P32A-01 INVITED
Overview of Initial Results from CRISM
The Mars Reconnaissance Orbiter (MRO) reached 100 days of primary science phase operations on February 15th, 2007. Over this time period, the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) has acquired high spatial resolution hyperspectral observations and contextual multispectral survey data of type localities that record water-rock interaction through much of the geologic history of Mars. CRISM's primary science objectives are to characterize the mineralogical record of past aqueous environments and to monitor the contemporary spatial and seasonal distributions of volatiles in the surface-atmosphere system. These objectives are accomplished through an observation strategy that includes targeted data acquisition, atmospheric and seasonal monitoring, and global mapping. Targeted observations are acquired by gimbaling the instrument along-track to reduce apparent ground motion, resulting in a spatial resolution of 15-20 m/pixel in 544 wavelengths from 362 to 3920 nm. As a part of each targeted observation 10 additional spatially binned images are acquired at different atmospheric path lengths, creating an emission phase function (EPF) that allows surface-atmosphere separation in the analysis of the observed radiance. The atmospheric and seasonal monitoring campaigns consist of global grids of EPF measurements at regular Ls intervals. In CRISM's global mapping campaign, data are acquired in a push broom observing mode at a reduced spatial and spectral resolution of 200m/pxl and 72 selected spectral channels. Initial data analysis reveals evidence for environmental variability throughout Martian history. Noachian deposits exhibit diverse phyllosilicate mineralogy in a greater number of geologic units than previously recognized. Distinct mineralogic signatures are sometimes separated only by hundreds of meters, indicating variability in alteration environment or parent rock composition. Hesperian layered deposits exhibit strong vertical heterogeneity with different abundances and types of sulfate minerals, suggesting local environmental changes on short geologic timescales. The Amazonian north polar layered deposits exhibit complex vertical layering in the abundance and/or grain size of water ice. The underlying basal unit shows little evidence for ice except in restricted locations where the morphology is consistent with subsequent modification of the deposits by fluid flow. Multispectral mapping is nearly complete at the high northern latitudes and shows evidence for significant hydrated mineral content in portions of the basal unit.
P32A-02 INVITED
Mars Through the Eye of HiRISE
The High Resolution Imaging Science Experiment (HiRISE) has acquired more than 2 Tb of data in more than
1,000 images of Mars at resolutions as high as 25 cm/pixel in the 3 PM mapping orbit of Mars Reconnaissance
Orbiter. Each image consists of data from up to 14 CCD detectors and could contain as many as 3 giga-pixels.
Early results include (1) improved knowledge of the stratigraphy of the north polar layered deposits and the origin
of the thick basal unit; (2) discovery that rocks are uniformly abundant in the Vastitas Borealis Formation covering
the northern lowlands; (3) imaging of past landing sites has provided new insights and surprises about the
nature of these surfaces; (4) fine layered deposits in Valles Marineris, Meridiani Planum, Arabia Terra and
elsewhere are often cut by indurated and/or bleached joints and faults, most likely due to precipitation from fluids;
(5) regions of Mars rich in phyllosilicate minerals [Murchie et al., submitted] are seen to consist of layered
deposits with fine-scale fractures and polygons; (6) lava flows through Athabasca Valles were surprisingly thick
flows that were deflated and drained, leaving behind a veneer of lava with abundant evidence for lava-water
interactions; (7) stratigraphic studies reveal two major episodes of fluvial/lacustrine activity in Holden crater, and
we've detected exposures of ancient megabreccia in the crater walls; (8) recent large (3-60 km) impact craters
have created a range of apparently fluvially-modified landforms; (9) a small cluster of craters from a very recent
impact event created a large (~2 km) wide blast zone with thousands of dust avalanches; (10) relatively bright
deposits associated with very recent activities in gullies appear to consist of materials eroded from the crater
slopes; (11) the south polar residual cap of CO2 has a range of newly-discovered morphologies that constrain
models for landscape evolution; and(12) geysers or cold jets associated with sublimation of the seasonal CO2
frost are being monitored.
http:hirise.lpl.arizona.edu/
P32A-03
HiRISE Observations of Layered Deposits In and Around Valles Marineris
The HiRISE camera on the Mars Reconnaissance Orbiter is providing spectacular images of Mars in color and at approximately 30-60 cm/pixel resolution. Stereo images produced by taking two images at different roll angles are also valuable for viewing topography and stratigraphy. We have used the HiRISE data to examine the light- toned layered deposits (LTLD), both inside Valles Marineris and on the plains outside of the canyons. The high- resolution images show extensive layering with variable lithologies. Inside of Valles Marineris, massive blocky lithologies can be interbedded with meter-scale layered units, suggesting either different depositional environments or post-deposition modification of local areas. Folding is evident in West Candor Chasma near the contact with the wallrock, indicating post-deposition disruption, perhaps associated with further extension in Valles Marineris. Stereo images reveal tilting of layered beds in several locations. Fractures, joints, and faults in the LTLD are also commonly seen in several locations. The LTLD outside of Valles Marineris are concentrated near Ius Chasma, Melas Chasma, and Juventae Chasma. These layered deposits have darker units interbedded with light-toned deposits, and other color variations are also visible. While the ages of the LTLD inside Valles Marineris relative to the formation of the canyons is still under debate, those on the plains are stratigraphically above the Hesperian lavas and consequently represent a relatively younger period of LTLD emplacement. Even at the highest resolution, there is a paucity of impact craters on the LTLD, suggesting the units are friable in nature, although rapid burial beneath dark mantle deposits and formerly overlying units may also explain why there are so few craters. Why LTLD are in specific, but not all, locations within and adjacent to Valles Marineris is still being debated.
P32A-04 INVITED
Results From The Mars Rover Opportunity At Victoria Crater
Victoria crater is an impact crater about 800 meters in diameter that lies roughly 5 km south of the landing site of the Opportunity rover. After a drive of more than 900 sols, Opportunity has arrived at Victoria crater, and is now engaged in exploration of this, the largest impact crater encountered by either rover. The shape of Victoria crater is unusual. The rim is characterized by a number of prominent alcoves that are U- shaped in plan view, separated by sharp promontories that project toward the crater interior. The alcoves are clearly sites of mass wasting, and this distinctive shape indicates that the crater has been enlarged significantly by mass wasting processes. Since arriving at the crater's rim, Opportunity has been traversing along the rim imaging the stratigraphy exposed on the promontories. The promontories are steep, and most of them expose several to many meters of intact bedrock on near-vertical faces. Because Victoria crater is so large, by imaging these faces we can for the first time study lateral sedimentary facies variations at Meridiani over horizontal length scales of hundreds of meters. On most of the promontories, the uppermost unit is crater ejecta consisting a jumbled breccia of blocks up to a meter or more in size. The ejecta blanket is entirely dominated by blocks of sulfate-rich sandstone; no other material is evident in significant quantities. The ejecta blanket overlies a zone in which sulfate bedrock is extensively fractured in place, with an abrupt contact that is clearly visible around most of the crater rim. We interpret this contact to represent the pre-impact surface. Beneath the fractured zone lies intact bedrock. Mini-TES observations reveal this bedrock to be sulfate-rich over all depths observed to date. Pancam observations of the bedrock show the promontories on the north side of Victoria crater to be dominated by eolian facies. No clasts are visible in Pancam images; evidently the grain size is too small everywhere to be revealed by Pancam, as is the case everywhere else at Meridiani. Bedding, however, is prominent. In several locations, most notably a promontory named Cape St. Mary, there is spectacular eolian cross stratification exposed on the cliff faces, with high-angle truncations indicative of former dune deposits. Elsewhere we see the subparallel bedding and low-angle truncations expected for eolian sand sheets. Generally, then, the stratigraphy at Victoria is consistent with what was observed at Endurance crater, although much better exposed over significantly larger vertical and horizontal scales. Small cobbles have been found on the plains near the crater that are markedly different in composition from the sulfate-rich sandstone that is otherwise so dominant at Victoria. The cobbles lie well within the crater's annulus, and so may represent a minor fraction of the crater ejecta that is more resistant to wind erosion than the very friable sulfate-rich material, and hence better preserved. Compositional data on the cobble Santa Catarina indicate an elemental composition similar to that of the rock Barberton, a pebble near Endurance crater that we concluded was meteoritic on the basis of its kamacite content. Santa Catarina does not contain detectable kamacite, but does contain a significant quantity of troilite. Santa Catarina is also probably meteoritic in origin.
P32A-05 INVITED
The Spirit Rover at Gusev Crater
The Spirit rover has traversed approximately 7 km in 1100 sols of operations at the Gusev Crater landing site. Highlights relevant to the goal of understanding the role of liquid water at the martian surface include the following: (1) The discovery of ferric sulfates, likely hydrated, in deposits which have the unmistakable chemical signatures of nearby rocks. The movement of low pH hydrothermal fluids and/or vapors through local rocks prior to precipitation of these materials is consistent with the observations. (2) Goethite (alpha-FeOOH), a mineral phase which requires water to form, represents ~20% to 35% of the iron in numerous rock samples (Clovis Class) on the West Spur of the Columbia Hills. Aqueous alteration is clearly indicated by this presence of goethite. (3) Nearly isochemical signatures were found in elemental analyses of over ten distinct samples (Wishstone/Watchtower class rocks), but the ratio of ferric iron to total iron varied from ~0.4 to 0.95. Small quantities of water, insufficient to flush cations from the samples, were likely responsible for this weathering. (4) Also relevant to the characterizing the role of liquid water is the discovery of an ultramafic sequence of rocks where over 70% of the iron is in unaltered olivine and the ferric to total iron ratio is ~0.1. This result indicates that certain materials at the martian surface have been protected from aqueous alteration.
P32A-06 INVITED
Composition and Mineralogy of Martian Soils
The soils of Mars--the fine-grained, porous, uppermost layer of the planet's regolith--appear to have been created by a combination of physical and chemical weathering processes that can provide insights about the evolution of the martian surface and climate. Remote sensing and in situ measurements and analyses of soils from five different landing sites have revealed both surprising similarities and important (sometimes unexpected) differences among soils across the planet. Among the similarities are the ubiquitous presence and homogeneity of "dust" at widely-separated landing sites. Dust is the finest-grained (less than 5 microns) fraction of the soil, and the fact that it is easily suspended and transported by dust devils and dust storms explains its ubiquity. The reddish color and small size of dust particles had been cited as evidence for its origin as perhaps physically or chemically comminuted and heavily-oxidized (ferric) secondary weathering products. New results from the MER Sprit and Opportunity missions, however, indicate that dust grains may instead be volumetrically mostly unoxidized (ferrous) material, with visual color properties imparted by only a thin rind or coating of ferric oxides/oxyhydroxides. Another fine-grained global-scale unit is dark, silt- to sand-sized soils that occur in dunes, drifts, and ripples. Dark sands exhibit rather homogeneous composition and mineralogy (dominated by olivine and pyroxene) across the landing sites, suggesting that they, too, are globally-transported materials. Examples of the kinds of variability detected in martian soils are the hematite-rich spherules, sulfur/jarosite-rich outcrop- derived soils, and basaltic clastic fragments encountered in Meridiani Planum, the hematite, goethite, and ferric- sulfate bearing soils encountered in Gusev crater, and crusted/armored soils and rinds encountered at both Viking and both MER sites. Much of the observed martian soil variability may result from the action of local-scale weathering processes and/or reflect the diversity of local precursor bedrock sources. This presentation will provide an overview of what we know about the composition and mineralogy of martian soils, will review current models for martian soil formation in light of the currently-available data, and will describe ways that these models might be tested with ongoing and future Mars surface exploration missions.
P32A-07
Salty Soils at Gusev Crater investigated by Mars Exploration Rover Spirit
Mg-sulfate enriched salty soils were suggested by compositional correlation based on APXS data in two trenches made by the Mars Exploration Rover Spirit on the basaltic plains at Gusev Crater. During Spirit's traverse in the Columbia Hills region, light-toned salty soils were exposed again at eight loca-tions, with Paso Robles, Arad, and Tyrone having the largest exposures among them. The sites of Arad and Tyrone occur in local topographic minima, almost totally enclosed by surrounding ridges, while other exposures occur at the bases of hills, ridges, and outcrops. Where measured, the chemistry of the salts typically reflects the character of nearby rock, suggesting that the salts were formed locally rather than transported from a distant source. Candidate formation mechanisms include fumarolic processes and precipitation from salt-rich fluids. The salty soils at all eight locations were imaged with the Pancam 13 "geology" filter set that covers the VIS-NIR spectral region from 434 to 1009 nm. Spirit dragged its right-front wheel through the Tyrone area, that caused exposure of deeper light-toned soils ("yellowish" soils in Pancam false-color images) with 830-860 nm spectral absorption bands. In addition, these soils have a steeper spectral slope from 432 nm to 670 nm than the shallower soils ("whiteish" soils) exposed by the other five wheels. Similarly, more than one type of Pancam spectra, suggesting ferric sulfates, were observed at the Paso Robles and Arad areas. Mini-TES spectra from Paso Robles, Arad, and Tyrone all exhibit a 6 micrometer spectral feature suggesting hydrous materials. Three sets of in situ investigations were made at Paso Robles, Arad, and Tyrone, which indicate that ferric sulfates would be the important constituent of these light-toned salty soils, and possibly co-existing Mg- and Ca- sulfates. Further considering that Mg-sulfates are the major salts found in the two trenches on the basaltic plain, and that Ca-sulfates are the major sulfates within West Spur rocks, the heterogene-ous chemical nature of these sulfates found at Gusev Crater appears to demonstrate a correlation with the degree of alteration of local rocks/outcrops. After over 200 sols' exposure to current martian surface conditions (diurnal and seasonal cycles of tem-perature, dust, relative humidity, and low water vapor pressure), a relative change in the Pancam spectra of "yellowish" soils was detected from the seven repeated sets of Pancam 13-filter observations on Tyrone. The R(753 nm) over R(432 nm) slope in the spectra of "yellowish" soils decreased whereas that of "whiteish" soils did not change. This observation supports our model of the layered structure of salty soils at Tyrone. Indeed, we hypothesize that the "yellowish" soils were originally not in equilibrium with surface conditions because they were buried deeper. After exposure, the "yellowish" soils began to equilibrate with the current surface conditions, whereas the "whiteish" soils were more or less in equilibrium with surface conditions because of their originally much shallower burial depth. Laboratory experiments on the spectral features of some ferric sulfates suggests that dehydration can introduce the reduc-tion of spectral slope similar to what we see in the Pancam data of Tyrone. We are continuing to explore other possible origins for these changes.
P32A-08
Overview of the magnetic properties experiments onboard the two Mars Exploration Rovers, Spirit and Opportunity
The two Mars Exploration Rovers, Spirit and Opportunity, are each equipped with seven magnets designed for three different purposes: 1. The Filter and Capture magnets collect dust from the atmosphere. The dust can be investigated by the science instruments on the robotic arm and imaged by the Panoramic Camera. Analyzes of the dust shows that the magnetic component in the martian dust is magnetite, hematite together with paramagnetic and possibly superparamagnetic compounds is responsible for the yellowish color of the dust and the presence of olivine shows that the dust is formed without any appreciable presence of water. 2. The ring shaped Sweep magnet is design to detect non-magnetic particles. The experiment has been negative so far, showing that all particles must be composite and magnetic. This experience has been used to design a new camera calibration target for the Phoenix 2007, the sweep effect significantly preventing the calibration target to get dusty during the mission. 3. The Rock Abrasion Tool magnets are design to support the Mössbauer measurements on rocks giving additional information about the magnetic minerals contained in rocks. We here report on the results from the rovers and the neer future prospective for magnetic properties experiments on Mars.