P53B-1442
A new technique for identification of minerals in hyperspectral images. Application to robust characterization of phyllosilicate deposits at Mawrth Vallis using CRISM images.
Mapping of Mars by MRO has revealed the presence of numerous small phyllosilicate outcrops. These are typically identified in CRISM images using "summary products" (Pelkey, 2007) that consist of band ratios, depths and spectral slopes around diagnostic wavelengths. The summary products are designed to capture spectral features related to both surface mineralogy and atmospheric gases and aerosols. Such products, as an analysis tool to characterize composition as well as a targeting tool to identify areas of mineralogical interest, have been successful in capturing the known diversity of the Martian surface, and in highlighting locations with strong spectral signatures. Here we present alternative mineral mapping technique that 1) aims to increase the robustness of mineral detections with respect to the specific CRISM artifacts, 2) takes advantage of the spatial context of each pixel and 3) develops new parameters for the discrimination of species in the phyllosilicates family. We include spatial context by evaluating spectral shapes, band depths and spectral slopes for the current pixel based on its spatial neighbors within the same geological unit. Furthermore, the parameters are based on estimates that are more robust to CRISM speckling noise that might alter the parameters and potentially the mineral interpretation. As an effort to distinguish between phyllosilicates species, we are augmenting the suite of existent parameters with a set of mineral parameters that involve the position, number and shapes of diagnostic phyllosilicate absorptions. We are comparing the effectiveness of this new approach to the summary product procedure. The study shows that homogeneous mineral maps and diagnostic spectral identifications are possible as a result of the application of such new parameters. We applied the technique to the discrimination of kaolinite in Mawrth Vallis. The experiments show several small kaolinite outcrops dispersed within the more extensive Al-rich phyllosilicates in regions around the MSL landing sites. Another test was the discrimination of montmorillonite and nontronite in Mawrth Vallis that can be successfully accomplished by band depths summary products near 2.2 and 2.3 μm. The new technique produces improved maps with lower noise levels and lower percentage of false detections.
P53B-1443
Emissivity of Phyllosilicates From the Berlin Emissivity Database (BED) in the [3, 50] Micron Spectral Range in Support of Remote Sensed Data Analysis
Phyllosilicates on Mars have been identified few years ago by the OMEGA instrument on the ESA Mars Express mission. Confirmation of the detection came recently from the CRISM spectrometer, on board the NASA's Mars Reconnaissance Orbiter. These minerals formed on Mars in the Noachian period, when moderate pH and large amount of available water occurred. Emissivity spectra of several terrestrial phyllosilicates have been measured in the Planetary Emissivity Laboratory (PEL) at DLR in Berlin, to build a spectral library of analogue materials. This dataset can be very useful for the interpretation of OMEGA and CRISM data in the 3 to 5 micron spectral region. On the other hand, such spectral library is essential for the analysis of data from the PFS on Mars Express and TES on NASA Mars Global Surveyor missions.
P53B-1444
Characterization of Natural Mixed-Layer Illite/Smectite and Physical Mixtures of Illite and Smectite Using TIR and VNIR Spectroscopy: Are Mixed-Layer Clays on Mars?
Interpretations of visible/near-infrared (VNIR) spectral data from OMEGA and CRISM identify a variety of phyllosilicate minerals in Noachian terrains on Mars, including Fe/Mg smectites, montmorillonite, kaolinite, muscovite or illite, and chlorite [Bibring et al., 2005 and 2006, Poulet et al., 2006, Wray et al., 2008, Mustard et al., 2008, and Ehlmann et al., 2008]. In many areas, different phyllosilicates are found in close proximity to one another. For example, OMEGA and CRISM data from Mawrth Vallis provide evidence for the presence of extensive outcrops rich in Fe/Mg smectites and montmorillonite, while CRISM data from Nili Fossae provide evidence for the presence of limited outcrops rich in high-Fe chlorite, kaolinite, and muscovite/illite [Mustard et al., 2008]. The identification of multiple types of clay minerals in close proximity introduces the question: Could any of these outcrops contain mixed-layer clay minerals? Mixed-layer clays form as a result of chemical weathering or low-temperature hydrothermal alteration in volcanic environments or due to low-grade metamorphism [Srodon, 1999]. It is important to be able to identify mixed-layer clays through remote sensing measurements for two reasons. Evidence for hydrothermal alteration (silica-enriched deposits in Gusev crater [Squyres et al., 2008]) and chemical weathering (global iron oxidation and the enrichment of a high-silica phase in northern mid to high latitudes [Kraft et al., 2007]) suggests that mixed-layer clays are likely on Mars. Secondly, the ratios of the individual clay components formed from hydrothermal alteration can act as a geothermometer and constrain the temperature of the environment of formation [Srodon, 1999]. In this study, we compare VNIR and thermal IR spectral data from natural mixed-layer illite-smectite samples to physical mixtures of illite and smectite in similar ratios to determine how to recognize mixed-layer clays and distinguish them from mixtures of individual clays. This study will provide the basis needed to further interpret martian VNIR spectra of clay-rich regions and investigate the presence of mixed-layer clays.
P53B-1445
Global Mapping of Minerals on Mars With OMEGA Hyperspectral Data Using a Linear Unmixing Algorithm
Since December 2003, the OMEGA imaging spectrometer onboard Mars Express has completed a near global coverage of Mars in 352 spectral channels from 0.3 to 5.2 µm. The data set covers two martian years. We have analyzed the global data set (up to orbit 5200) with an automated linear unmixing algorithm (MELSUM) which is described in Combe et al. (Planet. Space. Sci., 2008). In this approach, we seek for each OMEGA pixel the best linear combination of a suite of laboratory spectra of pure minerals covering the main families (mafics, sulfates, oxides, carbonates, phyllosilicates). Two ices endmembers (H20 and CO2) are included in the input library to account for atmospheric clouds and surface frost. Artificial pure slopes endmembers complement the spectral library in order to correct at first order for scattering and grain size effects. Global distribution maps have been produced for each of the endmembers in the input library. One of the challenges in computing these maps (representing ~500 GB of raw data), is to filter the data in order to account for the variations in atmospheric conditions, viewing geometry, seasonal frost or dust cover, and instrumental effects. Several filters have been used, such as an ice detection criterion, a spectrum quality index, an incidence angle threshold, and the Root Mean Square residue of the linear unmixing algorithm. This provides homogeneous maps of the distribution of the main mineral families. Clinopyroxenes and orthopyroxenes are found mostly in the southern hemisphere, which is consistent with previous studies. Olivine is found in very localized spots such as Nili Fossae or Nili Patera. Iron oxides appear with a low signal in the northern bright areas, and with a very strong signal in localized areas such as Aram Chaos and Meridiani Planum over light toned layered deposits, or in their vicinity. The Ferrihydrite endmember map indicates a possible occurrence of this mineral in northern Meridiani Planum and in Aram Chaos, and in the oldest terrains surrounding Syrtis Major.
P53B-1446
Clays and Sulfates in a Potential Lacustrine Evaporite Sequence at Columbus Crater, Mars
From orbit, phyllosilicates and hydrated sulfates on Mars have typically been observed in distinct geographic locales and are thought to record different types of ancient aqueous environments [1]. However, these two mineral classes have recently been found in close association in each of two large impact craters in the Terra Sirenum region of the Southern highlands [2, 3]. In one of these, the D~100 km crater Columbus, CRISM observations show that a polyhydrated non-Fe sulfate is the spatially dominant phase, whereas other distinct layers have spectra consistent with the iron sulfates jarosite and szomolnokite, respectively. Another distinct spectral unit may contain hydrated chloride, or a different non-Fe sulfate. A kaolin group clay is the most commonly detected phyllosilicate, occurring in all CRISM scenes that show the polyhydrated sulfate, but Fe/Mg-phyllosilicates are also seen in small exposures. The polyhydrated sulfate occurs in a light-toned, finely layered, indurated deposit that extends around ~270 degrees of the inner crater wall. The kaolinite unit is commonly stratigraphically beneath the polyhydrated sulfate unit, but some interbedding of the two materials is tentatively observed. Hydrated materials are also present in strata exposed on the crater floor. Kaolinite, sulfates, and chlorides are observed precipitating out of terrestrial acid-saline lakes and ground waters [4], which may be analogs for the environment that deposited the materials in Columbus crater. The overall structure of the deposit is reminiscent of terrestrial "bathtub ring" evaporite deposits. Alternatively, the exposed ring could be part of a preexisting subsurface layer exposed by the impact event; however, the mineral assemblage seen here (kaolinite and polyhydrated sulfate) has not yet been observed in any other craters or intercrater bedrock exposures in the region. Further imaging and topographic data will be used to test the evaporite hypothesis by carefully examining the stratigraphic relationship between the hydrated deposits and crater wall slump blocks. The acidity and salinity implied by the observed mineral assemblage would have posed significant challenges to Martian life here, but fossils preserved in terrestrial acid-saline lake evaporites [5] suggest that sediments in Columbus may also be capable of preserving potential biosignatures until the present day. [1] Bibring, J.-P., et al. (2006), Science 312, 400-404. [2] Wray, J. J., et al. (2008), DPS 40, #03.04. [3] Swayze, G. A., et al. (2008), this conference. [4] Benison, K. C., et al. (2007), J. Sed. Res. 77, 366-388. [5] Benison, K. C., et al. (2008), Astrobiology, in press.
P53B-1447
Possible origins for phyllosilicate-rich materials observed at Mawrth Vallis: Evidence from fracture patterns and reflectance spectra
Al-OH and (Mg)Fe-OH absorptions attributable to phyllosilicate minerals have been observed in OMEGA and CRISM imaging spectrometer data from the Mawrth Vallis region of Mars. These deposits have been characterized in terms of their mineralogy and textural characteristics; however, the origin of these deposits is still very much a mystery. Here we consider possible origin hypotheses for these materials. A lithostratigraphic sequence has been determined for the light-toned Mawrth Vallis strata based on their reflectance characteristics. A basal layer of nontronite and/or (Fe)Mg bearing smectites is surmounted by materials with less well defined absorption bands. An absorption near 2.3 microns and a broad band centered near 1 micron in these layers suggest the presence of ferrous iron bearing phyllosilicates. These materials are surmounted by materials with different forms of 2.2 micron absorptions. Depending on where they occur in the sequence and where they occur laterally there are spectra more characteristic of montmorillonite, other materials with a broad 2.2 micron band which have been interpreted as hydrated silica, but which we suggest might be consistent with a kaolinite-smectite mixture, and other materials with a doublet at 2.2 microns consistent with kaolinite or dickite. These layers also have associated fracture patterns unique to the layers. Hypotheses for the nature of the fracture patterns have generally centered on hypotheses such as the desiccation of wet fine grained sediments (clays/silts) and/or the mechanism of ground ice contraction and expansion. Given that the Mawrth Vallis layered materials apparently were buried and are currently being uncovered, we suggest that the fractures might be the result of tectonic stresses imposed by an overburden. Terrestrial sedimentary rocks display different fracture patterns based on their different rheologic character which is in turn dictated by composition. An intriguing analogy might be that of layer-unique fracture patterns revealed from seismic surveys of smectite-rich mudstones (derived from a volcanic ash protolith) and overlying coarser-grained sediments in the North Sea. In the North Sea basin, fracture patterns, display several endmember fracture patterns including rectilinear, curved, and irregular. Similar patterns are observed in HiRISE images of Mawrth Vallis surfaces. Also, in the North Sea basin deposits, the fine-grained and fractured smectite-rich beds are overlain by coarser-grained (and mostly non- fractured) kaolinite, illite, and chlorite rich beds. It has been suggested that the Al-bearing phyllosilicate layers at Mawrth Vallis are draped over pre-existing topography so the North Sea analogy might be imperfect, but it shows how analysis of fracture patterns in association with lithology might provide insight into the origin of the Mawrth Vallis deposits.
P53B-1448
Geologic Context of Al-rich Phyllosilicate Deposits in Meridiani
Exposures of Al-rich phyllosilicate-bearing deposits are detected using MRO CRISM spectral data in fluvially dissected cratered terrain to the south of the sulfate and hematite-bearing plains unit analyzed by the Opportunity rover. Specifically, Al-rich phyllosilicates, including montmorillonite and kaolinite, are identified in association with Fe/Mg smectites. Although Fe/Mg smectites have been previously detected in Sinus Meridiani using OMEGA and CRISM images, this is the first identification of Al-rich phyllosilicates in this region. Al and Fe/Mg phyllosilicates have been identified in relatively large, compositionally stratified deposits within Mawrth Vallis. Although the Meridiani phyllosilicate deposits are exposed over a more limited area than the Mawrth deposits, initial analyses suggest that the Meridiaini phyllosilicate deposits are also compositionally stratified. The phyllosilicates occur in remnants of higher standing terrain. Analysis of superposition relationships using image and topographic data demonstrate that, after formation, the phyllosilicate deposits were incised via fluvial erosion and later embayed by the hematite-bearing plains unit.
P53B-1449
Geological Relationships Between Hydrated Minerals And Fluvial Landforms In Tyrrhena Terra, Mars.
The phyllosian period of Mars displays rocks that are altered at different levels, containing phyllosilicates of various nature, revealing that liquid water played a strong role in their formation. However, debates currently exist to know if this alteration was conduced at the surface due to a different climate, or in the subsurface from hydrothermal circulation. Here, we display results in the Tyrrhena Terra region, which is of interest to address this issue. Indeed, Tyrrhena Terra is located in cratered Noachian highlands in the southern hemisphere, south of Isidia Planitia and north of Hellas basin. This region displays highland terrains partially dissected by fluvial valleys and several intercrater plains. Phyllosilicates are identified by the combination of 1.9 and 2.3 micron features in the OMEGA imaging spectrometer data. They are frequently located on craters ejecta and pieces of outcrops close to the highlands. Olivine and pyroxenes are also identified, and are associated mainly to the intercrater plains when present together. We focus our interest on regions where a single 1.9 micron signature is observed (with small 2.3 micron features observed locally), and where pyroxene is found in the same area. This detection suggests a partial alteration or a spatial mixing with unaltered material as highlighted by the presence of pyroxene signatures at the same location. The geologic study of these areas of interest shows that these hydrous minerals are located at the foothills of highlands, especially in locations where valley networks end in plains. This leads to the conclusion that these hydrous minerals are observed in alluvial plains collecting material from the highlands. This example shows that external cycles of running water are involved in alteration minerals deposition. We currently study these regions in details to know if the alteration was a result of this process during sedimentation (alteration coeval to fluvial activity), or if the alteration occurred earlier in the crust with later erosion and transport into the alluvial plains (without relation with fluvial episodes).
P53B-1450
Mineralogic and morphologic signatures of Noachian water in the Argyre impact basin
The Argyre basin is a >1500 km, well preserved impact basin in the southern highlands of Mars. The associated geologic units (USGS map I-1802-A) span the Noachian to Hesperian age of the surrounding plateau plains, making Argyre an ideal probe of compositional layering of ancient highland rocks. There are both morphologic and mineralogic indications of the past presence of water. One of the major geologic units associated with Argyre is unit Npld, interpreted as a Noachian mixture of lavas, pyroclastics, and impact breccia eroded by fluvial processes. Also, the Uzboi Vallis system can be traced to the north rim of Bond crater in north-central Argyre; many researchers have suggested that Uzboi drained a water-filled Argyre at the location where Hale and Bond craters now obscure the Argyre rim. Phyllosilicates are common alteration minerals on Earth, frequently forming during weathering and hydrothermal activity, in the presence of water. Phyllosilicates have been detected in nine 20 m/pixel resolution CRISM targeted observations of the Argyre basin. The data were corrected for illumination by dividing by the cosine of the solar incidence angle and a multiplicative correction for atmospheric gas absorption was applied. We use tetracorder, a software tool which utilizes an expert system decision methodology to analyze spectra to identify components in the spectrum, to interpret the CRISM data. In northwest Argyre a laterally extensive phyllosilicate deposit has been identified directly below a thin, pyroxene-rich Hesperian (Hpl3) cap-rock but stratigraphically above a unit of Noachian high-calcium pyroxene. Nontronite, a smectite clay that frequently forms due to the alteration of basalt or by precipitation of iron-rich hydrothermal fluids, is identified directly below the cap-rock while chlorite is identified stratigraphically below the nontronite. Nontronite is known to convert to chlorite in 1) shallow water environments, 2) where wet-dry cycling occurs or 3) in the presence of iron-rich waters. Both phyllosilicates are associated with unit Npld, as is the underlying HCP. Phyllosilicates have also been observed on the north-central Argyre rim around Hale and Bond craters, where Argyre-draining waters have been theorized, and in a ~14 km crater southwest of Hale towards the Argyre interior, in a region of probable fluvial dissection. Also, at least two high-standing knobs in the northwestern Agyre interior have a strong phyllosilicate signature. A targeted observation of one of the knobs indicates prehnite, which is known to form due to the hydrothermal alteration of mafic igneous rocks. Observations of the other phyllosilicate locations indicate the presence of chlorite and other minerals that form due to the hydrothermal alteration of ferromagnesian minerals. In all cases, these phyllosilicates are found stratigraphically above (or between) pyroxene-rich materials.
P53B-1451
Modeling the Martian neutral particle radiation - predictions for ExoMars/IRAS and implications for Martian habitability during the Noachian
The exciting results of recent Mars exploration missions indicate that water existed on the Martian surface, which provides a possibility for life on Mars. Thus, there is an enhanced interest in analyzing the conditions for habitability on Mars, especially in the Noachian epoch. An important aspect of habitability is the radiation level of charged and neutral particles in possible habitats. Using Planetocosmics, we calculate particle radiation in the Martian atmosphere and at ground level for present-day conditions. These calculations allow us to make predictions for the measurements of the Ionizing Radiation Sensor (IRAS) on ExoMars. By changing atmosphere conditions and varying the water-content of the Martian soil, we can derive radiation levels expected during the Noachian period. We will discuss the implications of these model results in terms of Noachian habitability.
P53B-1452
Martian Interior Structures and the Termination of Martian Dynamo
Several recent research results on the Martian crustal magnetic anomalies and the giant impacts on the surface provide new insights on the Martian dynamo and the likely correlation of its timing with the formation of the giant impact basins on the Mars: the Martian dynamo could be subcritical during this period, i.e. it can be terminated by small perturbations (≤ 1%) to the heat flow (the Rayleigh number) across the CMB and, once terminated, it could not be reactivated unless substantial increases in the heat flow (e.g. 25%). The giant impacts during the early to mid-Noachian period could be sufficient to provide the perturbations to turn off the Martian dynamo. Could Martian interior structures introduce complexities to this scenario? The numerical simulation of the subcritical dynamo is carried out with a finite solid inner core of a radius approximately one third of the core- mantle boundary radius and with a uniform heat flux across the CMB. It is very likely that the heat flux is heterogeneous due to geophysical processes outside the CMB. The inner core size is unknown even if it was formed in the dynamo era. What are the consequences of these complications, in particular the inner core dimension, to the Martian dynamo and its termination? We continue our numerical simulations with three different core sizes, focusing on exciting dynamos from purely convecting states and termination of an existing dynamo. Our initial results show that the critical Rayleigh number for the dynamo onset increases when the inner core size is reduced. This could imply a larger subcritical domain, provided that the critical Rayleigh numbers for the termination of the dynamos do not increase equally fast. In addition, numerical results suggest multiple dynamo states near the onset of the dynamo, which could bring multiple subcritical branches of the subcritical Martian dynamos.
P53B-1453
A Sustained Greenhouse Climate and Erosion Period on Mars Following an Impact Event
The existence of craters of size 200 km and greater proves that large (> 30 km diameter) impacts were abundant in the early history of Mars. Injected water from three sources (the impactor, water innate to the crater, and from melting of the polar caps) provides periods of rain following such impacts. Very hot, global debris blankets are another consequence of these large impacts, and these layers create a thermal pulse that propagates into the subsurface, melting additional water. The melted and precipitated water and debris blanket combine to produce a temporarily altered climate. The effects of moderate-sized (30-100 km diameter) impacts on Mars were studied using a 1-dimensional radiative-convective model. The model computes the evolution of temperature following an impact and includes: a subsurface model to compute the evolution of the ground temperature; a hydrological cycle to follow the evaporation, condensation and precipitation of injected and surface evaporated water; a radiative transfer code to compute greenhouse warming by CO2, water vapor, and water clouds; and an atmospheric thermodynamics module to compute the latent heating due to cloud formation/dissipation. We have found that parts of the Martian regolith may be kept above freezing for 95 days to decades by the modeled events. However if we include the radiative effects of water clouds, a sustained greenhouse climate is computed for impactors 50 km in size that could be centuries-long. The amount of water precipitated out of the atmosphere from vaporization of impactor, target, and polar caps, yields global rainfall totals ranging from 40 cm to 18 m depending on the size of the impactor and assumed background CO2 atmosphere. We also estimate the surface erosion following precipitation events and find that the total erosion done by all impactors in time is the same order of magnitude as the total erosion estimated [Golombek and Bridges, 2000] to have occurred on Early Mars.
P53B-1454
Volatile Mobilization by Large Impacts: Constraining the Initial Conditions of an Impact- generated Martian Greenhouse.
There is substantial evidence for the presence of liquid water on the surface of Mars contemporary to the Late Heavy Bombardment. Large asteroid and comet impacts have been suggested by Carr (Water on Mars, 1996) and Segura et al. (Science, 2002) as possible triggers of warm and wet climate episodes early in Martian history. Here we model impacts into complex, stratigraphically realistic models of Noachian Mars as described by Nimmo and Tanaka (Ann. Rev. E. P. Sci. 2005). We do this in order to determine a lower bound on the energy and size scales of impact events that could trigger such a climate shift, and thus establish an upper bound on the frequency of such events. The frequency, magnitude, and surface effects of these large impacts would have had a significant effect on the habitability of Noachian Mars. This effort is supported by LANL/IGPP (CSP, RPW, KHW), by NASA PG&G (EA), and by NASA MFR (CSP, DGK).
P53B-1455
Very Large Impacts in the Pre-Noachian on Mars: Conditioning the Noachian Environment
There are at least 20 very large impact basins on Mars with diameters greater than 1000km. Crater retention ages for these indicate that most of them formed in a relatively short interval of time: a conversion to a Hartmann-Neukum chronology suggests 15 of 20, including 4 of the 5 largest (with diameters larger than 2500 km), may have formed in only 100 million years and 18 of the 20 may have formed in only 200 million years. The short, spike-like duration supports a Nice-like Late Heavy Bombardment (LHB) scenario which may have produced a Terminal Lunar Cataclysm on the Moon at about 3.9 BYA, and which would have produced a similar cataclysm on Mars and the other planets of the inner solar system at the same time. The Noachian period on Mars which followed was clearly conditioned by these surface-sterilizing, atmosphere- disrupting impacts which may also have contributed to the demise of the global magnetic field. It is clear that the martian global field disappeared in perhaps less than a few tens of millions of years near the end of the period of large basin formation, based on which basins were and were not remagnetized after their formation. Recent thermal modeling suggests the impacts could produce the necessary perturbation across the core- mantle boundary to kill of a subcritical dynamo. Without a magnetic field, the Noachian atmosphere was subject to solar wind erosion, further reducing the habitability of this early time. But the relatively brief duration of the large impact bombardment (less than 200 million years) may allow a longer (400 million year?) more habitable earlier time prior to the bombardment, when the magnetic field was still present and the surface relatively unaffected by such large impacts.
P53B-1456
Physical Diversity of Phyllosilicate Deposits at the MSL Candidate Landing Sites
The identification of phyllosilicates on Mars implies aqueous activity at the time of their formation and is important for understanding the history of Martian water and the past habitability of Mars. In addition, a significant fraction of the global water budget of Mars may be locked into clay mineral deposits within the Martian crust. As a result, six out of seven final landing sites being considered for the Mars Science Laboratory are sites where phyllosilicates have been identified in CRISM and OMEGA data. The physical characteristics of these materials, as identified using thermal inertia data, are an important component for understanding the geologic history of these deposits. Thermal inertia values provide information regarding effective particle size and help to constrain the possible presence of duricrust, rocks, and exposed bedrock at these locations. These identified physical characteristics suggest the degree of resistivity to erosion, which has implications for the post-emplacement modification of these deposits. At the aforementioned six locations (Nili Fossae Trough, Holden Crater, Mawrth Vallis, Miyamoto crater, southern Meridiani Planum, and Gale crater) the physical properties were quantified using THEMIS-derived thermal inertia data to characterize the physical properties at each site and identify the presence or absence of physical diversity among these materials. I identified a wide range of surface properties at these locations ranging from indurated surfaces intermixed with unconsolidated aeolian material (thermal inertia of 150-460 J m-2 K-1 s- 1/2) at Mawrth Vallis, to exposures of in-place bedrock and the presence of rocky material (thermal inertia exceeding 800 J m-2 K-1 s-1/2) in Gale crater. In addition, the surface texture and morphologic features observed in high-resolution visible images (such as narrow-angle MOC, HiRISE, and CTX) are dissimilar across these phyllosilicate exposures, and confirm the interpretation of thermal inertia values. The diversity of the physical nature of these materials implies that the environment that deposited phyllosilicates on Mars and their post-emplacement modification is not consistent across all deposits. This result has important implications for the interpretation of their emplacement and subsequent history, and the potential role of water in these regions.
P53B-1457
Cerro Negro, Nicaragua: A key Mars Analog Environment for Acid-Sulfate Weathering
Sulfate-rich bedrock has been discovered in many locations on Mars and has been studied by both orbiting spacecraft and landers. It appears that in most cases these minerals are produced by acid-sulfate weathering of igneous rocks, which may have been a widespread process for the first billion years of Mars' history. The origin of life on Earth may have occurred in iron-sulfur hydrothermal settings and it is conceivable that early Mars had similar environmental conditions. An excellent terrestrial analog for acid- sulfate weathering of Mars-like basalts exists at Cerro Negro (CN), Nicaragua, where sulfur-bearing gases interact with recently erupted basaltic ash in numerous fumaroles. To date, we have made two expeditions to CN to assess the chemical, mineralogical, and biological conditions. At the fumaroles pH ranges from <1 to 5 and temperatures range from 40 to 400° C. Basalts with a chemical composition very similar to those on Mars are being chemically altered in the solfatara setting. In a few years, freshly erupted basalt can be converted into predominately Ca-, Mg-, and Fe-sulfates, Fe-hydroxides (including jarosite), clays, and free silica. Altered rocks have up to 30 wt% SO3 equivalent, which is similar to the Meridiani Planum bedrocks and inferred in other sulfate-bearing bedrock on Mars. Moreover, heavily weathered rocks have silica contents up to 80 wt%, similar to silica-rich soils at Gusev Crater that possibly formed in hydrothermal environments. Samples were collected for biological analysis including enrichment and isolation of novel thermophiles as well as molecular characterization of thermophile diversity. The low water and nutrient levels found in solfatara environments lead to less biomass when compared to hot springs with similar geochemical conditions. Nonetheless, microbes are thriving in these hot, acidic vent environments. At Cerro Negro solfatara, we are characterizing the metabolic and phylogenetic diversity of resident microbial communities in order to yield clues to the habitability of similar environments on early Mars.