Publications
Results
- Showing results for:
- Reset all filters
Search results
-
Journal articleMcLennan SM, Sephton MA, Allen C, et al., 2012,
Planning for Mars Returned Sample Science:Final Report of the MSR End-to-End InternationalScience Analysis Group (E2E-iSAG)
, Astrobiology, Vol: 12, Pages: 175-230, ISSN: 1531-1074 -
Journal articleCourt RW, Sephton MA, 2012,
Extrasolar Planets And False Atmospheric Biosignatures: The Role Of Micrometeoroids
, Planetary and Space Science, Vol: 73, Pages: 233-242, ISSN: 0032-0633The coexistence of oxygen and a reduced gas such as methane in the atmosphere of an extrasolar planet is considered to be strong evidence for the presence of a biosphere. Proposed spacecraft such as Darwin or Terrestrial Planet Finder are designed to be capable of spectroscopically characterising the atmospheres of exoplanets, detecting chemical disequilibrium indicative of life. However, methane can be produced by various abiological mechanisms, including the ablation of carbonaceous micrometeoroids upon atmospheric entry, and it is possible that extrasolar planets in dust-rich systems might receive enough micrometeoroidal infall to produce a false atmospheric biosignature. Here, we review the production of methane from carbonaceous meteoroids upon atmospheric ablation in our solar system and discuss its application to extrasolar planets. The current paucity of data regarding dust densities in systems possessing terrestrial planets in the habitable zones of their stars makes firm conclusions difficult. However, the data suggest that only very young systems possessing very dense debris disks, or systems undergoing reorganisation similar to the Late Heavy Bombardment in our early solar system, would be capable of producing sufficient methane to be mistaken for an atmospheric biosignature.
-
Journal articleLarner F, Sampson B, Rehkamper M, et al., 2012,
High precision isotope measurements show poorer control of copper metabolism in Parkinsonism.
, Movement Disorders -
Journal articleChan HS, Martins Z, Sephton MA, 2012,
Amino acid analysis of type 3 chondrites Colony, Ornans, Chainpur and Bishunpur
, Meteoritics & Planetary Science, Vol: 47, Pages: 1502-1516, ISSN: 1086-9379The CO3s Colony and Ornans and LL3s Chainpur and Bishunpur were analyzed for the first time for amino acids using gas chromatography–mass spectrometry (GC-MS). Type 3 chondrites have relatively unaltered metamorphic and petrological histories. Chainpur was the most amino acid rich of the four type 3 chondrites with a total amino acid abundance of 3330 parts per billion (ppb). The other type 3 chondrites had total amino acid abundances that ranged from 660 to 1110 ppb. A d/l ratio of <0.7 for all proteic amino acids suggests at least some amino acid terrestrial contamination. However, a small fraction of indigenous extraterrestrial amino acids cannot be excluded because of the presence of the nonprotein amino acid α-aminoisobutyric acid (α-AIB), and unusually high relative abundances (to glycine) of β-alanine and γ-ABA. The comparisons between the free and total amino acid contents of the samples also indicate a low free/total amino acid ratio (ranging from about 1:4 in CO chondrites to about 1:50 in Chainpur), which indicate that amino acids are present mainly in the bound form and were made detectable after acid hydrolysis.
-
Journal articleCourt RW, Rix CS, Sims MR, et al., 2012,
Extraction of polar and nonpolar biomarkers from the martian soil using aqueous surfactant solutions
, Planetary and Space Science, Vol: 67, Pages: 109-118, ISSN: 0032-0633The Life Marker Chip is being designed to detect the chemical evidence of life in the martian soil. It will use an aqueous surfactant solution to extract polar and nonpolar biomarkers from the martian soil and to transport them into an antibody-based detector for characterisation. Currently, a solution of 1.5 g l−1 polysorbate 80 in 20:80 (vol:vol) methanol:water is being considered and appears to be suitable. Here, we have investigated the ability of a range of other surfactant solutions to extract a suite of eight standards spiked on the surfaces of the martian soil simulant JSC Mars-1 and tested the compatibility of the best two surfactants with a representative antibody assay for the detection of pyrene. The results show that using 20:80 (vol:vol) methanol:water as the solvent leads to increased recoveries of standards than using water alone. The poloxamer surfactants Pluronic® F-68 and Pluronic® F-108 are not effective at extracting the standards from JSC Mars-1 at any of the concentrations tested here. The fluorosurfactant Zonyl® FS-300 is able to extract the standards, but not as efficiently as polysorbate 80 solutions. Most successful of the alternative surfactants was the polysiloxane poly[dimethylsiloxane-co-[3-(2-(2-hydroxyethoxy)ethoxy)propyl]methylsiloxane] (PDMSHEPMS) which is able to extract the standards from JSC Mars-1 with an efficiency approximately equal to that of polysorbate 80 solutions of the same concentration. Enhanced recovery of the standards using polysorbate 80 and PDMSHEPMS solutions can be achieved by increasing the concentration of surfactant, from 1.5 g l−1 to 10 g l−1, leading to an increase in the recovery of standards of about 50%. Polysorbate 80 at concentrations of 1.5 g l−1 and 10 g l−1 and Zonyl® FS-300 and PDMSHEPMS (both at a concentration of 10 g l−1) are also compatible with the representative pyrene antibody assay.
-
Journal articleCourt RW, Sephton MA, 2012,
Insights into the nature of cometary organic matter from terrestrial analogues
, International Journal of Astrobiology, Vol: 11, Pages: 83-92, ISSN: 1473-5504The nature of cometary organic matter is of great interest to investigations involving the formation and distribution of organic matter relevant to the origin of life. We have used pyrolysis–Fourier transform infrared (FTIR) spectroscopy to investigate the chemical effects of the irradiation of naturally occurring bitumens, and to relate their products of pyrolysis to their parent assemblages. The information acquired has then been applied to the complex organic matter present in cometary nuclei and comae. Amalgamating the FTIR data presented here with data from published studies enables the inference of other comprehensive trends within hydrocarbon mixtures as they are progressively irradiated in a cometary environment, namely the polymerization of lower molecular weight compounds; an increased abundance of polycyclic aromatic hydrocarbon structures; enrichment in 13C; reduction in atomic H/C ratio; elevation of atomic O/C ratio and increase in the temperature required for thermal degradation. The dark carbonaceous surface of a cometary nucleus will display extreme levels of these features, relative to the nucleus interior, while material in the coma will reflect the degree of irradiation experienced by its source location in the nucleus. Cometary comae with high methane/water ratios indicate a nucleus enriched in methane, favouring the formation of complex organic matter via radiation-induced polymerization of simple precursors. In contrast, production of complex organic matter is hindered in a nucleus possessing a low methane/water ration, with the complex organic matter that does form possessing more oxygen-containing species, such as alcohol, carbonyl and carboxylic acid functional groups, resulting from reactions with hydroxyl radicals formed by the radiolysis of the more abundant water. These insights into the properties of complex cometary organic matter should be of particular interest to both remote observation and space missions involving in situ an
-
Journal articleSephton MA, 2012,
Pyrolysis and mass spectrometry studies of meteoritic organic matter.
, Mass Spectrom Rev, Vol: 31, Pages: 560-569Meteorites are fragments of extraterrestrial materials that fall to the Earth's surface. The carbon-rich meteorites are derived from ancient asteroids that have remained relatively unprocessed since the formation of the Solar System 4.56 billion years ago. They contain a variety of extraterrestrial organic molecules that are a record of chemical evolution in the early Solar System and subsequent aqueous and thermal processes on their parent bodies. The major organic component (>70%) is a macromolecular material that resists straightforward solvent extraction. In response to its intractable nature, the most common means of investigating this exotic material involves a combination of thermal decomposition (pyrolysis) and mass spectrometry. Recently the approach has also been used to explore controversial claims of organic matter in meteorites from Mars. This review summarizes the pyrolysis data obtained from meteorites and outlines key interpretations. © 2012 Wiley Periodicals, Inc. Mass Spec Rev 31:560-569, 2012.
-
Journal articleWatson JS, Fraser WT, Sephton MA, 2012,
Formation of a polyalkyl macromolecule from the hydrolysable component within sporopollenin during heating/pyrolysis experiments with Lycopodium spores
, Journal of Analytical and Applied Pyrolysis, Vol: 95, Pages: 138-144The most resistant component of Lycopodium spores is the macromolecule sporopollenin. The recent and fossil representatives of this material are structurally distinct and the transformations that bring about this chemical discord are poorly understood. To investigate the diagenesis of spores and their biopolymer, solvent extracted and saponified examples of Lycopodium clavatum underwent simulated diagenesis by heating (100–400 ◦C) under vacuum for 48 h. Following simulated maturation, spores were analysed by pyrolysis-gas chromatography–mass spectrometry (Py-GC–MS) and thermochemolysis-GC–MS. Py-GC–MS data clearly demonstrate that there is an increase in the polyalkyl hydrocarbon material in the pyrolysable component with increasing anhydrous maturation temperature. Hydrous pyrolysis of spores leads to similar changes but with an increased response from aliphatic relative to aromatic material. If the spores are hydrolysed prior to heating the generation of the polyalkyl portion of the macromolecule is markedly reduced. It appears, therefore, that the polyalkyl portion of fossil sporopollenin may be formed by maturation-induced polymerisation of the ‘labile’ hydrolysable component to form a recalcitrant polyalkyl network.
-
Journal articleBray VJ, Schenk PM, Melosh HJ, et al., 2012,
Ganymede crater dimensions – Implications for central peak and central pit formation and development
, Icarus, Vol: 217, Pages: 115-129The morphology of impact craters on the icy Galilean satellites differs from craters on rocky bodies. Thedifferences are thought due to the relative weakness of ice and the possible presence of sub-surface waterlayers. Digital elevation models constructed from Galileo images were used to measure a range of dimensionsof craters on the dark and bright terrains of Ganymede. Measurements were made from multipleprofiles across each crater, so that natural variation in crater dimensions could be assessed and averagedscaling trends constructed. The additional depth, slope and volume information reported in this work hasenabled study of central peak formation and development, and allowed a quantitative assessment of thevarious theories for central pit formation. We note a possible difference in the size-morphology progressionbetween small craters on icy and silicate bodies, where central peaks occur in small craters beforethere is any slumping of the crater rim, which is the opposite to the observed sequence on the Moon. Conversely,our crater dimension analyses suggest that the size-morphology progression of large lunar cratersfrom central peak to peak-ring is mirrored on Ganymede, but that the peak-ring is subsequentlymodified to a central pit morphology. Pit formation may occur via the collapse of surface material intoa void left by the gradual release of impact-induced volatiles or the drainage of impact melt intosub-crater fractures.
-
BookElmore RD, Muxworthy AR, Aldana MM, et al., 2012,
Remagnetization and chemical alteration of sedimentary rocks
, London, Publisher: Geological Society -
Journal articleViera da Silva N, Morgan JV, MacGregor L, et al., 2012,
A finite element multifrontal method for 3D CSEM modeling in the frequency domain
, Geophysics, Vol: 77, Pages: E101-E115There has been a recent increase in the use of controlled-source electromagnetic (CSEM) surveys in the exploration for oil and gas. We developed a modeling scheme for 3D CSEM modeling in the frequency domain. The electric field was decomposed in primary and secondary components to eliminate the singularity originated by the source term. The primary field was calculated using a closed form solution, and the secondary field was computed discretizing a second-order partial differential equation for the electric field with the edge finite element. The solution to the linear system of equations was obtained using a massive parallel multifrontal solver, because such solvers are robust for indefinite and ill-conditioned linear systems. Recent trends in parallel computing were investigated for their use in mitigating the computational overburden associated with the use of a direct solver, and of its feasibility for 3D CSEM forward modeling with the edge finite element. The computation of the primary field was parallelized, over the computational domain and the number of sources, using a hybrid model of parallelism. When using a direct solver, the attainment of multisource solutions was only competitive if the same factors are used to achieve a solution for multi right-hand sides. This aspect was also investigated using the presented methodology. We tested our proposed approach using 1D and 3D synthetic models, and they demonstrated that it is robust and suitable for 3D CSEM modeling using a distributed memory system. The codes could thus be used to help design new surveys, as well to estimate subsurface conductivities through the implementation of an appropriate inversion scheme.
-
ReportBeaty DW, Kminek G, Allwood AC, et al., 2012,
Report of the 2018 Joint Mars Rover Mission Joint Science Working Group (JSWG)
, Publisher: Mars Exploration Analysis Group (MEPAG) -
Journal articlePotter RWK, Collins GS, Kiefer WS, et al., 2012,
Constraining the size of the South Pole-Aitken basin impact
, Icarus, Vol: 220, Pages: 730 - 743-730 - 743, ISSN: 0019-1035 -
Journal articleDavison TM, Ciesla FJ, Collins GS, 2012,
Post-Impact Thermal Evolution of Porous Planetesimals
, Geochimica et Cosmochimica Acta, Vol: 95, Pages: 252-269, ISSN: 0016-7037 -
Journal articleMatthewman R, Cotton LJ, Martins Z, et al., 2012,
Organic geochemistry of Late Jurassic paleosols (Dirt Beds) of Dorset, UK
, Marine and Petroleum Geology, Vol: 37, Pages: 41-52, ISSN: 0264-8172Paleosols from the lower part of the Purbeck Limestone Group, which crops out extensively in Dorset, southern England, are shown to contain type IV kerogens. Comparisons with Mesozoic organic materials suggest that some of the paleosol kerogen is composed of fossil charcoal. The charcoal would have been produced by wildfires in the undergrowth of Purbeck gymnosperm forests. Contrasting the paleosol charcoal with laboratory produced counterparts suggest that, originally, significant amounts of functionalised organic matter should have persisted. Secondary oxidation and decay processes, therefore, must have removed all but the most resistant aromatic units in the charcoal. The importance of post-fire processes implies a strong influence on preservation from oxygen supply, water washing and host sediment type. These factors may have been related to pedogenesis, relative sea level and local fault movement in the late Jurassic.
-
Journal articleChan HS, Martins Z, Sephton MA, 2012,
Spectrofluorometric analysis of amino acid mixtures: Implications for future space missions
, Planetary and Space Science, Vol: 60, Pages: 336-341 -
Conference paperMuxworthy AR, Bland PA, Collins GS, et al., 2011,
Heterogeneous Shock In Porous Chondrites: Implications For Allende Magnetization
, AGU Fall -
Conference paperRoberts AP, Chang L, Rowan CJ, et al., 2011,
Magnetic properties of sedimentary greigite (Fe3S4): An update (Invited)
, AGU Fall -
Journal articleCollins GS, Elbeshausen D, Davison TM, et al., 2011,
The size-frequency distribution of elliptical impact craters
, Earth and Planetary Science Letters, Vol: 310, Pages: 1-8, ISSN: 0012-821X -
Journal articleDavison TM, Collins GS, Elbeshausen D, et al., 2011,
Numerical modeling of oblique hypervelocity impacts on strong ductile targets
, METEORITICS & PLANETARY SCIENCE, Vol: 46, Pages: 1510-1524, ISSN: 1086-9379- Author Web Link
- Open Access Link
- Cite
- Citations: 61
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.