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The ability of tardigrades to survive impact shocks in the kilometer per second and gigapascal range was investigated. When rocks impact planetary surfaces, the impact speeds and shock pressures are in the kilometer per second and gigapascal range. This investigation tested whether tardigrades can survive in impacts typical of those that occur naturally in the Solar System. We found that they can survive impacts up to 0.9 km s-1, which is equivalent to 1.14 GPa shock pressure, but cannot survive impacts above this. This is significantly less than the static pressure limit and has implications for tardigrade survival in panspermia models. The potential survival of tardigrades in impacts of terrestrial impact ejecta on the Moon is shown to be impossible for the average lunar impact speed of such ejecta. However, a notable fraction (around 40%) of such ejecta impact at vertical speeds low enough to permit survival. Similarly, martian impact ejecta striking Phobos, for example, at a typical im�pact speed will not permit viable transfer of tardigrade-like organisms, but if a fraction of such material had a lower impact speed, survival may be possible. We also consider the implications of this for the collection of viable samples by spacecraft transiting the plumes of icy water worlds such as Europa and Enceladus. We have found the limit on survival of shocks to be around 1 GPa, which is instrumental in determining appropriate mission scenarios and collection methods for the acquisition of viable materials.

The decade of the 2020s promises to be when humanity returns to space beyond Earth orbit, with several nations trying to place astronauts on the Moon, before going further into deep space. As part of such a programme, NASA and partner organisations, propose to build a Deep Space Gateway in lunar orbit by the mid-2020s. This would be visited regularly and offer a platform for science as well as for human activity. Payloads that can be mounted externally on the Gateway offer the chance to, amongst other scientific goals, monitor and observe the dust flux in the vicinity of the Moon. This paper looks at relevant technologies to measure dust which will impact the exposed surface at high speed. Flux estimates and a model payload of detectors are described. It is predicted that the flux is sufficient to permit studies of cometary vs. asteroidal dust and their composition, and to sample interstellar dust streams. This may also be the last opportunity to measure the natural dust flux near the Moon before the current, relatively pristine environment, is contaminated by debris, as humanity’s interest in the Moon generates increased activity in that vicinity in coming decades. ISSN:0273-1177 ISSN:1879-1948

Polyaromatic hydrocarbons (PAHs) are found throughout the universe. The ubiquity of these organic molecules means that they are of considerable interest in the context of cosmic dust, which typically travels at hypervelocities (>1 km s–1) within our solar system. However, studying such fast-moving micrometer-sized particles in laboratory-based experiments requires suitable synthetic mimics. Herein, we use ball-milling to produce microparticles of anthracene, which is the simplest member of the PAH family. Size control can be achieved by varying the milling time in the presence of a suitable anionic commercial polymeric dispersant (Morwet D-425). These anthracene microparticles are then coated with a thin overlayer of polypyrrole (PPy), which is an air-stable organic conducting polymer. The uncoated and PPy-coated anthracene microparticles are characterized in terms of their particle size, surface morphology, and chemical structure using optical microscopy, scanning electron microscopy, laser diffraction, aqueous electrophoresis, FT-IR spectroscopy, Raman microscopy, and X-ray photoelectron spectroscopy (XPS). Moreover, such microparticles can be accelerated up to hypervelocities using a light gas gun. Finally, studies of impact craters indicate carbon debris, so they are expected to serve as the first synthetic mimic for PAH-based cosmic dust.

Several icy bodies in the outer Solar system have extensive internal oceans. In several bodies the oceans are believed to be so extensive they decouple the interior core from the icy surface. A major evolutionary driver in the Solar System is high speed impacts – which lead to cratering or even disruption of the target body. Here we consider how the presence of an internal ocean modifies the energy density needed to disrupt an icy body with an internal ocean. We find that in laboratory experiments on decimetre scale bodies, the energy density to cause disruption is 16.25 ± 1.35 J kg−1, compared to 18.0 ± 0.7 J kg−1 for solid ice bodies. This suggests that for the purposes of impacts the bodies behave as if a solid with the same density. Predictions of the lifetimes of such icy bodies against impact disruption thus need not take the interior ocean into account.

Penny J Wozniakiewicz and Mark J Burchell survey the dust environment around our planet, now and in the future, as discussed at an RAS Specialist Discussion meeting.

The variation of impact crater size in rock has been investigated as a function of target temperature in the range 150 K – 1150 K. Three rock types were used: limestone, sandstone and basalt. A total of thirty impacts were observed, at a typical impact speed of 5 km s-1 with a 0.8 mm diameter stainless steel spherical projectile. The three rocks behaved in two ways. The craters in limestone and sandstone initially grew in size, until a maximum was reached at around 500 K. Crater size then fell again as temperature increased further. For basalt however, crater size fell as temperature increased, reaching a constant level above 800 K. This strongly suggests that crater sizes seen in experiments on Earth, should not be taken as typical, rather they are a function of rock temperature. It proved difficult to relate crater size to target strength, as data in the literature on rock strength vs. temperature were in some cases contradictory.

Impact events are ubiquitous across the entire Solar System; craters are observed from Mercury to distant Pluto. This process has been occurring since the Solar System formed and is still occurring today. During such events, which typically occur at speeds measured in kilometers per second, extreme pressures and elevated temperatures are created. In order to understand the physical processes that occur under such conditions, we have been using a two-stage light gas gun to recreate hypervelocity impacts on a range of targets that are representative (in both composition and physical condition) of the surfaces of all objects within the Solar System. Within this paper we describe the advances we have made in light-gas gun technology, specifically focusing on the University of Kent’s light gas-gun, over the past 30 years which have led to significant advancements in Planetary Science and the general field of shock physics.

Many bodies in the outer solar system are theorized to have an ice shell with a different subsurface material below, be it chondritic, regolith, or a subsurface ocean. This layering can have a significant influence on the morphology of impact craters. Accordingly, we have undertaken laboratory hypervelocity impact experiments on a range of multilayered targets, with interiors of water, sand, and basalt. Impact experiments were undertaken using impact speeds in the range of 0.8–5.3 km s?1, a 1.5 mm Al ball bearing projectile, and an impact incidence of 45°. The surface ice crust had a thickness between 5 and 50 mm, i.e., some 3–30 times the projectile diameter.\ud \ud The thickness of the ice crust as well as the nature of the subsurface layer (liquid, well consolidated, etc.) have a marked effect on the morphology of the resulting impact crater, with thicker ice producing a larger crater diameter (at a given impact velocity), and the crater diameter scaling with impact speed to the power 0.72 for semi-infinite ice, but with 0.37 for thin ice. The density of the subsurface material changes the structure of the crater, with flat crater floors if there is a dense, well-consolidated subsurface layer (basalt) or steep, narrow craters if there is a less cohesive subsurface (sand). The associated faulting in the ice surface is also dependent on ice thickness and the substrate material.\ud \ud We find that the ice layer (in impacts at 5 km s?1) is effectively semi-infinite if its thickness is more than 15.5 times the projectile diameter. Below this, the crater diameter is reduced by 4% for each reduction in ice layer thickness equal to the impactor diameter. Crater depth is also affected. In the ice thickness region, 7–15.5 times the projectile diameter, the crater shape in the ice is modified even when the subsurface layer is not penetrated. For ice thicknesses

The results of catastrophic disruption experiments on static and rotating targets are reported. The experiments used cement spheres of diameter 10 cm as the targets. Impacts were by mm sized stainless steel spheres at speeds of between 1 and 7.75 km s−1. Energy densities (Q) in the targets ranged from 7 to 2613 J kg−1. The experiments covered both the cratering and catastrophic disruption regimes. For static, i.e. non-rotating targets the critical energy density for disruption (Q*, the value of Q when the largest surviving target fragment has a mass equal to one half of the pre-impact target mass) was Q* = 1447 ± 90 J kg−1. For rotating targets (median rotation frequency of 3.44 Hz) we found Q* = 987 ± 349 J kg−1, a reduction of 32% in the mean value. This lower value of Q* for rotating targets was also accompanied by a larger scatter on the data, hence the greater uncertainty. We suggest that in some cases the rotating targets behaved as static targets, i.e. broke up with the same catastrophic disruption threshold, but in other cases the rotation helped the break up causing a lower catastrophic disruption threshold, hence both the lower value of Q* and the larger scatter on the data. The fragment mass distributions after impact were similar in both the static and rotating target experiments with similar slopes.

Kuebler et al. (2006) identified variations in olivine Raman spectra based upon the composition of individual olivine grains, leading to identification of olivine composition from Raman spectra alone. However, shock on a crystal lattice has since been shown to result in a structural change to the original material, which produces a shift in the Raman spectra of olivine grains compared with the original un-shocked olivine (Foster et al., 2013). This suggests that the use of the compositional calculations from the Raman spectra, reported in Kuebler et al. (2006), may provide an incorrect compositional value for material that has experienced shock. Here we have investigated the effect of impact speed (and hence peak shock pressure) on the shift in the Raman spectra for San Carlos olivine (Fo91) impacting Al. foil. Powdered San Carlos olivine (grain size 1 to 10 ?m) was fired at a range of impact speeds from 0.6 – 6.1 km s-1 (peak shock pressures 5 – 86 GPa) at Al. foil to simulate capture over a wide range of peak shock pressures. A permanent change in the Raman spectra was found to be observed only for impact speeds greater than ~5 km s-1. The process that causes the shift is most likely linked to an increase in the peak pressure produced by the impact, but only after a minimum shock pressure associated with the speed at which the effect is first observed (here 65 – 86 GPa). At speeds around 6 km s-1 (peak shock pressures ~86 GPa) the shift in Raman peak positions is in a similar direction (red shift) to that observed by Foster et al. (2013) but of twice the magnitude.

Over the last decade or so, a range of polypyrrole-based particles have been designed and evaluated for space science applications. This electrically conductive polymer enables such particles to efficiently acquire surface charge, which in turn allows their acceleration up to the hypervelocity regime (>1 km s(-1)) using a Van de Graaff accelerator. Either organic latex (e.g. polystyrene or poly(methyl methacrylate)) or various inorganic materials (such as silica, olivine or pyrrhotite) can be coated with polypyrrole; these core-shell particles are useful mimics for understanding the hypervelocity impact ionisation behaviour of micro-meteorites (a.k.a. cosmic dust). Impacts on metal targets at relatively low hypervelocities (10 km s(-1)) generate predominately atomic species, since many more chemical bonds are cleaved if the particles impinge with higher kinetic energy. Such fundamental studies are relevant to the calibration of the cosmic dust analyser (CDA) onboard the Cassini spacecraft, which was designed to determine the chemical composition of Saturn's dust rings. Inspired by volcanism observed for one of the Jupiter's moons (Io), polypyrrole-coated sulfur-rich latexes have also been designed to help space scientists understand ionisation spectra originating from sulfur-rich dust particles. Finally, relatively large (20 mu m diameter) polypyrrole-coated polystyrene latexes have proven to be useful for understanding the extent of thermal ablation of organic projectiles when fired at ultralow density aerogel targets at up to 6.1 km s(-1) using a Light Gas Gun. In this case, the sacrificial polypyrrole overlayer simply provides a sensitive spectroscopic signature (rather than a conductive overlayer), and the scientific findings have important implications for the detection of organic dust grains during the Stardust space mission.

Hard X-ray, quantitative, fluorescence elemental imaging was performed on the ID22NI nanoprobe and ID22 microprobe beam lines of the European Synchrotron Research facility (ESRF) in Grenoble, France, on eight interstellar candidate impact features in the framework of the NASA Stardust Interstellar Preliminary Examination (ISPE). Three features were unambiguous tracks, and the other five were identified as possible, but not definite, impact features. Overall, we produced an absolute quantification of elemental abundances in the 15 ? Z ? 30 range by means of corrections of the beam parameters, reference materials, and fundamental atomic parameters. Seven features were ruled out as interstellar dust candidates (ISDC) based on compositional arguments. One of the three tracks, I1043,1,30,0,0, contained, at the time of our analysis, two physically separated, micrometer-sized terminal particles, the most promising ISDCs, Orion and Sirius. We found that the Sirius particle was a fairly homogenous Ni-bearing particle and contained about 33 fg of distributed high-Z elements (Z > 12). Orion was a highly heterogeneous Fe-bearing particle and contained about 59 fg of heavy elements located in hundred nanometer phases, forming an irregular mantle that surrounded a low-Z core. X-ray diffraction (XRD) measurements revealed Sirius to be amorphous, whereas Orion contained partially crystalline material (Gainsforth et al. 2014). Within the mantle, one grain was relatively Fe-Ni-Mn-rich; other zones were relatively Mn-Cr-Ti-rich and may correspond to different spinel populations. For absolute quantification purposes, Orion was assigned to a mineralogical assemblage of forsterite, spinel, and an unknown Fe-bearing phase, while Sirius was most likely composed of an amorphous Mg-bearing material with minor Ni and Fe. Owing to its nearly chondritic abundances of the nonvolatile elements Ca, Ti, Co, and Ni with respect to Fe, in combination with the presence of olivine and spinel as inferred from XRD measurements, Orion had a high probability of being extraterrestrial in origin.

We discuss the inherent difficulties that arise during "ground truth" characterization of the Stardust interstellar dust collector. The challenge of identifying contemporary interstellar dust impact tracks in aerogel is described within the context of background spacecraft secondaries and possible interplanetary dust particles and beta-meteoroids. In addition, the extraction of microscopic dust embedded in aerogel is technically challenging. Specifically, we provide a detailed description of the sample preparation techniques developed to address the unique goals and restrictions of the Interstellar Preliminary Exam. These sample preparation requirements and the scarcity of candidate interstellar impact tracks exacerbate the difficulties. We also illustrate the role of initial optical imaging with critically important examples, and summarize the overall processing of the collection to date.

–Here, we report the identification of 69 tracks in approximately 250 cm 2 of aerogelcollectors of the Stardust Interstellar Dust Collector. We identified these tracks throughStardust@home, a distributed internet-based virtual microscope and search engine, in which> 30,000 amateur scientists collectively performed >9 9 10 7 searches on approximately 10 6 fields of view. Using calibration images, we measured individual detection efficiency, andfound that the individual detection efficiency for tracks > 2.5 lm in diameter was >0.6, andwas >0.75 for tracks >3 lm in diameter. Because most fields of view were searched >30times, these results could be combined to yield a theoretical detection efficiency near unity.The initial expectation was that interstellar dust would be captured at very high speed. Theactual tracks discovered in the Stardust collector, however, were due to low-speed impacts,and were morphologically strongly distinct from the calibration images. As a result, thedetection efficiency of these tracks was lower than detection efficiency of calibrationspresented in training, testing, and ongoing calibration. Nevertheless, as calibration imagesbased on low-speed impacts were added later in the project, detection efficiencies for low-speed tracks rose dramatically. We conclude that a massively distributed, calibrated search,with amateur collaborators, is an effective approach to the challenging problem ofidentification of tracks of hypervelocity projectiles captured in aerogel.1510 A. J. Westphal et al.

Under the auspices of the Stardust Interstellar Preliminary Examination, picokeystones extracted from the Stardust Interstellar Dust Collector were examined with synchrotron Fourier transform infrared (FTIR) microscopy to establish whether they contained extraterrestrial organic material. The picokeystones were found to be contaminated with varying concentrations and speciation of organics in the native aerogel, which hindered the search for organics in the interstellar dust candidates. Furthermore, examination of the picokeystones prior to and post X-ray microprobe analyses yielded evidence of beam damage in the form of organic deposition or modification, particularly with hard X-ray synchrotron X-ray fluorescence. From these results, it is clear that considerable care must be taken to interpret any organics that might be in interstellar dust particles. For the interstellar candidates examined thus far, however, there is no clear evidence of extraterrestrial organics associated with the track and/or terminal particles. However, we detected organic matter associated with the terminal particle in Track 37, likely a secondary impact from the Al-deck of the sample return capsule, demonstrating the ability of synchrotron FTIR to detect organic matter in small particles within picokeystones from the Stardust interstellar dust collector.

On the basis of an interstellar dust model compatible with Ulysses and Galileo observations, we calculate and predict the trajectories of interstellar dust (ISD) in the solar system and the distribution of the impact speeds, directions, and flux of ISD particles on the Stardust Interstellar Dust Collector during the two collection periods of the mission. We find that the expected impact velocities are generally low (less than 10 km per second) for particles with the ratio of the solar radiation pressure force to the solar gravitational force beta greater than 1, and that some of the particles will impact on the cometary side of the collector. If we assume astronomical silicates for particle material and a density of 2 grams per cubic centimeter, and use the Ulysses measurements and the ISD trajectory simulations, we conclude that the total number of (detectable) captured ISD particles may be on the order of 50. In companion papers in this volume, we report the discovery of three interstellar dust candidates in the Stardust aerogel tiles. The impact directions and speeds of these candidates are consistent with those calculated from our ISD propagation model, within the uncertainties of the model and of the observations.

Using synchrotron-based X-ray diffraction measurements, we identified crystalline material in two particles of extraterrestrial origin extracted from the Stardust Interstellar Dust Collector. The first particle, I1047,1,34 (Hylabrook), consisted of a mosaiced olivine grain approximately 1 mu m in size with internal strain fields up to 0.3%. The unit cell dimensions were a - 4.85 +/- 0.08 angstrom, b - 10.34 +/- 0.16 angstrom, c - 6.08 +/- 0.13 angstrom (2 sigma). The second particle, I1043,1,30 (Orion), contained an olivine grain approximate to 2 mu m in length and > 500 nm in width. It was polycrystalline with both mosaiced domains varying over approximate to 20 degrees and additional unoriented domains, and contained internal strain fields < 1%. The unit cell dimensions of the olivine were a = 4.76 +/- 0.05 angstrom, b = 10.23 +/- 0.10 angstrom, c = 5.99 +/- 0.06 angstrom (2 sigma), which limited the olivine to a forsteritic composition [Fo(65) (2 sigma). Orion also contained abundant spinel nanocrystals of unknown composition, but unit cell dimension a = 8.06 +/- 0.08 angstrom (2 sigma). Two additional crystalline phases were present and remained unidentified. An amorphous component appeared to be present in both these particles based on STXM and XRF results reported elsewhere.

Experimental data are shown for survival of fossilized diatoms undergoing shocks in the GPa range. The results were obtained from hypervelocity impact experiments which fired fossilized diatoms frozen in ice into water targets. After the shots, the material recovered from the target water was inspected for diatom fossils. Nine shots were carried out, at speeds from 0.388 to 5.34 km s −1 , corresponding to mean peak pressures of 0.2–19 GPa. In all cases, fragmented fossilized diatoms were recovered, but both the mean and the maximum fragment size decreased with increasing impact speed and hence peak pressure. Examples of intact diatoms were found after the impacts, even in some of the higher speed shots, but their frequency and size decreased significantly at the higher speeds. This is the first demonstration that fossils can survive and be transferred from projectile to target in hypervelocity impacts, implying that it is possible that, as suggested by other authors, terrestrial rocks ejected from the Earth by giant impacts from space, and which then strike the Moon, may successfully transfer terrestrial fossils to the Moon.

We report the quantitative characterization by synchrotron soft X-ray spectroscopy of 31 potential impact features in the aerogel capture medium of the Stardust Interstellar Dust Collector. Samples were analyzed in aerogel by acquiring high spatial resolution maps and high energy-resolution spectra of major rock-forming elements Mg, Al, Si, Fe, and others. We developed diagnostic screening tests to reject spacecraft secondary ejecta and terrestrial contaminants from further consideration as interstellar dust candidates. The results support an extraterrestrial origin for three interstellar candidates: I1043,1,30 (Orion) is a 3 pg particle with Mg-spinel, forsterite, and an iron-bearing phase. I1047,1,34 (Hylabrook) is a 4 pg particle comprising an olivine core surrounded by low-density, amorphous Mg-silicate and amorphous Fe, Cr, and Mn phases. I1003,1,40 (Sorok) has the track morphology of a high-speed impact, but contains no detectable residue that is convincingly distinguishable from the background aerogel. Twenty-two samples with an anthropogenic origin were rejected, including four secondary ejecta from impacts on the Stardust spacecraft aft solar panels, nine ejecta from secondary impacts on the Stardust Sample Return Capsule, and nine contaminants lacking evidence of an impact. Other samples in the collection included I1029,1,6, which contained surviving solar system impactor material. Four samples remained ambiguous: I1006,2,18, I1044,2,32, and I1092,2,38 were too dense for analysis, and we did not detect an intact projectile in I1044,3,33. We detected no radiation effects from the synchrotron soft X-ray analyses; however, we recorded the effects of synchrotron hard X-ray radiation on I1043,1,30 and I1047,1,34.

The Stardust mission returned cometary, interplanetary and (probably) interstellar dust in 2006 to Earth that have been analysed in Earth laboratories worldwide. Results of this mission have changed our view and knowledge on the early solar nebula. The Rosetta mission is on its way to land on comet 67P/Churyumov-Gerasimenko and will investigate for the first time in great detail the comet nucleus and its environment starting in 2014. Additional astronomy and planetary space missions will further contribute to our understanding of dust generation, evolution and destruction in interstellar and interplanetary space and provide constraints on solar system formation and processes that led to the origin of life on Earth. One of these missions, SARIM-PLUS, will provide a unique perspective by measuring interplanetary and interstellar dust with high accuracy and sensitivity in our inner solar system between 1 and 2 AU. SARIM-PLUS employs latest in-situ techniques for a full characterisation of individual micrometeoroids (flux, mass, charge, trajectory, composition()) and collects and returns these samples to Earth for a detailed analysis. The opportunity to visit again the target comet of the Rosetta mission 67P/Churyumov-Gerasimeenternko, and to investigate its dusty environment six years after Rosetta with complementary methods is unique and strongly enhances and supports the scientific exploration of this target and the entire Rosetta mission. Launch opportunities are in 2020 with a backup window starting early 2026. The comet encounter occurs in September 2021 and the reentry takes place in early 2024. An encounter speed of 6 km/s ensures comparable results to the Stardust mission.

International audience; The maximum size of impact craters on finite bodies marks the largest impact that can occur short of impact induced disruption of the body. Recently attention has started to focus on large craters on small bodies such as asteroids and rocky and icy satellites. Here the large crater on the recently imaged asteroid (2867) Steins (with crater diameter to mean asteroid radius ratio of 0.79) is shown to follow a limit set by other similar sized bodies with moderate macroporosity (i.e. fractured asteroids). Thus whilst large, the crater size is not novel, nor does it requires Steins to possess an extremely large porosity. In one of the components of the binary asteroid (90) Antiope there is the recently reported presence of an extremely large depression, possibly a crater, with depression diameter to mean asteroid radius ratio of ∼(1.4 - 1.62). This is consistent with the maximum size of a crater expected from previous observations of very porous rocky bodies (i.e. rubble-pile asteroids). Finally, a relationship between crater diameter (normalised to body radius) is proposed as a function of body porosity which suggests that the doubling of porosity between fractured asteroids and rubble-pile asteroids, nearly doubles the size ( value) of the largest crater sustainable on a rocky body.

We consider the largest impact craters observed on small satellites and asteroids and the impact disruption of such bodies. Observational data are considered from 21 impact-like structures on 13 satellites and 8 asteroids (target body radii in the range 0.7–265 km). If the radius of the target body is R and the diameter of the largest crater observed on this body D, the ratio D / R is then the main observational parameter of interest. This is found on the observed bodies and compared to data obtained in the laboratory. Taking the largest observed value for D / R as a proxy for the ratio D c / R (where D c is the diameter of the largest crater that can be formed on a body without shattering it) it was found that for the observed icy satellites D c , icy ≈ 1.2 R and for the asteroids and the rocky satellites D c , rocky ≈ 1.6 R . In laboratory experiments with ice targets at impactor speeds of 1 to 3 km s−1 we obtained D c , icy ≈ 1.64 R .

Impacts into Marine and Icy Environments.- Biotic Responses to the Mjolnir Meteorite Impact, Barents Sea: Evidence from a Core Drilled within the Crater.- Near-field Erosional Features at the Mjolnir Impact Crater: the Role of Marine Sedimentary Target.- Global Effects of the Chicxulub Impact on Terrestrial Vegetation - Review of the Palynological Record from New Zealand Cretaceous/Tertiary Boundary.- The Neugrund Marine Impact Structure (Gulf of Finland, Estonia).- Structure-filling Sediments of the Wetumpka Marine-target Impact Structure (Alabama, USA).- Krk-breccia, Possible Impact-Crater Fill, Island of Krk in Eastern Adriatic Sea (Croatia).- Did the Puchezh-Katunki Impact Trigger an Extinction?.- Geochemistry of a Langhian Pelagic Marly Limestone Sequence of the Conero Riviera, Ancona (Italy) and the Search for a Ries Impact Signature: A Progress Report.- Titan: A New World Covered in Submarine Craters?.- Estimating Crater Size for Hypervelocity Impacts on Small Icy Bodies (e.g. Comet Nucleus).- Survivability of Bacteria in Hypervelocity Impacts on Ice.- Impact Cratering of Icy and Rocky Targets in Planetary Sciences and in the Laboratory.- Paleomagnetism and 40Ar/39Ar Age Determinations of Impactites from the Ilyinets Structure, Ukraine.- Cathodoluminescence, Electron Microscopy, and Raman Spectroscopy of Experimentally Shock Metamorphosed Zircon Crystals and Naturally Shocked Zircon from the Ries Impact Crater.- A Brief Introduction to Hydrocode Modeling of Impact Cratering.

This is an overview of the preliminary results of\(\bar pp\) annihilation at incident\(\bar p\) momenta of 600, 1200 and 1940 MeV/c(*). The data was taken at LEAR with the Crystal Barrel Detector (E. Akeret al.:Nucl. Instrum. Methods A,321, 108 (1992)). In the two pseudoscalar final states seven different channels are observable and their angular distributions are measured. They are compared to older data, if existent, and are found to be equal within the experimental errors. In the three-meson final states, an overview of the already examined final states is given. Striking signals in the Dalitz plots and invariant-mass projections for a set of final states are observed. In the final states ηηπ0 and ηηη a signal ηη with the invariant mass of 1480 MeV/c2 and a width of aboutΓ≈≈70 MeV/c2 is visible. In the final-state ωηπ0 a signal in the ωη invariant-mass spectrum at 1680 MeV/c2 with a widthΓ≈150 MeV/c2 is observed. Finally, in the final-state ωωπ0 two visible structures in the Dalitz plot are detected at 1600 MeV/c2 (Γ≈90 MeV/c2) and 1900 MeV/c2 (Γ≈150 MeV/c2).

Results are presented on meson spectroscopy, two-body final states and meson decay modes observed in\(\bar pp\) annhilation at rest by the Crystal Barrel experiment at LEAR.

This paper presents results on charm photoproduction in the energy interval 40 to 160 GeV, obtained from the high-statistics charm samples of the NA 14/2 experiment at CERN. We measure the charm cross-section, the distributions inxF andp2T and various production ratios and charge asymmetries. The total non-diffractive open-charm cross-section per nucleon is measured to be\(\sigma _{(\gamma N \to c\bar cX)} \) at 〈Eγ〉 =100 GeV. We discuss the photoproduction of charm in terms of theoretical and phenomenological models. We compare the measuredp2T andxF distributions with first-order QCD calculations of photon-gluon fusion and obtain a value for the charm-quark mass ofmc=1.5+0.2−0.1GeV/c2.

The crystal Barrel spectrometer used at LEAR, CERN to study the products of pd annihilations is described. A 1380 element array of Csl crystals measures photons from the decay of π0, η, η′ and ω mesons. A segmented drift chamber in a 1.5T magnetic field is used to identify and measure charged particles. A fast on-line trigger on charged and neutral multiplicities and on the invariant mass of secondary particles is available. The performance of the detector is discussed.

Antiproton-proton annihilations at rest into 3 π 0 are analyzed in terms of π 0 π 0 final state interactions. A J PC = 2 + + resonance at a mass of 1515 ± 10 MeV with a width of 120 ± 10 MeV is required to explain the data. This result is supported by previous observations made on the ππ system in p p and p n annihilations which show that the resonance has I = 0. This resonance is practically degenerate in mass with the f′ 2 (1525) but the two resonances have very different production and decay characteristics.

Properties ofD mesons produced in the photo-production experiment NA 14/2 at CERN are reported. The following ratios of branching fractions were measured: $$\begin{gathered} Br(D^0 \to K^ + K^ - )/Br(D^0 \to K^ - \pi ^ + ) = 0.16 \pm 0.05, \hfill \\ Br(D^0 \to K^ - \pi ^ + \pi ^0 )/Br(D^0 \to K^ - \pi ^ + ) = 4.0 \pm 0.09 \pm 1.0, \hfill \\ Br(D^0 \to K^ - \pi ^ + \pi ^ + \pi ^ - )/Br(D^0 \to K^ - \pi ^ + ) \hfill \\ = 1.9 \pm 0.25 \pm 0.20 \hfill \\ \end{gathered} $$ . TheD 0→K − π + π + π − decay was analysed and the contribution of resonant subprocesses found consistent with 1ρ 0 and 0.23 $$\bar K$$ *0 per event. The angular distributions ofD 0→ $$\bar K$$ *0 showed parity violation and destructive interference betweenS- andD-waves. From a Dalitz-plot analysis of the decayD +→K − π + π + the contribution from the quasi two-body decayD +→ $$\bar K$$ *0 π + was measured to be 0.14±0.04±0.04.

A new method is demonstrated to detect impacts of hypervelocity particles in real-time and to determine the size of particles. It uses a resistive grid on a thin substrate (here Duroid). Penetration of the substrate in an impact breaks lines on the grid, changing the overall resistance of the grid. The change in resistance is proportional to the width of the damaged area (i.e. number of resistive lines that are broken), which is in turn proportional to the impactor size. This method provides a large area, low mass, low power detector for measuring the flux of small dust particles in space. Based on experimental data (taken in a two-stage light gas gun), we show that impacts at 5 km s-1 demonstrate that the principle works as described for particles 150 μm and above and that in theory could work for impacts down to size scales as small as 50 μm.

The NA14 photoproduction experiment, carried out at the CERN SPS, has measured the inclusive cross section of events with a prompt photon at high p T in the final state. Here we present a study of the topology of the final state of these events. The topology differs from that observed for events with an identified π 0 in the same kinematical domain. Using these differences we have extracted the contribution from the Born term to the inclusive prompt photon cross section. The result is in good agreement with theoretical predictions and supports the assignment of a fractional electric charge to the quarks.

A quantitative test of QCD from high energy photoproduction of large transverse momentum charged hadrons, using incident γ energies between 50 and 150 GeV, is presented. The inclusive hadron P 1 and P t distributions show a clear excess over the VDM contribution. This excess is found to be in good agreement with second-order QCD calculations. This agreement does not depend critically on the choice of the gluon fragmentation function, and is observed over the large kinematical domain covered by this experiment.