P21A-0196 0800h
Pancam Photometric Observations at the Mars Exploration Rover Landing Sites
The Panoramic Cameras (Pancam) on the Spirit and Opportunity Mars Exploration Rovers have made dedicated multispectral reflectance observations of rocks and soils at different incidence, emission, and phase angles that will be used for photometric modeling of surface materials. Pancam filters normally used for these observations were 432, 601, 753, and 1003 nm. Spirit has made observations at four locations in the Gusev plains pointed along the antisunset and antisunrise directions (photometric equator) at 2-3 times per day. On two occasions these data sets were complemented by additional measurements pointed in orthogonal directions. At the rim of "Bonneville" crater, observations of the crater rim and interior were made at 5 times of day and are supplemented by images acquired as part of panoramas at 4 other times of day. At the Opportunity landing site, three sets of measurements were acquired along the photometric equator within the confines of "Eagle" crater, encompassing both dark soils and outcrop materials. These were supplemented by two near-field, targeted observations of regions containing many hematite-rich spheroidal granules. Additional images were acquired in the plains between "Eagle" and "Endurance" craters at 4 times of day along the photometric equator and at orthogonal directions. Stereo images acquired as part of these sequences are being used to construct surface normal maps from which incidence, emission, and phase angle images are derived for local surface facets (Soderblom et al., this issue). This will improve corrections for diffuse vs. direct sunlight and the derivation of photometric functions and Hapke parameters for rock and soil surfaces. Phase angle coverage at both sites extends from 0 deg to 155 deg. Preliminary analysis of these data reveals increasing reflectance at low phase angles associated with the opposition effect, and increasing reflectance at high phase angles (forward-scattering), particularly for smooth rock facets, fine-grained drift materials, and spherules. These findings are consistent with the results from the Viking and Mars Pathfinder lander cameras. Photometric imaging sequences during the Extended Mission will include the outcrops at the Columbia Hills (Spirit) and the dunes in the interior of "Endurance" crater (Opportunity), acquired during lower atmospheric opacity conditions.
P21A-0197 0800h
True Color and Chromaticity of the Martian Surface and Sky from Mars Exploration Rover Pancam Observations
We calculate the quantitative color of Mars using calibrated data from the Panoramic Cameras (Pancams) on the Mars Exploration Rovers Spirit and Opportunity. Measured color values allow us to directly compare the color properties of the rover landing sites with the Mars Pathfinder and Viking Lander sites, to quantify systematic changes in color over time, and to increase our perceptual understanding of conditions on the Martian surface. By converting calculated color values to the sRGB color space employed by the majority of modern computer monitors and printers, "true color" representations of the martian surface and sky are produced. Initial colorimetry values are calculated as CIE tristimulus values (the red, green, and blue components of human color vision). Calibrated radiance images from the six discrete left eye Pancam narrow band filters (centered at 753, 673, 601, 535, 482, and 432 nm) are splined to estimate an entire human visible spectrum (360 to 830 nm) for each pixel. Tristimulus values are found by discretely summing over the products of the spectra and 3 CIE color matching functions, allowing chromaticities (normalized tristimulus values) to be calculated. CIE tristimulus values are convolved with a transformation matrix to create sRGB tristimulus values which are then fit to a 2.2 gamma curve and scaled to the range of 0 to 255, 24 bit encoding (8 bits/channel) used by the majority of color displays. An average normalized surface spectrum is used to approximate chromaticities for images with only partial left eye filter sets. Chromaticity values of the martian sky and surface at various points throughout the mission generally match those from the Pathfinder and Viking landing sites. Using the color designation method defined by the ISCC-NBS, the martian sky is "light to moderate yellowish brown," while average rocks and soil vary between "dark grayish yellowish brown" to "moderate brown". Study of changes in the colors of the rover calibration targets over the first 200 sols of each mission show that the chromaticities are trending towards the "dark yellowish brown" portion of the color space, indicating that the calibration targets are getting covered by martian dust as the mission progresses and allowing a quantitative estimate of dust deposition rates. A similar study of sky chromaticities throughout the missions shows trends in the color of the sky towards "very light yellowish brown." Comparing these trends with measured dust opacities throughout the missions would predict that, to the human eye, the "true" martian sky (with no suspended dust) would appear a very light yellowish brown color - almost directly opposite from the color of Earth's sky. However, this hypothesis needs to be tested against multiple scattering radiative transfer models of the martian sky radiance field.
P21A-0198 0800h
Mars Exploration Rover Pancam Photometric Data QUBs: Definition and Example Uses.
Pancam multi-spectral observations acquired at the Mars Exploration Rover Spirit and Opportunity landing sites are being assembled into a multi-layer format know as a QUB. For any given pixel in a Pancam image the QUB will contain values for the radiance factor, incidence (i), emission (e), and phase (g) angles, X, Y, and Z distance in a rover-based coordinate system, disparity in number of pixels between the left and right eye images and range data. Good range data is required for the generation of a Pancam QUB. The radiance factor (I/F, where I is the measured scene radiance on sensor and $\pi$F is the incident solar irradiance) is calculated using a combination of preflight calibration data and information obtained from near-simultaneous observations of an onboard reflectance calibration target. The range, X, Y, Z and disparity data, and i, e, and g are calculated using routines developed by JPL's MIPL and Cornell. When possible, these data have been interpolated to maximize parameter coverage; a map of non-interpolated data is also included in each QUB. QUBs should prove very useful in photometric studies ({\it e.g.}, Johnson {\it et al.}; Seelos, {\it et al.}, this conference), detailed spectral analyses ({\it e.g.}, Bell {\it et al.}, this conference), and detailed topographic/DTM studies. Here we present two examples of the utilization of the information contained in Pancam QUBs. In one example we remove the photometric variability from spectra collected from multiple facets of a rock using knowledge of i, e, g and derived photometric functions. This is necessary if one wishes to conduct comparative studies of observations acquired under varying geometries and lighting conditions. In another example we present an analysis using the discrete ordinate multiple scattering radiative transfer code DISORT where we separate the atmosphere and surface contributions of the surface reflectance.
P21A-0199 0800h
Radiative Transfer Photometric Analysis of Surface Materials at the Mars Exploration Rover Landing Sites
The Mars Exploration Rover (MER) Panoramic Camera (Pancam) observation strategy included the acquisition of multispectral data sets specifically designed to support the photometric analysis of Martian surface materials (J. R. Johnson, this conference). We report on the numerical inversion of observed Pancam radiance-on-sensor data to determine the best-fit surface bidirectional reflectance parameters as defined by Hapke theory. The model bidirectional reflectance parameters for the Martian surface provide constraints on physical and material properties and allow for the direct comparison of Pancam and orbital data sets. The parameter optimization procedure consists of a spatial multigridding strategy driving a Levenberg-Marquardt nonlinear least squares optimization engine. The forward radiance models and partial derivatives (via finite-difference approximation) are calculated using an implementation of the DIScrete Ordinate Radiative Transfer (DISORT) algorithm with the four-parameter Hapke bidirectional reflectance function and the two-parameter Henyey-Greenstein phase function defining the lower boundary. The DISORT implementation includes a plane-parallel model of the Martian atmosphere derived from a combination of Thermal Emission Spectrometer (TES), Pancam, and Mini-TES atmospheric data acquired near in time to the surface observations. This model accounts for bidirectional illumination from the attenuated solar beam and hemispherical-directional skylight illumination. The initial investigation was limited to treating the materials surrounding the rover as a single surface type, consistent with the spatial resolution of orbital observations. For more detailed analyses the observation geometry can be calculated from the correlation of Pancam stereo pairs (J. M. Soderblom et al., this conference). With improved geometric control, the radiance inversion can be applied to constituent surface material classes such as ripple and dune forms in addition to the soils on the Meridiani plain. Under the assumption of a Henyey-Greenstein phase function, initial results for the Opportunity site suggest a single scattering albedo on the order of 0.25 and a Henyey-Greenstein forward fraction approaching unity at an effective wavelength of 753 nm. As an extension of the photometric modeling, the radiance inversion also provides a means of calculating surface reflectance independent of the radiometric calibration target. This method for determining observed reflectance will provide an additional constraint on the dust deposition model for the calibration target.
P21A-0200 0800h
Magnetic properties of dust on Mars - Results from the Mars Exploration Rovers
Results from the "Magnetic Properties Experiments" onboard the Mars Exploration Rovers Spirit and Opportunity will be presented. Each rover carries seven magnets for detailed investigation of the magnetic properties of airborne dust and rocks on Mars, each magnet with a specific scientific purpose. The ring shaped sweep magnet has attracted airborne dust and the results from analysis of Pancam images from both rovers show that essentially all the dust suspended in the Martian atmosphere is somewhat magnetic in the sense that the particles are attracted to permanent magnets. The capture and filter magnet are designed so that the capture magnet is as strong as possible, and therefore has attracted all magnetic dust particles within its reach, while the filter magnet is designed to preferentially attract the more strongly magnetic dust particles. Differences in reflectivity spectra from these two magnets as observed by Pancam show that the filter magnet have succeded in picking out a more magnetic fraction of the airborne particles on both rovers. This provides interesting samples for further studies by the Microscopic Imager, the APX spectrometer and the Mossbauer spectrometer. The four RAT magnets, placed in the Rock Abrasion Tool, provide information about the magnetic material present within the rocks. There are three different RAT magnets; two of the four magnets (#1) are identical and very strong. These magnets are designed to attract all magnetic particles from the grinding process that happen to come close to this magnet, while the two other RAT magnets (#2 and #3) are different and designed - as the filter magnet - to different degrees to attract and hold preferentially the more strongly magnetic particles liberated by the grinding process.
P21A-0201 0800h
Terrain Roughness from MER Traverse Profiles at Gusev Crater and Meridiani Planum
During the traverses of the Mars Exploration Rovers Spirit and Opportunity over their respective landing sites, telemetry data were collected from the rover inertial measurement unit (IMU) and suspension system at 2-8 Hz. Joint angles in the rover's rocker-bogie suspension system, rover attitude, and rover reported position were used to calculate x-y-z coordinates of each of the six rover wheels. These data were used to create mm-scale topographic profiles along selected rover traverses. Terrain at Meridiani Planum is remarkably flat, consistent with predictions from orbital data. For example, the 140.9 m long sol 82 traverse shows a variation of 40.3 cm over the total traverse with a height standard deviation of only 3.2 cm over the first 55 m. In contrast, profiles from the Gusev crater landing site are rougher and characteristic of a surface with abundant rocks and hollows. The sol 45 and 50 traverses show the profile of Laguna Hollow, a ~20 m wide and half meter deep crater. At both landing sites, cm scale periodicity is evident in some segments of the traverse, suggesting the wavelength and amplitude of aeolian bedforms is being sensed and recorded by the rover wheels. Data are being analyzed to compute surface roughness statistics (RMS height, RMS deviation, and Hurst exponent) and evaluate azimuthal dependency of roughness. These statistics, when compared to those of analog terrestrial terrains, provide insight into the geomorphological processes shaping the martian surface in Gusev Crater and at Meridiani Planum. Further, along with stereo imaging from Pancam and Navcam, examination of topographic profiles allows ground truthing over multiple length scales terrain roughness estimates derived from radar scattering and MOLA pulse width.
P21A-0202 0800h
The Size-Frequency and Areal Distribution of Rock Clasts at the Spirit Landing Site, Gusev Crater, Mars
Data returned by the Mars Exploration Rover, Spirit, have revealed important information about the processes that have shaped landscapes in Gusev crater. In this work, we add to an understanding of surface processes by examining the size-frequency distributions and spacings of rock clasts along the Spirit traverses from its landing site to the base of the Columbia Hills (an $\sim$3.5 km distance via wheel odometry). Panoramic and Navigation Camera images reveal a surface that has been modified by volcanic, impact, and eolian processes. Size-frequency measurements of clasts between $\sim$0.1 and 10 cm reveal geometric mean clast sizes that increase along the approach to the $\sim$180 m diameter Bonneville crater. Clasts on the intercrater plains are finer-grained and better sorted than clasts found on the rim of Bonneville and the rims of hollows (presumed secondary impact craters). Further, statistical analysis relative to randomly dispersed clasts indicates that clasts on the intercrater plains are evenly spaced. We suggest that these clasts (geometric mean: 1.8 cm, geometric standard deviation: 1.6) were evenly dispersed by wind to the point where surface roughness became too low to initiate further clast motion. In fact, the clast threshold velocities for movement are too high under current atmospheric conditions. This implies that the clast evening process probably occurred when the atmosphere was denser in the Martian past. In contrast, our analyses indicate that the evenly spaced clasts on Earth that we have inventoried could have been moved under current terrestrial atmospheric conditions.
P21A-0203 0800h
Hyperspectral Imaging of a Chemosynthetic Seep System in the Panoche Hills, California: A Possible Terrestrial Analog for Mixed Carbonate-Silicate Deposits on Mars
Chemosynthetic communities and carbonate substrate forming at cold seeps represent a unique ecosystem for studying life in extreme environments, such as Mars. Carbonate hardgrounds form due to the upward seepage of bicarbonate saturated fluid derived from methane oxidation. Carbonates can precipitate in the subsurface, resulting in high preservation potential. In the Panoche Hills of California, carbonate seep deposits contain fossilized chemosynthetic organisms and have negative carbon isotopic compositions, similar to other ancient cold seep deposits. The carbonates occur as mounds, concretions and pavements. The carbonate seep deposits of the Panoche Hills have been mapped in detail in the central portion of the field area and identified in the northern portion. These carbonates are well exposed, which make them good targets for remote sensing. Our remote sensing information is a 2 km by 8 km swath of HyMap hyperspectral data centered on the geologically well-mapped area. HyMap has 126 bands from visible to short wave infrared wavelengths (0.45 to 2.5 YYm). Carbonates have a diagnostic absorption feature at 2.34 YYm, within the range of HyMap's accuracy. Further, the carbonate seeps measure up to 10 meters across, and are detectable with HyMap's spatial resolution of 3-meter pixels. The methane derived carbonates of the Panoche Hills formed below the sediment-water interface and incorporated a significant amount of silicate minerals, complicating the spectral identification of carbonate. Spectra and GPS locations collected in the field provided data for comparison and helped to classify carbonates associated with siliciclastic material. A spectral library, based on field spectra, was used as input for classifying with ENVI remote sensing software. The successful inputs applied to the data set found potential unmapped carbonate localities as well as correct identification of previously mapped locations. Spectroscopic investigations on Mars suggest the presence of a small amount of dispersed carbonate minerals in the Martian dust and hematite concretions within sulfate deposits; carbonate formation probably followed sulfate development during evolution to the present atmospheric state. The remote detection of carbonate seeps at the Panoche Hills may serve as a terrestrial analog in the search for Martian carbonates.
P21A-0204 0800h
Martian Regolith Analog Experiments
We describe a set of laboratory experiments designed to investigate Martian regolith hydrodynamics and to test the MAGHNUM computer model. A previous study with MAGHNUM (JGR-Planets 108: 8040-8054) indicated that if H2O is present in the Martian regolith, as is widely believed, then liquid water could be present beneath the cryosphere and it should be in a convective state, locally thinning the cryosphere above warm, upwelling hydrothermal plumes. Our experimental system is designed to match the Rayleigh number believed appropriate for the Martian regolith. The tank is 1.5 m wide, 0.5 m tall, 0.1 m thick, insulated on front and back sides. A constant temperature is applied to the bottom, and a chiller maintains the surface at subzero temperatures. The tank is filled with 37% porosity pea gravel. Both de-ionized pure water as well as salt (CaCl2) solutions are used. Qualitatively, experimental results and MAGHNUM simulations agree. In all cases, hydrothermal convection develops beneath a frozen layer. Convection with salt solutions exhibits more time dependence than with pure water, both in the experiments and in numerical simulations. Quantitative comparisons are in progress.
P21A-0205 0800h
Hydrated Salts: Dehydration, Dissolution, and Incongruent Melting In Terrestrial Evaporites and at Meridiani Planum, Mars
The Opportunity rover and orbital observations of Meridiani Planum (Mars) have revealed much about the region's stratigraphy, chemistry, sedimentology, and mineralogy of what appears to be a layered lacustrine sedimentary sequence, including chemical sediments deposited by evaporative or freezing processes in a large, saline lake or sea. The roles of evaporation versus freezing are not clearly elucidated in the data, but both freezing and evaporation are likely on Mars for any paleoclimate scenario that minimizes excursions from current climate. The rock sequences reveal many interesting features reported in press accounts, NASA press releases, and in conference presentations by the MER science teams. The topic dealt with here concerns indirect sedimentologic indications of phase changes that seem to have generated negative volume changes due to dehydration, dissolution, and/or annealing. These indicators include microkarstic and polygonal structures in the laminated chemical sediments. These processes have operated on a small scale at Meridiani Planum, and serve as possible analogs for processes operative on mega scales elsewhere on Mars. Comparable processes are common in terrestrial evaporite basins and in sequences of evaporitic rocks. Fluctuations of mineral water content drive large changes in volume and pore fluid pressure, and these exert stresses that can drive extensional fracturing and faulting, folding, thrusting, and diapirism. These processes may be even more important on Mars than on Earth, because on Mars solid salts may be more abundant, more widespread, and subject to larger ranges of hydration states; the effects of these processes may be better preserved for lack of erasure by fluvial erosional processes and other degradational processes on Earth's more active surface. Specific processes and reactions proposed here can account for the sedimentologic structures observed at Meridiani Planum based on aqueous chemical phase equilibria and phase-volume data applied to the mineralogies and chemistries observed or inferred from spacecraft data. Dehydration and/or open-system incongruent dissolution of Mg-Fe-Ca-sulfate hydrates can explain both the microkarstic and decimeter-scale polygonal structures observed by the Opportunity rover. Close analogs of these inferred processes and observed features are common in terrestrial evaporite sequences. Considering scenarios for minimized excursions from current climate, we attribute the structures either to dehydration or dissolution etching by cryogenic acid brines-- or both operating in tandem or in sequence. These processes operating at low rates may remain active even as Opportunity observes the layered/laminated rock sequence. Inclusion on future spacecraft of simple soil pH measurements would do much to resolve questions of possible present-day activity of acidic brine films. Because many salt dehydration steps occur at temperatures far below the melting point of ice, future differential scanning calorimetry/thermal analysis must consider very small increments of heating in the 200-400 K temperature range if we are to understand adequately the composition and hydration states of Martian salts.
P21A-0206 0800h
Spectroscopic Study of Sulfates Applied to Mars
Definitive evidence for sulfates on Mars has been presented in 2004, including the Mars Exploration Rover Moessbauer spectroscopic identification of jarosite in Meridiani Planum and the Mars Express OMEGA visible/near infrared spectroscopic identification of kieserite in Valles Marineris and elsewhere. In addition to Moessbauer and VIS/NIR, other spectroscopic techniques can be employed for determining which sulfate minerals are present on Mars. This study focuses on the use of the thermal infrared range of the electromagnetic spectrum and the study of sulfates using emission spectroscopy to uniquely identify sulfate minerals. The fundamental molecular vibrational modes of sulfates are present in thermal infrared spectra. These modes influence the overtones and combination bands seen in VIS/NIR data. Clearly sulfate minerals are important Martian geologic materials and, because sulfates form under diverse environmental conditions, can help understand the specific formational and chemical settings that once existed on Mars.
P21A-0207 0800h
Salt Attack on Rocks and Expansion of Soils on Mars
Salt-rich sediments observed by the MER rover Opportunity at Meridiani Planum show that brines have been present on Mars in the past, but a role for groundwater in widespread rock weathering and soil formation is uncertain. Experiments by several groups suggest instead the action of acid fog over long time spans, with episodic input of volcanic gases, as a more significant agent of Mars weathering. Salt minerals formed in these acid weathering experiments consistently include gypsum and alunogen, with epsomite or hexahydrite forming where olivine provides a source of Mg. Analogous to the martian acid fog scenario are terrestrial acid rain or acid fog attacks on building and monument stone by chemical action and mechanical wedging through growth of gypsum, anhydrite, epsomite, hexahydrite, kieserite, and other sulfate minerals. Physical effects can be aggressive, operating by both primary salt growth and hydration of anhydrous or less-hydrous primary salts. In contrast, soils evolve to states where chemical attack is lessened and salt mineral growth leads to expansion with cementation; in this situation the process becomes constructive rather than destructive. We have made synthetic salt-cemented soils (duricrusts) from clays, zeolites, palagonites and other media mixed with ultrapure Mg-sulfate solutions. Although near-neutral in pH, these solutions still exchange or leach Ca from the solids to form cements containing gypsum as well as hexahydrite. At low total P (1 torr) and low RH ($ < $1%) hexahydrite becomes amorphous but gypsum does not. If allowed to rehydrate from vapor at higher RH, the Mg-sulfate component of the duricrust expands by formation of a complex mixture of Mg-sulfate phases with various hydration states. The expanded form is retained even if the duricrust is again dehydrated, suggesting that soil porosity thus formed is difficult to destroy. These processes can be considered in the context of Viking, Pathfinder, and MER evidence for differing salt components in the weathered surfaces of rocks versus duricrust-like materials in soils. The divergent chemical trends indicate that soil formation on Mars is not merely a result of enhanced weathering of locally comminuted rock but requires an eolian component. The resulting soils thus appear to be a three-component mixture of local detritus, a regional or global eolian component, and acid fog additions. In the absence of rainfall or groundwater action, expanded and salt-cemented soil horizons are likely to persist as a regolith component in soil-atmosphere interactions over long time spans.
P21A-0208 0800h
Acid fog Deposition of Crusts on Basaltic Tephra Deposits in the Sand Wash Region of Kilauea Volcano: A Possible Mechanism for Siliceous-Sulfatic Crusts on Mars
Although the presence of sulfate minerals in martian outcrops may imply the prior existence of standing bodies of surface water, in terrestrial volcanic settings, sulfatic alteration may also occur above the water table within the vadose zone. On the summit of Kilauea volcano, sulfur dioxide, which is continuously emitted from Halemaumau crater and rapidly sequestered into sulfuric acid-rich aerosol entrained in the prevailing trade winds, is subsequently precipitated as acid-fog immediately downwind from the caldera in the Kau Desert. The characteristic pH of surface tephra deposits is $ < $ 4.0 in Sand Wash, a region of continuous, acidic aerosol fall-out immediately SW of the caldera. The upper portion of the Keanakakoi Ash tephra in Sand Wash, deposited in the late 18th century, has a ubiquitous, 0.1-0.2 mm-thick coating of amorphous silica. Conversely, vertical walls of unconsolidated tephra, exposed within small, dry gullies eroded into the ca. 3-4 m-thick Keanakakoi section at Sand Wash, are coated with ca. 0.5-1.0 mm-thick, mixed amorphous silica and jarosite-bearing crusts. Since these crusts are denuded from their outcrops during ephemeral, but probably annual flooding events in Sand Wash, we believe that they must accumulate rapidly. These crusts are apparently formed via an evaporative mechanism whereby acidic pore fluids, circulating in the upper few m's within the highly porous tephra, are wicked towards the walls of the gullies. Geochemical modeling of the crust-forming process implies that the sulfate formation via evaporation occurs subsequent to minimal interaction of acidic pore fluids with the basaltic tephra. This also suggests that the cycle from acid-fog fall-out to precipitation of the siliceous-sulfatic crusts must occur quite rapidly. Production of siliceous-sulfatic crusts via acid-fog alteration may also be occurring on Mars. The occurrence of evaporitic sulfate and silica at Sand Wash in Kilauea may serve as an example of how the jarosite-bearing outcrop at Meridiani may have formed.
P21A-0209 0800h
Spectroscopy of Salt-Cemented Materials; Evidence for the Occurrence of Water in the Martian Surface Layer
Salt-cemented surfaces on Mars are key indicators of the role water played in the planet's past. Crusts and salts have been observed at the Martian landing sites and have been inferred from orbital measurements of thermal inertia and albedo. If water exists or existed at the surface of Mars, salt crusts would be expected to form, coating and cementing the upper layers of sediment. To date there is a lack of information on the infrared spectral properties of salt-cemented materials. Studies of playa environments have suggested that spectra of cemented surfaces may be very different from mixtures of particulates. Properties affecting the spectral features of salt-cemented surfaces include surface texture, spatial relationship to non-salt particles, abundance of salt, the degree of induration, the composition of the salt as well as the properties of the cemented material. In analyzing spectral observations of the Martian surface it is essential to characterize the unique spectral properties of salt-cemented materials. This study explores the formation of salt crusts and coatings and their relation to spectral properties in the thermal infrared. Laboratory results will be used to analyze thermal infrared data for Mars to constrain the mineralogy and abundance of salts on Mars and provide insight into the amount and distribution of water present at the surface.
P21A-0210 0800h
Mineralogy of Natural Basalt Weathering Rinds With Application to Thermal Emission Spectra of Mars
Mineralogy of Natural Basalt Weathering Rinds With Application to Thermal Emission Spectra of Mars M.D. Kraft, J.R. Michalski, T.G. Sharp, (and P.R. Christensen?) Chemically weathered rocks have been suggested to cover a significant portion of the Martian surface based on orbiter observations, and rocks investigated by the Mars Exploration Rover at the Gusev landing site show evidence of chemical alteration and weathering rinds. To understand remote mineralogical and chemical measurements of altered rock surfaces, whether in situ or from orbit, it is important to understand the general characteristics of weathering rinds (e.g., secondary mineralogy and microstructure in rinds) and how these characteristics affect remote observations. We are investigating a suite of weathered rocks of the Columbia River Basalt Group (CRBG) to identify chemical, mineralogical, and micro-structural changes associated with weathering and determine how these changes influence thermal emission measurements. Preliminary work shows that thermal emission spectra of weathered surfaces can vary substantially from spectra of fresh rocks despite rather low degrees of alteration in weathered surfaces. In rocks studied thus far, the predominant difference between the unweathered rock and weathering rind is an increase in porosity in the rind due to dissolution and/or volume expansion, causing a substantial increase in the volume density of micron-scale cracks. Mineralogical differences are imparted in the rind by the (partial) infilling of cracks by secondary materials that are Si, Al, and Fe-rich. A previous investigation by Colman (1982) showed that secondary silicates in basalt weathering rinds were dominantly X-ray amorphous. High-resolution secondary electron imaging of crack-filling products reveals spheroid-shaped materials, 10s of nm in diameter, which are consistent with short-range order allophane. We are currently performing additional analyses using XRD and TEM to constrain the mineralogy of secondary phases in CRGB weathering rinds, including the crystallinity of secondary silicates. Assessing chemical weathering on Mars may rely largely on the ability to detect and constrain the mineralogy of short-range order silicates, which may be the dominant Martian weathering products. Thermal emission spectroscopic data of Mars, with the detailed understanding that we intend to provide with this study, provides a unique and excellent means of constraining the nature of silicate weathering on Mars.
P21A-0211 0800h
Mars Orbit and Temperature: Why and When an Early wet Mars
It is the intent of this work to present a model which predicts the time when liquid water was present on Mars. Experimental evidence indicates that liquid water existed on the planet Mars at 2.9 - 3.4 billion years ago, when Mars was considered to be cold. A model is presented that predicts Mars orbit and temperature variations based on solar radiative and non-radiative (solar wind) mass losses which affect planetary orbits. Mars orbits are predicted between 198 and 206 million Km at its formation five billion years ago vs. presently 228 million Km. The correlation between the solar (radiative) constant and planetary orbit estimates the transition from liquid water to ice (273K) to have occurred at about 3.4-3.8 billion years before the present time, which is in good agreement with the experimental estimate (2.9 - 3.4 Byr). Additional effects that are expected to extend higher Mars surface temperatures closer to the present are discussed. Examples are the planetary cooling rate after formation and effects due to hothouse gases, like carbon dioxide and water vapor, and effects dependent on variations in solar volume.
P21A-0212 0800h
Toward Probing Martian Ground Ice Using Microwave Emission: Data and Calculations from Antarctic Dry Valley Analogs
Recent observations and modeling indicate widespread, near-surface ground ice on Mars, but leave its depth of occurrence and form (e.g., interstitial or massive) significantly uncertain. We show here that the propagation of surface temperature variations to depth, together with thermal microwave emission that originates from commensurate depths and which is observed over time, provide a basis to probe the nature and depth of ice deposits. We utilize analogs in Antarctic Dry Valley soils, where time-resolved temperature profiles reveal that surface temperature variations on daily and longer time scales propagate to depths of decimeters and greater, especially in desiccated, fine-grained (low thermal inertia) soils. For example, diurnal surface variations of 10C produce 3C variations at 20 cm depth in desiccated soil in Beacon Valley. Ice-cemented (but not saturated) soils in Victoria Valley, by contrast, show diurnal variations (with similar thermal forcing) of only a fraction of a degree at similar depths. Thus thermal microwave emission at wavelengths that probe to decimeter depths will also differ between cases. We compute expected properties of microwave brightness temperature time series using measurements of mineral dielectric properties (including observations of Martian analogs), mixing formulae to account for ice content, and recent theory from Winebrenner et al. (Annals of Glaciology, v 39, 2004). According to the latter theory, a single parameter governs the relationship between surface and brightness temperature time series. That parameter is a characteristic time-scale given by the square of the microwave emission depth-scale over the soil thermal diffusivity. Calculations show that the characteristic time-scale increases strongly with increasing ice content and with decreasing burial depth. Based on such variations, we outline a remote sensing method to estimate characteristics of ground ice based on infrared surface temperature and microwave brightness temperature observations with specified temporal resolution and duration. Existing satellite observations of spatially extensive terrestrial analogs can be used to develop this method for flight-readiness.
P21A-0213 0800h
Is Mars hiding some ice in Terra Arabia?
Only a few years ago the common notion was that Mars today is a dry place. With the excellent dataset of the Gamma and Neutron spectrometer (GRS and HEND) on board of Mars Odyssey this view had to be corrected. The instrument detected water abundance of at least 8wt% in the equatorial regions. There are three main explanations for this observed amount of water which are not mutually exclusive. Some of the water measured is most likely adsorbed water. However this mechanism can not explain the high abundances measured in some place. We might see highly hydrated minerals, which are capable of holding large quantities of water. The last and maybe most exciting possibility are near surface ice deposits. The question is, how did they survive close to the surface under the hyper-arid conditions we encounter on present day Mars? We do not have any direct evidence for ice at lower latitudes. From the GRS and HEND measurements we know that the polar caps extend under the surface. The near surface ice deposits one see at low latitudes might be only the tip of a global ice reservoir in shallow depths. The ice deposits at low latitudes could also be the remnants of the last Martian ice age, caused by obliquity changes. In this case one only sees the dwindling remains of large equatorial glaciers covering these regions during the last ice age. Both ice related scenarios would imply that Mars has, or at least had in the very recent past, large quantities of ice on or close to the surface. While working on model calculations for the stability of ice on Mars today we discovered a possible third scenario. We have studied cases where the soil consists of layers with very different thermo-physical properties. One of the scenarios we have looked at is a low thermal conductivity dust layer on top of a sand layer with a significantly higher thermal conductivity. Such configurations can be found for example in the Terra Arabia region. For this case we observed the formation of an ice lens at the boundary between the dust/sand material, effectively closing the pore space and significantly reducing downward diffusion. This leads to an actual enrichment of ice compared to the initially assumed mass of more than 50% within the dust layer. Results depend on the thickness and the parameters used of the layers. We will discuss the implication of such a scenario on our understanding of ice on Mars. The ice enriched layer might lead to an overestimation of the global ice inventory based on GRS and HEND measurements. The process of enriching the ice significantly slows the movement of the ice table to greater depth and can therefore stabilize ice over several thousands of years close to the surface. This implicates that we might indeed observe today the remains of the last Martian ice ages, but the assumed amount of ice moved across the planet can be significantly smaller than previously thought. Furthermore some of the "young" glacial feature one see today would have been formed not during, but after the last ice age and might even exist until today.
http://solarsystem.dlr.de/TP/BMST_en.shtml
P21A-0214 0800h
The HRSC Experiment on Mars Express: First Imaging Results from the Commissioning Phase
The ESA Mars Express spacecraft was launched from Baikonur on June 2, 2003, entered Mars orbit on December 25, 2003, and reached the nominal mapping orbit on January 28, 2004. Observing conditions were favorable early on for the HRSC (High Resolution Stereo Camera), designed for the mapping of the Martian surface in 3-D. The HRSC is a pushbroom scanner with 9 CCD line detectors mounted in parallel and perpendicular to the direction of flight on the focal plane. The camera can obtain images at high resolution (10 m/pix), in triple stereo (20 m/pix), in four colors, and at five different phase angles near-simultaneously. An additional Super-Resolution Channel (SRC) yields nested-in images at 2.3 m/pix for detailed photogeologic studies. Even for nominal spacecraft trajectory and camera pointing data from the commissioning phase, solid stereo image reconstructions are feasible. More yet, the three-line stereo data allow us to identify and correct errors in navigation data. We find that $ > $ 99% of the stereo rays intersect within a sphere of radius $ < $ 20m after orbit and pointing data correction. From the HRSC images we have produced Digital Terrain Models (DTMs) with pixel sizes of 200 m, some of them better. HRSC stereo models and data obtained by the MOLA (Mars Orbiting Laser Altimeter) show good qualitative agreement. Differences in absolute elevations are within 50 m, but may reach several 100 m in lateral positioning (mostly in the spacecraft along-track direction). After correction of these offsets, the HRSC topographic data conveniently fill the gaps between the MOLA tracks and reveal hitherto unrecognized morphologic detail. At the time of writing, the HRSC has covered approx. 22.5 million square kilometers of the Martian surface. In addition, data from 5 Phobos flybys from May through August 2004 were obtained. The HRSC is beginning to make major contributions to geoscience, atmospheric science, photogrammetry, and cartography of Mars (papers submitted to Nature).
P21A-0215 0800h
Hematite in Valles Marineris: Context, Composition, Distribution, Morphology, Physical Properties, and Comparison to Other Mars Hematite Deposits
Gray, crystalline hematite deposits have been identified by data from MGS TES at three areas on Mars: Meridiani Planum, Aram Chaos, and Valles Marineris. Remote sensing studies of the deposits at Meridiani Planum and Aram Chaos indicate that hematite occurs in relatively large, coherent, in-place stratigraphic units. In situ studies at the Meridiani Planum site by the MER Opportunity have revealed that the hematite is likely carried in spheroidal concretions that form lag deposits as they weather out of in-situ sedimentary layered deposits. The hematite occurrences in Valles Marineris are small, 5 - 35 km in diameter, and are discontinuous throughout the canyon system. In this study THEMIS, MOC, MOLA and TES data are used to investigate the geomorphology, composition, and thermophysical characteristics of hematite bearing deposits throughout the canyon system and compare them to the other hematite deposits on Mars. Hematite bearing deposits in Valles Marineris span an total elevation range of 5600m. Preliminary evaluation indicates no clear correlation of with latitude or longitude. In Ophir and Candor Chasmata, hematite is associated with relatively dark materials near or within interior layered deposits and may represent in-place units or erosional remnants. Deconvolution of TES spectra from Candor Chasma show hematite abundances from 5 to 12%. Associated materials exhibit compositions similar to TES Surface Type II, which has been described as a basaltic andesite or weathered basalt. In Capri Chasma hematite signatures generally correlate with layered units, which lie at similar elevations, and are within 1km of the mean. Dunes overlying and obscuring layered deposits do not contain hematite. Benches and breaks in slope near the boundaries of many layered deposits provide further evidence that the layers may represent in-place, stratigraphic units. Hematite in Capri Chasma may have formed in a single event, which involved deposition or reworking in standing water.
P21A-0216 0800h
Hematite Spherules of Meridiani Planum: Implications for Aqueous History at the Site
The thermal infrared spectral signature of bulk, grey hematite was the chemical "beacon" that focused the selection of Meridiani Planum as the landing site for the Mars Exploration Rover Opportunity, and aqueous processes were favored for its formation. Orbital data suggesting more bound water in accessory minerals at this location also supported this interpretation. After landing January 24, 2004, the Mini-TES instrument rapidly confirmed the thermal spectral signature of bulk hematite in soils on the plains surrounding Eagle crater and unevenly distributed within the crater. Observations within Eagle crater soon uncovered unusual spherical grains in abundance surrounding the outcrop and Microscopic Imager (MI) showed these grains eroding from within these rocks. They were dubbed "blueberries" by the team due to their spherical nature and their grey or blue appearance compared to their surroundings in various color composites of Pancam images. Extensive observations with the Mossbauer, Alpha-Particle X-ray Spectrometer (APXS) and Mini-TES instruments, especially of the "Berry Bowl" (i.e. with berries and adjacent berry-free rock), confirmed that these spherules are dominantly composed of hematite. Pancam spectra of individual spheres also match laboratory spectra of hematite. These spheres are found within and around outcrop rocks, across the plains of Meridiani, and rolling into the interior of Endurance crater. They are ubiquitous and remarkably even in size and tone. Grains are spherical to subspherical typically 2 to 6 mm in diameter. Opportunity has performed numerous operations with the Rock Abrasion Tool (RAT), and has sliced through individual spherules. The appearance after ratting shows limited or no interior structure and they remain uniformly grey in color. They can preserve scratches from the grinding wheel or become dislodged by ratting, indicating they are harder than the host rock. Several lines of evidence suggest the spheres are post-depositional diagenetic products. On Earth, oolitic iron occurs as concretions in Utah and in the Clinton Formation outcropping from New York into Alabama. Ferromanganese nodules occur in abundance on the modern sea floor and are found in the Great Lakes. Although diagenetic in origin, these terrestrial analogs have strong contrasts with what is observed on Mars, including diverse size, shape and composition of terrestrial samples, significant interior lamination and presence of nucleation centers that are lacking in the Martian spheres. The uniformity of composition and size of the Martian examples provide clues to the redox state of fluids at the time of formation and by analogy with seafloor nodules a rough estimate of the time required for growth.
P21A-0217 0800h
Target Transformation and Factor Analysis of Mini-TES Spectra and Comparison to TES and Laboratory Hematite Spectra
A main objective of sending the MER Opportunity rover to Meridiani Planum was to investigate the occurrence of gray, crystalline hematite detected by the Mars Global Surveyor Thermal Emission Spectrometer (MGS-TES) instrument. Among the instruments on the rover payload is the Mini-TES instrument, which serves as a complement to the orbital TES instrument and mid-infrared laboratory studies of hematite. The characteristic mid-infrared hematite spectrum contains strong absorptions at ~300, 450, and 540 cm$^{-1}$. An additional minor absorption is sometimes present at 390 cm$^{-1}$. The exact position, shape and relative strengths of these absorptions vary depending on the hematite formation process. The gray hematite at Meridiani Planum is present in the form of spherules that have been interpreted as concretions weathering out of a sulfate-rich outcrop. The spherules are also abundant on the plains of Meridiani and may be present as a lag. The shapes of the hematite features in Mini-TES spectra have not varied substantially despite many rock and soil observations made over the course of the mission, implying that the spherules have a uniform composition. Although neither the TES nor the Mini-TES instrument covers the full wavelength range over which the hematite spectral features are seen, the hematite spectra from both instruments are broadly similar. The TES and Mini-TES hematite spectra are matched best by a laboratory spectrum of a hematite sample that was produced by dehydroxylating goethite at $300\deg$C. However, there are some small differences between the Mini-TES hematite spectra and hematite spectra from MGS-TES and laboratory measurements that may yield some new insight into the hematite formation process. Target transformation and factor analysis techniques will be applied to Mini-TES spectra to isolate the various components, including hematite, to provide the best possible comparison.
P21A-0218 0800h
Explaining Meridiani Planum: The Modeled Frequency and Spatial Extensiveness of Episodes Warm Enough to Allow Ponding in Hesperian Mars
We have compounded a model of the evolution of Mars' inventories of CO$_2$ over its lifetime [1] in an effort to understand the likely path of evolution of Mars' climate from an apparently wet early Hesperian [2], suggestive of a large inventory of free CO$_2$, to what is expected to be a very low CO$_2$ inventory at present. Here we investigate the opportunity for diurnally averaged temperatures greater than the melting point of water on Mars during the Hesperian by utilizing sub-seasonal insolation patterns, especially during periods with high eccentricity. While recent MER Opportunity observations suggest an extensive body of water [2], observations of Hesperian valley networks suggest they are immature [3]. Hypsometric analysis [4] confirms that martian drainage basins are systematically different from terrestrial drainage basins, with very little erosion. The immaturity of martian drainage basins suggests they were formed by infrequent episodic fluvial action. Our evolutionary model was used to investigate the frequency of such episodes by incorporating obliquity and eccentricity variations consistent with recent Laskar et al. findings [5]. We develop a measure of the trend in the frequency of ponding by calculating the area-normalized fraction of degree-days above 273 K over 10 Myr time bins. Models that produce ponding in the Hesperian and reproduce the atmospheric pressure of the present show a rapid decline in ponding during the Hesperian, a result of sequestration of CO$_2$ into carbonate rocks. {\bf References} [1] Manning, C. V., et al. (2004) \emph{Icarus} submitted [2] Hynek, B. M. (2004) \emph{Nature} {\bf 431}, 156. [3] Irwin, R. et al. (2004) \emph{LPI Conf.} {\bf 35}, 1991. [4] Stepinski, T. F., (2004) \emph{JGR} {\bf E18}, 2005 [5] Laskar, J. et al. (2004) \emph{Icarus}, {\bf 170}, 343.
P21A-0219 0800h
Geomorphic and Spectral Mapping of Meridiani Planum Eastern Etched Terrain
Mars Orbiter Camera (MOC), Mars Orbiter Laser Altimeter (MOLA), Thermal Emission Imaging System (THEMIS), and Mars Express (OMEGA) data were compiled and coregistered for analysis of exposures of etched terrain materials in the eastern portion of Meridiani Planum (latitude: -$2.5\deg$ to $5\deg$N, longitude: $0\deg$ to $8\deg$E). The etched terrain in this region is a useful analog to the terrain underlying the hematite-bearing deposits at the Opportunity landing site. Etched materials in the study area are exposed in a NE-SW trending basin approximately 400 meters deep, 185 kilometers wide, and 315 kilometers long. We have mapped a stack (200 meters thick) of layered deposits which unconformably overlie the Noachian dissected cratered terrain. The surfaces range morphologically from smooth plains, patterned ground, and plains cut by interconnected ridges. Further, the units have distinct spectral signatures in OMEGA hyperspectral data (0.35 to 5.1 $\mu$m) acquired on orbit 485. Detailed morphologic and mineralogic maps for the eastern etched terrain will be presented and discussed.
P21A-0220 0800h
Chemistry and Mineralogy of the Regolith at the Gusev Plains
During sols 91 to 158, the Spirit rover traveled 2.3 km across the plains between the Bonneville crater and the Columbia Hills at Gusev crater. A fast traverse was designed for this part of the mission, to save time and rover resources for further investigations once Spirit arrived at the Columbia Hills. Nevertheless, a set of systematic science observations was conducted by Spirit during this travel for the morphologic, chemical, and mineralogical characterization of the rocks and soils of the plains. In addition to near- and mid-field rock surveys, thermophysical property measurements of soils, and atmospheric observations, one set of rover track observations (Pancam multicolor images and MiniTES spectra) was carried out every fourth driving sol. Two trenches were dug by the right-front wheel of Spirit at sols 113 and 135. Subsurface regolith at different depths was exposed in the wheel tracks and trenches. The trenches were studied by the full Athena science instrument payload. Also, short integration Moessbauer and APXS measurements were made inside of two rover tracks in addition to standard Pancam and MiniTES observations. For the regolith within both trenches (Big Hole ~ 6 cm and Boroughs ~ 11 cm deep), compared with the surface analyses, the APXS data showed higher S, Mg, Cl, the Moessbauer and Pancam spectral analyses showed higher oxidation state, and the Microscopic Imager revealed differences in soil cementation. In the Boroughs trench, Fe2+ in olivine decreases with increasing Fe3+/Fetotal. A normative calculation using APXS data, along with Moessbauer curve-fitting results to constrain the Fe-oxides, suggests a 16-20 wt% of MgSO4 and a decrease in olivine, Ca-feldspar, and Ca-pyroxene proportions in the regolith comparing with the Gusev surface regolith. Our analysis suggests a relatively low degree of alteration of the rocks and regolith around the trench site in a probably acidic environment. During the alteration, olivine grains were partially dissolved; some Fe2+olivine may have converted into Fe-oxides; magnesium ions were released from olivine and transported by fluids, and eventually deposited as Mg-sulfate in the regolith of topographically low plains. The fluids involved in this alteration may have been short-lived, sporadic, and present only in small quantities. The vertical profiles of S, Mg, and Fe3+ in the regolith at the Boroughs may reflect the combination of fluid collection, evaporation, and mineral deposition. Alteration of basaltic material by water is clearly indicated by the investigations at the plains during the travel from the Bonneville crater to the Columbia Hills. Based on the geology, mineralogy, and chemistry, we consider that the plains are distinct in character from the Bonneville crater ejecta, and from the Columbia Hills now under exploration.
P21A-0221 0800h
A Quantitative Analysis of Extraction of Organic Molecules from Terrestrial Sedimentary Deposits
There are several factors determining the ability to detect organic molecules as part of a robotic astrobiology mission to planets. These include the quantity of organics present in a sample, the efficiency of extracting those organics from the matrix that they reside in (i.e. sample processing) and finally the detection efficiencies of the analytical instrumentation aboard the robotic platform. Once the detection limits of the analytical instrumentation is established, the efficiency of extraction becomes the overriding factor in the detectability of these molecules, and needs to be factored in. We analyzed four different terrestrial field samples, which were initially created in aqueous environments, are sedimentary in nature. These particular samples were chosen because they possibly represent a terrestrial analog of Mars [1] and they represent a best case scenarios for finding organic molecules on the Martian surface. The extraction efficiencies of amino acids (smallest building blocks of life) from the samples using pyrolysis and solvent extraction techniques (with seven different solvents: water, hydrochloric acid, butane, ethanol, isoproponal, methanol, n=propanal) are reported. In order to remove any instrumental bias, we used a standard laboratory bench-top high pressure liquid chromatograph (HPLC). We determined both absolute quantity of organics as well as the D/L ratio to determine the preservation of that information in the processing step. Acknowledgment: The research described here was carried out at the Jet Propulsion Laboratory, and was sponsored by the NASA PIDDP and ASTID program offices. References: [1] Malin M.C. and Edgett K.S. (2003) Science 302 1931-1934.