156 results found
Johnson BC, Collins GS, Minton DA, et al., 2016, Spherule layers, crater scaling laws, and the population of ancient terrestrial craters, Icarus, Vol: 271, Pages: 350-359, ISSN: 1090-2643
Ancient layers of impact spherules provide a record of Earth's early bombardment history. Here, we compare different bombardment histories to the spherule layer record and show that 3.2-3.5 Ga the flux of large impactors (10-100 km in diameter) was likely 20-40 times higher than today. The E-belt model of early Solar System dynamics suggests that an increased impactor flux during the Archean is the result of the destabilization of an inward extension of the main asteroid belt (Bottke, W.F., Vokrouhlický, D., Minton, D., Nesvorný, D., Morbidelli, A., Brasser, R., Simonson, B., Levison, H.F., 2012. Nature 485, 78–81). Here, we find that the nominal flux predicted by the E-belt model is 7-19 times too low to explain the spherule layer record. Moreover, rather than making most lunar basins younger than 4.1 Gyr old, the nominal E-belt model, coupled with a corrected crater diameter scaling law, only produces two lunar basins larger than 300 km in diameter. We also show that the spherule layer record when coupled with the lunar cratering record and careful consideration of crater scaling laws can constrain the size distribution of ancient terrestrial impactors. The preferred population is main-belt-like up to ∼50 km in diameter transitioning to a steep distribution going to larger sizes.
Asphaug E, Collins GS, Jutzi M, 2015, Global Scale Impacts, Asteroids IV, Editors: Michel, DeMeo, Bottke, Publisher: University of Arizona Press, Pages: 661-678, ISBN: 9780816532131
Global scale impacts modify the physical or thermal state of a substantial fraction of a target asteroid. Specific effects include accretion, family formation, reshaping, mixing and layering, shock and frictional heating, fragmentation, material compaction, dilatation, stripping of mantle and crust, and seismic degradation. Deciphering the complicated record of global scale impacts, in asteroids and meteorites, will lead us to understand the original planet-forming process and its resultant populations, and their evolution in time as collisions became faster and fewer. We provide a brief overview of these ideas, and an introduction to models.
Baker DMH, Head JW, Collins GS, et al., 2015, The formation of peak-ring basins: working hypotheses and path forward in using observations to constrain models of impact-basin formation, Icarus, Vol: 273, Pages: 146-163, ISSN: 0019-1035
Impact basins provide windows into the crustal structure and stratigraphy of planetary bodies; however, interpreting the stratigraphic origin of basin materials requires an understanding of the processes controlling basin formation and morphology. Peak-ring basins (exhibiting a rim crest and single interior ring of peaks) provide important insight into the basin-formation process, as they are transitional between complex craters with central peaks and larger multi-ring basins. New image and altimetry data from the Lunar Reconnaissance Orbiter as well as a suite of remote sensing datasets have permitted a reassessment of the origin of lunar peak-ring basins. We synthesize morphometric, spectroscopic, and gravity observations of lunar peak-ring basins and describe two working hypotheses for the formation of peak rings that involve interactions between inward collapsing walls of the transient cavity and large central uplifts of the crust and mantle. Major facets of our observations are then compared and discussed in the context of numerical simulations of peak-ring basin formation in order to plot a course for future model refinement and development.
Milbury C, Johnson BC, Melosh HJ, et al., 2015, Preimpact porosity controls the gravity signature of lunar craters, Geophysical Research Letters, Vol: 42, Pages: 9711-9716, ISSN: 1944-8007
We model the formation of lunar complex craters and investigate the effect of preimpact porosity on their gravity signatures. We find that while preimpact target porosities less than ~7% produce negative residual Bouguer anomalies (BAs), porosities greater than ~7% produce positive anomalies whose magnitude is greater for impacted surfaces with higher initial porosity. Negative anomalies result from pore space creation due to fracturing and dilatant bulking, and positive anomalies result from destruction of pore space due to shock wave compression. The central BA of craters larger than ~215 km in diameter, however, are invariably positive because of an underlying central mantle uplift. We conclude that the striking differences between the gravity signatures of craters on the Earth and Moon are the result of the higher average porosity and variable porosity of the lunar crust.
Ormo J, Melero-Asensio I, Housen K, et al., 2015, Scaling and reproducibility of craters produced at the Experimental Projectile Impact Chamber (EPIC), Centro de Astrobiología, Spain, Meteoritics & Planetary Science, ISSN: 1086-9379
Monteux J, Collins GS, Tobie G, et al., 2015, Consequences of large impacts on Enceladus' core shape, Icarus, Vol: 264, Pages: 300-310, ISSN: 1090-2643
The intense activity on Enceladus suggests a differentiated interior consisting of a rocky core, an internal ocean and an icy mantle. However, topography and gravity data suggests large heterogeneity in the interior, possibly including significant core topography. In the present study, we investigated the consequences of collisions with large impactors on the core shape. We performed impact simulations using the code iSALE2D considering large differentiated impactors with radius ranging between 25 and 100 km and impact velocities ranging between 0.24 and 2.4 km/s. Our simulations showed that the main controlling parameters for the post-impact shape of Enceladus’ rock core are the impactor radius and velocity and to a lesser extent the presence of an internal water ocean and the porosity and strength of the rock core. For low energy impacts, the impactors do not pass completely through the icy mantle. Subsequent sinking and spreading of the impactor rock core lead to a positive core topographic anomaly. For moderately energetic impacts, the impactors completely penetrate through the icy mantle, inducing a negative core topography surrounded by a positive anomaly of smaller amplitude. The depth and lateral extent of the excavated area is mostly determined by the impactor radius and velocity. For highly energetic impacts, the rocky core is strongly deformed, and the full body is likely to be disrupted. Explaining the long-wavelength irregular shape of Enceladus’ core by impacts would imply multiple low velocity (<2.4 km/s) collisions with deca-kilometric differentiated impactors, which is possible only after the LHB period.
Potter RWK, Kring DA, Collins GS, 2015, Scaling of basin-sized impacts and the influence of target temperature, Geological Society of America Special Papers, Vol: 518, Pages: 99-113, ISSN: 0072-1077
We produce a set of scaling laws for basin-sized impacts using data from a suiteof lunar basin numerical models. The results demonstrate the importance of preimpacttarget temperature and thermal gradient, which are shown to greatly infl uencethe modifi cation phase of the impact cratering process. Impacts into targets withcontrasting thermal properties also produce very different crustal and topographicprofi les for impacts of the same energy. Thermal conditions do not, however, signifi -cantly infl uence the excavation stage of the cratering process; results demonstrate,as a consequence of gravity-dominated growth, that transient crater radii are generallywithin 5% of each other over a wide range of thermal gradients. Excavationdepth-to-diameter ratios for the basin models (~0.12) agree well with experimental,geological, and geophysical estimates, suggesting basins follow proportional scaling.This is further demonstrated by an agreement between the basin models andPi- scaling laws based upon fi rst principles and experimental data. The results of thiswork should also be applicable to basin-scale impacts on other silicate bodies, includingthe Hadean Earth.
Forman LV, Bland PA, Timms NE, et al., 2015, RECOVERING THE PRIMORDIAL IMPACT HISTORY OF CHONDRITES IN UNPRECEDENTED DETAIL USING MASSIVE EBSD DATASETS, 78th Annual Meeting of the Meteoritical-Society, Publisher: WILEY-BLACKWELL, ISSN: 1086-9379
Muxworthy AR, Bland PA, Collins G, et al., 2015, MAGNETIC FABRICS IN ALLENDE: IMPLICATIONS FOR MAGNETIC REMANENCE ACQUISITION., 78th Annual Meeting of the Meteoritical-Society, Publisher: WILEY, ISSN: 1086-9379
Miljkovic K, Wieczorek MA, Collins GS, et al., 2015, Excavation of the lunar mantle by basin-forming impact events on the Moon, EARTH AND PLANETARY SCIENCE LETTERS, Vol: 409, Pages: 243-251, ISSN: 0012-821X
Jacobs CT, Goldin TJ, Collins GS, et al., 2015, An improved quantitative measure of the tendency for volcanic ash plumes to form in water: implications for the deposition of marine ash beds, JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH, Vol: 290, Pages: 114-124, ISSN: 0377-0273
Collins GS, 2015, Rock Avalanche, Encyclopedia of Planetary Landforms, Publisher: Springer New York, Pages: 1807-1811, ISBN: 9781461431336
Potter RWK, Kring DA, Collins GS, 2015, Scaling of basin-sized impacts and the influence of target temperature, Geological Society of America Special Papers, Publisher: Geological Society of America, Pages: 99-113, ISBN: 9780813725185
Bland PA, Collins GS, Davison TM, et al., 2014, Pressure-temperature evolution of primordial solar system solids during impact-induced compaction, NATURE COMMUNICATIONS, Vol: 5, ISSN: 2041-1723
Collins GS, 2014, Numerical simulations of impact crater formation with dilatancy, JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS, Vol: 119, Pages: 2600-2619, ISSN: 2169-9097
Davison TM, Cielsa FJ, Collins GS, et al., 2014, The effect of impact obliquity on shock heating in planetesimal collisions, Meteoritics & Planetary Science, Vol: 49, Pages: 2252-2265, ISSN: 1086-9379
Hill J, Collins GS, Avdis A, et al., 2014, How does multiscale modelling and inclusion of realistic palaeobathymetry affect numerical simulation of the Storegga Slide tsunami?, Ocean Modelling, Vol: 83, Pages: 11-25, ISSN: 1463-5003
The ∼8.15 ka Storegga submarine slide was a large (∼3000 km3), tsunamigenic slide off the coast of Norway. The resulting tsunami had run-up heights of around 10–20 m on the Norwegian coast, over 12 m in Shetland, 3–6 m on the Scottish mainland coast and reached as far as Greenland. Accurate numerical simulations of Storegga require high spatial resolution near the coasts, particularly near tsunami run-up observations, and also in the slide region. However, as the computational domain must span the whole of the Norwegian-Greenland sea, employing uniformly high spatial resolution is computationally prohibitive. To overcome this problem, we present a multiscale numerical model of the Storegga slide-generated tsunami where spatial resolution varies from 500 m to 50 km across the entire Norwegian-Greenland sea domain to optimally resolve the slide region, important coastlines and bathymetric changes. We compare results from our multiscale model to previous results using constant-resolution models and show that accounting for changes in bathymetry since 8.15 ka, neglected in previous numerical studies of the Storegga slide-tsunami, improves the agreement between the model and inferred run-up heights in specific locations, especially in the Shetlands, where maximum run-up height increased from 8 m (modern bathymetry) to 13 m (palaeobathymetry). By tracking the Storegga tsunami as far south as the southern North sea, we also found that wave heights were high enough to inundate Doggerland, an island in the southern North Sea prior to sea level rise over the last 8 ka.
Miljković K, Collins GS, Bland PA, 2014, Reply to comment on: “Supportive comment on: “Morphology and population of binary asteroid impact craters”, by K. Miljković, G.S. Collins, S. Mannick and P.A. Bland – An updated assessment”, Earth and Planetary Science Letters, Vol: 405, Pages: 285-286, ISSN: 0012-821X
In Miljković et al. (2013) we resolved the apparent contradiction that while 15% of the Near Earth Asteroid (impactor) population are binaries, only 2–4% of craters formed on Earth and Mars (target planet) are doublet craters. Using 3D hydrocode simulations to explore the physics of binary impacts, we showed that only 2% of binary asteroid impacts produced well-separated doublets, while the rest covered morphologies ranging from overlapping to elliptical or even circular. We then generated a complete classification dataset to aid in the identification of the (sometimes subtle) morphological characteristics consistent with a binary asteroid impact. We thank Schmieder et al. (2013) for providing additional detailed geochronological constraints which indicate that our lower bound of 2% doublet craters on Earth may in fact be ≤1.5%.
Milbury C, Johnson BC, Melosh HJ, et al., 2014, THE EFFECT OF POROSITY AND DILATANCY ON THE GRAVITY SIGNATURE OF CRATERS ON THE MOON., 77th Annual Meeting of the Meteoritical-Society, Publisher: WILEY-BLACKWELL, Pages: A283-A283, ISSN: 1086-9379
Bray VJ, Collins GS, Morgan JV, et al., 2014, Hydrocode simulation of Ganymede and Europa cratering trends - How thick is Europa's crust?, ICARUS, Vol: 231, Pages: 394-406, ISSN: 0019-1035
Neal WD, Appleby-Thomas GJ, Collins GS, 2014, Meso-scopic deformation in brittle granular materials, 18TH APS-SCCM AND 24TH AIRAPT, PTS 1-19, Vol: 500, ISSN: 1742-6588
Jacobs CT, Collins GS, Piggott MD, et al., 2014, MULTIPHASE FLOW MODELLING OF EXPLOSIVE VOLCANIC ERUPTIONS USING AN ADAPTIVE UNSTRUCTURED MESH-BASED APPROACH, 11th World Congress on Computational Mechanics (WCCM) / 5th European Conference on Computational Mechanics (ECCM) / 6th European Conference on Computational Fluid Dynamics (ECFD), Publisher: INT CENTER NUMERICAL METHODS ENGINEERING, Pages: 7406-7417
Collins GS, 2014, Terraced Crater Wall (Mass Wasting), Encyclopedia of Planetary Landforms, Publisher: Springer New York, Pages: 1-6
Ciesla FJ, Davison TM, Collins GS, et al., 2013, Thermal consequences of impacts in the early Solar System., Meteoritics and Planetary Science, Vol: 48, Pages: 2559-2567, ISSN: 1086-9379
Miljkovic K, Wieczorek MA, Collins GS, et al., 2013, Asymmetric Distribution of Lunar Impact Basins Caused by Variations in Target Properties, Science, Vol: 342, Pages: 724-726, ISSN: 0036-8075
Maps of crustal thickness derived from NASA’s Gravity Recovery and Interior Laboratory (GRAIL) mission revealed more large impact basins on the nearside hemisphere of the Moon than on its farside. The enrichment in heat-producing elements and prolonged volcanic activity on the lunar nearside hemisphere indicate that the temperature of the nearside crust and upper mantle was hotter than that of the farside at the time of basin formation. Using the iSALE-2D hydrocode to model impact basin formation, we found that impacts on the hotter nearside would have formed basins with up to twice the diameter of similar impacts on the cooler farside hemisphere. The size distribution of lunar impact basins is thus not representative of the earliest inner solar system impact bombardment.
Davison TM, O'Brien DP, Ciesla FJ, et al., 2013, The early impact histories of meteorite parent bodies, Meteoritics and Planetary Science, Vol: 48, Pages: 1894-1918, ISSN: 1086-9379
We have developed a statistical framework that uses collisional evolution models, shock physics modeling and scaling laws to determine the range of plausible collisional histories for individual meteorite parent bodies. It is likely that those parent bodies that were not catastrophically disrupted sustained hundreds of impacts on their surfaces — compacting, heating, and mixing the outer layers; it is highly unlikely that many parent bodies escaped without any impacts processing the outer few kilometers. The first 10 - 20 Myr were the most important time for impacts, both in terms of the number of impacts and the increase of specific internal energy due to impacts. The model has been applied to evaluate the proposed impact histories of several meteorite parent bodies: up to 10 parent bodies that were not disrupted in the first 100 Myr experienced a vaporizing collision of the type necessary to produce the metal inclusions and chondrules on the CB chondrite parent; around 1 -- 5\% of bodies that were catastrophically disrupted after 12 Myr sustained impacts at times that match the heating events recorded on the IAB/winonaite parent body; more than 75\% of 100 km radius parent bodies which survived past 100 Myr without being disrupted sustained an impact that excavates to the depth required for mixing in the outer layers of the H chondrite parent body; and to protect the magnetic field on the CV chondrite parent body, the crust would have had to have been thick (~ 20 km) in order to prevent it being punctured by impacts.
Bland PA, Collins GS, Dyl KA, et al., 2013, Impact-induced compaction of primordial materials and the effect on the chondrite record., 76th Annual Meeting of the Meteoritical-Society, Publisher: WILEY-BLACKWELL, Pages: A63-A63, ISSN: 1086-9379
Oishi Y, Piggott MD, Maeda T, et al., 2013, Three-dimensional tsunami propagation simulations using an unstructured mesh finite element model, Journal of Geophysical Research: Solid Earth, Vol: 118, Pages: 2998-3018, ISSN: 2169-9313
Miljković K, Collins GS, Mannick S, et al., 2013, Morphology and population of binary asteroid impact craters, Earth and Planetary Science Letters, Vol: 363, Pages: 121-132, ISSN: 0012-821X
Observational data show that in the Near Earth Asteroid (NEA) region 15% of asteroids are binary. However, the observed number of plausible doublet craters is 2–4% on Earth and 2–3% on Mars. This discrepancy between the percentage of binary asteroids and doublets on Earth and Mars may imply that not all binary systems form a clearly distinguishable doublet crater owing to insufficient separation between the binary components at the point of impact. We simulate the crater morphology formed in close binary asteroid impacts in a planetary environment and the range of possible crater morphologies includes: single (circular or elliptical) craters, overlapping (tear-drop or peanut shaped) craters, as well as clearly distinct, doublet craters. While the majority of binary asteroids impacting Earth or Mars should form a single, circular crater, about one in four are expected to form elongated or overlapping impact craters and one in six are expected to be doublets. This implies that doublets are formed in approximately 2% of all asteroid impacts on Earth and that elongated or overlapping binary impact craters are under-represented in the terrestrial crater record. The classification of a complete range of binary asteroid impact crater structures provides a template for binary asteroid impact crater morphologies, which can help in identifying planetary surface features observed by remote sensing.
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