[show abstract][hide abstract] ABSTRACT: The Rock Abrasion Tool (RAT) serves as the sample preparation device on
the Mars Exploration Rovers (MER) science payload. The RAT grinds a
circular area 45 millimeter in diameter and to a depth of 0-15 mm into
Martian rock. This is intended to remove the altered outer layers of
rock as well as overlying surface fines in preparation for imaging and
spectral observations. In addition to acting as a facilitator for other
instruments, RAT telemetry acquired during grinding may be used to
assess the physical properties of the rocks that it grinds. The most
direct rock measurement extractable from the RAT grinding process is the
energy expended per unit of rock volume removed. This has been termed
the RAT Specific Grind Energy (SGE) and in terms of rock bulk physical
properties, correlates roughly with unconfined compressive strength.
Recent results from the Mars Exploration Rovers will be presented as
will comparisons between Earth rocks and Martian rocks in terms of their
SGEs and other physical properties. Although SGE is an uncommon metric
for rock physical properties, the SGE calculated from the RAT
engineering data, and linked with data from other instruments in the
payload, represent the most comprehensive database yet created of the
physical properties of Martian rocks. RAT SGE continues to be helpful
in understanding the geologic history of Mars and will be of great value
in instrument design for future Mars missions.
[show abstract][hide abstract] ABSTRACT: In situ composition and isotopic analyses of the lunar regolith will be required to establish the abundance and origin of water-ice or other volatiles at the lunar poles. The VAPoR instrument is one concept that should be considered for a future lunar mission.
[show abstract][hide abstract] ABSTRACT: The Athena Science Instrument payload onboard the Spirit rover in Gusev
crater is providing datasets that suggest the outcrops and rocks on the
West Spur of the Columbia Hills are altered by water.
[show abstract][hide abstract] ABSTRACT: Outcrops of salt-rich silicic sediments at Meridiani Planum were
analyzed using sample preparation via grinding to reveal rock interiors.
X-ray fluorescence and Moessbauer analysis are combined with IR
spectroscopy to infer mineral composition.
[show abstract][hide abstract] ABSTRACT: The Mars Exploration Rover Opportunity has investigated the landing site in Eagle crater and the nearby plains within Meridiani Planum. The soils consist of fine-grained basaltic sand and a surface lag of hematite-rich spherules, spherule fragments, and other granules. Wind ripples are common. Underlying the thin soil layer, and exposed within small impact craters and troughs, are flat-lying sedimentary rocks. These rocks are finely laminated, are rich in sulfur, and contain abundant sulfate salts. Small-scale cross-lamination in some locations provides evidence for deposition in flowing liquid water. We interpret the rocks to be a mixture of chemical and siliciclastic sediments formed by episodic inundation by shallow surface water, followed by evaporation, exposure, and desiccation. Hematite-rich spherules are embedded in the rock and eroding from them. We interpret these spherules to be concretions formed by postdepositional diagenesis, again involving liquid water.
[show abstract][hide abstract] ABSTRACT: Analyses of outcrops created by the impact craters Endurance, Fram and Eagle reveal the broad lateral continuity of chemical sediments at the Meridiani Planum exploration site on Mars. Approximately ten mineralogical components are implied in these salt-rich silicic sediments, from measurements by instruments on the Opportunity rover. Compositional trends in an apparently intact vertical stratigraphic sequence at the Karatepe West ingress point at Endurance crater are consistent with non-uniform deposition or with subsequent migration of mobile salt components, dominated by sulfates of magnesium. Striking variations in Cl and enrichments of Br, combined with diversity in sulfate species, provide further evidence of episodes during which temperatures, pH, and water to rock ratios underwent significant change. To first order, the sedimentary sequence examined to date is consistent with a uniform reference composition, modified by movement of major sulfates upward and of minor chlorides downward. This reference composition has similarities to martian soils, supplemented by sulfate anion and the alteration products of mafic igneous minerals. Lesser cementation in lower stratigraphic units is reflected in decreased energies for grinding with the Rock Abrasion Tool. Survival of soluble salts in exposed outcrop is most easily explained by absence of episodes of liquid H2O in this region since the time of crater formation.
Earth and Planetary Science Letters, v.240, 73-94 (2005). 01/2005;
[show abstract][hide abstract] ABSTRACT: The location of the Opportunity landing site was determined to better than 10-m absolute accuracy from analyses of radio tracking data. We determined Rover locations during traverses with an error as small as several centimeters using engineering telemetry and overlapping images. Topographic profiles generated from rover data show that the plains are very smooth from meter- to centimeter-length scales, consistent with analyses of orbital observations. Solar cell output decreased because of the deposition of airborne dust on the panels. The lack of dust-covered surfaces on Meridiani Planum indicates that high velocity winds must remove this material on a continuing basis. The low mechanical strength of the evaporitic rocks as determined from grinding experiments, and the abundance of coarse-grained surface particles argue for differential erosion of Meridiani Planum.
[show abstract][hide abstract] ABSTRACT: The precise location and relative elevation of Spirit during its traverses from the Columbia Memorial station to Bonneville crater were determined with bundle-adjusted retrievals from rover wheel turns, suspension and tilt angles, and overlapping images. Physical properties experiments show a decrease of 0.2% per Mars solar day in solar cell output resulting from deposition of airborne dust, cohesive soil-like deposits in plains and hollows, bright and dark rock coatings, and relatively weak volcanic rocks of basaltic composition. Volcanic, impact, aeolian, and water-related processes produced the encountered landforms and materials.
[show abstract][hide abstract] ABSTRACT: The magnetic properties experiments are designed to help identify the magnetic minerals in the dust and rocks on Mars-and to determine whether liquid water was involved in the formation and alteration of these magnetic minerals. Almost all of the dust particles suspended in the martian atmosphere must contain ferrimagnetic minerals (such as maghemite or magnetite) in an amount of approximately 2% by weight. The most magnetic fraction of the dust appears darker than the average dust. Magnetite was detected in the first two rocks ground by Spirit.
[show abstract][hide abstract] ABSTRACT: The Mars Exploration Rover Spirit and its Athena science payload have been used to investigate a landing site in Gusev crater. Gusev is hypothesized to be the site of a former lake, but no clear evidence for lacustrine sedimentation has been found to date. Instead, the dominant lithology is basalt, and the dominant geologic processes are impact events and eolian transport. Many rocks exhibit coatings and other characteristics that may be evidence for minor aqueous alteration. Any lacustrine sediments that may exist at this location within Gusev apparently have been buried by lavas that have undergone subsequent impact disruption.
[show abstract][hide abstract] ABSTRACT: The Spirit landing site in Gusev Crater on Mars contains dark, fine-grained, vesicular rocks interpreted as lavas. Pancam and Mini-Thermal Emission Spectrometer (Mini-TES) spectra suggest that all of these rocks are similar but have variable coatings and dust mantles. Magnified images of brushed and abraded rock surfaces show alteration rinds and veins. Rock interiors contain </=25% megacrysts. Chemical analyses of rocks by the Alpha Particle X-ray Spectrometer are consistent with picritic basalts, containing normative olivine, pyroxenes, plagioclase, and accessory FeTi oxides. Mössbauer, Pancam, and Mini-TES spectra confirm the presence of olivine, magnetite, and probably pyroxene. These basalts extend the known range of rock compositions composing the martian crust.