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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: 0032-0633
The 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 articleLomax BH, Fraser WT, Harrington G, et al., 2012,
A novel palaeoaltimetry proxy based on spore and pollen wall chemistry, Earth and Planetary Science Letters, Vol: 353-354, Pages: 22-28, ISSN: 0012-821X
Understanding the uplift history and the evolution of high altitude plateaux is of major interest to a wide range of geoscientists and has implications for many disparate fields. Currently the majority of palaeoaltimetry proxies are based on detecting a physical change in climate in response to uplift, making the relationship between uplift and climate difficult to decipher. Furthermore, current palaeoaltimetry proxies have a low degree of precision with errors typically greater than 1 km. This makes the calculation of uplift histories and the identification of the mechanisms responsible for uplift difficult to determine. Here we report on advances in both instrumentation and our understanding of the biogeochemical structure of sporopollenin that are leading to the establishment of a new proxy to track changes in the flux of UV-B radiation over geological time. The UV-B proxy is based on quantifying changes in the concentration of UV-B absorbing compounds (UACs) found in the spores and pollen grains of land plants, with the relative abundances of UACs increasing on exposure to elevated UV-B radiation. Given the physical relationship between altitude and UV-B radiation, we suggest that the analysis of sporopollenin chemistry, specifically changes in the concentration of UACs, may offer the basis for the first climate independent palaeoaltimetry proxy. Owing to the ubiquity of spores and pollen in the fossil record, our proposed proxy has the potential to enable the reconstruction of the uplift history of high altitude plateaux at unprecedented levels of fidelity, both spatially and temporally.
Journal articleCourt RW, Sims MR, Cullen DC, et al., 2012,
Potential failure of life detection experiments on Mars resulting from adsorption of organic compounds on to common instrument materials, Planetary and Space Science, Vol: 73, Pages: 262-270, ISSN: 0032-0633
Some life detection instruments under development for operation on Mars use solvents to extract organic compounds from samples of martian regolith and rock and to transfer the extracts to dedicated detectors. However, it is possible that organic compounds extracted from martian samples and dissolved in the solvent could adsorb to instrument surfaces, potentially resulting in a failure to detect organic matter that could have been avoided by using more appropriate instrument materials. If successful detection and characterisation is to take place it is therefore essential to understand the interactions between dissolved organic targets and the surfaces of space instrument components. One such life detection instrument is the Life Marker Chip (LMC) being developed for the ExoMars mission, which relies on a novel surfactant-based solvent system and antibody-based detectors. We have tested the ability of a range of materials, including titanium, stainless steel, aluminium, the fluoropolymer Viton™, polytetrafluoroethylene (PTFE), nylon, polypropylene, polyethersulfone and cellulose acetate to adsorb a range of organic standards from the surfactant solution intended to be used by the LMC. Results indicate that aromatic hydrocarbons, specifically anthracene, are more prone to adsorption than straight chain, branched and cyclic aliphatic species. Titanium, aluminium and stainless steel show little adsorption ability and are suitable for larger-area applications. PTFE and Viton™ are suitable for use in small-area applications such as seals and filters. Nylon, polypropylene, polyethersulfone and cellulose acetate show stronger adsorption characteristics and should be avoided in the forms employed here. The ability of some materials to selectively adsorb organic compounds from solvent extracts can lower the sensitivity of life detection instruments. In future, it would be prudent to test all space instrument materials for their ability to adsorb target organic com
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
Conference paperMontgomery WB, Court RW, Watson JS, et al., 2012,
Quantitative laboratory assessment of aquathermolysis chemistry during steam-assisted recovery of heavy oils and bitumen, World Heavy Oil Congress Paper WHOC12-402
In order to quantitatively study aquathermolysis chemistry during the thermal (steam-assisted) recovery of heavy oils & bitumen we have subjected a well-characterized heavy oil sample to 325°C and 2000 psi (13.8 MPa) in the continued presence of liquid water for 24 hours. The reaction products include gases, oil flotate, water-soluble products, and water-insoluble residues. All have been studied with a variety of analytical techniques, including FTIR spectroscopy, chromatographic fractionation (SARA analysis), and GC-MS. Results suggests that some in-situ upgrading of the oil occurs under these conditions. The methods discussed will be useful for the measurement of data to support model development for use in the engineering design of facilities for the thermal recovery of heavy oils and bitumen.
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: 0264-8172
Paleosols 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 articleSims MR, Cullen DC, Rix CS, et al., 2012,
Development Status of the Life Marker Chip Instrument for ExoMars, Planetary and Space Science, ISSN: 0032-0633
The Life Marker Chip (LMC) is one of the instruments being developed for possible flight on the 2018 ExoMars mission. The instrument uses solvents to extract organic compounds from samples of martian regolith and to transfer the extracts to dedicated detectors based around the use of antibodies. The scientific aims of the instrument are to detect organics in the form of biomarkers that might be associated with extinct life, extant life or abiotic sources of organics. The instrument relies on a novel surfactant-based solvent system and bespoke, commercial and research-developed antibodies against a number of distinct biomarkers or molecular types. The LMC comprises a number of subsystems designed to accept up to four discrete samples of martian regolith or crushed rock, implement the solvent extraction, perform microfluidic-based multiplexed antibody-assays for biomarkers and other targets, optically detect the fluorescent output of the assays, control the internal instrument pressure and temperature, in addition to the associated instrument control electronics and software. The principle of operation, the design and the instrument development status as of December 2011 are reported here. The instrument principle can be extended to other configurations and missions as needed.
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, 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: 0032-0633
The 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: 1473-5504
The 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: 560-569
Meteorites 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: 138-144
The 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: 115-129
The 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.
Journal articleChan HS, Martins Z, Sephton MA, 2012,
Fluorescence spectroscopy for the detection of life in the Salten Skov Mars regolith analogue, Planetary and Space Science, Vol: 68, Pages: 42-47
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 articleBorovicka J, Abe S, Shrbeny L, et al., 2011,
Photographic and Radiometric Observations of the HAYABUSA Re-Entry, PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN, Vol: 63, Pages: 1003-1009, ISSN: 0004-6264
- Author Web Link
- Citations: 7
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
- Citations: 57
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