156 results found
Kenkmann T, Collins GS, Wuennemann K, 2013, The modification stage of crater formation, Impact Cratering: Processes and Products, Editors: Osinski, Pierazzo, Publisher: Wiley-Blackwell, ISBN: 9781405198295
Potter RWK, Collins GS, 2013, Numerical modeling of asteroid survivability and possible scenarios for the Morokweng crater-forming impact, Meteoritics & Planetary Science, Vol: 48, Pages: 744-757, ISSN: 1945-5100
Elbeshausen D, Wünnemann K, Collins GS, 2013, The transition from circular to elliptical impact craters, Journal of Geophysical Research: Planets, Vol: 118, Pages: 2295–2309-2295–2309, ISSN: 2169-9100
Elliptical impact craters are rare among the generally symmetric shape of impact structures on planetary surfaces. Nevertheless, a better understanding of the formation of these craters may significantly contribute to our overall understanding of hypervelocity impact cratering. The existence of elliptical craters raises a number of questions: Why do some impacts result in a circular crater whereas others form elliptical shapes? What conditions promote the formation of elliptical craters? How does the formation of elliptical craters differ from those of circular craters? Is the formation process comparable to those of elliptical craters formed at subsonic speeds? How does crater formation work at the transition from circular to elliptical craters? By conducting more than 800 three-dimensional (3-D) hydrocode simulations, we have investigated these questions in a quantitative manner. We show that the threshold angle for elliptical crater generation depends on cratering efficiency. We have analyzed and quantified the influence of projectile size and material strength (cohesion and coefficient of internal friction) independently from each other. We show that elliptical craters are formed by shock-induced excavation, the same process that forms circular craters and reveal that the transition from circular to elliptical craters is characterized by the dominance of two processes: A directed and momentum-controlled energy transfer in the beginning and a subsequent symmetric, nearly instantaneous energy release.
Potter RWK, Kring DA, Collins GS, 2013, Quantifying the attenuation of structural uplift beneath large lunar craters, Geophysical Research Letters, Vol: 40, Pages: 5615–5620-5615–5620, ISSN: 1944-8007
Terrestrial crater observations and laboratory experiments demonstrate that target material beneath complex impact craters is uplifted relative to its preimpact position. Current estimates suggest maximum uplift is one tenth of the final crater diameter for terrestrial complex craters and one tenth to one fifth for lunar central peak craters. These latter values are derived from an analytical model constrained by observations from small craters and may not be applicable to larger complex craters and basins. Here, using numerical modeling, we produce a set of relatively simple analytical equations that estimate the maximum amount of structural uplift and quantify the attenuation of uplift with depth beneath large lunar craters.
Jacobs CT, Collins GS, Piggott MD, et al., 2013, Multiphase flow modelling of volcanic ash particle settling in water using adaptive unstructured meshes, Geophysical Journal International, Vol: 192, Pages: 647-665
Small-scale experiments of volcanic ash particle settling in water have demonstrated that ash particles can either settle slowly and individually, or rapidly and collectively as a gravitationally unstable ash-laden plume. This has important implications for the emplacement of tephra deposits on the seabed. Numerical modelling has the potential to extend the results of laboratory experiments to larger scales and explore the conditions under which plumes may form and persist, but many existing models are computationally restricted by the fixed mesh approaches that they employ. In contrast, this paper presents a new multiphase flow model that uses an adaptive unstructured mesh approach. As a simulation progresses, the mesh is optimized to focus numerical resolution in areas important to the dynamics and decrease it where it is not needed, thereby potentially reducing computational requirements. Model verification is performed using the method of manufactured solutions, which shows the correct solution convergence rates. Model validation and application considers 2-D simulations of plume formation in a water tank which replicate published laboratory experiments. The numerically predicted settling velocities for both individual particles and plumes, as well as instability behaviour, agree well with experimental data and observations. Plume settling is clearly hindered by the presence of a salinity gradient, and its influence must therefore be taken into account when considering particles in bodies of saline water. Furthermore, individual particles settle in the laminar flow regime while plume settling is shown (by plume Reynolds numbers greater than unity) to be in the turbulent flow regime, which has a significant impact on entrainment and settling rates. Mesh adaptivity maintains solution accuracy while providing a substantial reduction in computational requirements when compared to the same simulation performed using a fixed mesh, highlighting the benefits of an adapt
Potter RWK, Kring DA, Collins GS, et al., 2013, Numerical modeling of the formation and structure of the Orientale impact basin, Journal of Geophysical Research: Planets, Pages: n/a-n/a, ISSN: 2169-9100
Potter RWK, Kring DA, Collins GS, et al., 2012, Estimating transient crater size using the crustal annular bulge: Insights from numerical modeling of lunar basin-scale impacts, GEOPHYSICAL RESEARCH LETTERS, Vol: 39, ISSN: 0094-8276
Smith A, Crawford IA, Gowen RA, et al., 2012, Lunar Net-a proposal in response to an ESA M3 call in 2010 for a medium sized mission, EXPERIMENTAL ASTRONOMY, Vol: 33, Pages: 587-644, ISSN: 0922-6435
Collins GS, 2012, Moonstruck magnetism, Science, Vol: 335, Pages: 1176-1177
Collins GS, Melosh HJ, Osinski GR, 2012, The Impact-Cratering Process, ELEMENTS, Vol: 8, Pages: 25-30, ISSN: 1811-5209
Miljkovic K, Collins GS, Chapman DJ, et al., 2012, HIGH-VELOCITY IMPACTS IN POROUS SOLAR SYSTEM MATERIALS, 7th Biennial Conference of the American-Physical-Society-Topical-Group on Shock Compression of Condensed Matter, Publisher: AMER INST PHYSICS, ISSN: 0094-243X
Davison 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
Potter 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
Bray 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.
Davison 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
Collins 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
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
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
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
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
Miljkovic K, Mannick S, Collins GS, et al., 2011, HYDROCODE SIMULATIONS OF BINARY ASTEROID IMPACTS, 74th Annual Meeting of the Meteoritical-Society, Publisher: WILEY-BLACKWELL, Pages: A161-A161, 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
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.
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.
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
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
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
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