is taken as an analogue this enclosed lake is nearly surrounded and underlain by partially serpentinized harzburgite hydromagnesite stromatolites microbialites up to 7 m high coalesce to form a group of small islands 200 m across the microbialites are seen to be growing near the mouth of the usually dry salda river in the southwestern sector smaller developments of hydromagnesite encircle the lake and image processing of satellite data reveals a second extensive zone beneath the lake surface over a delta in the southeast individual columns a few centimetres high constitute bulbous mounds which are about 2 m in diameter these columns terminate in domes a centimetre or so across the domes are often annulated and are covered with a green biofilm a few millimetres thick comprised of cyanobactrial filaments the columns consist of alternating fine and coarse hydromagnesite layers differentiated on a millimetric scale the coarser layers near the surface still contain traces of the biofilm fossil microbialites were also discovered in the friable hydromagnesite cliffs shoreward of the main developments though the structures of the individual microbes have not survived instead the vestiges of microbialites are easily recognized and delineated by their coarse grain size and high porosity annular structures on their upper surfaces can be seen in places the intervening and overlying material also comprised of hydromagnesite is a semi lithified mud bulbous megascopic structures separated by finer grained magnesium carbonate mudstone within strata in the 9white rock9 would be strong evidence of a photosynthetic microbial genesis another deposit of white rock on the western margin of juventae chasma could have a similar origin

orbital identification of carbonate bearing rocks on mars geochemical models for mars predict carbonate formation during aqueous alteration carbonate bearing rocks had not previously been detected on mars surface but mars reconnaissance orbiter mapping reveals a regional rock layer with near infrared spectral characteristics that are consistent with the presence of magnesium carbonate in the nili fossae region the carbonate is closely associated with both phyllosilicate bearing and olivine rich rock units and probably formed during the noachian or early hesperian era from the alteration of olivine by either hydrothermal fluids or near surface water the presence of carbonate as well as accompanying clays suggests that waters were neutral to alkaline at the time of its formation and that acidic weathering proposed to be characteristic of hesperian mars did not destroy these carbonates and thus did not dominate all aqueous environments

mars a water rich planet abstract mars had outgassed at least 0 5 to 1 km of water 10 to 20 bar of co2 and 0 1 to 0 3 bar of n2 the volatiles that have been retained are mostly in the cratered uplands terrain softening fretted channels debris flows and closed depressions indicate that at least the upper 2 km of the cratered uplands at high latitudes 30 contain ice in amounts that exceed the porosity estimated to be 10 20 theoretical studies and lack of these features in the cratered uplands at low latitudes suggest that the upper 1 km of the uplands at low latitudes is ice poor however valley networks indicate that water was present near the surface early in the planet s history although in amounts smaller than at high latitudes the entire upper 1 km planetwide is estimated to have contained 75 125 m of water at the end of heavy bombardment the largest sink for water is the megaregolith below 1 km episodic eruption of water from the deep megaregolith cut many of the large outflow channels from the volume of water needed to cut the circum chryse channels and assuming uniform planetwide distribution of water the deep megaregolith is estimated to have contained at least 350 m of water at the end of heavy bombardment thereby giving a total minimum inventory of 424 475 m planetwide most of the water lost from the low latitude uplands by diffusion and in cutting the valley networks is now believed to be in the polar layered terrains most of the water involved in cutting the outflow channels is in the low lying northern plains where a variety of features that have been attributed to ground ice is present a large fraction of the planet s surface has been overplated with water poor volcanics of which we have samples in the snc meteorites the younger volcanics have reacted extensively with the old volatile rich basement some of the co2 and n2 outgassed was lost during heavy bombardment by impact erosion of the atmosphere and other processes the remaining was fixed carbonates and folded deep into the megaregolith during heavy bombardment

the surface of syrtis major composition of the volcanic substrate and mixing with altered dust and soil syrtis major is an old low relief volcanic plateau near the equatorial regions of mars it is a persistent low albedo feature on the planet and is thought to contain a high abundance of exposed bedrock and or locally derived surface material and debris spatially resolved variations in surface spectral properties and therefore composition are investigated with data from the imaging spectrometer for mars ism instrument ism obtained 128 wavelength channel spectra from 0 76 to 3 16 m for contiguous pixels approximately 22 22 km in size across much of the plateau the value and spatial distribution of four primary spectral variables albedo continuum slope wavelength of the ferric ferrous band minimum area of the ferric ferrous absorption are mapped and coregistered to viking digital photomosaics analysis of these maps shows that although there is a high degree of overall spectral variability on the plateau the key indicators of mafic mineralogy are relatively homogeneous detailed examination of reflectance spectra from representative areas across the plateau indicate the volcanic surface is dominated by augite bearing basalts and the pyroxene composition in the basalts is estimated to be 0 275 0 075 ca ca fe mg and 0 3 0 1 fe fe ca mg additional mineral components may include olivine feldspar and glass most of the spectral variability on the plateau is interpreted to result from mixing of volcanic bedrock and or locally derived surface material and debris with highly altered dust and soil in western syrtis major the altered material is a transient component on the surface or occurs in large spatially coherent patches e g crater rims in eastern syrtis major it is apparent that the dust components are firmly fixed to the basaltic substrate as a stable oxide rind or coating

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

methane seeps on an early jurassic dysoxic seafloor abstract the rhythmically bedded limestone marl shale succession of the blue lias formation lias group early jurassic age of kilve in somerset sw england preserves a suite of large conical concretions that formed around methane seeps these are 1 2 m high and elliptical in plan axes 2 4 m with an outer limestone shell forming the flanks of the cone the cone flank is composed of micritic carbonate 20 30 cm thick which locally includes sheets and pods of intraclasts and bioclasts the cycle forming limestone beds of the host strata are composed of dark grey micrite with carbon isotope values 13c 0 6 to 0 8 consistent with carbon sourced from a mixture of seawater and by sulphate reduction and oxygen isotope values 18o 6 suggesting some degree of later diagenesis the pale grey micrite that forms the sides of the mounds includes three dimensional ammonites and intraclasts and thus cemented close to the sediment water interface prior to compaction the mound forming carbonate is markedly isotopically light with respect to carbon but not with respect to oxygen 13c 24 3 to 26 4 18o 2 to 3 5 the isotope signature indicates that cements were probably derived from a mixture of sources that included biogenic methane the intraclasts within the limestone suggest that syn depositional physical brecciation and mixing of cements had occurred and thus mixing of methane rich fluids with the overlying surface waters is likely also to have occurred the relatively heavy oxygen isotope values may be indicative of anaerobic oxidation of methane the mound bearing interval of the blue lias formation is benthos poor and comprises predominantly laminated black shales characteristic of poor bottom water oxygenation the largest of the mounds is however capped with fossiliferous breccias thus the mounds either formed benthic islands that elevated the biota into an oxic zone or alternatively they may have supported a chemotrophic community although cold seep deposits have been documented previously they are still comparatively rare this example is one of the oldest in europe and is unusual amongst described ancient seeps in preserving relief that extended above the ancient seafloor

snc meteorites clues to martian petrologic evolution the shergottites nakhlites and chassigny snc meteorites are apparently cumulate mafic and ultramafic rocks that crystallized at shallow levels in the crust of their parent body the mineralogy and chemistry of these meteorites are remarkably like equivalent terrestrial rocks although their ratios of fe fe mg and certain incompatible elements and their oxygen isotopic compositions are distinctive all have crystallization ages of 1 3 b y or younger and formed from magmas produced by partial melting of previously fractionated source regions isotope systematics suggest that the snc parent body had a complex and protracted thermal history spanning most of geologic time some meteorites have been severely shock metamorphosed and all were ejected from their parent body at relatively recent times possibly in several impact events late crystallization ages complex petrogenesis and possible evidence for a large gravitational field suggest that these meteorites are derived from a large planet trapped gases in shergottite shock melts have compositions similar to the composition measured in the martian atmosphere ejection of martian meteorites may have been accomplished by acceleration of near surface spalls or other mechanisms not fully understood if snc meteorites are of martian origin they provide important information on planetary composition and evolution the bulk composition and redox state of the martian mantle as constrained by shergottite phase equilibria must be more earthlike than most current models planetary thermal models should benefit from data on the abundances of radioactive heat sources the melting behavior of the mantle and the timing of planetary differentiation calculated depletion of chalcophile elements in source regions indicates a core dominated by sulfides and paleomagnetic measurements suggest the presence of a weak magnetic field within the last several hundred thousand years concentrations of volatile elements indicate that the snc parent body was not volatile depleted and trapped atmospheric components measured in shock melts may be useful in understanding planetary degassing by providing comparisons for spectral reflectance data and viking soil analyses these meteorites may also constrain surface mineralogy and weathering mechanisms