Imperial College London

Dr Thomas M Davison

Faculty of EngineeringDepartment of Earth Science & Engineering

Teaching Fellow in Computational Data Science
 
 
 
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Contact

 

+44 (0)20 7594 2019thomas.davison Website CV

 
 
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Location

 

4.85Royal School of MinesSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

60 results found

Davison TM, Collins GS, 2022, Complex crater formation by oblique impacts on the Earth and Moon, Geophysical Research Letters, Vol: 49, Pages: 1-9, ISSN: 0094-8276

Almost all meteorite impacts occur at oblique incidence angles, but the effect of impact angle on crater size is not well understood, especially for large craters. To improve oblique impact crater scaling, we present a suite of simulations of complex crater formation on Earth and the Moon over a range of impact angles, velocities and impactor sizes. We show that crater diameter is larger than predicted by existing scaling relationships for oblique impacts; there is little dependence on obliquity for impacts steeper than 45° from the horizontal. Crater depth, volume and diameter depend on impact angle in different ways—relatively shallower craters are formed by more oblique impacts. Our simulation results have implications for how crater populations are determined from impactor populations and vice-versa. They suggest that existing approaches to account for impact obliquity may underestimate the number of complex craters larger than a given size by as much as one-third.

Journal article

Luther R, Raducan S, Burger C, Wuennemann K, Jutzi M, Schaeffer C, Koschny D, Davison T, Collins G, Zhang Y, Michel Pet al., 2022, Momentum enhancement during kinetic impacts in the low-intermediate-strength regime: benchmarking & validation of impact shock physics codes, The Planetary Science Journal, Vol: 3, Pages: 1-14, ISSN: 2632-3338

In September 2022, the DART spacecraft (NASA’s contribution to the Asteroid Impact & Deflection Assessment collaboration, AIDA) will impact the asteroid Dimorphos, the secondary in the Didymos system. The crater formation and material ejection will affect the orbital period. In 2027, Hera (ESA’s contribution to AIDA) will investigate the system, observe the crater caused by DART, and characterise Dimorphos. Before Hera’s arrival, the target properties are not well constrained. The relationships between observed orbital change and specific target properties are not unique, but Hera’s observations will add additional constraints for the analysis of the impact event, which will narrow the range of feasible target properties. In this study, we use three different shock physics codes to simulate momentum transfer from impactor to target and investigate the agreement between the results from the codes for well defined target materials. In contrast to previous studies, care is taken to use consistent crushing behaviour (e.g., distension as a function of pressure) for a given porosity for all codes. First, we validate the codes against impact experiments into a regolith simulant. Second, webenchmark the codes at the DART impact scale for a range of target material parameters (10-50% porosity, 1.4 - 100 kPa cohesion). Aligning the crushing behaviour improves theconsistency of the derived momentum enhancement between the three codes to within +/- 5%for most materials used. Based on the derived mass-velocity distributions from all three codes, we derive scaling parameters that can be used for studies of the ejecta curtain.

Journal article

Cashion MD, Johnson BC, Krot AN, Kretke KA, Wakita S, Davison TMet al., 2022, Chondrule formation via impact jetting in the icy outer solar system, ICARUS, Vol: 384, ISSN: 0019-1035

Journal article

Wakita S, Genda H, Kurosawa K, Davison TM, Johnson BCet al., 2022, Effect of Impact Velocity and Angle on Deformational Heating and Postimpact Temperature, JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS, Vol: 127, ISSN: 2169-9097

Journal article

North TL, Muxworthy AR, Collins GS, Davison TMet al., 2022, THERMOREMANENT MAGNETISATION RECORDED DURING IMPACT-INDUCED COMPACTION EXPERIMENTS ON SYNTHETIC CHONDRITIC METEORITES, Publisher: WILEY, ISSN: 1086-9379

Conference paper

North TL, Collins GS, Davison TM, Muxworthy AR, Steele SC, Fu RRet al., 2022, THE HETEROGENEOUS RESPONSE OF MARTIAN METEORITE ALLAN HILLS 84001 TO PLANAR SHOCK, Publisher: WILEY, ISSN: 1086-9379

Conference paper

Davison TM, Baijal N, Collins GS, 2022, HIGH-RESOLUTION OBLIQUE IMPACT SIMULATIONS OF THE FORMATION OF THE SOUTH POLE-AITKEN, Publisher: WILEY, ISSN: 1086-9379

Conference paper

Raducan SD, Jutzi M, Davison TM, Collins GSet al., 2022, IMPACT FORMATION MODELS OF METAL-RICH BODIES AND IMPLICATIONS FOR ASTEROID (16) PSYCHE, Publisher: WILEY, ISSN: 1086-9379

Conference paper

Raducan SD, Jutzi M, Davison TM, DeCoster ME, Graninger DM, Owen JM, Stickle AM, Collins GSet al., 2022, Influence of the projectile geometry on the momentum transfer from a kinetic impactor and implications for the DART mission, International Journal of Impact Engineering, Vol: 162, Pages: 104147-104147, ISSN: 0734-743X

The DART spacecraft will impact Didymos’s secondary, Dimorphos, at the end of 2022 and cause a change in the orbital period of the secondary. For simplicity, most previous numerical simulations of the impact used a spherical projectile geometry to model the DART spacecraft. To investigate the effects of alternative, simple projectile geometries on the DART impact outcome we used the iSALE shock physics code in two and thee-dimensions to model vertical impacts of projectiles with a mass and speed equivalent to the nominal DART impact, into porous basalt targets. We found that the simple projectile geometries investigated here have minimal effects on the crater morphology and momentum enhancement. Projectile geometries modelled in two-dimensions that have similar surface areas at the point of impact, affect the crater radius and the crater volume by less than 5%. In the case of a more extreme projectile geometry (i.e., a rod, modelled in three-dimensions), the crater was elliptical and 50% shallower compared to the crater produced by a spherical projectile of the same momentum. The momentum enhancement factor in these test cases, commonly referred to as , was within 7% for the 2D simulations and within 10% for the 3D simulations, of the value obtained for a uniform spherical projectile. The most prominent effects of projectile geometry are seen in the ejection velocity as a function of launch position and ejection angle of the fast ejecta that resides in the so-called ‘coupling zone’. These results will inform the LICIACube ejecta cone analysis.

Journal article

Raducan SD, Davison TM, Collins GS, 2022, Ejecta distribution and momentum transfer from oblique impacts on asteroid surfaces, Icarus, Vol: 374, Pages: 1-16, ISSN: 0019-1035

NASA’s Double Asteroid Redirection Test (DART) mission will impact its target asteroid, Dimorphos, at anoblique angle that will not be known prior to the impact. We computed iSALE-3D simulations of DARTlike impacts on asteroid surfaces at different impact angles and found that the vertical momentum transferefficiency, 𝛽, is similar for different impact angles, however, the imparted momentum is reduced as the impactangle decreases. It is expected that the momentum imparted from a 45◦impact is reduced by up to 50%compared to a vertical impact. The direction of the ejected momentum is not normal to the surface, howeverit is observed to ‘straighten up’ with crater growth. iSALE-2D simulations of vertical impacts provide contextfor the iSALE-3D simulation results and show that the ejection angle varies with both target properties andwith crater growth. While the ejection angle is relatively insensitive to the target porosity, it varies by upto 30◦ with target coefficient of internal friction. The simulation results presented in this paper can helpconstrain target properties from the DART crater ejecta cone, which will be imaged by the LICIACube. Theresults presented here represent the basis for an empirical scaling relationship for oblique impacts and canbe used as a framework to determine an analytical approximation of the vertical component of the ejectamomentum, 𝛽 − 1, given known target properties.

Journal article

Wakita S, Johnson BC, Garrick-Bethell I, Kelley MR, Maxwell RE, Davison TMet al., 2021, Impactor material records the ancient lunar magnetic field in antipodal anomalies, NATURE COMMUNICATIONS, Vol: 12

Journal article

Wakita S, Johnson BC, Denton CA, Davison TMet al., 2021, Jetting during oblique impacts of spherical impactors, ICARUS, Vol: 360, ISSN: 0019-1035

Journal article

Halim SH, Crawford IA, Collins GS, Joy KH, Davison TMet al., 2021, Assessing the survivability of biomarkers within terrestrial material impacting the lunar surface, Icarus, Vol: 354, Pages: 1-15, ISSN: 0019-1035

The history of organic and biological markers (biomarkers) on the Earth is effectively non-existent in the geological record >3.8 Ga ago. Here, we investigate the potential for terrestrial material (i.e., terrestrial meteorites) to be transferred to the Moon by a large impact on Earth and subsequently survive impact with the lunar surface, using the iSALE shock physics code. Three-dimensional impact simulations show that a typical basin-forming impact on Earth can eject solid fragments equivalent to ~10−3 of an impactor mass at speeds sufficient to transfer from Earth to the Moon. Previous modelling of meteorite survivability has relied heavily upon the assumption that peak-shock pressures can be used as a proxy for gauging survival of projectiles and their possible biomarker constituents. Here, we show the importance of considering both pressure and temperature within the projectile, and the inclusion of both shock and shear heating, in assessing biomarker survival. Assuming that they survive launch from Earth, we show that some biomarker molecules within terrestrial meteorites are likely to survive impact with the Moon, especially at the lower end of the range of typical impact velocities for terrestrial meteorites (2.5 km s−1). The survival of larger biomarkers (e.g., microfossils) is also assessed, and we find limited, but significant, survival for low impact velocity and high target porosity scenarios. Thermal degradation of biomarkers shortly after impact depends heavily upon where the projectile material lands, whether it is buried or remains on the surface, and the related cooling timescales. Comparing sandstone and limestone projectiles shows similar temperature and pressure profiles for the same impact velocities, with limestone providing slightly more favourable conditions for biomarker survival.

Journal article

Raducan S, 2020, Impact ejecta and crater formation on asteroid surfaces

Asteroids in the Solar System are numerous and have varied composition. Analysis of impact crater sizes and morphologies on asteroids can provide a direct diagnosis of the surface material properties and near-surface structures. This thesis describes numerical simulations of impacts into low-gravity asteroid surfaces using the iSALE shock physics code to inform this diagnosis. Asteroids may pose a future catastrophic threat to Earth and to avoid it, the incoming asteroid can be deflected by a spacecraft impact. However, the efficiency of the deflection is determined by target properties. This work considered different target scenarios to determine the sensitivity of crater morphology, ejecta mass-velocity distribution and momentum transferred, to asteroid surface properties and shallow structures. For homogeneous targets, the surface cohesion, initial porosity, and internal friction were found to greatly influence ejecta mass/velocity distributions and the amount an asteroid can be deflected. In a two-layer target scenario, the presence of a less porous, stronger lower layer can cause both amplification and reduction of ejected mass and momentum relative to the homogeneous case. Impacts into targets with decreasing porosity with depth only produced an enhancement in the ejected momentum for sharp exponential decreases in porosity. Using reasonable estimates for the material properties of the Double Asteroid Redirection Test (DART) asteroid target, the simulations show that the ejecta produced from the impact can enhance the deflection 2 to 4 times. Simulations of impacts into possible target structures on Psyche show large diversity in possible crater morphologies that the ‘Psyche’ mission could encounter. If Psyche’s interior is homogeneous, then the mission will find simple bowl-shaped craters, with a depth-diameter ratio diagnostic of rock or iron. If Psyche has a layered structure, the spacecraft could find craters with more complex morphologie

Thesis dissertation

Raducan SD, Davison TM, Collins GS, 2020, Morphological diversity of impact craters on asteroid (16) Psyche: insight from numerical models, Journal of Geophysical Research: Planets, Vol: 125, Pages: 1-19, ISSN: 2169-9097

The asteroid (16) Psyche, target of NASA's “Psyche” mission, is thought to be one of the most massive exposed iron cores in the solar system. Earth‐based observations suggest that Psyche has a metal‐rich surface; however, its internal structure cannot be determined from ground‐based observations. Here we simulate impacts into a variety of possible target structures on Psyche and show the possible diversity in crater morphologies that the “Psyche” mission could encounter. If Psyche's interior is homogeneous, then the mission will find simple bowl‐shaped craters, with a depth‐diameter ratio diagnostic of rock or iron. Craters will be much deeper than those on other visited asteroids and possess much more spectacular rims if the surface is dominated by metallic iron. On the other hand, if Psyche has a layered structure, the spacecraft could find craters with more complex morphologies, such as concentric or flat‐floored craters. Furthermore, if ferrovolcanism occurred on Psyche, then the morphology of craters less than 2 km in diameter could be even more exotic. Based on three to four proposed large craters on Psyche's surface, model size‐frequency distributions suggest that if Psyche is indeed an exposed iron core, then the spacecraft will encounter a very old and evolved surface, that would be 4.5 Gyr old. For a rocky surface, then Psyche could be at least 3 Gyr old.

Journal article

Collins G, Patel N, Davison T, Rae A, Morgan J, Gulick S, IODPICDP Expedition 364 & Third-Party Scientistset al., 2020, A steeply-inclined trajectory for the Chicxulub impact, Nature Communications, Vol: 11, Pages: 1-10, ISSN: 2041-1723

The environmental severity of large impacts on Earth is influenced by their impact trajectory. Impact direction and angle to the target plane affect the volume and depth of origin of vaporized target, as well as the trajectories of ejected material. The asteroid impact that formed the 66 Ma Chicxulub crater had a profound and catastrophic effect on Earth’s environment,but the impact trajectory is debated. Here we show that impact angle and direction can be diagnosed by asymmetries in the subsurface structure of the Chicxulub crater. Comparison of 3D numerical simulations of Chicxulub-scale impacts with geophysical observations suggests that the Chicxulub crater was formed by a steeply-inclined (45 -60° to horizontal) impact from the northeast; several lines of evidence rule out a low angle (< 30°) impact. Asteeply-inclined impact produces a nearly symmetric distribution of ejected rock and releases more climate-changing gases per impactor mass than either a very shallow or near-vertical impact.

Journal article

Stickle AM, Bruck Syal M, Cheng AF, Collins GS, Davison TM, Gisler G, Güldemeister N, Heberling T, Luther R, Michel P, Miller P, Owen JM, Rainey ESG, Rivkin AS, Rosch T, Wünnemann Ket al., 2020, Benchmarking impact hydrocodes in the strength regime: Implications for modeling deflection by a kinetic impactor, Icarus, Vol: 338, Pages: 1-24, ISSN: 0019-1035

The Double Asteroid Redirection Test (DART) is a NASA-sponsored mission that will be the first direct test of the kinetic impactor technique for planetary defense. The DART spacecraft will impact into Didymos-B, the moon of the binary system 65803 Didymos, and the resulting period change will be measured from Earth. Impact simulations will be used to predict the crater size and momentum enhancement expected from the DART impact. Because the specific material properties (strength, porosity, internal structure) of the Didymos-B target are unknown, a wide variety of numerical simulations must be performed to better understand possible impact outcomes. This simulation campaign will involve a large parameter space being simulated using multiple different shock physics hydrocodes. In order to understand better the behaviors and properties of numerical simulation codes applicable to the DART impact, a benchmarking and validation program using different numerical codes to solve a set of standard problems was designed and implemented. The problems were designed to test the effects of material strength, porosity, damage models, and target geometry on the ejecta following an impact and thus the momentum transfer efficiency. Several important results were identified from comparing simulations across codes, including the effects of model resolution and porosity and strength model choice: 1) momentum transfer predictions almost uniformly exhibit a larger variation than predictions of crater size; 2) the choice of strength model, and the values used for material strength, are significantly more important in the prediction of crater size and momentum enhancement than variation between codes; 3) predictions for crater size and momentum enhancement tend to be similar (within 15‐20%) when similar strength models are used in different codes. These results will be used to better design a modeling plan for the DART mission as well as to better understand the potential results that may be

Journal article

Erickson TM, Kirkland CL, Timms NE, Cavosie AJ, Davison TMet al., 2020, Precise radiometric age establishes Yarrabubba, Western Australia, as Earth’s oldest recognised meteorite impact structure, Nature Communications, Vol: 11, Pages: 1-8, ISSN: 2041-1723

The ~70 km-diameter Yarrabubba impact structure in Western Australia is regarded as among Earth’s oldest, but has hitherto lacked precise age constraints. Here we present U–Pb ages for impact-driven shock-recrystallised accessory minerals. Shock-recrystallised monazite yields a precise impact age of 2229 ± 5 Ma, coeval with shock-reset zircon. This result establishes Yarrabubba as the oldest recognised meteorite impact structure on Earth, extending the terrestrial cratering record back >200 million years. The age of Yarrabubba coincides, within uncertainty, with temporal constraint for the youngest Palaeoproterozoic glacial deposits, the Rietfontein diamictite in South Africa. Numerical impact simulations indicate that a 70 km-diameter crater into a continental glacier could release between 8.7 × 1013 to 5.0 × 1015 kg of H2O vapour instantaneously into the atmosphere. These results provide new estimates of impact-produced H2O vapour abundances for models investigating termination of the Paleoproterozoic glaciations, and highlight the possible role of impact cratering in modifying Earth’s climate.

Journal article

Raducan SD, Davison TM, Collins GS, 2020, The effects of asteroid layering on ejecta mass-velocity distribution and implications for impact momentum transfer, Planetary and Space Science, Vol: 180, ISSN: 0032-0633

Most bodies in the Solar System do not have a homogeneous structure. Understanding the outcome of an impact into regolith layers of different properties is especially important for NASA’s Double Asteroid Redirection Test (DART) and ESA’s Hera missions. Here we used the iSALE shock physics code to simulate the DART impact into three different target scenarios in the strength regime: a homogeneous porous half-space; layered targets with a porous weak layer overlying a stronger bedrock; and targets with exponentially decreasing porosity with depth. For each scenario we determined the sensitivity of crater morphology, ejecta mass-velocity distribution and momentum transferred from the impact for deflection, , to target properties and structure. We found that for a homogeneous porous half-space, cohesion and porosity play a significant role and the DART impact is expected to produce a between 1 and 3. In a two-layer target scenario, the presence of a less porous, stronger lower layer close to the surface can cause both amplification and reduction of ejected mass and momentum relative to the homogeneous upper-layer case. For the case of DART, the momentum enhancement can change by up to 90%. Impacts into targets with an exponentially decreasing porosity with depth only produced an enhancement in the ejected mass and momentum for sharp decreases in porosity that occur within 6 m of the asteroid surface. Together with measurements of the DART crater by the Hera mission, these results can be used to test the predictive capabilities of numerical models of asteroid deflection.

Journal article

Wakita S, Genda H, Kurosawa K, Davison TMet al., 2019, Enhancement of impact heating in pressure-strengthened rocks in oblique impacts, Geophysical Research Letters, Vol: 46, Pages: 13678-13686, ISSN: 0094-8276

Shock‐induced metamorphism in meteorites informs us about the collisional environment and history of our solar system. Recently, the importance of material strength in impact heating was reported from head‐on impact simulations. Here, we perform three‐dimensional oblique impact simulations and confirm the additional heating due to material strength for oblique impacts. Despite a large difference in the peak pressure at the impact point at a given impact velocity, we find that the heated mass for an oblique impact is nearly the same as that for a head‐on impact. Thus, our results differ from the previous finding that the heated mass decreases as the impact becomes more oblique and show that the additional shear heating is more effective for oblique impacts than for head‐on impacts. This also indicates that material ejected during oblique impact tends to experience lower shock pressures but higher temperatures.

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

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, Vol: 54, Pages: 1604-1618, 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

Derrick JG, Rutherford ME, Chapman DJ, Davison TM, Duarte JPP, Farbaniec L, Bland PA, Eakins DE, Collins GSet al., 2019, Investigating shock processes in bimodal powder compaction through modelling and experiment at the mesoscale, International Journal of Solids and Structures, Vol: 163, Pages: 211-219, 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

Bowling TJ, Ciesla FJ, Davison TM, Scully JEC, Castillo-Rogez JC, Marchi S, Johnson Bet al., 2019, Post-impact thermal structure and cooling timescales of Occator Crater on Asteroid 1 Ceres, Icarus, Vol: 320, Pages: 110-118, ISSN: 0019-1035

Occator crater is perhaps the most distinct surface feature observed by NASA's Dawn spacecraft on the Cerean surface. Contained within the crater are the highest albedo features on the planet, Cerealia Facula and Vinalia Faculae, and relatively smooth lobate flow deposits. We present hydrocode simulations of the formation of Occator crater, varying the water to rock ratio of our pre-impact Cerean surface. We find that at water to rock mass ratios up to 0.3, sufficient volumes of Occator's post-impact subsurface would be above the melting point of water to allow for the deposition of Faculae like deposits via impact-heat driven hydrothermal effusion of brines. This reservoir of hydrothermally viable material beneath the crater is composed of a mixture of impactor material and material uplifted from 10’s of kilometers beneath the pre-impact surface, potentially sampling a deep subsurface volatile reservoir. Using a conductive cooling model, we estimate that the lifetime of hydrothermal activity within such a system, depending on choice of material constants, is between 0.4 and 4 Myr. Our results suggest that impact heating from the Occator forming impact provides a viable mechanism for the creation of observed faculae, with the proviso that the faculae formed within a relatively short time window after the crater itself formed.

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, Vol: 124, Pages: 396-417, 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

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., 2018, 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

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

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

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