Publications

Search or filter publications

Filter by type:

Filter by publication type

Filter by year:

to

Results

  • Showing results for:
  • Reset all filters

Search results

  • Journal article
    Sephton MA, 2010,

    Drilling in Extreme Environments: Penetration and Sampling on Earth and other Planets, Yoseph Bar-Cohen, Kris Zacny (Eds.), Wiley-VCH, 2010. (Book Review)

    , International Journal of Rock Mechanics and Mining Science, Vol: 47, Pages: 1405-1405, ISSN: 1365-1609
  • Book chapter
    Verchovsky AB, Sephton MA, 2010,

    Noble Gases - Space

    , The Encyclopedia of Mass Spectrometry, Editors: Gross, Houk, Publisher: Elsevier Science Ltd, ISBN: 9780080438047

    In addition to accelerator mass spectrometry and isotope ratio mass spectrometry (formeasurement of isotope abundances in nature), the work reviews ionization ...
  • Journal article
    Watson JS, Sephton MA, Gilmour I, 2010,

    Thermochemolysis of the Murchison meteorite: identification of oxygen bound and occluded units in the organic macromolecule

    , INT J ASTROBIOL, Vol: 9, Pages: 201-208, ISSN: 1473-5504

    An organic macromolecular residue, prepared from the Murchison meteorite by treatment with hydrofluoric and hydrochloric acids, was subjected to online thermochemolysis with tetramethylammonium hydroxide (TMAH). The most abundant compound released by thermochemolysis was benzoic acid. Other abundant compounds include methyl and dimethyl benzoic acids as well as methoxy benzoic acids. Short chain dicarboxylic acids (C4–8) were also released from the organic macromolecule. Within the C1 and C2 benzoic acids all possible structural isomers are present reflecting the abiotic origin of these units. The most abundant isomers include 3,4-dimethylbenzoic acid (DMBA), 3,5-DMBA, 2,6-DMBA and phenylacetic acid. Thermochemolysis also liberates hydrocarbons that are not observed during thermal desorption; these compounds include naphthalene, methylnaphthalenes, biphenyl, methylbiphenyls, acenaphthylene, acenaphthene, phenanthrene, anthracene, fluoranthene and pyrene. The lack of oxygen containing functional groups in these hydrocarbons indicates that they represent non-covalently bound, occluded molecules within the organic framework. This data provides a valuable insight into oxygen bound and physically occluded moieties in the Murchison organic macromolecule and implies a relative order of synthesis or agglomeration for the detected organic constituents.
  • Journal article
    Hezel DC, Needham AW, Armytage R, Georg B, Abel RL, Kurahashi E, Coles BJ, Rehkamper M, Russell SSet al., 2010,

    A nebula setting as the origin for bulk chondrule Fe isotope variations in CV chondrites

    , Earth and Planetary Science Letters, Vol: 296, Pages: 423-433, ISSN: 0012-821X

    We combined micro computer tomography with Fe and Si isotope measurements of Mokoia, Allende and Grosnaja chondrules. Ten Mokoia chondrules contain 0.9 to 11.8 vol.% opaque phases (metal + sulfide), and 6 Allende chondrules contain 0.0 to 6.6 vol.% opaque phases. Hence, the Fe isotope composition of many chondrules is dominated by the Fe isotope composition of their opaque phases. We studied Fe isotopes of 35 bulk chondrules. The range is different for each of the three meteorites studied and largest for Allende with delta Fe-56 ranging from -0.82 to + 0.37%.. Six out of seven chondrules analysed for their Si isotope composition in Mokoia and Grosnaja have similar delta Si-29 of around -0.12%.. One anomalous chondrule in Mokoia has a delta Si-29 of +0.58%. We exclude isotopically heterogeneous chondrule precursors and different isotopic chondrule reservoirs as the source of the observed Fe isotope variation among bulk chondrules. We conclude that the observed bulk chondrule Fe isotope variation is the result of evaporation and re-condensation processes in a nebula setting with high dust densities, required to explain the comparatively low isotope fractionations. Subsequent parent body alteration slightly overprinted this pre-accretionary Fe isotope variation. (C) 2010 Elsevier B.V. All rights reserved.
  • Journal article
    Court RW, Baki AO, Sims MA, Cullen D, Sephton MAet al., 2010,

    Novel solvent systems for in situ extraterrestrial sample analysis

    , PLANET SPACE SCI, Vol: 58, Pages: 1470-1474, ISSN: 0032-0633

    The life marker chip (LMC) is being designed to test for the chemical signature of life in the soil and rocks of Mars. It will use an antibody array as part of its detection and characterisation system and aims to detect both polar and non-polar molecules at the sub-ppm to tens of ppb level. It is necessary to use a solvent to transfer organic compounds from the Martian samples to the LMC itself, but organic solvents such as dichloromethane or hexane, commonly used to dissolve non-polar molecules, are incompatible with the LMC antibodies. Hence, an aqueous-based solvent capable of dissolving the biomarkers that might exist in the soil or rocks of Mars is required. Solvent extractions of a Martian soil analogue, JSC Mars-1, spiked with a range of standards show that a 20:80 (vol:vol) mixture of methanol and water is incapable of extracting compounds insoluble in water. However, addition of 1.5 mg ml−1 of the surfactant polysorbate 80 produces extraction efficiencies of the aliphatic standards, hexadecane and phytane, equal to 25–30% of those produced by the common organic solvent mixture 93:7 (vol:vol) dichloromethane:methanol. Extraction of squalene and stigmasterol using the polysorbate solution is less efficient but still successful, at 5–10% of the efficiency of 93:7 dichloromethane:methanol. Such aliphatic compounds with occasional functional groups represent the compound classes to which most fossil organic biomarkers belong. The polysorbate solution did not extract the aromatic compounds pyrene and anthracene with great efficiency. A solvent of 20:80 methanol:water with 1.5 mg ml−1 polysorbate 80 is therefore capable of selectively extracting aliphatic biomarkers from Martian samples and transferring them to the antibody sites on the life marker chip.
  • Journal article
    Sephton MA, 2010,

    Organic Geochemistry and the Exploration of Mars

    , J COSMOLOGY, Vol: 5, Pages: 1141-1149

    The Red Planet provides a relatively accessible world on which theories of life’s diversity and origin can be tested. Such examinations are imminent with a number of missions to Mars forthcoming. These missions contain several life detection instruments that will sample the surface and subsurface. Organic geochemical knowledge from terrestrial studies can inform our search for organic matter in Mars rocks. Recent data on Mars minerals and atmospheric gases suggest which methods may be most useful to access any organic records present. A mineralogically-diverse Mars provides varying opportunities for the preservation of past and present life. Extinct or extant life will occupy specific size fractions that must be targeted. Studies suggest that methane is most likely derived from the subsurface. Even if abiotic in origin, the combination of reduced gases and oxidised minerals provides opportunities for life. In the near subsurface methane may be polymerised by cosmic radiation to form abiotic organic matter. This paper considers terrestrial approaches that may be useful in a Martian context.
  • Journal article
    Meredith W, Gomes RL, Cooper M, Snape CE, Sephton MAet al., 2010,

    Hydropyrolysis over a platinum catalyst as a preparative technique for the compound-specific carbon isotope ratio measurement of C27 steroids

    , RAPID COMMUN MASS SP, Vol: 24, Pages: 501-505, ISSN: 1097-0231

    Compound-specific stable carbon isotope analysis by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) is an important method for the determination of the 13C/12C ratios of biomolecules such as steroids, for a wide range of applications. However, steroids in their natural form exhibit poor chromatographic resolution, while derivatisation adds carbon thereby corrupting the stable isotopic composition. Hydropyrolysis with a sulphided molybdenum catalyst has been shown to defunctionalise the steroids, while leaving their carbon skeleton intact, allowing for the accurate measurement of carbon isotope ratios. The presence of double bonds in unsaturated steroids such as cholesterol resulted in significant rearrangement of the products, but replacing the original catalyst system with one of platinum results in higher conversions and far greater selectivity. The improved chromatographic performance of the products should allow GC/C/IRMS to be applied to more structurally complex steroid hormones and their metabolites.
  • Journal article
    Grant J, Westall F, Beaty D, Cady S, Carr M, Ciarletti V, Coradini A, Elfving A, Glavin D, Goesmann F, Hurowitz J, Ori JG, Phillips R, Salvo C, Sephton MA, Syvertson M, Vargo Jet al., 2010,

    Two Rovers to the Same Site on Mars, 2010: Possibilities for Cooperative Science

    , Astrobiology, Vol: 10, Pages: 663-685, ISSN: 1531-1074
  • Conference paper
    Paterson GA, Muxworthy AR, Heslop D, 2009,

    The statistics of paleointensity distributions (poster)

    , AGU Fall
  • Journal article
    Elbeshausen D, Wuennemann K, Collins GS, 2009,

    Scaling of oblique impacts in frictional targets: Implications for crater size and formation mechanisms

    , ICARUS, Vol: 204, Pages: 716-731, ISSN: 0019-1035
  • Conference paper
    Emmerton S, Muxworthy AR, 2009,

    First-Order Reversal Curve (FORC) analysis of chondrule magnetism (poster)

    , AGU Fall
  • Journal article
    Baker RGA, Rehkaemper M, Hinkley TK, Nielsen SG, Toutain JPet al., 2009,

    Investigation of thallium fluxes from subaerial volcanism-Implications for the present and past mass balance of thallium in the oceans

    , GEOCHIMICA ET COSMOCHIMICA ACTA, Vol: 73, Pages: 6340-6359, ISSN: 0016-7037
  • Journal article
    Bland PA, Jackson MD, Coker RF, Cohen BA, Webber JBW, Lee MR, Duffy CM, Chater RJ, Ardakani MG, McPhail DS, McComb DW, Benedix GKet al., 2009,

    Why aqueous alteration in asteroids was isochemical: High porosity ≠ high permeability

    , EARTH AND PLANETARY SCIENCE LETTERS, Vol: 287, Pages: 559-568, ISSN: 0012-821X
  • Journal article
    Kenkmann T, Collins GS, Wittmann A, Wünnemann K, Reimold WU, Melosh HJet al., 2009,

    A model for the formation of the Chesapeake Bay impact crater as revealed by drilling and numerical simulation

    , Geological Society of America Special Paper, Vol: 458, Pages: 571-586
  • Conference paper
    Muxworthy AR, 2009,

    Re-visiting the cooling rate dependency of thermoremanence acquisition

    , IAGA
  • Conference paper
    Davison TM, Collins GS, Ciesla F, 2009,

    Quantifying heating in porous planetesimal collisions

    , 72nd Annual Meeting of the Meteoritical-Society, Publisher: Meteoritical Society, Pages: A58-A58, ISSN: 1086-9379
  • Conference paper
    Ciesla FJ, Davison TM, Collins GS, 2009,

    Cooling of porous planetesimals after impacts: Implications for the thermal evolution of primitive bodies

    , 72nd Annual Meeting of the Meteoritical-Society, Publisher: Meteoritical Society, Pages: A51-A51, ISSN: 1086-9379
  • Journal article
    Fehr MA, Rehkaemper M, Halliday AN, Hattendorf B, Guenther Det al., 2009,

    Tellurium isotope compositions of calcium-aluminum-rich inclusions

    , METEORITICS & PLANETARY SCIENCE, Vol: 44, Pages: 971-984, ISSN: 1086-9379
  • Conference paper
    Collins GS, Wuennemann K, 2009,

    NUMERICAL MODELING OF IMPACT EJECTION PROCESSES IN POROUS GEOLOGIC MATERIALS

    , 72nd Annual Meeting of the Meteoritical-Society, Publisher: METEORITICAL SOC, Pages: A53-A53, ISSN: 1086-9379
  • Conference paper
    Ciesla FJ, Collins GS, Davison TM, O'Brien DPet al., 2009,

    Collisions among porous planetesimals and the water content of planetary embryos

    , 19th Annual VM Goldschmidt Conference, Publisher: Elsevier, Pages: A227-A227, ISSN: 0016-7037

This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.

Request URL: http://www.imperial.ac.uk:80/respub/WEB-INF/jsp/search-t4-html.jsp Request URI: /respub/WEB-INF/jsp/search-t4-html.jsp Query String: id=416&limit=20&page=15&respub-action=search.html Current Millis: 1716324446950 Current Time: Tue May 21 21:47:26 BST 2024