Day: April 3, 2017

Bacterial survival following shock compression in the GigaPascal range

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1,3Rachael Hazael, 2Brianna C. Fitzmaurice, 1,4Fabrizia Foglia, 2Gareth J. Appleby-Thomas, 1Paul F McMillan
Icarus (in Press) Link to Article [http://dx.doi.org/10.1016/j.icarus.2017.03.031]
1Christopher Ingold Laboratories, Department of Chemistry, University College London, London WC1H 0AJ, UK
2Cranfield Defense and Security, Cranfield University, Shrivenham, Swindon SN6 8LA, UK
3Department of Earth Sciences, University College London, London WC1E 6BT
4Department of Chemical Engineering, Imperial College London, London SW7 2AZ, UK
Copyright Elsevier

The possibility that life can exist within previously unconsidered habitats is causing us to expand our understanding of potential planetary biospheres. Significant populations of living organisms have been identified at depths extending up to several km below the Earth’s surface; whereas laboratory experiments have shown that microbial species can survive following exposure to GigaPascal (GPa) pressures. Understanding the degree to which simple organisms such as microbes survive such extreme pressurization under static compression conditions is being actively investigated. The survival of bacteria under dynamic shock compression is also of interest. Such studies are being partly driven to test the hypothesis of potential transport of biological organisms between planetary systems. Shock compression is also of interest for the potential modification and sterilization of foodstuffs and agricultural products. Here we report the survival of Shewanella oneidensis bacteria exposed to dynamic (shock) compression. The samples examined included: (a) a “wild type” (WT) strain and (b) a “pressure adapted” (PA) population obtained by culturing survivors from static compression experiments to 750 MPa. Following exposure to peak shock pressures of 1.5 and 2.5 GPa the proportion of survivors was established as the number of colony forming units (CFU) present after recovery to ambient conditions. The data were compared with previous results in which the same bacterial samples were exposed to static pressurization to the same pressures, for 15 minutes each. The results indicate that shock compression leads to survival of a significantly greater proportion of both WT and PA organisms. The significantly shorter duration of the pressure pulse during the shock experiments (2-3 μs) likely contributes to the increased survival of the microbial species. One reason for this can involve the crossover from deformable to rigid solid-like mechanical relaxational behavior that occurs for bacterial cell walls on the order of seconds in the time-dependent strain rate.

Sedimentary laminations in the Isheyevo (CH/CBb) carbonaceous chondrite formed by gentle impact-plume sweep-up

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1,2Laurence A.J. Garvie, 2L. Paul Knauth, 2,3Melissa A. Morris
Icarus (in Press) Link to Article [http://dx.doi.org/10.1016/j.icarus.2017.03.021]
1Center for Meteorite Studies, Arizona State University, Tempe, Arizona 85287-6004, USA.
2School of Earth and Space Exploration, Arizona State University, Tempe, Arizona 85287-6004, USA.
3State University of New York, Cortland, NY 13045, USA
Copyright Elsevier

Prominent macroscopic sedimentary laminations, consisting of mm- to cm-thick alternating well-sorted but poorly mixed silicate-rich and metal-rich layers cut by faults and downward penetrating load structures, are prevalent in the Isheyevo (CH/CBb) carbonaceous chondrite. The load structures give the up direction of this sedimentary rock that accumulated from in-falling metal- and silicate-rich grains under near vacuum conditions onto the surface of an accreting planetesimal. The Isheyevo meteorite is the end result of a combination of events and processes that we suggest was initiated by the glancing blow impact of two planetesimals. The smaller impactor was disrupted forming an impact plume downrange of the impact. The components within the plume were aerodynamically size sorted by the nebular gas and swept up by the impacted planetesimal before turbulent mixing within the plume could blur the effects of the sorting. This plume would have contained a range of materials including elementally zoned Fe-Ni metal grains that condensed in the plume to disrupted unaltered material from the crust of the impactor, such as the hydrated matrix lumps. The juxtaposition of hydrated matrix lumps, some of which have not been heated above 150°C, together with components that formed above 1000°C, is compelling evidence that they were swept up together. Sweep-up would have occurred as the rotating impactor moved through the plume producing layers of material: the Isheyevo sample thus represents material accumulated while that part of the rotating planetesimal moved into the plume. Vibrations from subsequent impacts helped to form the load structures and induced weak grading within the layers via kinetic sieving. Following sweep-up, the particles were compacted under low static temperatures as evidenced by the preservation of elementally zoned Fe-Ni metal grains with preserved martensite α2 cores, distinct metal-metal grain boundaries, and metal-deformation microstructures. This meteorite provides evidence of gentle layer-by-layer accretion in the early Solar System, and also extends the terrestrial sedimentary source-to-sink paradigm to a near vacuum environment where neither fluvial nor aeolian processes operate.