With this addendum we provide some correction and additional information regarding the above cited publication. It addresses the following two topics. (1) Clarification for a correct application of the criteria for certain shock stages of chondrites, in particular stage C‐S6. (2) Correction of a printing error in the table that contains the shock classification system of chondrites.

We reevaluate the systematics and geologic setting of terrestrial, lunar, Martian, and asteroidal “impactites” resulting from single or multiple impacts. For impactites derived from silicate rocks and sediments, we propose a unified and updated system of progressive shock metamorphism. “Shock‐metamorphosed rocks” occur as lithic clasts or melt particles in proximal impactites at impact craters, and rarely in distal impactites. They represent a wide range of metamorphism, typically ranging from unshocked to shock melted. As the degree of shock metamorphism, at a given shock pressure, depends primarily on the mineralogical composition and the porosity of a rock or sediment sample, different shock classification systems are required for different types of planetary rocks and sediments. We define shock classification systems for eight rock and sediment classes which are assigned to three major groups of rocks and sediments (1) crystalline rocks with classes F, M, A, and U; (2) chondritic rocks (class C); and (3) sedimentary rocks and sediments with classes SR, SE, and RE. The abbreviations stand for felsic (F), mafic (M), anorthositic (A), ultramafic (U), sedimentary rocks (SR), unconsolidated sediments (SE), and regoliths (RE). In each class, the progressive stages of shock metamorphism are denominated S1 to Sx. These progressive shock stages are introduced as: S1–S7 for F, S1–S7 for M, S1–S6 for A, S1–S7 for U, S1–S7 for C, S1–S7 for SR, S1–S5 for SE, and S1–S6 for RE. S1 stands for “unshocked” and Sx (variable between S5 and S7) stands for “whole rock melting.” We propose a sequence of symbols characterizing the degree of shock metamorphism of a sample, i.e., F‐S1 to F‐S7 with the option to add the tabulated pressure ranges (in GPa) in parentheses.

We investigated the ejection mechanics by a complementary approach of cratering experiments, including the microscopic analysis of material sampled from these experiments, and 2-D numerical modeling of vertical impacts. The study is based on cratering experiments in quartz sand targets performed at the NASA Ames Vertical Gun Range. In these experiments, the preimpact location in the target and the final position of ejecta was determined by using color-coded sand and a catcher system for the ejecta. The results were compared with numerical simulations of the cratering and ejection process to validate the iSALE shock physics code. In turn the models provide further details on the ejection velocities and angles. We quantify the general assumption that ejecta thickness decreases with distance according to a power-law and that the relative proportion of shocked material in the ejecta increase with distance. We distinguish three types of shock metamorphic particles (1) melt particles, (2) shock lithified aggregates, and (3) shock-comminuted grains. The agreement between experiment and model was excellent, which provides confidence that the models can predict ejection angles, velocities, and the degree of shock loading of material expelled from a crater accurately if impact parameters such as impact velocity, impactor size, and gravity are varied beyond the experimental limitations. This study is relevant for a quantitative assessment of impact gardening on planetary surfaces and the evolution of regolith layers on atmosphereless bodies.

We analyzed the interaction of spherical, 6.36-mm-diameter, Cu-bearing aluminum projectiles with quartz sand targets in hypervelocity impact experiments performed at NASA Ames Vertical Gun Range. Impact velocities and inferred peak shock pressures varied between 5.9 and 6.5km/s and ∼41 and 48GPa, respectively. Shocked particles (“impact melt particles”) coated with thin crusts of molten projectile material were recovered from the floors of the ca. 33-cm-diameter craters and the respective ejecta blankets. Through petrographic and chemical (optical microscopy, FE-EMPA, SEM-EDX, and XRF) analysis we show that these particles have a layered structure manifested in distinct layers of decreasing shock metamorphism. These can be characterized by the following physical and chemical reactions and alteration products: (i) complete melting and subsequent recrystallization of the projectile, forming a distinct crystallization texture in the fused metal crust; (ii) projectile–target mixing, involving a redox reaction between Cu-bearing Al alloy und SiO2, leading to formation of khatyrkite (CuAl2), Al2O3 melt, euhedral silicon crystals, and spherical droplets of silicon; (iii) melting of quartz to lechatelierite and formation of planar deformation features in relic quartz grains; and (iv) shock lithification of quartz grains with fracturing of grains, grain-boundary melting, planar deformation features, and complete loss of porosity. To our knowledge, this is the first report of khatyrkite formed experimentally in hypervelocity impact experiments. These results have implications for the understanding of a similar redox reaction between Al–Cu metal and siliceous impact melt recently postulated for the Khatyrka CV3 carbonaceous chondrite. Moreover, these results bear on the processes that lead to layers of regolith on the surfaces of planetary bodies without atmospheres, such as asteroids in the main belt (e.g., 4 Vesta), and on the Moon. Specifically, impacts of mm-sized projectiles at velocities between 4 and 6km/s into regolith-covered, asteroidal surfaces in the main belt should yield similar impact melt particles that feature a continuum of shock effects, i.e., partially to completely molten projectile remnants adhering to impact-melted regolith agglomerates, as well as projectile-contaminated impact melts and local shock melting along grain boundaries.

We present the results of numerical modeling of the formation of the Ries crater utilizing the two hydrocodes SOVA and iSALE. These standard models allow us to reproduce crater shape, size, and morphology, and composition and extension of the continuous ejecta blanket. Some of these results cannot, however, be readily reconciled with observations: the impact plume above the crater consists mainly of molten and vaporized sedimentary rocks, containing very little material in comparison with the ejecta curtain; at the end of the modification stage, the crater floor is covered by a thick layer of impact melt with a total volume of 611km3; the thickness of true fallback material from the plume inside the crater does not exceed a couple of meters; ejecta from all stratigraphic units of the target are transported ballistically; no separation of sedimentary and crystalline rocksas observed between suevites and Bunte Breccia at Riesis noted. We also present numerical results quantifying the existing geological hypotheses of Ries ejecta emplacement from an impact plume, by melt flow, or by a pyroclastic density current. The results show that none of these mechanisms is consistent with physical constraints and/or observations. Finally, we suggest a new hypothesis of suevite formation and emplacement by postimpact interaction of hot impact melt with water or volatile-rich sedimentary rocks.

Why Study Impact Craters?" is the title of a fundamental contribution by one of the pioneers of impact crater research, Eugene M. Shoemaker, in a landmark book in this field: Impact and Explosion Cratering (Roddy et al. 1977). In his far-reaching vision, Shoemaker wrote: "I submit that impact of solid bodies is the most fundamental of all processes that have taken place on the terrestrial planets. Without impacts, Earth, Mars, Venus, and Mercury wouldn't exist. Collisions of smaller objects are the process by which the terrestrial planets were born." As a result of planetary exploration missions, we now know that impacts are ubiquitous in the Solar System. The Earth is the most geologically active of the terrestrial planets and, therefore, most of its impact structures have been destroyed over geologic time. Nevertheless, the Earth's impact record is the only source of three-dimensional lithological and structural ground-truth data on natural impacts and their consequences. For obvious reasons, natural impact phenomena are not fully amenable to experimental duplication.

The transport mechanism of suevite parti- cles during impact cratering is poorly under- stood and was studied at the 15 Ma Ries crater in southern Germany. Two emplace- ment modes of suevite deposits are generally discussed: (1) fallback of plume material into the crater and its periphery upon collapse of an ejecta plume; and (2) horizontal transport of ejected material, akin to emplacement of pyroclastic deposits erupting from volcanic centers. In order to differentiate between the two emplacement modes of suevite deposition, we analyzed the shape fabrics of suevite components from two localities out- side the Ries crater by fishape-fabric ellipsoids to measured shape-fabric ellipses and by applying high-resolution, X-ray- computed tomography to analyze the three- dimensional shape and orientation of the suevite particles. We show that the preferred orientation of long axes of elongate particles is disposed either radially or concentrically with respect to the crater center. Our obser- vations indicate that suevite material was not only derived from an ejecta plume, but was transported by lateral fl ow under viscous conditions upon fallback. This fl ow regime resembles that known from pyroclastic fl ows.

Large-volume pseudotachylite bodies in impact structures are dike like and consist of angular and rounded wall-rock fragments enveloped by a microcrystalline and sporadically glassy matrix that crystallized from a melt. Knowledge of the formation of pseudotachylite bodies is important for understanding mechanics of complex crater formation. Most current hypotheses of pseudotachylite formation inherently assume that fragmentation and melt generation occur during a single process. Based on the structure of pseudotachylite bodies at Sudbury (Canada) and Vredefort (South Africa), we show that these processes differ in time and space. We demonstrate that the centimeter- to kilometer-scale bodies are effectively fragment-and melt-filled tension fractures that formed by differential rotation of target rock during cratering. Highly variable pseudotachylite characteristics can be accounted for by a single process, i.e., drainage of initially superheated impact melt into tension fractures of the crater floor.

CRATER, SOUTHERN GERMANY. W.U. Reimold, B.K. Hansen, I. McDonald, C. Koeberl, J. Jacob, D. Stöffler, and C. Meyer, Museum für Naturkunde, Leibniz-Institute at Humboldt University Berlin, Invalidenstrasse 43, 10115 Berlin, Germany (uwe.reimold@mfn-berlin.de), School of Earth and Ocean Sciences, Cardiff University, Park Place, Cardiff CF10 3YE, U.K; Department of Lithospheric Research, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria.

Introduction: The Ries of Nördlingen (diameter: 26 km, age: 14.35 Ma) is the type locality of suevite which is the most characteristic rock type formed in impact craters. Though studied since 1834 [1], the formation and emplacement of suevite in the Ries and in impact craters in general is still enigmatic. As information from suevite can contribute significantly with regard to understanding the cratering process in general and the ejecta plume in particular, we have reevaluated suevite genesis in the context of modern modelling capabilities in conjunction with new petro-graphic studies [2] Geology of the Ries crater: The crater is formed in a 500 to 700 m thick layer of Mesozoic sediments underlain by crystalline basement [3]. It has 5 major structural elements (Fig. 1): (1) a central, ~ 700 m deep cavity (radius r = 6 km), (2) an uplifted inner ring and (3) a megablock zone from r = 6 to 13 km, (4) a " tectonic " rim at r = 13-15 km, and (5) an outer ejecta blanket from r = 13 to ca. 45 km. Types of suevite and their geological setting: At the Ries suevite occurs in three different geological settings [4, 5]: (1) a thick continuous layer in the central crater cavity inside the inner ring (" crater suevite " = CS), (2) thin isolated patches on top of the continuous ejecta blanket (previously called " fallout suevite " [5]; we propose to call it " outer suevite " = OS), and (3) dikes in the crater basement and in displaced megablocks. Crater suevite CS. The CS is exposed in several industrial and research drillings. Only the drill core Nördlingen 1973 (Fig. 1; [6]) provides a complete section. There, we distinguish severals subunits based on texture and modal composition: An upper unit A comprising ~ 60 m of " reworked " suevite underlain by ~ 17 m of " sorted " suevite (probably more than one cycle), a middle unit B of ~ 194 m of " high temperature " , i.e., melt-rich suevite, and a lower unit C of ~ 77 m of " low temperature " suevite characterized by a low melt content that decreases with depth. Units A and C display no or only extremely low reversed remanent magnetization, whereas unit B is strongly magnetized [7]. Except for unit A the crater suevite is not stratified and has a very …

Abstract— A rare three‐phase symplectite consisting of Ca‐rich pyroxene, Fe‐rich olivine, and a silica phase is frequently found rimming pyroxene in the Martian meteorite Los Angeles. This assemblage is usually interpreted as the breakdown product of metastable pyroxferroite, a very rare pyroxenoid mineral itself. However, its origin is not entirely understood, mainly because the extremely small average size of the constituent phases represents a challenge for precise high‐resolution analysis. In addition to electron microbeam methods, the present study uses time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) to overcome the limits of spatial resolution and to comprehensively study this mineral assemblage. The prevailing breakdown hypothesis is supported by the following results: (1) The three symplectite phases are very homogenous in composition from 100 μm down to the micrometer scale. (2) The silica phase could be shown to be almost pure SiO2. (3) The symplectite bulk composition is consistent with pyroxferroite. Sub‐micrometer sized Ti‐oxide grains are found within the symplectite (but not within the Ca‐rich pyroxene) and probably represent a minor breakdown phase in addition to the three main phases.

The scenario of lithopanspermia describes the viable transport of microorganisms via meteorites. To test the first step of lithopanspermia, i.e., the impact ejection from a planet, systematic shock recovery experiments within a pressure range observed in martian meteorites (5-50 GPa) were performed with dry layers of microorganisms (spores of Bacillus subtilis, cells of the endolithic cyanobacterium Chroococcidiopsis, and thalli and ascocarps of the lichen Xanthoria elegans) sandwiched between gabbro discs (martian analogue rock). Actual shock pressures were determined by refractive index measurements and Raman spectroscopy, and shock temperature profiles were calculated. Pressure-effect curves were constructed for survival of B. subtilis spores and Chroococcidiopsis cells from the number of colony-forming units, and for vitality of the photobiont and mycobiont of Xanthoria elegans from confocal laser scanning microscopy after live/dead staining (FUN-I). A vital launch window for the transport of rock-colonizing microorganisms from a Mars-like planet was inferred, which encompasses shock pressures in the range of 5 to about 40 GPa for the bacterial endospores and the lichens, and a more limited shock pressure range for the cyanobacterium (from 5-10 GPa). The results support concepts of viable impact ejections from Mars-like planets and the possibility of reseeding early Earth after asteroid cataclysms.

Meteoritics & Planetary ScienceVolume 43, Issue S7 p. A13-A14 Free Access 2008 Service Award for Drew Barringer Dieter Stöffler, Dieter Stöffler Museum for Natural History Humboldt University Berlin GermanySearch for more papers by this authorDavid A. Kring, David A. Kring USRA-Lunar and Planetary Institute Houston, Texas USASearch for more papers by this author Dieter Stöffler, Dieter Stöffler Museum for Natural History Humboldt University Berlin GermanySearch for more papers by this authorDavid A. Kring, David A. Kring USRA-Lunar and Planetary Institute Houston, Texas USASearch for more papers by this author First published: 26 January 2010 https://doi.org/10.1111/j.1945-5100.2008.tb00710.xAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL No abstract is available for this article. Volume43, IssueS7July 2008Pages A13-A14 RelatedInformation

ABSTRACT Impact-induced ejections of rocks from planetary surfaces are frequent events in the early history of the terrestrial planets and have been considered as a possible first step in the potential interplanetary transfer of microorganisms. Spores of Bacillus subtilis were used as a model system to study the effects of a simulated impact-caused ejection on rock-colonizing microorganisms using a high-explosive plane wave setup. Embedded in different types of rock material, spores were subjected to extremely high shock pressures (5 to 50 GPa) lasting for fractions of microseconds to seconds. Nearly exponential pressure response curves were obtained for spore survival and linear dependency for the induction of sporulation-defective mutants. Spores of strains defective in major small, acid-soluble spore proteins (SASP) (α/β-type SASP) that largely protect the spore DNA and spores of strains deficient in nonhomologous-end-joining DNA repair were significantly more sensitive to the applied shock pressure than were wild-type spores. These results indicate that DNA may be the sensitive target of spores exposed to ultrahigh shock pressures. To assess the nature of the critical physical parameter responsible for spore inactivation by ultrahigh shock pressures, the resulting peak temperature was varied by lowering the preshock temperature, changing the rock composition and porosity, or increasing the water content of the samples. Increased peak temperatures led to increased spore inactivation and reduced mutation rates. The data suggested that besides the potential mechanical stress exerted by the shock pressure, the accompanying high peak temperatures were a critical stress parameter that spores had to cope with.