Imperial College London

Professor Gareth Collins

Faculty of EngineeringDepartment of Earth Science & Engineering

Professor of Planetary Science
 
 
 
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Contact

 

+44 (0)20 7594 1518g.collins Website

 
 
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Location

 

4.83Royal School of MinesSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
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138 results found

Gulick SPS, Bralower T, Ormö J, Hall B, Grice K, Schaefer B, Lyons S, Freeman KH, Morgan J, Artemieva N, Kaskes P, de Graaff SJ, Whalen M, Collins G, Tikoo SM, Verhagen C, Christeson GL, Claeys P, Coolen M, Goderis S, Goto K, Grieve R, McCall N, Osinski G, Rae A, Riller U, Smit J, Vajda V, Wittmann A, and the Expedition 364 Scientistset al., The first day of the cenozoic, Proceedings of the National Academy of Sciences, ISSN: 0027-8424

Journal article

Raducan SD, Davison TM, Luther R, Collins GSet al., 2019, The role of asteroid strength, porosity and internal friction in impact momentum transfer, Icarus, Vol: 329, Pages: 282-295, ISSN: 0019-1035

Earth is continually impacted by very small asteroids and debris, and a larger object, though uncommon, could produce a severe natural hazard. During impact crater formation the ballistic ejection of material out of the crater is a major process, which holds significance for an impact study into the deflection of asteroids. In this study we numerically simulate impacts into low-gravity, strength dominated asteroid surfaces using the iSALE shock physics code, and consider the Double Asteroid Redirection Test (DART) mission as a case study. We find that target cohesion, initial porosity, and internal friction coefficient greatly influence ejecta mass/velocity/launch-position distributions and hence the amount by which an asteroid can be deflected. Our results show that as the cohesion is decreased the ratio of ejected momentum to impactor momentum, β − 1, increases; β − 1 also increases as the initial porosity and internal friction coefficient of the asteroid surface decrease. Using nominal impactor parameters and reasonable estimates for the material properties of the Didymos binary asteroid, the DART target, our simulations show that the ejecta produced from the impact can enhance the deflection by a factor of 2 to 4. We use numerical impact simulations that replicate conditions in several laboratory experiments to demonstrate that our approach to quantify ejecta properties is consistent with impact experiments in analogous materials. Finally, we investigate the self-consistency between the crater size and ejection speed scaling relationships previously derived from the point-source approximation for impacts into the same target material.

Journal article

McMullan S, Collins GS, Davison TM, 2019, ASTEROID TO AIRBURST; COMPARING SEMI-ANALYTICAL AIRBURST MODELS TO HYDROCODES, 82nd Annual Meeting of the Meteoritical-Society (MetSoc), Publisher: WILEY, ISSN: 1086-9379

Conference paper

McMullan S, Daly L, Collins GS, Bland Pet al., 2019, THE UK FIREBALL NETWORK: STAGE TWO OF THE GLOBAL FIREBALL OBSERVATORY., 82nd Annual Meeting of the Meteoritical-Society (MetSoc), Publisher: WILEY, ISSN: 1086-9379

Conference paper

Rae ASP, Collins G, Morgan J, Salge T, Christeson GL, Leung J, Lofi J, Gulick SPS, Poelchau M, Riller U, Gebhardt C, Grieve RA, Osinski GRet al., Impact-induced porosity and micro-fracturing at the Chicxulub impact structure, Journal of Geophysical Research: Planets, ISSN: 2169-9097

Porosity and its distribution in impact craters has an important effect on the petrophysical properties of impactites: seismic wave-speeds and reflectivity, rock permeability, strength, and density. These properties are important for the identification of potential craters and the understanding of the process and consequences of cratering. The Chicxulub impact structure, recently drilled by the joint International Ocean Discovery Program and International Continental scientific Drilling Program Expedition 364, provides a unique opportunity to compare direct observations of impactites with geophysical observations and models. Here, we combine small scale petrographic and petrophysical measurements with larger scale geophysical measurements and numerical simulations of the Chicxulub impact structure. Our aim is to assess the cause of unusually high porosities within the Chicxulub peak ring and the capability of numerical impact simulations to predict the gravity signature and the distribution and texture of porosity within craters. We show that high porosities within the Chicxulub peak ring are primarily caused by shock-induced micro-fracturing. These fractures have preferred orientations, which can be predicted by considering the orientations of principal stresses during shock, and subsequent deformation during peak-ring formation. Our results demonstrate that numerical impact simulations, implementing the Dynamic Collapse Model of peak-ring formation, can accurately predict the distribution and orientation of impact-induced micro-fractures in large craters which plays an important role in the geophysical signature of impact structures.

Journal article

McMullan S, Collins GS, 2019, Uncertainty quantification in continuous fragmentation airburst models, Icarus, Vol: 327, Pages: 19-35, ISSN: 0019-1035

As evidenced by the Chelyabinsk and Tunguska airburst events in Russia, decameter-scale Near-Earth Objects (NEOs) can pose a hazard to human life and infrastructure from the energy they deposit in the atmosphere as they break up. To understand the potential damage these small NEOs can cause on Earth's surface, it is imperative to be able to model their atmospheric entry quickly and accurately. Here we compare three semi-analytical models of asteroid airbursts that differ in their descriptions of fragment separation and spreading. Each model can be calibrated to produce a good fit to the energy deposition curve inferred from Chelyabinsk observations, but in each case the implied initial meteoroid strength is different and when the calibrated models are upscaled to Tunguska, the results diverge. This introduces an inter-model uncertainty that compounds the large range of uncertain physical and model parameters that influence probabilistic hazard assessment. Uncertainty quantification of airburst energy deposition was performed for a theoretical impacting object with H-magnitude 27, assuming no prior knowledge of any other impactor or model parameter. Each of the three models produces a different distribution of airburst outcomes, however, the variation attributable to physical parameter uncertainty is far larger than the inter-model differences. To constrain the initial conditions of the Tunguska event, the same uncertainty quantification was performed for an H-magnitude 24 event. Among the scenarios consistent with Tunguska observations (5–10 km burst altitude, 10–60° trajectory angle, 3–50 MT TNT total energy release) the most likely range of impact conditions was: radius of 25–75 m, mass of 1× 10 8 – 2.5× 10 9 kg, initial velocity of 11.5–33 km/s, and angle of 25–60°.

Journal article

Lyons RJ, Bowling TJ, Ciesla FJ, Davison T, Collins Get al., 2019, The effects of impacts on the cooling rates of iron meteorites, Meteoritics and Planetary Science, ISSN: 1086-9379

Iron meteorites provide a record of the thermal evolution of their parent bodies, with cooling rates inferred from the structures observed in the Widmanstätten pattern. Traditional planetesimal thermal models suggest that meteorite samples derived from the same iron core would have identical cooling rates, possibly providing constraints on the sizes and structures of their parent bodies. However, some meteorite groups exhibit a range of cooling rates or point to uncomfortably small parent bodies whose survival is difficult to reconcile with dynamical models. Together, these suggest that some meteorites are indicating a more complicated origin. To date, thermal models have largely ignored the effects that impacts would have on the thermal evolution of the iron meteorite parent bodies. Here we report numerical simulations investigating the effects that impacts at different times have on cooling rates of cores of differentiated planetesimals. We find that impacts that occur when the core is near or above its solidus, but the mantle has largely crystallized can expose iron near the surface of the body, leading to rapid and nonuniform cooling. The time period when a planetesimal can be affected in this way can range between 20 and 70 Myr after formation for a typical 100 km radius planetesimal. Collisions during this time would have been common, and thus played an important role in shaping the properties of iron meteorites.

Journal article

Timms NE, Pearce MA, Erickson TM, Cavosie AJ, Rae ASP, Wheeler J, Wittmann A, Ferriere L, Poelchau MH, Tomioka N, Collins GS, Gulick SPS, Rasmussen C, Morgan JV, Gulick SPS, Morgan JV, Chenot E, Christeson GL, Claeys P, Cockell CS, Coolen MJL, Ferriere L, Gebhardt C, Goto K, Green S, Jones H, Kring DA, Lofi J, Lowery CM, Ocampo-Torres R, Perez-Cruz L, Pickersgill AE, Poelchau MH, Rae ASP, Rasmussen C, Rebolledo-Vieyra M, Riller U, Sato H, Smit J, Tikoo SM, Tomioka N, Urrutia-Fucugauchi J, Whalen MT, Wittmann A, Xiao L, Yamaguchi KEet al., 2019, New shock microstructures in titanite (CaTiSiO5) from the peak ring of the Chicxulub impact structure, Mexico, Contributions to Mineralogy and Petrology, Vol: 174, ISSN: 0010-7999

Accessory mineral geochronometers such as apatite, baddeleyite, monazite, xenotime and zircon are increasingly being recognized for their ability to preserve diagnostic microstructural evidence of hypervelocity-impact processes. To date, little is known about the response of titanite to shock metamorphism, even though it is a widespread accessory phase and a U–Pb geochronometer. Here we report two new mechanical twin modes in titanite within shocked granitoid from the Chicxulub impact structure, Mexico. Titanite grains in the newly acquired core from the International Ocean Discovery Program Hole M0077A preserve multiple sets of polysynthetic twins, most commonly with composition planes (K1) = ~  {1¯11} , and shear direction (η1) = < 110 > , and less commonly with the mode K1 = {130}, η1 = ~ <522 > . In some grains, {130} deformation bands have formed concurrently with the deformation twins, indicating dislocation slip with Burgers vector b = < 341 > can be active during impact metamorphism. Titanite twins in the modes described here have not been reported from endogenically deformed rocks; we, therefore, propose this newly identified twin form as a result of shock deformation. Formation conditions of the twins have not been experimentally calibrated, and are here empirically constrained by the presence of planar deformation features in quartz (12 ± 5 and ~ 17 ± 5 GPa) and the absence of shock twins in zircon (< 20 GPa). While the lower threshold of titanite twin formation remains poorly constrained, identification of these twins highlight the utility of titanite as a shock indicator over the pressure range between 12 and 17 GPa. Given the challenges to find diagnostic indicators of shock metamorphism to identify both ancient

Journal article

Urrutia-Fucugauchi J, Pérez-Cruz L, Morgan J, Gulick S, Wittmann A, Lofi J, Morgan JV, Gulick SPS, Chenot E, Christeson G, Claeys P, Cockell C, Coolen MJL, Ferrière L, Gebhardt C, Goto K, Jones H, Kring DA, Lofi J, Lowery C, Mellett C, Ocampo-Torres R, Perez-Cruz L, Pickersgill A, Poelchau M, Rae A, Rasmussen C, Rebolledo-Vieyra M, Riller U, Sato H, Smit J, Tikoo-Schantz S, Tomioka N, Urrutia-Fucugauchi J, Whalen M, Wittmann A, Xiao L, Yamaguchi KE, Bralower T, Collins GSet al., 2019, Peering inside the peak ring of the Chicxulub Impact Crater—its nature and formation mechanism, Geology Today, Vol: 35, Pages: 68-72, ISSN: 0266-6979

© 2019 John Wiley & Sons Ltd, The Geologists' Association & The Geological Society of London The IODP-ICDP Expedition 364 drilled into the Chicxulub crater, peering inside its well-preserved peak ring. The borehole penetrated a sequence of post-impact carbonates and a unit of suevites and clast-poor impact melt rock at the top of the peak ring. Beneath this sequence, basement rocks cut by pre-impact and impact dykes, with breccias and melt, were encountered at shallow depths. The basement rocks are fractured, shocked and uplifted, consistent with dynamic collapse, uplift and long-distance transport of weakened material during collapse of the transient cavity and final crater formation.

Journal article

Bellucci JJ, Nemchin AA, Grange M, Robinson KL, Collins G, Whitehouse MJ, Snape JF, Norman MD, Kring DAet al., 2019, Terrestrial-like zircon in a clast from an Apollo 14 breccia, Earth and Planetary Science Letters, Vol: 510, Pages: 173-185, ISSN: 0012-821X

A felsite clast in lunar breccia Apollo sample 14321, which has been interpreted as Imbrium ejecta, has petrographic and chemical features that are consistent with formation conditions commonly assigned to both lunar and terrestrial environments. A simple model of Imbrium impact ejecta presented here indicates a pre-impact depth of 30–70 km, i.e. near the base of the lunar crust. Results from Secondary Ion Mass Spectrometry trace element analyses indicate that zircon grains recovered from this clast have positive Ce/Ce ⁎ anomalies corresponding to an oxygen fugacity +2 to +4 log units higher than that of the lunar mantle, with crystallization temperatures of 771±88 to 810 ± 37 °C (2σ) that are unusually low for lunar magmas. Additionally, Ti-in-quartz and zircon calculations indicate a pressure of crystallization of 6.9±1.2 kbar, corresponding to a depth of crystallization of 167±27 km on the Moon, contradicting ejecta modelling results. Such low-T, high-fO 2 , and high-P have not been observed for any other lunar clasts, are not known to exist on the Moon, and are broadly similar to those found in terrestrial magmas. The terrestrial-like redox conditions inferred for the parental magma of these zircon grains and other accessory minerals in the felsite contrasts with the presence of Fe-metal, bulk clast geochemistry, and the Pb isotope composition of K-feldspar grains within the clast, all of which are consistent with a lunar origin. The dichotomy between redox conditions and the depth of origin inferred from the zircon compositions compared to the ejecta modelling necessitates a multi-stage petrogenesis. Two, currently unresolvable hypotheses for the origin and history of the clast are allowed by these data. The first postulates that the relatively oxidizing conditions were developed in a lunar magma, possibly by fractional crystallization and enrichment of incompatible elements in a fluid-rich, phosphate-saturated magma

Journal article

Hopkins RT, Osinski GR, Collins GS, 2019, Formation of complex craters in layered targets with material anisotropy, Journal of Geophysical Research: Planets, Vol: 124, Pages: 349-373, ISSN: 2169-9097

Meteorite impacts often occur in layered targets, where the strength of the target varies as a function of depth, but this complexity is often not represented in numerical impact simulations because of the high computational cost of resolving thin layers. To address this limitation, we developed a method to approximate the effect of multiple thin weak layers within a sedimentary sequence using a single material layer to represent the entire sequence. Our approach, implemented in the iSALE (impact‐Simplified Arbitrary Lagrangian Eulerian) shock physics code, combines an anisotropic yield criterion with a cell‐based method to track the orientation of layers. To demonstrate the efficacy of the method and constrain parameters of the anisotropic strength model required to replicate the effects of thin, weak layers, we compare results of simulations of a ~20 – 25‐km diameter complex crater on Earth using the new method to those from simulations that explicitly resolve multiple thin weak layers. We show that our approach allows for a reduction in computational cost, negating the need for an increase in spatial resolution to resolve thin layers in the target, while replicating crater formation and final morphology from the high‐resolution models. In keeping with field observations, we also find that anisotropic layers may be responsible for a lack of central uplift expression observed at many craters formed in targets with thick sedimentary layers (e.g., the Haughton and Ries impact structures).

Journal article

Rae A, Collins G, Poelchau M, Riller U, Davison T, Grieve R, Osinski G, Morgan J, IODPICDP Expedition 364 Scientistset al., 2019, Stress-strain evolution during peak-ring formation: a case study of the Chicxulub impact structure, Journal of Geophysical Research: Planets, ISSN: 2169-9097

Deformation is a ubiquitous process that occurs to rocks during impact cratering; thus, quantifying the deformation of those rocks can provide first‐order constraints on the process of impact cratering. Until now, specific quantification of the conditions of stress and strain within models of impact cratering has not been compared to structural observations. This paper describes a methodology to analyze stress and strain within numerical impact models. This method is then used to predict deformation and its cause during peak‐ring formation: a complex process that is not fully understood, requiring remarkable transient weakening and causing a significant redistribution of crustal rocks. The presented results are timely due to the recent Joint International Ocean Discovery Program and International Continental Scientific Drilling Program drilling of the peak ring within the Chicxulub crater, permitting direct comparison between the deformation history within numerical models and the structural history of rocks from a peak ring. The modeled results are remarkably consistent with observed deformation within the Chicxulub peak ring, constraining the following: (1) the orientation of rocks relative to their preimpact orientation; (2) total strain, strain rates, and the type of shear during each stage of cratering; and (3) the orientation and magnitude of principal stresses during each stage of cratering. The methodology and analysis used to generate these predictions is general and, therefore, allows numerical impact models to be constrained by structural observations of impact craters and for those models to produce quantitative predictions.

Journal article

Rutherford ME, Derrick JG, Chapman DJ, Collins GS, Eakins DEet al., 2019, Insights into local shockwave behavior and thermodynamics in granular materials from tomography-initialized mesoscale simulations, Journal of Applied Physics, Vol: 125, ISSN: 0021-8979

Interpreting and tailoring the dynamic mechanical response of granular systems relies upon understanding how the initial arrangement of grains influences the compaction kinetics and thermodynamics. In this article, the influence of initial granular arrangement on the dynamic compaction response of a bimodal powder system (soda-lime distributed throughout a porous, fused silica matrix) was investigated through continuum-level and mesoscale simulations incorporating real, as-tested microstructures measured with X-ray tomography. By accounting for heterogeneities in the real powder composition, continuum-level simulations were brought into significantly better agreement with previously reported experimental data. Mesoscale simulations reproduced much of the previously unexplained experimental data scatter, gave further evidence of low-impedance mixture components dominating shock velocity dispersion, and crucially predicted the unexpectedly high velocities observed experimentally during the early stages of compaction. Moreover, only when the real microstructure was accounted for did simulations predict that small fractions of the fused silica matrix material would be driven into the β-quartz region of phase space. These results suggest that using real microstructures in mesoscale simulations is a critical step in understanding the full range of shock states achieved during dynamic granular compaction and interpreting solid phase distributions found in real planetary bodies.

Journal article

Derrick JG, Rutherford ME, Chapman DJ, Davison TM, Duarte JPP, Farbaniec L, Bland PA, Eakins DE, Collins GSet al., 2018, Investigating shock processes in bimodal powder compaction through modelling and experiment at the mesoscale, International Journal of Solids and Structures, ISSN: 0020-7683

Impact-driven compaction is a proposed mechanism for the lithification of primordial bimodal granular mixtures from which many meteorites derive. We present a numerical-experimental mesoscale study that investigates the fundamental processes in shock compaction of this heterogeneous matter, using analog materials. Experiments were performed at the European Synchrotron Radiation Facility generating real-time, in-situ, X-ray radiographs of the shock's passage in representative granular systems. Mesoscale simulations were performed using a shock physics code and set-ups that were geometrically identical to the experiments. We considered two scenarios: pure matrix, and matrix with a single chondrule. Good agreement was found between experiments and models in terms of shock position and post-shock compaction in the pure powder setup. When considering a single grain embedded in matrix we observed a spatial porosity anisotropy in its vicinity; the compaction was greater in the region immediately shockward of the grain, and less in its lee. We introduced the porosity vector, C, which points in the direction of lowest compaction across a chondrule. This direction-dependent observation may present a new way to decode the magnitude, and direction, of a single shock wave experienced by a meteorite in the past.

Journal article

Daubar I, Lognonné P, Teanby NA, Miljkovic K, Stevanović J, Vaubaillon J, Kenda B, Kawamura T, Clinton J, Lucas A, Drilleau M, Yana C, Collins GS, Banfield D, Golombek M, Kedar S, Schmerr N, Garcia R, Rodriguez S, Gudkova T, May S, Banks M, Maki J, Sansom E, Karakostas F, Panning M, Fuji N, Wookey J, van Driel M, Lemmon M, Ansan V, Böse M, Stähler S, Kanamori H, Richardson J, Smrekar S, Banerdt WBet al., 2018, Impact-seismic investigations of the InSight mission, Space Science Reviews, Vol: 214, ISSN: 0038-6308

Impact investigations will be an important aspect of the InSight mission. One of the scientific goals of the mission is a measurement of the current impact rate at Mars. Impacts will additionally inform the major goal of investigating the interior structure of Mars. In this paper, we review the current state of knowledge about seismic signals from impacts on the Earth, Moon, and laboratory experiments. We describe the generalized physical models that can be used to explain these signals. A discussion of the appropriate source time function for impacts is presented, along with spectral characteristics including the cutoff frequency and its dependence on impact momentum. Estimates of the seismic efficiency (ratio between seismic and impact energies) vary widely. Our preferred value for the seismic efficiency at Mars is 5 × 10 − 4, which we recommend using until we can measure it during the InSight mission, when seismic moments are not used directly. Effects of the material properties at the impact point and at the seismometer location are considered. We also discuss the processes by which airbursts and acoustic waves emanate from bolides, and the feasibility of detecting such signals. We then consider the case of impacts on Mars. A review is given of the current knowledge of present-day cratering on Mars: the current impact rate, characteristics of those impactors such as velocity and directions, and the morphologies of the craters those impactors create. Several methods of scaling crater size to impact energy are presented. The Martian atmosphere, although thin, will cause fragmentation of impactors, with implications for the resulting seismic signals. We also benchmark several different seismic modeling codes to be used in analysis of impact detections, and those codes are used to explore the seismic amplitude of impact-induced signals as a function of distance from the impact site. We predict a measurement of the current impact flux will be possibl

Journal article

Johnson BC, Andrews-Hanna JC, Collins G, Freed AM, Melosh HJ, Zuber MTet al., 2018, Controls on the formation of lunar multiring basins, Journal of Geophysical Research: Planets, Vol: 123, Pages: 3035-3050, ISSN: 2169-9097

Multiring basins dominate the crustal structure, tectonics, and stratigraphy of the Moon. Understanding how these basins form is crucial for understanding the evolution of ancient planetary crusts. To understand how preimpact thermal structure and crustal thickness affect the formation of multiring basins, we simulate the formation of lunar basins and their rings under a range of target and impactor conditions. We find that ring locations, spacing, and offsets are sensitive to lunar thermal gradient (strength of the lithosphere), temperature of the deep lunar mantle (strength of the asthenosphere), and preimpact crustal thickness. We also explore the effect of impactor size on the formation of basin rings and reproduce the observed transition from peak‐ring basins to multiring basins and reproduced many observed aspects of ring spacing and location. Our results are in broad agreement with the ring tectonic theory for the formation of basin rings and also suggest that ring tectonic theory applies to the rim scarp of smaller peak‐ring basins.

Journal article

Riller U, Poelchau MH, Rae A, Schulte FM, Collins GS, Melosh HJ, Grieve RAF, Morgan JV, Gulick SPS, Lofi J, Diaw A, McCall N, Kring DAet al., 2018, Rock fluidization during peak-ring formation of large impact structures, Nature, Vol: 562, Pages: 511-518, ISSN: 0028-0836

Large meteorite impact structures on the terrestrial bodies of the Solar System contain pronounced topographic rings, which emerged from uplifted target (crustal) rocks within minutes of impact. To flow rapidly over large distances, these target rocks must have weakened drastically, but they subsequently regained sufficient strength to build and sustain topographic rings. The mechanisms of rock deformation that accomplish such extreme change in mechanical behaviour during cratering are largely unknown and have been debated for decades. Recent drilling of the approximately 200-km-diameter Chicxulub impact structure in Mexico has produced a record of brittle and viscous deformation within its peak-ring rocks. Here we show how catastrophic rock weakening upon impact is followed by an increase in rock strength that culminated in the formation of the peak ring during cratering. The observations point to quasi-continuous rock flow and hence acoustic fluidization as the dominant physical process controlling initial cratering, followed by increasingly localized faulting.

Journal article

Luther R, Zhu M-H, Collins GS, Wunnemann Ket al., 2018, Effect of target properties and impact velocity on ejection dynamics and ejecta deposition, Meteoritics and Planetary Science, Vol: 53, Pages: 1705-1732, ISSN: 1086-9379

Impact craters are formed by the displacement and ejection of target material. Ejection angles and speeds during the excavation process depend on specific target properties. In order to quantify the influence of the constitutive properties of the target and impact velocity on ejection trajectories, we present the results of a systematic numerical parameter study. We have carried out a suite of numerical simulations of impact scenarios with different coefficients of friction (0.0–1.0), porosities (0–42%), and cohesions (0–150 MPa). Furthermore, simulations with varying pairs of impact velocity (1–20 km s−1) and projectile mass yielding craters of approximately equal volume are examined. We record ejection speed, ejection angle, and the mass of ejected material to determine parameters in scaling relationships, and to calculate the thickness of deposited ejecta by assuming analytical parabolic trajectories under Earth gravity. For the resulting deposits, we parameterize the thickness as a function of radial distance by a power law. We find that strength—that is, the coefficient of friction and target cohesion—has the strongest effect on the distribution of ejecta. In contrast, ejecta thickness as a function of distance is very similar for different target porosities and for varying impact velocities larger than ~6 km s−1. We compare the derived ejecta deposits with observations from natural craters and experiments.

Journal article

Collins GS, Rae ASP, Morgan JV, Gulick Set al., 2018, THE FORMATION OF PEAK RINGS IN LARGE IMPACT CRATERS, 81st Annual Meeting of the Meteoritical-Society, Publisher: WILEY, Pages: 6215-6215, ISSN: 1086-9379

Conference paper

Derrick J, LaJeunesse J, Davison T, Collins G, Borg Jet al., 2018, Mesoscale simulations of shock compaction of a granular ceramic: effects of mesostructure and mixed-cell strength treatment, Modelling and Simulation in Materials Science and Engineering, Vol: 26, ISSN: 0965-0393

The shock response of granular materials is important in a variety of contexts but the precise dynamics of grains during compaction is poorly understood. Here we use 2D mesoscale numerical simulations of the shock compaction of granular tungsten carbide to investigate the effect of internal structure within the particle bed and ’stiction’ between grains on the shock response. An increase in the average number of contactswith other particles, per particle, tends to shift the Hugoniot to higher shock velocities, lower particle velocities and lower densities. This shift is sensitive to inter-particle shear resistance. Eulerian shock physics codes approximate friction between, and interlocking of, grains with their treatment of mixed cell strength (stiction) and here we show thatthis has a significant effect on the shock response. When studying the compaction of particle beds it is not common to quantify the pre-compaction internal structure, yet our results suggest that such differences should be taken into account, either by usingidentical beds or by averaging results over multiple experiments.

Journal article

Derrick J, Rutherford M, Davison T, Chapman D, Eakins D, Collins Get al., Interrogating Heterogeneous Compaction of Analogue Materials at the Mesoscale Through Numerical Modeling and Experiments, 20th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter, Publisher: AIP Publishing, ISSN: 1551-7616

Conference paper

Brooker LM, Balme MR, Conway SJ, Hagermann A, Barrett AM, Collins GS, Soare RJet al., 2017, Clastic polygonal networks around Lyot crater, Mars: Possible formation mechanisms from morphometric analysis, Icarus, Vol: 302, Pages: 386-406, ISSN: 0019-1035

Polygonal networks of patterned ground are a common feature in cold-climate environments. They can form through the thermal contraction of ice-cemented sediment (i.e. formed from fractures), or the freezing and thawing of ground ice (i.e. formed by patterns of clasts, or ground deformation). The characteristics of these landforms provide information about environmental conditions. Analogous polygonal forms have been observed on Mars leading to inferences about environmental conditions. We have identified clastic polygonal features located around Lyot crater, Mars (50°N, 30°E). These polygons are unusually large ( > 100 m diameter) compared to terrestrial clastic polygons, and contain very large clasts, some of which are up to 15 metres in diameter. The polygons are distributed in a wide arc around the eastern side of Lyot crater, at a consistent distance from the crater rim. Using high-resolution imaging data, we digitised these features to extract morphological information. These data are compared to existing terrestrial and Martian polygon data to look for similarities and differences and to inform hypotheses concerning possible formation mechanisms. Our results show the clastic polygons do not have any morphometric features that indicate they are similar to terrestrial sorted, clastic polygons formed by freeze-thaw processes. They are too large, do not show the expected variation in form with slope, and have clasts that do not scale in size with polygon diameter. However, the clastic networks are similar in network morphology to thermal contraction cracks, and there is a potential direct Martian analogue in a sub-type of thermal contraction polygons located in Utopia Planitia. Based upon our observations, we reject the hypothesis that polygons located around Lyot formed as freeze-thaw polygons and instead an alternative mechanism is put forward: they result from the infilling of earlier thermal contraction cracks by wind-blown material, which then beca

Journal article

Davison TM, Derrick JG, Collins GS, Bland PA, Rutherford ME, Chapman DJ, Eakins DEet al., 2017, Impact-induced compaction of primitive solar system solids: The need for mesoscale modelling and experiments, Procedia Engineering, Vol: 204, Pages: 405-412, ISSN: 1877-7058

Primitive solar system solids were accreted as highly porous bimodal mixtures of mm-sized chondrules and sub-μm matrix grains. To understand the compaction and lithification of these materials by shock, it is necessary to investigate the process at the mesoscale; i.e., the scale of individual chondrules. Here we document simulations of hypervelocity compaction of primitive materials using the iSALE shock physics model. We compare the numerical methods employed here with shock compaction experiments involving bimodal mixtures of glass beads and silica powder and find good agreement in bulk material response between the experiments and models. The heterogeneous response to shock of bimodal porous mixtures with a composition more appropriate for primitive solids was subsequently investigated: strong temperature dichotomies between the chondrules and matrix were observed (non-porous chondrules remained largely cold, while the porous matrix saw temperature increases of 100’s K). Matrix compaction was heterogeneous, and post-shock porosity was found to be lower on the lee-side of chondrules. The strain in the matrix was shown to be higher near the chondrule rims, in agreement with observations from meteorites. Chondrule flattening in the direction of the shock increases with increasing impact velocity, with flattened chondrules oriented with their semi-minor axis parallel to the shock direction.

Journal article

Holm-Alwmark S, Rae A, Ferriere L, Alwmark C, Collins GSet al., 2017, Combining shock barometry with numerical modeling: insights into complex crater formation – The example of the Siljan impact structure (Sweden), Meteoritics and Planetary Science, Vol: 52, Pages: 2521-2549, ISSN: 1086-9379

Siljan, central Sweden, is the largest known impact structure in Europe. It was formed at about 380 Ma, in the late Devonian period. The structure has been heavily eroded to a level originally located underneath the crater floor, and to date, important questions about the original size and morphology of Siljan remain unanswered. Here we present the results of a shock barometry study of quartz-bearing surface and drill core samples combined with numerical modeling using iSALE. The investigated 13 bedrock granitoid samples show that the recorded shock pressure decreases with increasing depth from 15 to 20 GPa near the (present) surface, to 10–15 GPa at 600 m depth. A best-fit model that is consistent with observational constraints relating to the present size of the structure, the location of the downfaulted sediments, and the observed surface and vertical shock barometry profiles is presented. The best-fit model results in a final crater (rim-to-rim) diameter of ~65 km. According to our simulations, the original Siljan impact structure would have been a peak-ring crater. Siljan was formed in a mixed target of Paleozoic sedimentary rocks overlaying crystalline basement. Our modeling suggests that, at the time of impact, the sedimentary sequence was approximately 3 km thick. Since then, there has been around 4 km of erosion of the structure.

Journal article

Kring DA, Claeys P, Gulick SPS, Morgan JV, Collins GSet al., 2017, Chicxulub and the Exploration of Large Peak-Ring Impact Craters through Scientific Drilling, GSA Today, Vol: 27, Pages: 4-8, ISSN: 1052-5173

The Chicxulub crater is the only well-preserved peak-ring crater on Earth and linked, famously, to the K-T or K-Pg mass extinction event. For the first time, geologists have drilled into the peak ring of that crater in the International Ocean Discovery Program and International Continental Scientific Drilling Program (IODP-ICDP) Expedition 364. The Chicxulub impact event, the environmental calamity it produced, and the paleobiological consequences are among the most captivating topics being discussed in the geologic community. Here we focus attention on the geological processes that shaped the ~200-km-wide impact crater responsible for that discussion and the expedition’s first year results.

Journal article

Watters WA, Hundal CB, Radford A, Collins GS, Tornabene LLet al., 2017, Dependence of secondary crater characteristics on downrange distance: high-resolution morphometry and simulations, Journal of Geophysical Research: Planets, Vol: 122, Pages: 1773-1800, ISSN: 2169-9097

On average, secondary impact craters are expected to deepen and become more symmetric as impact velocity (vi) increases with downrange distance (L). We have used high-resolution topography (1–2 m/pixel) to characterize the morphometry of secondary craters as a function of L for several well-preserved primary craters on Mars. The secondaries in this study (N = 2644) span a range of diameters (25 m ≤D≤400 m) and estimated impact velocities (0.4 km/s ≤vi≤2 km/s). The range of diameter-normalized rim-to-floor depth (d/D) broadens and reaches a ceiling of d/D≈0.22 at L≈280 km (vi= 1–1.2 km/s), whereas average rim height shows little dependence on vi for the largest craters (h/D≈0.02, D > 60 m). Populations of secondaries that express the following morphometric asymmetries are confined to regions of differing radial extent: planform elongations (L< 110–160 km), taller downrange rims (L < 280 km), and cavities that are deeper uprange (L< 450–500 km). Populations of secondaries with lopsided ejecta were found to extend to at least L ∼ 700 km. Impact hydrocode simulations with iSALE-2D for strong, intact projectile and target materials predict a ceiling for d/D versus L whose trend is consistent with our measurements. This study illuminates the morphometric transition from subsonic to hypervelocity cratering and describes the initial state of secondary crater populations. This has applications to understanding the chronology of planetary surfaces and the long-term evolution of small crater populations.

Journal article

Melosh HJ, Bland PA, Collins GS, Johnson BCet al., 2017, A SPECULATIVE "FIEFDOM" MODEL FOR CHONDRITE ORIGINS., 80th Annual Meeting of the Meteoritical-Society, Publisher: WILEY, Pages: A232-A232, ISSN: 1086-9379

Conference paper

Muxworthy AR, Bland PA, Davison TM, Moore J, Collins GS, Ciesla FJet al., 2017, Evidence for an impact-induced magnetic fabric in Allende, and exogenous alternatives to the core dynamo theory for Allende magnetization, Meteoritics & Planetary Science, Vol: 52, Pages: 2132-2146, ISSN: 1086-9379

We conducted a paleomagnetic study of the matrix of Allende CV3 chondritic meteorite, isolating the matrix’s primary remanent magnetization, measuring its magnetic fabric and estimating the ancient magnetic field intensity. A strong planar magnetic fabric was identified; the remanent magnetization of the matrix was aligned within this plane, suggesting a mechanism relating the magnetic fabric and remanence. The intensity of the matrix’s remanent magnetization was found to be consistent and low (~6 μT). The primary magnetic mineral was found to be pyrrhotite. Given the thermal history of Allende, we conclude that the remanent magnetization formed during or after an impact event. Recent mesoscale impact mode ling, where chondrules and matrix are resolved, has shown that low-velocity collisions can generate significant matrix temperatures, as pore-space compaction attenuates shock energy and dramatically increases the amount of heating. Non-porous chondrules are unaffected, and act as heat-sinks, so matrix temperature excursions are brief. We extend this work to model Allende, and show that a 1km/s planar impact generates bulk porosity, matrix porosity, and fabric in our target that match the observed values. Bimodal mixtures of a highly porous matrix and nominally zero-porosity chondrules, make chondrites uniquely capable of recording transient or unstable fields. Targets that have uniform porosity, e.g., terrestrial impact craters, will not record transient or unstable fields. Rather than a core dynamo, it is therefore possible that the origin of the magnetic field in Allende was the impact itself, or a nebula field recorded during transient impact heating.

Journal article

Jourdan F, Timms NE, Eroglu E, Mayers C, Free A, Bland PA, Collins G, Davison T, Abe M, Yada Tet al., 2017, Collisional history of asteroid Itokawa, Geology, Vol: 45, Pages: 819-822, ISSN: 1943-2682

In situ extrate rrestrial samples returned for study (e.g., from the Moon) are crucial in understanding the origin and evolution of the Solar System as, contrary to meteorites, they provide a known geological context for the samples and their analyses. Asteroid 25143 Itokawa is a rubble pile asteroid consisting of reaccumulated fragments from a catastrophically disrupted monolithic parent asteroid, and from which regolith dust particles have been recovered by the Hayabusa space probe. We analyzed two dust particles using Electron Backscatter Diffraction (EBSD) and 40 Ar/39 Ar dating techniques. One of the grains showing signs of 15–25 GPa impact shock pressure, yielded a 40 Ar/Ar plateau age of 2.3 ± 0.1 Ga. We develop a novel temperature -pressure-porosity model, coupled with diffusion models to show that the relatively low pressure and high temperature involved in the impact process can be reconciled only if the asteroid was already made of porous material at ~2.3 Ga and thus, if asteroid Itokawa was already formed, thereby providing a minimum age for catastrophic asteroid breakup. A second particle shows no sign of deformation indicating shock pressure of ˂ 10 GPa and a calculated maximum temperature of ~200 °C. This low temperature estimate is compatible with a lack of isotopic resetting for this particle. This suggests that the breakup of Itokawa’s parent was a relatively low-temperature process at the scale of the asteroid, and occurred on a pre-shattered parent body.

Journal article

Rutherford ME, Chapman DJ, Derrick JG, Patten JRW, Bland PA, Rack A, Collins GS, Eakins DEet al., 2017, Probing the early stages of shock-induced chondritic meteorite formation at the mesoscale, Scientific Reports, Vol: 7, ISSN: 2045-2322

Chondritic meteorites are fragments of asteroids, the building blocks of planets, that retain a record of primordialprocesses. Important in their early evolution was impact-driven lithification, where a porous mixture of millimetre-scale chondrule inclusions and sub-micrometre dust was compacted into rock. In this Article, the shock compression ofanalogue precursor chondrite material was probed using state of the art dynamic X-ray radiography. Spatially-resolvedshock and particle velocities, and shock front thicknesses were extracted directly from the radiographs, representinga greatly enhanced scope of data than could be measured in surface-based studies. A statistical interpretation of themeasured velocities showed that mean values were in good agreement with those predicted using continuum-levelmodelling and mixture theory. However, the distribution and evolution of wave velocities and wavefront thicknesseswere observed to be intimately linked to the mesoscopic structure of the sample. This Article provides the first detailedexperimental insight into the distribution of extreme states within a shocked powder mixture, and represents the firstmesoscopic validation of leading theories concerning the variation in extreme pressure-temperature states during theformation of primordial planetary bodies.

Journal article

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