Chemistry of rocks and soils at Meridiani Planum from the Alpha Particle X-ray Spectrometer.
ABSTRACT The Alpha Particle X-ray Spectrometer on the Opportunity rover determined major and minor elements of soils and rocks in Meridiani Planum. Chemical compositions differentiate between basaltic rocks, evaporite-rich rocks, basaltic soils, and hematite-rich soils. Although soils are compositionally similar to those at previous landing sites, differences in iron and some minor element concentrations signify the addition of local components. Rocky outcrops are rich in sulfur and variably enriched in bromine relative to chlorine. The interaction with water in the past is indicated by the chemical features in rocks and soils at this site.
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ABSTRACT: The survival motor neuron (SMN) protein plays an essential role in the assembly of uridine-rich small nuclear ribonuclear protein complexes. Phosphorylation of SMN can regulate its function, stability, and sub-cellular localization. This study shows that protein kinase A (PKA) phosphorylates SMN both in vitro and in vivo. Bioinformatic analysis predicts 12 potential PKA phosphorylation sites in human SMN. Mass spectrometric analysis of a tryptic digest of SMN after PKA phosphorylation identified five distinct phosphorylation sites in SMN (serines 4, 5, 8, 187 and threonine 85). Mutagenesis of this subset of PKA-phosphorylated sites in SMN affects association of SMN with Gemin2 and Gemin8. This result indicates that phosphorylation of SMN by PKA may play a role in regulation of the in vivo function of SMN.Biochimica et Biophysica Acta 09/2011; 1814(9):1134-9. · 4.66 Impact Factor
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ABSTRACT: 1] Signals from the Shallow Radar were intended to penetrate hundreds of meters or more into Mars, but subsurface reflections are abundant only in known or inferred ice‐rich units and young (middle to late Amazonian), apparently pristine, volcanic units. As volcanic units age, fewer subsurface reflections are detected. Also, no subsurface reflections are detected from any northern hemisphere units inferred to be altered by water. We suggest that the general lack of subsurface reflections on Mars is not likely an indication that the shallow interior is devoid of structure and stratigraphy but rather an indication that dielectric contrasts cannot be detected due to signal attenuation originating from scattering and/or absorption. We constrained the attenuation rate in regions with no subsurface reflections to 0.065–0.27 dB/m. This corresponds to scattering losses from meter‐scale fractures and/or lithologic density variations of 0.27–1.03 g/cm 3 . Alternatively, our laboratory measurements have shown that three monolayers of adsorbed water on 2.2–14 vol % smectite clays can completely absorb radar energy and would be equivalent to a global water layer just ∼0.2–0.6 m thick. We suggest that the increased attenuation in volcanic units comes from an increase in fracture density. Attenuation in water‐altered units may be due to the greater heterogeneity in sedimentary units and/or chemical alteration that has formed high‐surface‐area smectites capable of holding the necessary amount of adsorbed water. Overall, the lack of widespread, deep subsurface reflections is due to the more Earth‐like radar properties of Mars, as compared to the Moon‐like properties that were anticipated.Journal of Geophysical Research 01/2011; 116. · 3.17 Impact Factor
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ABSTRACT: This paper describes karst landforms observed in the northern Sinus Meridiani region of Mars, located between 1°20′–2°20′ N and 2°50′ W–1°E and covering an area of about 20,000 km2.The karst is characterised by spectral signatures of mono- and poly-hydrated sulphates. A morphologic and morphometric survey of the study area was performed through an integrated analysis of 18 Mars Reconnaissance Orbiter High Resolution Imaging Science Experiment. Four distinct karst terrains were observed in the study area; they resemble landforms in a variety of karst terrains on Earth. The Martian landforms are characterised by different doline depression features and display different kinds and degrees of karstification. This variation seems to indicate differences in relative karst susceptibility due to the solutional properties of the four units, and enables the use of the karst landforms as significant geomorphic markers to distinguish units compositionally and/or mineralogically in the Sinus Meridiani area.Planetary and Space Science 01/2012; · 2.11 Impact Factor