135 results found
Davison TM, Ciesla FJ, Collins GS, 2011, Quantification of the post-impact thermal evolution of planetesimals, 74th Annual Meeting of the Meteoritical-Society, Publisher: Wiley-Blackwell, Pages: A53-A53, ISSN: 1086-9379
Collins GS, Davison TM, Ciesla FJ, 2011, The effects of planetesimal collisions, 74th Annual Meeting of the Meteoritical-Society, Publisher: Wiley-Blackwell, Pages: A46-A46, ISSN: 1086-9379
Bland PA, Muxworthy AR, Collins GS, et al., 2011, Heterogeneous shock in porous chondrites: Implications for Allende magnetization, 74th Annual Meeting of the Meteoritical-Society, Publisher: Wiley-Blackwell, Pages: A22-A22, ISSN: 1086-9379
Wozniakiewicz PJ, Ishii HA, Kearsley AT, et al., 2011, Investigation of iron sulfide impact crater residues: A combined analysis by scanning and transmission electron microscopy, METEORITICS & PLANETARY SCIENCE, Vol: 46, Pages: 1007-1024, ISSN: 1086-9379
Collins GS, Melosh HJ, Wunnemann K, 2011, Improvements to the epsilon-alpha porous compaction model for simulating impacts into high-porosity solar system objects, INTERNATIONAL JOURNAL OF IMPACT ENGINEERING, Vol: 38, Pages: 434-439, ISSN: 0734-743X
We describe improvements to the epsilon-alpha porous compaction model for simulating solar system impacts. To improve the treatment of highly porous materials, we modified the epsilon-alpha model to account for thermal expansion of the matrix during compaction. We validated the improved model by demonstrating good agreement between numerically computed Hugoniot curves for porous iron (up to initial porosities of similar to 80%) using the improved epsilon-alpha model and experimentally-derived Hugoniot data. Moreover, we verified that the model improvements are easily implemented into a hydrocode and preserve the efficiency advantage of a strain-based compaction function. We used the improved epsilon-alpha porous compaction model in the iSALE hydrocode to reproduce 2-km/s porous-target laboratory impact experiments. The simulation results were in qualitative agreement with the experiments but produced craters that were consistently deeper and larger in volume than the experiments. The results of the hydrocode simulations and laboratory experiments show a reduction in crater efficiency with increasing porosity. This reduction is more dramatic if the impactor density and velocity are higher. (C) 2010 Elsevier Ltd. All rights reserved.
Davison TM, 2011, Numerical modelling of heat generation in porous planetesimal collisions
An important unanswered question in planetary science is how planetesimals, the ~1–100 km [≈ distance covered by one degree of latitude on Earth's surface] solid precursors to asteroids and planets, were heated in the early Solar System. This thesis quantifies one possible heat source: planetesimal collisions. Recent work has predicted that collision velocities and planetesimal porosities were likely to have been higher than previously thought; this is likely to have significant implications on collision heating. The approach adopted in this research was to numerically model shock heating during planetesimal collisions. Simulations showed that an increase in porosity can significantly increase heating: in a 5 km s-1 collision between equal sized, non-porous planetesimals, no material was heated to the solidus, compared to two thirds of the mass of 50% porous planetesimals. Velocity also strongly influences heating: at 4 km s-1, an eighth of the mass of 50% porous planetesimals was heated to the solidus, compared to the entire mass at 6 km s-1. Further simulations quantified the influence on heating of the impactor-to-target mass ratio, the initial planetesimal temperature and the impact angle. A Monte Carlo model was developed to examine the cumulative heating caused by a population of impactors striking a parent body. In the majority of collisions the impactor was much smaller than the parent body, and only minor heating was possible. However, some larger or faster impactors were capable of causing significant heating without disrupting the parent body; these collisions could have heated up to 10% of the parent body to the solidus. To cause global heating, the collision must have catastrophically disrupted the parent body. The increase in specific internal energy from collisions was compared with the decay of short-lived radionuclides. In the first ~6 Ma, radioactive decay was the most important heat source. After ~10 Ma, the energy caused by collisions
Gowen RA, Smith A, Fortes AD, et al., 2011, Penetrators for in situ subsurface investigations of Europa, ADV SPACE RES, Vol: 48, Pages: 725-742, ISSN: 0273-1177
We present the scientific case for inclusion of penetrators into the Europan surface, and the candidate instruments which could significantly enhance the scientific return of the joint ESA/NASA Europa-Jupiter System Mission (EJSM). Moreover, a surface element would provide an exciting and inspirational mission highlight which would encourage public and political support for the mission.Whilst many of the EJSM science goals can be achieved from the proposed orbital platform, only surface elements can provide key exploration capabilities including direct chemical sampling and associated astrobiological material detection, and sensitive habitability determination. A targeted landing site of upwelled material could provide access to potential biological material originating from deep beneath the ice.Penetrators can also enable more capable geophysical investigations of Europa (and Ganymede) interior body structures, mineralogy, mechanical, magnetic, electrical and thermal properties. They would provide ground truth, not just for the orbital observations of Europa, but could also improve confidence of interpretation of observations of the other Jovian moons. Additionally, penetrators on both Europa and Ganymede, would allow valuable comparison of these worlds, and gather significant information relevant to future landed missions. The advocated low mass penetrators also offer a comparatively low cost method of achieving these important science goals.A payload of two penetrators is proposed to provide redundancy, and improve scientific return, including enhanced networked seismometer performance and diversity of sampled regions.We also describe the associated candidate instruments, penetrator system architecture, and technical challenges for such penetrators, and include their current status and future development plans.
Morgan JV, Warner MR, Collins GS, et al., 2011, Full waveform tomographic images of the peak ring at the Chicxulub impact crater, Journal of Geophysical Research, Vol: 116
Peak rings are a feature of large impact craters on the terrestrial planets and are generally believed to be formed from deeply buried rocks that are uplifted during crater formation. The precise lithology and kinematics of peak ring formation, however, remains unclear. Previous work has revealed a suite of bright inward-dipping reflectors beneath the peak ring at the Chicxulub impact crater and that the peak ring was formed from rocks with a relatively low seismic velocity. New 2D full-waveform tomographic velocity images show that the uppermost lithology of the peak ring is formed from a thin (~100-200 m thick) layer of low-velocity (~3000-3200 m/s) rocks. This low-velocity layer is most likely to be composed of highly porous, allogenic impact breccias. Our models also show that the change in velocity between lithologies within and outside the peak ring is more abrupt than previously realized and occurs close to the location of the dipping reflectors. Across the peak ring, velocity appears to correlate well with predicted shock pressures from a dynamic model of crater formation, where the rocks that form the peak ring originate from uplifted basement that has been subjected to high shock pressures (10-50 GPa), and lie above downthrown sedimentary rocks that have been subjected to shock pressures of < 5 GPa. These observations suggest that low-velocities within the peak ring may be related to shock effects and that the dipping reflectors underneath the peak ring might represent the boundary between highly-shocked basement and weakly-shocked sediments.
Wuennemann K, Collins GS, Weiss R, 2010, IMPACT OF A COSMIC BODY INTO EARTH'S OCEAN AND THE GENERATION OF LARGE TSUNAMI WAVES: INSIGHT FROM NUMERICAL MODELING, REVIEWS OF GEOPHYSICS, Vol: 48, ISSN: 8755-1209
Davison TM, Collins GS, Ciesla F, et al., 2010, Cumulative impact heating of planetesimals, 73rd Annual Meeting of the Meteoritical-Society, Publisher: Wiley-Blackwell, Pages: A43-A43, ISSN: 1086-9379
Pasek MA, Collins GS, Carter EA, et al., 2010, SHOCKED QUARTZ IN A FULGURITE, 73rd Annual Meeting of the Meteoritical-Society, Publisher: WILEY-BLACKWELL PUBLISHING, INC, Pages: A163-A163, ISSN: 1086-9379
Davison TM, Collins GS, Ciesla FJ, 2010, Numerical modelling of heating in porous planetesimal collisions, ICARUS, Vol: 208, Pages: 468-481, ISSN: 0019-1035
Schulte P, Alegret L, Arenillas I, et al., 2010, The Chicxulub Asteroid Impact and Mass Extinction at the Cretaceous-Paleogene Boundary, SCIENCE, Vol: 327, Pages: 1214-1218, ISSN: 0036-8075
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
Kenkmann T, Collins GS, Wittmann A, et 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
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
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
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
Ciesla FJ, Collins GS, Davison TM, et 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
Ham DA, Farrell PE, Gorman GJ, et al., 2009, Spud 1.0: generalising and automating the user interfaces of scientific computer models, Geoscientific Model Development, Vol: 2, Pages: 33-42
The interfaces by which users specify the scenarios to be simulated by scientific computer models are frequently primitive, under-documented and ad-hoc text files which make using the model in question difficult and error-prone and significantly increase the development cost of the model. In this paper, we present a model-independent system, Spud, which formalises the specification of model input formats in terms of formal grammars. This is combined with an automated graphical user interface which guides users to create valid model inputs based on the grammar provided, and a generic options reading module, libspud, which minimises the development cost of adding model options. Together, this provides a user friendly, well documented, self validating user interface which is applicable to a wide range of scientific models and which minimises the developer input required to maintain and extend the model interface.
Ham DA, Farrell PE, Gorman GJ, et al., 2009, Spud 1.0: generalising and automating the user interfaces of scientific computer models, GEOSCIENTIFIC MODEL DEVELOPMENT, Vol: 2, Pages: 33-42, ISSN: 1991-959X
Christeson GL, Collins GS, Morgan JV, et al., 2009, Mantle deformation beneath the Chicxulub impact crater, Earth and Planetary Science Letters, Vol: 284, Pages: 249-257, ISSN: 0012-821X
Osinski GR, Grieve RAF, Collins GS, et al., 2008, The effect of target lithology on the products of impact melting, METEORITICS & PLANETARY SCIENCE, Vol: 43, Pages: 1939-1954, ISSN: 1086-9379
Collins GS, Kenkmann T, Osinski GR, et al., 2008, Mid-sized complex crater formation in mixed crystalline-sedimentary targets: Insight from modeling and observation, METEORITICS & PLANETARY SCIENCE, Vol: 43, Pages: 1955-1977, ISSN: 1086-9379
Pierazzo E, Artemieva N, Asphaug E, et al., 2008, Validation of numerical codes for impact and explosion cratering: Impacts on strengthless and metal targets, METEORITICS & PLANETARY SCIENCE, Vol: 43, Pages: 1917-1938, ISSN: 1086-9379
Bray VJ, Collins GS, Morgan JV, et al., 2008, The effect of target properties on crater morphology: Comparison of central peak craters on the Moon and Ganymede., Meteoritics and Planetary Science, Vol: 43, Pages: 1979-1992
Davison TM, Collins GS, Ciesla FJ, 2008, Numerical modelling of shock heating in porous planetesmial collisions, 71st Annual Meeting of the Meteoritical-Society, Publisher: Meteoritical Society, Pages: A36-A36
Collins GS, Morgan J, Barton P, et al., 2008, Dynamic modeling suggests terrace zone asymmetry in the Chicxulub crater is caused by target heterogeneity, EARTH PLANET SC LETT, Vol: 270, Pages: 221-230, ISSN: 0012-821X
Wuennemann K, Collins GS, Osinski GR, 2008, Numerical modelling of impact melt production in porous rocks, EARTH AND PLANETARY SCIENCE LETTERS, Vol: 269, Pages: 529-538, ISSN: 0012-821X
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