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  • 1
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    Quantification of the dry history of the Martian soil inferred from in situ microscopy (2011)
    Wiley
    Details
    Publication Date: 2011-12-21
    Description: The particle size distribution (PSD) of a Martian soil sample, a useful indicator of the underlying soil formation processes, has been determined using optical and atomic-force microscopy data acquired by the Phoenix Mars lander. In particular, the presence and fraction of clay-sized particles in the PSD reflects the extent of aqueous interaction with the soil. Two size populations have been identified for the Martian sample: Larger, mostly rounded grains; and small reddish fines, notably with a very low mass proportion in the clay-size range below 2 μm. These fines reflect the smallest-scale formation processes, and indicate a single method of production for the particles up to 11 μm, a much larger value than that expected for the aqueous interaction of clay formation; this suggests the fines are predominantly the product of global aeolian weathering under very dry conditions. The proportion of clay-sized soils can be used to estimate that there has been much less than 5,000 years exposure to liquid water over the history of the soil. From the perspective of the PSD, lunar regolith, rather than terrestrial soil, is the best analog to Martian soil. A globally homogenous soil with such a PSD would be an unlikely habitat for the propagation of life on Mars.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Evidence that the reactivity of the martian soil is due to superoxide ions (2000)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2000-09-16
    Description: The Viking Landers were unable to detect evidence of life on Mars but, instead, found a chemically reactive soil capable of decomposing organic molecules. This reactivity was attributed to the presence of one or more as-yet-unidentified inorganic superoxides or peroxides in the martian soil. Using electron paramagnetic resonance spectroscopy, we show that superoxide radical ions (O2-) form directly on Mars-analog mineral surfaces exposed to ultraviolet radiation under a simulated martian atmosphere. These oxygen radicals can explain the reactive nature of the soil and the apparent absence of organic material at the martian surface.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Yen, A S -- Kim, S S -- Hecht, M H -- Frant, M S -- Murray, B -- New York, N.Y. -- Science. 2000 Sep 15;289(5486):1909-12.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA. Albert.Yen@jpl.nasa.gov〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/10988066" target="_blank"〉PubMed〈/a〉
    Keywords: Aluminum Silicates/chemistry ; Electron Spin Resonance Spectroscopy ; Exobiology ; Extraterrestrial Environment ; Ions ; *Mars ; Oxygen ; Potassium Compounds/chemistry ; *Soil ; *Superoxides/analysis/chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 3
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    De novo design, expression, and characterization of Felix: a four-helix bundle protein of native-like sequence (1990)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1990-08-24
    Description: The protein Felix was designed de novo to fold into an antiparallel four-helix bundle of specific topology. Its sequence of 79 amino acid residues is not homologous to any known protein sequence, but is "native-like" in that it is nonrepetitive and contains 19 of the 20 naturally occurring amino acids. Felix has been expressed from a synthetic gene cloned in Escherichia coli, and the protein has been purified to homogeneity. Physical characterization of the purified protein indicates that Felix (i) is monomeric in solution, (ii) is predominantly alpha-helical, (iii) contains a designed intramolecular disulfide bond linking the first and fourth helices, and (iv) buries its single tryptophan in an apolar environment and probably in close proximity with the disulfide bond. These physical properties rule out several alternative structures and indicate that Felix indeed folds into approximately the designed three-dimensional structure.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Hecht, M H -- Richardson, J S -- Richardson, D C -- Ogden, R C -- New York, N.Y. -- Science. 1990 Aug 24;249(4971):884-91.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Biochemistry, Duke University, Durham, NC 27710.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/2392678" target="_blank"〉PubMed〈/a〉
    Keywords: *Amino Acid Sequence ; Base Sequence ; DNA/genetics ; *Models, Chemical ; Models, Molecular ; Molecular Sequence Data ; *Protein Conformation ; Protein Denaturation ; *Proteins ; *Recombinant Proteins
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 4
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    Detection of perchlorate and the soluble chemistry of martian soil at the Phoenix lander site (2009)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2009-07-04
    Description: The Wet Chemistry Laboratory on the Phoenix Mars Lander performed aqueous chemical analyses of martian soil from the polygon-patterned northern plains of the Vastitas Borealis. The solutions contained approximately 10 mM of dissolved salts with 0.4 to 0.6% perchlorate (ClO4) by mass leached from each sample. The remaining anions included small concentrations of chloride, bicarbonate, and possibly sulfate. Cations were dominated by Mg2+ and Na+, with small contributions from K+ and Ca2+. A moderately alkaline pH of 7.7 +/- 0.5 was measured, consistent with a carbonate-buffered solution. Samples analyzed from the surface and the excavated boundary of the approximately 5-centimeter-deep ice table showed no significant difference in soluble chemistry.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Hecht, M H -- Kounaves, S P -- Quinn, R C -- West, S J -- Young, S M M -- Ming, D W -- Catling, D C -- Clark, B C -- Boynton, W V -- Hoffman, J -- Deflores, L P -- Gospodinova, K -- Kapit, J -- Smith, P H -- New York, N.Y. -- Science. 2009 Jul 3;325(5936):64-7. doi: 10.1126/science.1172466.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA. michael.h.hecht@jpl.nasa.gov〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/19574385" target="_blank"〉PubMed〈/a〉
    Keywords: *Anions ; *Cations ; Chemical Phenomena ; Extraterrestrial Environment ; Hydrogen-Ion Concentration ; *Mars ; Oxidation-Reduction ; *Perchlorates ; Solubility ; Spacecraft ; Temperature ; Water
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 5
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    Mars water-ice clouds and precipitation (2009)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2009-07-04
    Description: The light detection and ranging instrument on the Phoenix mission observed water-ice clouds in the atmosphere of Mars that were similar to cirrus clouds on Earth. Fall streaks in the cloud structure traced the precipitation of ice crystals toward the ground. Measurements of atmospheric dust indicated that the planetary boundary layer (PBL) on Mars was well mixed, up to heights of around 4 kilometers, by the summer daytime turbulence and convection. The water-ice clouds were detected at the top of the PBL and near the ground each night in late summer after the air temperature started decreasing. The interpretation is that water vapor mixed upward by daytime turbulence and convection forms ice crystal clouds at night that precipitate back toward the surface.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Whiteway, J A -- Komguem, L -- Dickinson, C -- Cook, C -- Illnicki, M -- Seabrook, J -- Popovici, V -- Duck, T J -- Davy, R -- Taylor, P A -- Pathak, J -- Fisher, D -- Carswell, A I -- Daly, M -- Hipkin, V -- Zent, A P -- Hecht, M H -- Wood, S E -- Tamppari, L K -- Renno, N -- Moores, J E -- Lemmon, M T -- Daerden, F -- Smith, P H -- New York, N.Y. -- Science. 2009 Jul 3;325(5936):68-70. doi: 10.1126/science.1172344.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Earth and Space Science and Engineering, York University, Toronto, Ontario, Canada. whiteway@yorku.ca〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/19574386" target="_blank"〉PubMed〈/a〉
    Keywords: Atmosphere ; Extraterrestrial Environment ; *Ice ; *Mars ; Spacecraft ; *Steam ; Temperature ; Time Factors
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 6
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    A Revised Calibration Function and Results for the Phoenix Mission TECP Relative Humidity Sensor (2016)
    Wiley
    Details
    Publication Date: 2016-03-15
    Description: A new calibration function for the humidity sensor in the Thermal and Electrical Conductivity Probe (TECP) on the Phoenix Mars mission has been developed. Two changes are incorporated: 1) it is now cast in terms of Frost Point ( T f ) rather than relative humidity ( R H ) and 2) flight data, taken when the atmosphere is independently known to be saturated, is included in the calibration data set. Daytime (6:00h – 19:00h) frost points ranged from 194K – 209K; the nighttime frost point ranged from 179K - 206K. The response of the sensor was smooth and continuous throughout. Daytime humidity exhibited large, high-frequency variance driven by turbulence whereas nighttime humidity varied smoothly with the temperature of the atmosphere. Nighttime saturation of the atmosphere begins at L s 101°, (sol 55), which is earlier than reported by either CRISM or SSI. Early mornings are the most humid part of the sol after L s 113° (sol 80), due to sublimation of surface ice that precipitates overnight. H 2 O is removed from the atmosphere into the regolith, mostly during the late afternoon, although this continues into the evening. The ground ice exposed by Phoenix operations masks the naturally-occurring process in the early evening, and may cause the atmosphere immediately around the lander to saturate somewhat earlier in the evening than it otherwise would have. The average H 2 O vapor density is close to the summertime value expected for equilibrium with ground ice. A discrepancy between the H 2 O column calculated from TECP data and the column measured by CRISM and SSI is likely due to comparable timescales between turbulent mixing through the PBL and adsorptive drawdown of H 2 O. We find R H is mostly 〈 5% (daytime) or 〉 95% (nighttime), and the transition between the two extremes is extremely rapid.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
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    Protein design by binary patterning of polar and nonpolar amino acids (1993)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1993-12-10
    Description: A general strategy is described for the de novo design of proteins. In this strategy the sequence locations of hydrophobic and hydrophilic residues were specified explicitly, but the precise identities of the side chains were not constrained and varied extensively. This strategy was tested by constructing a large collection of synthetic genes whose protein products were designed to fold into four-helix bundle proteins. Each gene encoded a different amino acid sequence, but all sequences shared the same pattern of polar and nonpolar residues. Characterization of the expressed proteins indicated that most of the designed sequences folded into compact alpha-helical structures. Thus, a simple binary code of polar and nonpolar residues arranged in the appropriate order can drive polypeptide chains to collapse into globular alpha-helical folds.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Kamtekar, S -- Schiffer, J M -- Xiong, H -- Babik, J M -- Hecht, M H -- New York, N.Y. -- Science. 1993 Dec 10;262(5140):1680-5.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Chemistry, Princeton University, NJ 08544.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/8259512" target="_blank"〉PubMed〈/a〉
    Keywords: Amino Acid Sequence ; Base Sequence ; Codon ; Gene Library ; Genes, Synthetic ; Molecular Sequence Data ; Molecular Weight ; Oligodeoxyribonucleotides ; *Protein Conformation ; *Protein Engineering ; Protein Folding ; Protein Structure, Secondary ; Proteins/*chemistry/genetics/isolation & purification
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 8
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    H2O at the Phoenix landing site (2009)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2009-07-04
    Description: The Phoenix mission investigated patterned ground and weather in the northern arctic region of Mars for 5 months starting 25 May 2008 (solar longitude between 76.5 degrees and 148 degrees ). A shallow ice table was uncovered by the robotic arm in the center and edge of a nearby polygon at depths of 5 to 18 centimeters. In late summer, snowfall and frost blanketed the surface at night; H(2)O ice and vapor constantly interacted with the soil. The soil was alkaline (pH = 7.7) and contained CaCO(3), aqueous minerals, and salts up to several weight percent in the indurated surface soil. Their formation likely required the presence of water.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Smith, P H -- Tamppari, L K -- Arvidson, R E -- Bass, D -- Blaney, D -- Boynton, W V -- Carswell, A -- Catling, D C -- Clark, B C -- Duck, T -- Dejong, E -- Fisher, D -- Goetz, W -- Gunnlaugsson, H P -- Hecht, M H -- Hipkin, V -- Hoffman, J -- Hviid, S F -- Keller, H U -- Kounaves, S P -- Lange, C F -- Lemmon, M T -- Madsen, M B -- Markiewicz, W J -- Marshall, J -- McKay, C P -- Mellon, M T -- Ming, D W -- Morris, R V -- Pike, W T -- Renno, N -- Staufer, U -- Stoker, C -- Taylor, P -- Whiteway, J A -- Zent, A P -- New York, N.Y. -- Science. 2009 Jul 3;325(5936):58-61. doi: 10.1126/science.1172339.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA. psmith@lpl.arizona.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/19574383" target="_blank"〉PubMed〈/a〉
    Keywords: Calcium Carbonate ; Extraterrestrial Environment ; Hydrogen-Ion Concentration ; *Ice ; *Mars ; Robotics ; Spacecraft ; Temperature ; *Water
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 9
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    Evidence for calcium carbonate at the Mars Phoenix landing site (2009)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2009-07-04
    Description: Carbonates are generally products of aqueous processes and may hold important clues about the history of liquid water on the surface of Mars. Calcium carbonate (approximately 3 to 5 weight percent) has been identified in the soils around the Phoenix landing site by scanning calorimetry showing an endothermic transition beginning around 725 degrees C accompanied by evolution of carbon dioxide and by the ability of the soil to buffer pH against acid addition. Based on empirical kinetics, the amount of calcium carbonate is most consistent with formation in the past by the interaction of atmospheric carbon dioxide with liquid water films on particle surfaces.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Boynton, W V -- Ming, D W -- Kounaves, S P -- Young, S M M -- Arvidson, R E -- Hecht, M H -- Hoffman, J -- Niles, P B -- Hamara, D K -- Quinn, R C -- Smith, P H -- Sutter, B -- Catling, D C -- Morris, R V -- New York, N.Y. -- Science. 2009 Jul 3;325(5936):61-4. doi: 10.1126/science.1172768.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA. wboynton@LPL.Arizona.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/19574384" target="_blank"〉PubMed〈/a〉
    Keywords: *Calcium Carbonate ; Carbon Dioxide ; Chemical Precipitation ; Extraterrestrial Environment ; Hot Temperature ; Hydrogen-Ion Concentration ; *Mars ; Spacecraft ; Water
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 10
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    Generic hydrophobic residues are sufficient to promote aggregation of the Alzheimer's Abeta42 peptide (2006)
    National Academy of Sciences
    Details
    Publication Date: 2006-10-12
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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