are the viking lander sites representative of the surface of mars abstract global remote sensing observations of mars are compared with remote sensing observations of the two viking lander site regions and with orbiter and lander imaging of the sites the lander sites do not fit most of the global trends of remote sensing data the presence of a duricrust in the top meter of the surface is inferred for most regions of high thermal inertia although the duricrust is thinner at the lander sites than elsewhere regions of low thermal inertia are covered by greater than several centimeters of unconsolidated dust a thin microns thick layer of bright dust appears at the surface at the lander sites and these locations may be regions of incipient formation of low thermal inertia the lander sites are intermediate in structure between classical bright and dark regions and are distinctive from most of the rest of the planet

geochemical constraints on chemolithoautotrophic metabolism by microorganisms in seafloor hydrothermal systems mixing of hydrothermal fluids and seawater at the ocean floor combined with slow reaction kinetics for oxidation reduction reactions provides a source of metabolic energy for chemolithotrophic microorganisms which are the primary biomass producers for an extensive submarine ecosystem that is essentially independent of photosynthesis thermodynamic models are used to explore geochemical constraints on the amount of metabolic energy potentially available from chemosynthetic reactions involving s c fe and mn compounds during mixing of hydrothermal fluids with seawater for the vent fluid used in the calculations epr 21 n obs the model indicates that mixing environments are favorable for oxidation of h2s ch4 fe2 and mn2 only below 38 c with methanogenesis and reduction of sulfate or s favored at higher temperatures suggesting that environments dominated by mixing provide habitats for mesophilic but not thermophilic aerobes and thermophilic but not mesophilic anaerobes a maximum of 760 cal per kilogram vent fluid is available from sulfide oxidation while between 8 and 35 cal kg vent fluid is available from methanotrophy methanogenesis oxidation of fe or mn or sulfate reduction the total potential for chemosynthetic primary production at deep sea hydrothermal vents globally is estimated to be about 1013 g biomass per year which represents 0 02 of the global primary production by photosynthesis in the oceans thermophilic methanogens and sulfate and s reducers are likely to be the predominant organisms in the walls of vent chimneys and in the diffuse mixing zones beneath warm vents where biological processes may contribute to the high methane concentrations of vent fluids and heavy 34s32s s ratios of vent sulfide minerals the metabolic processes taking place in these systems may be analogs of the first living systems to evolve on the earth

high temperature life without photosynthesis as a model for mars discoveries in biology and developments in geochemistry over the past two decades have lead to a radical revision of concepts relating to the upper temperature at which life thrives the genetic relationships among all life on earth links between organic and inorganic compounds in geologic processes and the geochemical supply of metabolic energy it is now apparent that given a source of geochemical energy in the form of a mixture of compounds that is far from thermodynamic equilibrium microorganisms can take advantage of the energy and thrive without the need for photosynthesis as a means of primary productivity this means that life can exist in the subsurface of a planet such as mars without necessarily exhibiting a surface expression theoretical calculations quantify the geochemically provided metabolic energy available to hyperthermophilic organisms in submarine hydrothermal systems on the earth and help to explain the enormous biological productivity of these systems efforts to place these models in the context of the early earth reveal that substantial geochemical energy would have been available and that organic synthesis would have been thermodynamically favored as hydrothermal fluids mix with seawater

co2 solubility in primitive martian basalts similar to yamato 980459 the effect of composition on co2 solubility of basalts and the evolution of the martian atmosphere to determine the influence of basalt composition on the co2 solubility in martian lavas we investigated experimentally a synthetic melt based on the martian meteorite yamato 980459 y 980459 an olivine phyric shergottite and a picritic rock 19 wt mgo thought to be a near primary liquid derived from high temperature 1540 c partial melting of the martian mantle experiments were performed in a piston cylinder apparatus at 1 2 gpa and 1600 1650 c co2 contents in quenched glasses were determined using fourier transform infrared spectroscopy ftir and range from 0 45 1 26 wt despite large differences in feo and mgo contents the co2 solubilities in y 980459 are similar to that in a less primitive synthetic martian basalt based on the humphrey rock and to a hawaiian tholeiite the lack of enhanced solubility in fe2 and mg2 rich melts is likely owing to the complex structural role of these cations in silicate melts acting partly as network formers rather than network modifiers the small sensitivity of co2 solubility to compositional variations among martian and tholeiitic basalts means that the experimentally determined solubilities may be applicable to a wide spectrum of martian magmatic products using experimentally determined co2 solubilities of y 980459 and humphrey allows the calibration of the thermodynamic parameters governing dissolution of co2 vapor as carbonate in martian basalts this relation facilitates calculation of the co2 dissolved in magmas derived from graphite saturated martian basalt source regions as a function of p t and f o2 the hot conditions in the source of y 980459 1540 10 c and 1 2 0 5 gpa are plausible for plume related magmas forming the giant tharsis volcanic complex which accounts for 50 of martian igneous activity since stabilization of the primordial crust if oxygen fugacity in the sources of hot tharsis magmatism were equivalent to that at the iron wustite buffer iw or 1 log unit above iw 1 respectively then the entire tharsis event would outgas 30 300 mbars of co2 to the martian atmosphere which is far from the 2 bars required to stabilize an equable climate in the late noachian and early hesperian epochs this mismatch could be reconciled if significant martian igneous activity derived from comparatively oxidized mantle sources i e iw 2 similar to those responsible for the nakhlite meteorites

a look at the date of snowmelt and correlations with the arctic oscillation spring snow cover across arctic lands has on average retreated 5 days earlier since the late 1980s compared to the previous 20 years however it appears that since about the late 1980s the date the snowline first retreats north during the spring has changed only slightly in the last 20 years snow has not been disappearing significantly earlier snowmelt changes observed since the late 1980s have been step like unlike the more continuous downward trend seen in arctic sea ice extent at 70 n several longitudinal segments of 10 show significant negative trends while only two longitudinal segments at 60 n show significant trends one positive and one negative these variations appear to be related to variations in the arctic oscillation ao when the springtime ao is strongly positive snow melts earlier when it is strongly negative snow disappears later in the spring the winter ao is less straightforward at higher latitudes 70 n a positive ao during the winter months is correlated with later snowmelt but at lower latitudes 50 n and 60 n a positive wintertime ao is correlated with earlier snowmelt if the ao during the winter months is negative the reverse is true similar stepwise changes since the late 1980s have been noted in sea surface temperatures and in phytoplankton abundance as well as in snow cover

europa s crust and ocean origin composition and the prospects for life abstract we have considered a wide array of scenarios for europa s chemical evolution in an attempt to explain the presence of ice and hydrated materials on its surface and to understand the physical and chemical nature of any ocean that may lie below we postulate that following formation of the jovian system the europan evolutionary sequence has as its major links a initial carbonaceous chondrite rock b global primordial aqueous differentiation and formation of an impure primordial hydrous crust c brine evolution and intracrustal differentiation d degassing of europa s mantle and gas venting e hydrothermal processes and f chemical surface alteration our models were developed in the context of constraints provided by galileo imaging near infrared reflectance spectroscopy and gravity and magnetometer data low temperature aqueous differentiation from a carbonaceous ci or cm chondrite precursor without further chemical processing would result in a crust ocean enriched in magnesium sulfate and sodium sulfate consistent with galileo spectroscopy within the bounds of this simple model a wide range of possible layered structures may result the final state depends on the details of intracrustal differentiation devolatilization of the rocky mantle and hydrothermal brine reactions could have produced very different ocean crust compositions e g an ocean crust of sodium carbonate or sulfuric acid or a crust containing abundant clathrate hydrates realistic chemical physical evolution scenarios differ greatly in detailed predictions but they generally call for a highly impure and chemically layered crust some of these models could lead also to lateral chemical heterogeneities by diapiric upwellings and or cryovolcanism we describe some plausible geological consequences of the physical chemical structures predicted from these scenarios these predicted consequences and observed aspects of europa s geology may serve as a basis for further analys is and discrimination among several alternative scenarios most chemical pathways could support viable ecosystems based on analogy with the metabolic and physiological versatility of terrestrial microorganisms

rates and mechanisms of iceberg ablation in the d urville sea southern ocean l action des vagues provoque l ablation dans une zone etroite de la ligne de flottaison d un iceberg jusqu a 0 3 m par jour dans de l eau a 1 c avec des vagues allant jusqu a 0 4 m de hauteur des velages subaeriens de glace s en suivent au meme rythme a partir des flancs de l iceberg la fusion sous marine a une action d un ordre de grandeur inferieur a celui de l action des vagues mais agit sur la face la plus etendue a l iceberg les vitesses d ablation prevues theoriquement ou statistiquement ailleurs pour des conditions comparables de l environnement sont en bonne concordance avec les mesures faites ici les icebergs en derivant trainent dans leur sillage un panache d eau de mer melangee un peu refroidie et diluee

low temperature alteration of serpentinized ultramafic rock and implications for microbial life abstract alteration serpentinization of ultramafic rocks is known to generate hydrogen through oxidation of ferrous iron in olivine or pyroxene and reduction of water hydrogen oxidation can act as a primary source for chemolithotrophic microbial communities and it is suggested that hydrogen availability is essential for the existence of a deep subsurface biosphere in this study we focus on ongoing low temperature water rock processes in partially serpentinized dunite from the leka ophiolite complex mid norway we aim to determine whether these reactions release reduced compounds and nutrients that can be utilized by the associated microbial communities the study is based on the chemical and physical alteration features of a 51 m deep rock core as well as the chemical composition of groundwater from the core s borehole the borehole intersects three main fracture zones observations during drilling indicated that water infiltration largely takes place along the deepest zone the rock in the fracture zones is nearly completely altered to serpentine brucite magnetite and minor calcite an increase in ph and decrease in mg si and alkalinity of the groundwater along the borehole from the deepest to the outermost fracture zone reflect ongoing water rock reactions where dissolution of brucite serpentine and calcite and precipitation of chrysotile hydromagnesite and iron hydroxide are most likely to occur detection of both h 2 and o 2 in the groundwater influenced by the outermost fracture zone suggests that the local development of highly reducing conditions in the narrow fractures is due to low water rock ratios and to dissolution of fe ii containing brucite and serpentine resulting in the formation and successive diffusion of h 2 into the oxic borehole oxidation of h 2 reduced fe and mn nh 4 and ch 4 are all potential energy yielding reactions that could be utilized by chemolithotrophic microorganisms using dissolved organic or inorganic carbon as possible carbon sources methane could result from microbial oxidation of h 2 and reduction of co 2 or from the degradation of organic matter the results demonstrate that low temperature water rock reactions in serpentinized ultramafic rock lead to production of reduced chemical species that could support primary producers in diverse microbial communities

hydrothermal plumes above the east scotia ridge an isolated high latitude back arc spreading centre we have identified first evidence for the presence of submarine hydrothermal activity along the east scotia ridge an isolated back arc spreading centre located at 55 60 s in the atlantic sector of the southern ocean using a combination of in situ optical light scattering sensor data and total dissolvable mn concentrations we demonstrate the existence of hydrothermal plumes overlying two segments of this 500 km ridge crest both segments exhibit anomalous topography and at least one segment is also underlain by an axial magma chamber seismic reflector future investigation of the fauna that inhabit these remote hydrothermal environments may provide an important missing link between the distinct biogeographical provinces delimited from previous investigation of northern atlantic versus eastern pacific vent sites

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

galileo s first images of jupiter and the galilean satellites the first images of jupiter io europa and ganymede from the galileo spacecraft reveal new information about jupiter s great red spot grs and the surfaces of the galilean satellites features similar to clusters of thunderstorms were found in the grs nearby wave structures suggest that the grs may be a shallow atmospheric feature changes in surface color and plume distribution indicate differences in resurfacing processes near hot spots on io patchy emissions were seen while io was in eclipse by jupiter the outer margins of prominent linear markings triple bands on europa are diffuse suggesting that material has been vented from fractures numerous small circular craters indicate localized areas of relatively old surface pervasive brittle deformation of an ice layer appears to have formed grooves on ganymede dark terrain unexpectedly shows distinctive albedo variations to the limit of resolution

martian plate tectonics the northern lowlands of mars may have been produced by plate tectonics preexisting old thick highland crust was subducted while seafloor spreading produced thin lowland crust during late noachian and early hesperian time in the preferred reconstruction a breakup margin extended north of cimmeria terra between daedalia planum and isidis planitia where the highland lowland transition is relatively simple south dipping subduction occurred beneath arabia terra and east dipping subduction beneath thatsis montes and tempe terra lineations associated with gordii dotsum are attributed to ridge parallel structures while phelegra montes and scandia colles are interpreted as transform parallel structures or ridge fault fault triple junction tracks other than for these few features there is little topographic roughness in the lowlands seafloor spreading if it occurred must have been relatively rapid quantitative estimates of spreading rate are obtained by considering the physics of seafloor spreading in the lower c 0 4 g gravity of mars the absence of vertical scarps from age differences across fracture zones and the smooth axial topography to the first order the height of vertical scarps across fracture zones does not involve gravity crustal thickness at a given potential temperature in the mantle source region scales inversely with gravity thus the velocity of the rough smooth transition for axial topography also scales inversely with gravity plate reorganizations where young crust becomes difficult to subduct are another constraint on spreading age possible plate reorganizations for example the end of spreading through alba patera occur when the ridge axis is far from the trench that is rapid plate motions are inferred to have placed young oceanic crust far from the ridge axis the preferred full spreading rate 900 from the plate pole is 80 mm yr 1 plate tectonics if it occurred dominated the thermal and stress history of the planet a geochemical implication is that the lower gravity of mars allows deeper hydrothermal circulation through cracks and hence more hydration of oceanic crust so that more water is easily subducted than on the earth age and structural relationships from photogeology as well as median wavelength gravity anomalies across the now dead breakup and subduction margins are the data most likely to test and modify hypotheses about mars plate tectonics

geophysical controls of chemical disequilibria in europa the ocean in jupiter s moon europa may have redox balance similar to earth s on earth low temperature hydration of crustal olivine produces substantial hydrogen comparable to any potential flux from volcanic activity here we compare hydrogen and oxygen production rates of the earth system with fluxes to europa s ocean even without volcanic hydrothermal activity water rock alteration in europa causes hydrogen fluxes 10 times smaller than earth s europa s ocean may have become reducing for a brief epoch for example after a thermal orbital resonance 2 gyr after accretion estimated oxidant flux to europa s ocean is comparable to estimated hydrogen fluxes europa s ice delivers oxidants to its ocean at the upper end of these estimates if its ice is geologically active as evidence of geologic activity and subduction implies

geochemical bioenergetics during low temperature serpentinization an example from the samail ophiolite sultanate of oman abstract various classes of microbial and biomolecular evidence from global studies in marine and continental settings are used to identify a set of reactions that appear to support microbial metabolism during serpentinization of ultramafic rocks geochemical data from serpentinizing ecosystems in the samail ophiolite of oman are used to evaluate the extent of disequilibria that can support this set of microbial metabolisms and to provide a ranking of potential metabolic energy sources in hyperalkaline fluids that are direct products of serpentinization results are used to construct hypotheses for how microbial metabolism may be supported in the subsurface for two cases ecosystems hosted in rocks that have already undergone significant serpentinization and those hosted by deeper active serpentinization processes

scenarios for the evolution of life on mars received 10 march 2005 revised 2 august 2005 accepted 7 september 2005 published 22 november 2005 1 as the environmental histories of earth and mars have diverged drastically after the first few hundred million years so would the history of any life on them while earth has had liquid water on its surface for billions of years mars most likely had long dry and cold environments interspersed with warmer and wetter periods life thrived on earth but may have been severely restricted on mars there it could be present today in liquid water in or beneath ice sheets or glaciers in subterranean aqueous reservoirs especially in regions of elevated heat flow or in protected habitats such as lava tubes caves or cracks and fissures the potential for life is enhanced in regions where elevated heat flow may occur such as in parts of the tharsis and elysium volcanic provinces possible organisms would be chemoautotrophic psychrophiles adapted to a nutrient poor environment or photoautotrophic life in selected near surface habitats alternatively life may have evolved alternating cycles between active and dormant forms in which case microbes could be present in dormant forms close to the surface and in active forms in protected environments periodic liquid water on mars could have provided opportunities for biologic activity as well as evolutionary progress at the surface during the short lived climatic perturbations ancient organisms from any of these environments may also have left a detectable fossil record

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

hydrothermal hydration of martian crust illustration via geochemical model calculations if hydrothermal systems existed on mars hydration of crustal rocks may have had the potential to affect the water budget of the planet we have conducted geochemical model calculations to investigate the relative roles of host rock composition temperature water to rock ratio and initial fluid oxygen fugacity on the mineralogy of hydrothermal alteration assemblages as well as the effectiveness of alteration to store water in the crust as hydrous minerals in order to place calculations for mars in perspective models of hydrothermal alteration of three genetically related icelandic volcanics a basalt andesite and rhyolite are presented together with results for compositions based on snc meteorite samples shergotty and chassigny temperatures from 150 c to 250 c water to rock ratios from 0 1 to 1000 and two initial fluid oxygen fugacities are considered in the models model results for water to rock ratios less than 10 are emphasized because they are likely to be more applicable to mars in accord with studies of low grade alteration of terrestrial rocks we find that the major controls on hydrous mineral production are host rock composition and temperature over the range of conditions considered the alteration of shergotty shows the greatest potential for storing water as hydrous minerals and the alteration of icelandic rhyolite has the lowest potential

the biological potential of mars the early earth and europa the potential biomass that could have existed on mars is constrained by the total amount of energy available to construct it from an inventory of the available geochemical sources of energy we estimate that from the time of the onset of the visible geologic record 4 b y ago to the present as much as 20 g cm 2 of biota could have been created this is the same amount that could have been constructed on the early earth in only 100 million years this indicates that there likely was sufficient energy available to support an origin of life on mars but not sufficient energy to create a ubiquitous and lush biosphere similar calculations for europa suggest that even less geochemical energy would have been available there

sulfur bearing phases detected by evolved gas analysis of the rocknest aeolian deposit gale crater mars the sample analysis at mars sam instrument suite detected so2 h2s ocs and cs2 from 450 to 800 c during evolved gas analysis ega of materials from the rocknest aeolian deposit in gale crater mars this was the first detection of evolved sulfur species from a martian surface sample during in situ ega so2 3 22 mol is consistent with the thermal decomposition of fe sulfates or ca sulfites or evolution desorption from sulfur bearing amorphous phases reactions between reduced sulfur phases such as sulfides and evolved o2 or h2o in the sam oven are another candidate so2 source h2s 41 109 nmol is consistent with interactions of h2o h2 and or hcl with reduced sulfur phases and or so2 in the sam oven ocs 1 5 nmol and cs2 0 2 1 nmol are likely derived from reactions between carbon bearing compounds and reduced sulfur sulfates and sulfites indicate some aqueous interactions although not necessarily at the rocknest site fe sulfates imply interaction with acid solutions whereas ca sulfites can form from acidic to near neutral solutions sulfides in the rocknest materials suggest input from materials originally deposited in a reducing environment or from detrital sulfides from an igneous source the presence of sulfides also suggests that the materials have not been extensively altered by oxidative aqueous weathering the possibility of both reduced and oxidized sulfur compounds in the deposit indicates a nonequilibrium assemblage understanding the sulfur mineralogy in rocknest materials which exhibit chemical similarities to basaltic fines analyzed elsewhere on mars can provide insight in to the origin and alteration history of martian surface materials

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

explosive lava water interactions in elysium planitia mars geologic and thermodynamic constraints on the formation of the tartarus colles cone groups 1 volcanic rootless constructs vrcs are the products of explosive lava water interactions vrcs are significant because they imply the presence of active lava and an underlying aqueous phase e g groundwater or ice at the time of their formation combined mapping of vrc locations age dating of their host lava surfaces and thermodynamic modeling of lava substrate interactions can therefore constrain where and when water has been present in volcanic regions this information is valuable for identifying fossil hydrothermal systems and determining relationships between climate near surface water abundance and the potential development of habitable niches on mars we examined the western tartarus colles region 25 27 n 170 171 e in northeastern elysium planitia mars and identified 167 vrc groups with a total area of 2000 km2 these vrcs preferentially occur where lava is 60 m thick crater size frequency relationships suggest the vrcs formed during the late to middle amazonian modeling results suggest that at the time of vrc formation near surface substrate was partially desiccated but that the depth to the midlatitude ice table was 42 m this ground ice stability zone is consistent with climate models that predict intermediate obliquity 35 between 75 and 250 ma with obliquity excursions descending to 25 32 for lava thicknesses ranging from 30 to 60 m and ground ice fractions ranging from 0 1 to 0 3 an ice volume of 4 23 km3 could have been melted and or vaporized by the time the lava solidified and the associated hydrothermal systems could have retained temperatures 273 k for up to 1300 years

expanding frontiers in deep subsurface microbiology abstract the subsurface biosphere on earth appears to be far more expansive and physiologically and phylogenetically complex than previously thought here several aspects of subsurface microbiology are discussed molecular and biogeochemical data as well as characteristics from new isolates suggest that ecosystems below deep sea hydrothermal vents are inhabited primarily by thermophilic archaea and bacteria the void spaces and conduits in basalt at mid ocean ridges and even more so at sediment covered hydrothermal vent sites represent promising hunting grounds for novel chemosynthetic archaea and bacteria as examples we highlight the subsurface microbial communities within the basalt flanks of the juan de fuca ridge off british columbia and the hydrothermal sediments at the guaymas basin in the gulf of california and at middle valley on the juan de fuca ridge in the deep continental subsurface microbial studies have primarily targeted aquifers in basaltic and granitic rock with an almost exclusive emphasis on h2 driven chemolithoautotrophy for example in the subsurface water from lidy hot springs idaho usa h2 consuming methanogenic archaea represent the most populous organisms comprising 95 of all cells besides h2 other potential sources of chemical energy reducing power are considered including abiotically synthesized organic matter and reduced sulfur compounds in addition the well established sequences of redox couples in microbial metabolism are investigated at elevated temperatures using a thermodynamic approach values of peo for 11 common reduction half reactions are tabulated at 25 50 100 and 150 c although many modes of metabolism may be employed by subsurface biota sulfate reduction appears to be one of the more ubiquitous strategies recent studies of sulfate reducing archaea and bacteria in marine and continental systems are reviewed

sources of nutrients and energy for a deep biosphere on mars hydrothermal vents appear to be the tip of the subsurface biosphere in the ocean crust the primary prducers in this biosphere are prokaryotes that tolerate a wide variety of physical and chemical conditions and are versatile in their use of inorganic compounds to drive metabolism a synthesis of chemical and mineralogical data from martian meteorites and measurements of the martian surface suggest that conditions similar to those that make life possible in earth s oceanic crust namely water carbon nutrients appropriate temperatures and gradients in redox conditions also occur within mars chemolithoautotrophic microorganisms capable of living below the seafloor on earth would probably survive in some regions of the martian subsurface

polymeric substances and biofilms as biomarkers in terrestrial materials implications for extraterrestrial samples organic polymeric substances are a fundamental component of microbial biofilms microorganisms especially bacteria secrete extracellular polymeric substances eps to form slime layers in which they reproduce in the sedimentary environment biofilms commonly contain the products of degraded bacteria as well as allochthonous and autochthonous mineral components they are complex structures which serve as protection for the colonies of microorganisms living in them and also act as nutrient traps biofilms are almost ubiquitous wherever there is an interface and moisture liquid liquid liquid solid liquid gas solid gas in sedimentary rocks they are commonly recognized as stromatolites we also discuss the distinction between bacterial biofilms and prebiotic films the eps and cell components of the microbial biofilms contain many cation chelation sites which are implicated in the mineralization of the films eps biofilms and their related components thus have strong preservation potential in the rock record fossilized microbial polymeric substances fps and biofilms appear to retain the same morphological characteristics as the unfossilized material and have been recognized in rock formations dating back to the early archaean 3 5 b y we describe fps and biofilms from hot spring deep sea volcanic lake and shallow marine littoral environments ranging up to 3 5 b y in age fps and biofilms are more commonly observed than fossil bacteria themselves especially in the older part of the terrestrial record the widespread distribution of microbial biofilms and their great survival potential makes their fossilized remains a useful biomarker as a proxy for life with obvious application to the search for life in extraterrestrial materials

energy for biologic sulfate reduction in a hydrothermally formed ocean on europa 1 formation of a sulfate bearing ocean on jupiter s satellite europa by quenched hydrothermal fluids provides a source of metabolic energy for low temperature sulfate reducing organisms that use dissolved h2 as an electron donor inhibition of thermodynamically favorable sulfate reduction in cooled hydrothermal fluids creates the potential for biologic reduction both high temperature and reduced conditions of ocean forming hydrothermal solutions favor sulfate reduction in quenched fluids the maximum amount of energy available to support autotrophic sulfate reduction is on the order of a few kilojoules per kilogram of water and is limited by the low abundances of either h2 or sulfate in ocean forming fluids although this irreplaceable energy source might have supported early life on europa maintenance of biologic sulfate reduction throughout the ocean s history would require a supply of organic compounds from endogenic sources or from the satellite s surface

sulfur isotope signatures for rapid colonization of an impact crater by thermophilic microbes in the 23 km diameter haughton impact structure canadian high arctic in sulfate rich bedrock widespread hydrothermal sulfide mineralization occurred in breccias formed during the impact the sulfides exhibit extreme sulfur isotopic fractionation relative to the original sulfate requiring microbial sulfate reduction by thermophiles throughout the crater this evidence of widespread microbial activity demonstrates that colonization could occur within the lifetime of a moderately sized impact induced hydrothermal system the pyrite was subsequently oxidized to jarosite which may also have been microbially mediated the successful detection of evidence for microbial life suggests that it would be a valuable technique to deploy in sulfate rich impact terrain on mars

does europa have a subsurface ocean evaluation of the geological evidence it has been proposed that jupiter s satellite europa currently possesses a global subsurface ocean of liquid water galileo gravity data verify that the satellite is differentiated into an outer h2o layer about 100 km thick but cannot determine the current physical state of this layer liquid or solid here we summarize the geological evidence regarding an extant subsurface ocean concentrating on galileo imaging data we describe and assess nine pertinent lines of geological evidence impact morphologies lenticulae cryovolcanic features pull apart bands chaos ridges surface frosts topography and global tectonics an internal ocean would be a simple and comprehensive explanation for a broad range of observations however we cannot rule out the possibility that all of the surface morphologies could be due to processes in warm soft ice with only localized or partial melting two different models of impact flux imply very different surface ages for europa the model favored here indicates an average age of 50 myr searches for evidence of current geological activity on europa such as plumes or surface changes have yielded negative results to date the current existence of a global subsurface ocean while attractive in explaining the observations remains inconclusive future geophysical measurements are essential to determine conclusively whether or not there is a liquid water ocean within europa today

experimental abiotic synthesis of methanol in seafloor hydrothermal systems during diking events abstract the abiotic synthesis of organic compounds in seafloor hydrothermal systems is one mechanism through which the subsurface environment could be supplied with reduced carbon a flow through fixed bed laboratory reactor vessel the catalytic reactor vessel crv system has been developed to investigate mineral surface promoted organic synthesis at temperatures up to 400 c and pressures up to 30 mpa conditions relevant to seafloor hydrothermal systems here we present evidence that metastable methanol can be directly synthesized from a gas rich co2 h2 h2o mixture in the presence of a mineral substrate experiments have been performed without a substrate with quartz and with a mixture of quartz and magnetite temperatures and pressures in the experiments ranged from 200 c to 350 c and from 15 to 18 mpa respectively maximum conversion of 5 8 10 4 co2 to ch3oh per hour was measured using a mixture of magnetite and quartz in the reactor after passivation of the stainless steel reactor vessel experiments demonstrate that methanol is formed at temperatures up to 350 c in the presence of magnetite and that the formation rate decreases over time the experiments also show a loss of surface reactivity at 310 c and a regeneration of surface reactivity with increased temperature up to 350 c concentrations of co2 and h2 used in the experiments simulate periodic localized and dynamic conditions occurring within the seafloor during and immediately following magmatic diking events high concentrations of co2 and h2 may be generated by dike injection accompanied by exsolution of co2 and reaction of dissolved h2o with feo in the magma to form h2 the experiments described here examine how the ephemeral formation of an h2 co2 rich vapor phase within seafloor hydrothermal systems may supply reactants for abiotic organic synthesis reactions these experiments show that the presence of specific minerals can promote the abiotic synthesis of simple organic molecules from common inorganic reactants such h2o co2 and h2 under geologically realistic conditions

chemical components of the martian soil melt degassing hydrothermal alteration and chondritic debris on the basis of measurements by the viking and soviet phobos missions the fine grained surficial drift material on mars is enriched in moderately volatile and mobile elements such as s cl k and br the compounds of these elements may amount to as much as 16 wt of the soil while the bulk of the soil appears to consist primarily of crustal material whose composition is similar to that of the basaltic mars meteorites clark 1993 three possible geochemical sources melt degassing hydrothermal alteration and accretion of chondritic material may have contributed to the enrichments we have evaluated possible chemical signatures for these sources by examining the relative abundances of chemical elements in the different components to the measured k abundance in the mars soil and have identified characteristic elements for each component the relative abundances of mobile elements in the different components are much less variable than their absolute abundances which strongly depend on conditions such as temperature and water composition the volatility controlled elemental signature of the melt degassing process includes enrichments of zn mo cd ba and w relative to the elemental abundances in the other components and martian meteorites hydrothermal alteration of minerals and glass controlled by low temperature solubility makes up a second component with a characteristic lithium enrichment signature a chondritic component is enriched in siderophile and chalcophile elements including ni compared to material derived from the martian mantle which was depleted in siderophile elements due to core formation unfortunately the existing data for the mars soil do not include any of these key signature elements and the uncertainties for the viking analyses could allow large amounts of each of these elements the mars pathfinder inorganic analysis experiment and the 2001 orbital gamma ray experiment have the potential to determine some of these characteristic elements and to reveal the possible contributions to the soil the enriched components of the soil especially cd and pb could also be a potential hazard for future martian explorers who will be exposed to the dust carried into their habitats on their space suits