Dr Mark Price

Senior Lecturer in Space Science

About

Dr Mark Price is interested in the effect of hypervelocity impacts on bodies in space. Such impacts generally occur at very high velocities ('hypervelocities', greater than 1000 m/sec). During such impacts the material of the target and the projectile is subjected to very high pressures and temperatures leading to a range of interesting phenomena.

Research interests

Dr Price's research can be broken down into two main areas:

  • Shock synthesis of complex molecules – during a shock, molecules can be broken down into constituent atoms, which can then recombine into more complex molecules. This project will investigate this process using experimental techniques and state-of-the-art analytical techniques.
  • Hydrocode modelling of impacts – impacts in space range in size from nanometre to kilometre scales. This project will use hydrocode modelling to investigate the physics that occur under the extreme physical conditions of a hypervelocity impact.

Publications

Showing 50 of 61 total publications in the Kent Academic Repository. View all publications.

Article

  • Burchell, M., Landers, K., Harriss, K. and Price, M. (2020). Catastrophic disruption of icy bodies with sub-surface oceans. Icarus [Online] 336:113457. Available at: https://doi.org/10.1016/j.icarus.2019.113457.
    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.
  • Hillier, J., Sternovsky, Z., Kempf, S., Trieloff, M., Guglielmino, M., Postberg, F. and Price, M. (2018). Impact ionisation mass spectrometry of platinum-coated olivine and magnesite-dominated cosmic dust analogues. Planetary and Space Science [Online] 156:96-110. Available at: https://doi.org/10.1016/j.pss.2017.10.002.
    Impact ionisation mass spectrometry enables the composition of cosmic dust grains to be determined in situ by spacecraft-based instrumentation. The proportion of molecular ions in the impact plasma is a function of the impact velocity, making laboratory calibration vital for the interpretation of the mass spectra, particularly at the low velocities typical of lunar or asteroid encounters. Here we present an analysis of laboratory impact ionisation mass spectra from primarily low (<15 km s−1) velocity impacts of both olivine and magnesite-dominated particles onto the SUrface Dust Mass Analyzer (SUDA) laboratory mass spectrometer. The cation mass spectra show characteristic peaks due to their constituent elements, with Mg, Al, Si, C, Ca, O and Fe frequently present. Contaminant species from the conductive coating process (B, Na, K, C, Pt) also occur, at varying frequencies. Possible saponite or talc inclusions in the magnesite particles are revealed by the presence of Si, Fe, Ca and Al in the magnesite mass spectra. Magnesium is clearly present at the lowest impact velocities (3 km s−1), at which alkali metals were presumed to dominate. Peaks attributed to very minor amounts of water or hydroxyl present in the grains are also seen at low velocities in both cation and anion mass spectra, demonstrating the feasibility of impact ionisation mass spectrometry in identifying hydrated or hydrous minerals, during very low velocity encounters or with very low abundances of water or hydroxy groups, in the impinging grains. Velocity thresholds for the reliable identification of the major elements within the magnesite and olivine cation spectra are presented. Additionally, relative sensitivity factors for Mg (5.1), Fe (1.5) and O (0.6) with respect to Si, in the olivine particles, at impact speeds >19 km s−1, were found to be very similar to those previously determined for orthopyroxene-dominated particles, despite different target and projectile materials. This confirms that quantitative analyses of mineral dust grain composition in space is viable despite initially poorly-constrained mineralogy.
  • Miller, C., Jossé, L., Brown, I., Povey, J., Yiangou, L., Price, M., Cinalt, J., Xue, W., Michaelis, M. and Tsaousis, A. (2018). A cell culture platform for Cryptosporidium that enables long-term cultivation and new tools for the systematic investigation of its biology. International Journal for Parasitology [Online] 48:197-201. Available at: https://doi.org/10.1016/j.ijpara.2017.10.001.
    Cryptosporidium parasites are a major cause of diarrhoea that pose a particular threat to children in developing areas and immunocompromised individuals. Curative therapies and vaccines are lacking, mainly due to lack of a long-term culturing system of this parasite. Here, we show that COLO-680N cells infected with two different Cryptosporidium parvum strains produce sufficient infectious oocysts to infect subsequent cultures, showing a substantial fold increase in production, depending on the experiment, over the most optimistic HCT-8 models. Oocyst identity was confirmed using a variety of microscopic- and molecular-based methods. This culturing system will accelerate research on Cryptosporidium and the development of anti-Cryptosporidium drugs.
  • Wozniakiewicz, P., Kearsley, A., Burchell, M., Price, M., Ishii, H. and Cole, M. (2018). Preparation of large Stardust aluminum foil craters for analysis. Meteoritics and Planetary Science [Online] 53:1066-1080. Available at: https://doi.org/10.1111/maps.13052?.
    Over the last decade, silica aerogel tracks and aluminum foil craters on the Stardust collector have been studied extensively to determine the nature of captured
    cometary dust grains. Analysis of particles captured in aerogel has been developed to a fine art, aided by sophisticated preparation techniques, and yielding revolutionary knowledge of comet dust mineralogy. The Stardust foil craters can be interpreted in terms of impacting particle size and structure, but almost all studies of composition for their contents have relied on in situ analysis techniques or relatively destructive extraction of materials. This has limited their examination and interpretation. However, numerous experimental hypervelocity impact studies under Stardust-Wild 2 encounter conditions have shown that abundant dust components are preserved in foil craters of all sizes. Using some of these analogue materials, we have previously shown that modern, nondestructive scanning
    electron microscope imaging and X-ray microanalysis techniques can document distribution of dust remnants both quickly and thoroughly within foil craters prior to any preparation. Here we present findings from our efforts to quantify the amount of residue and demonstrate a simple method of crater shape modification which can bring material into positions where it is much more accessible for in situ analysis, or safe removal of small subsamples. We report that approximately 50% of silicate-dominated impactors were retained as impact crater residue; however, <3% of organic impactors remained in the craters after impact.
  • Kearsley, A., Colaux, J., Ross, D., Wozniakiewicz, P., Gerlach, L., Anz-Meador, P., Griffin, T., Reed, B., Opiela, J., Palitsin, V., Grime, G., Webb, R., Jeynes, C., Spratt, J., Salge, T., Cole, M., Price, M. and Burchell, M. (2017). Hypervelocity impact in low earth orbit: finding subtle impactor signatures on the Hubble Space Telescope. Procedia Engineering [Online] 204:492-499. Available at: https://doi.org/10.1016/j.proeng.2017.09.746?.
    Return of materials from the Hubble Space Telescope (HST) during shuttle orbiter service missions has allowed inspection of large numbers of hypervelocity impact features from long exposure at about 615 km altitude in low Earth orbit (LEO) [1,2]. Here we describe the application of advanced X-ray microanalysis techniques on scanning electron microscopes (SEM), microprobes and a 2 MV Tandetron, to nearly 400 impacts on the painted metal surface of the Wide Field and Planetary Camera 2 (WFPC2) radiator shield [3,4]. We identified artificial Orbital Debris (OD) and natural Micrometeoroid (MM) origins for small [5] and even for larger particles [6], which usually may leave little or no detectable trace on HST solar arrays, as they penetrate through the full cell thickness [2,7].
  • Wickham-Eade, J., Burchell, M., Price, M., Hicks, L., MacArthur, J. and Bridges, J. (2017). Raman identification of olivine grains in fine grained mineral assemblages fired into aerogel. Procedia Engineering [Online] 204:413-420. Available at: https://doi.org/10.1016/j.proeng.2017.09.796.
    NASA’s Stardust mission returned from the comet 81P/Wild2 in 2006 and has yielded a plethora of research looking into the composition and attributes of the comet. The mission itself collected thousands of cometary dust particles as it flew through the coma of the comet at a relative speed of 6.1 km s-1. This work focuses on one of the most abundant minerals in the solar system – olivine. Previous work has shown capture affects on this mineral in similar impacts to that experienced during the Stardust mission. However, the past work looked into effects on isolated mineral grains which would be a rare occurrence in the Solar System. A more accurate representation of this would be to investigate the capture effects on olivine as a constituent of an assemblage of minerals. Accordingly, here we used samples from the NWA 10256 CR2 carbonaceous chondrite meteorite. This natural sample contains fine grains of olivine, and brings additional issues when analysing the olivine due to limited homogeneity. Shifts in the Raman spectra for olivine, enstatite and hematite were observed after capture due to shock effects. However, this work suggests that olivine may well experience a different shock effect during capture when part of a mineral assemblage as distinct from that experienced by single grains.
  • Hibbert, R., Cole, M., Price, M. and Burchell, M. (2017). The Hypervelocity Impact Facility at the University of Kent: Recent Upgrades and Specialized Capabilities. Procedia Engineering [Online] 204:208-214. Available at: https://doi.org/10.1016/j.proeng.2017.09.775.
    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.
  • Hicks, L., MacArthur, J., Bridges, J., Price, M., Wickham-Eade, J., Burchell, M., Hansford, G., Butterworth, A., Gurman, S. and Baker, S. (2017). Magnetite in Comet Wild 2: Evidence for parent body aqueous alteration. Meteoritics and Planetary Science [Online] 52:2075-2096. Available at: https://doi.org/10.1111/maps.12909.
    The mineralogy of comet 81P/Wild 2 particles, collected in aerogel by the Stardust mission, has been determined using synchrotron Fe-K X-ray absorption spectroscopy with in situ transmission XRD and X-ray fluorescence, plus complementary microRaman analyses. Our investigation focuses on the terminal grains of eight Stardust tracks: C2112,4,170,0,0; C2045,2,176,0,0; C2045,3,177,0,0; C2045,4,178,0,0; C2065,4,187,0,0; C2098,4,188,0,0; C2119,4,189,0,0; and C2119,5,190,0,0. Three terminal grains have been identified as near pure magnetite Fe3O4. The presence of magnetite shows affinities between the Wild 2 mineral assemblage and carbonaceous chondrites, and probably resulted from hydrothermal alteration of the coexisting FeNi and ferromagnesian silicates in the cometary parent body. In order to further explore this hypothesis, powdered material from a CR2 meteorite (NWA 10256) was shot into the aerogel at 6.1 km s?1, using a light-gas gun, and keystones were then prepared in the same way as the Stardust keystones. Using similar analysis techniques to the eight Stardust tracks, a CR2 magnetite terminal grain establishes the likelihood of preserving magnetite during capture in silica aerogel.
  • Avdellidou, C., Price, M., Delbo, M. and Cole, M. (2016). Survival of the impactor during hypervelocity collisions – II. An analogue for high-porosity targets. Monthly Notices of the Royal Astronomical Society [Online] 464:734-738. Available at: https://doi.org/10.1093/mnras/stw2381.
    We investigated how a target's porosity affects the outcome of a collision, with respect to the impactor's fate. Laboratory impact experiments using peridot projectiles were performed at a speed range between 0.3 and 3.0 km s?1, on to high-porosity water-ice (40 per cent) and fine-grained calcium carbonate (70 per cent) targets. We report that the amount of implanted material in the target body increases with increasing target's porosity, while the size frequency distribution of the projectile's ejecta fragments becomes steeper. A supplementary Raman study showed no sign of change of the Raman spectra of the recovered olivine projectile fragments indicate minimal physical change.
  • Steer, B., Gorbunov, B., Price, M. and Podoleanu, A. (2016). Raman spectroscopic identification of size-selected airborne particles for quantitative exposure assessment. Measurement Science & Technology [Online] 27:45801-45801. Available at: http://dx.doi.org/10.1088/0957-0233/27/4/045801.
    In this paper we present a method for the quantification of chemically distinguished airborne particulate matter, required for health risk assessment. Rather than simply detecting chemical compounds in a sample, we demonstrate an approach for the quantification of exposure to airborne particles and nanomaterials. In line with increasing concerns over the proliferation of engineered particles we consider detection of synthetically produced ZnO crystals. A multi-stage approach is presented whereby the particles are first aerodynamically size segregated from a lab-generated single component aerosol in an impaction sampler. These size fractionated samples are subsequently analysed by Raman spectroscopy. Imaging analysis is applied to Raman spatial maps to provide chemically specific quantification of airborne exposure against background which is critical for health risk evaluation of exposure to airborne particles. Here we present a first proof-of-concept study of the methodology utilising particles in the 2-4 μm aerodynamic diameter range to allow for validation of the approach by comparison to optical microscopy. The results show that the combination of these techniques provides independent size and chemical discrimination of particles. Thereby a method is provided to allow quantitative and chemically distinguished measurements of aerosol concentrations separated into exposure relevant size fractions. © 2016 IOP Publishing Ltd.
  • McDermott, K., Price, M., Cole, M. and Burchell, M. (2016). Survivability of copper projectiles during hypervelocity impacts in porous ice: A laboratory investigation of the survivability of projectiles impacting comets or other bodies. Icarus [Online] 268:102-117. Available at: http://doi.org/10.1016/j.icarus.2015.12.037.
  • Avdellidou, C., Price, M., Delbo, M., Ioannidis, P. and Cole, M. (2015). Survival of the impactor during hypervelocity collisions – I. An analogue for low porosity targets. Monthly Notices of the Royal Astronomical Society [Online] 456:2957-2965. Available at: http://doi.org/10.1093/mnras/stv2844.
    Recent observations of asteroidal surfaces indicate the presence of materials that do not match the bulk lithology of the body. A possible explanation for the presence of these exogenous materials is that they are products of interasteroid impacts in the Main Belt, and thus interest has increased in understanding the fate of the projectile during hypervelocity impacts. In order to gain insight into the fate of impactor, we have carried out a laboratory programme, covering the velocity range of 0.38–3.50 km s?1, devoted to measuring the survivability, fragmentation and final state of the impactor. Forsterite olivine and synthetic basalt projectiles were fired on to low porosity (<10 per cent) pure water-ice targets using the University of Kent's Light Gas Gun (LGG). We developed a novel method to identify impactor fragments which were found in ejecta and implanted into the target. We applied astronomical photometry techniques, using the source extractor software, to automatically measure the dimensions of thousands of fragments. This procedure enabled us to estimate the implanted mass on the target body, which was found to be a few per cent of the initial mass of the impactor. We calculated an order of magnitude difference in the energy density of catastrophic disruption, Q*, between peridot and basalt projectiles. However, we found very similar behaviour of the size frequency distributions for the hypervelocity shots (>1 km s?1). After each shot, we examined the largest peridot fragments with Raman spectroscopy and no melt or alteration in the final state of the projectile was observed.
  • Wozniakiewicz, P., Ishii, H., Kearsley, A., Bradley, J., Price, M., Burchell, M., Teslich, N. and Cole, M. (2015). The survivability of phyllosilicates and carbonates impacting Stardust Al foils: Facilitating the search for cometary water. Meteoritics & Planetary Science [Online] 50:2003-2023. Available at: http://dx.doi.org/10.1111/maps.12568.
    Comet 81P/Wild 2 samples returned by NASA's Stardust mission provide an unequalled opportunity to study the contents of, and hence conditions and processes operating on, comets. They can potentially validate contentious interpretations of cometary infrared spectra and in situ mass spectrometry data: specifically the identification of phyllosilicates and carbonates. However, Wild 2 dust was collected via impact into capture media at ~6 km s−1, leading to uncertainty as to whether these minerals were captured intact, and, if subjected to alteration, whether they remain recognizable. We simulated Stardust Al foil capture conditions using a two‐stage light‐gas gun, and directly compared transmission electron microscope analyses of pre‐ and postimpact samples to investigate survivability of lizardite and cronstedtite (phyllosilicates) and calcite (carbonate). We find the phyllosilicates do not survive impact as intact crystalline materials but as moderately to highly vesiculated amorphous residues lining resultant impact craters, whose bulk cation to Si ratios remain close to that of the impacting grain. Closer inspection reveals variation in these elements on a submicron scale, where impact‐induced melting accompanied by reducing conditions (due to the production of oxygen scavenging molten Al from the target foils) has resulted in the production of native silicon and Fe‐ and Fe‐Si‐rich phases. In contrast, large areas of crystalline calcite are preserved within the calcite residue, with smaller regions of vesiculated, Al‐bearing calcic glass. Unambiguous identification of calcite impactors on Stardust Al foil is therefore possible, while phyllosilicate impactors may be inferred from vesiculated residues with appropriate bulk cation to Si ratios. Finally, we demonstrate that the characteristic textures and elemental distributions identifying phyllosilicates and carbonates by transmission electron microscopy can also be observed by state‐of‐the‐art scanning electron microscopy providing rapid, nondestructive initial mineral identifications in Stardust residues.
  • Burchell, M., Cole, M., Ramkissoon, N., Wozniakiewicz, P., Price, M. and Foing, B. (2015). SMART-1 end of life shallow regolith impact simulations. Meteoritics & Planetary Science [Online] 50:1436-1448. Available at: http://doi.org/10.1111/maps.12479.
    The SMART-1 end-of-life impact with the lunar surface was simulated with impacts in a two stage light-gas gun onto inclined basalt targets with a shallow surface layer of sand. This simulated the probable impact site, where a loose regolith will have overlaid a well consolidated basaltic layer of rock. The impact angles used were at 5° and 10° from the horizontal. The impact speed was ~2 km s?1 and the projectiles were 2.03 mm diameter aluminum spheres. The sand depth was between approximately 0.8 and 1.8 times the projectile diameter, implying a loose lunar surface regolith of similar dimensions to the SMART-1 spacecraft. A crater in the basement rock itself was only observed in the impact at 10° incidence, and where the depth of loose surface material was less than the projectile diameter, in which case the basement rock also contained a small pit-like crater. In all cases, the projectile ricocheted away from the impact site at a shallow angle. This implies that at the SMART-1 impact site the crater will have a complicated structure, with exposed basement rock and some excavated rock displaced nearby, and the main spacecraft body itself will not be present at the main crater.
  • Lennox, R., Taylor, D., Stimpson, L., Stenning, G., Jura, M., Price, M., Rodriguez, E. and Arnold, D. (2015). PZT-like structural phase transitions in the BiFeO3–KNbO3 solid solution. Dalton Transactions [Online] 44:10608-10613. Available at: http://dx.doi.org/10.1039/C5DT00140D.
    Despite the high prominence of the perovskites BiFeO3 and KNbO3 the solid solution between the two has received little attention. We report a detailed neutron and synchrotron X-ray powder diffraction, and Raman spectroscopy study which demonstrates an R3c ? P4mm ? Amm2 series of structural phase transitions similar to that exhibited by the PbZrO3–PbTiO3 solid solution.
  • Wozniakiewicz, P., Price, M., Armes, S., Burchell, M., Cole, M., Fielding, L., Hillier, J. and Lovett, J. (2014). Micron-scale hypervelocity impact craters: Dependence of crater ellipticity and rim morphology on impact trajectory, projectile size, velocity, and shape. Meteoritics & Planetary Science [Online] 49:1929-1947. Available at: http://doi.org/10.1111/maps.12364.
    The interstellar collector on NASA's Stardust mission captured many particles from sources other than the interstellar dust stream. Impact trajectory may provide a means of discriminating between these different sources, and thus identifying/eliminating candidate interstellar particles. The collector's aerogel preserved a clear record of particle impact trajectory from the inclination and direction of the resultant tracks. However, the collector also contained aluminum foils and, although impact crater studies to date suggest only the most inclined impacts (>45° from normal) produce crater morphologies that indicate trajectory (i.e., distinctly elliptical), these studies have been restricted to much larger (mm and above) scales than are relevant for Stardust (?m). It is unknown how oblique impact crater morphology varies as a function of length scale, and therefore how well Stardust craters preserve details of impactor trajectory. Here, we present data from a series of impact experiments, together with complementary hydrocode modeling, that examine how crater morphology changes with impact angles for different-sized projectiles. We find that, for our smallest spherical projectiles (2 ?m diameter), the ellipticity and rim morphology provide evidence of their inclined trajectory from as little as 15° from normal incidence. This is most likely a result of strain rate hardening in the target metal. Further experiments and models find that variation in velocity and impactor shape complicate these trends, but that rim morphology remains useful in determining impact direction (where the angle of impact is >20° from normal) and may help identify candidate interstellar particle craters on the Stardust collector.
  • Flynn, G., Sutton, S., Lai, B., Wirick, S., Allen, C., Anderson, D., Ansari, A., Bajt, S., Bastien, R., Bassim, N., Bechtel, H., Borg, J., Brenker, F., Bridges, J., Brownlee, D., Burchell, M., Burghammer, M., Butterworth, A., Changela, H., Cloetens, P., Davis, A., Doll, R., Floss, C., Frank, D., Gainsforth, Z., Grün, E., Heck, P., Hillier, J., Hoppe, P., Hudson, B., Huth, J., Hvide, B., Kearsley, A., King, A., Leitner, J., Lemelle, L., Leroux, H., Leonard, A., Lettieri, R., Marchant, W., Nittler, L., Ogliore, R., Ong, W., Postberg, F., Price, M., Sandford, S., Tresseras, J., Schmitz, S., Schoonjans, T., Silversmit, G., Simionovici, A., Sol, V., Srama, R., Stadermann, F., Stephan, T., Sterken, V., Stodolna, J., Stroud, R., Trieloff, M., Tsou, P., Tsuchiyama, A., Tyliszczak, T., Vekemans, B., Vincze, L., Von Korff, J., Westphal, A., Wordsworth, N., Zevin, D. and Zolensky, M. (2014). Stardust Interstellar Preliminary Examination VII: Synchrotron X-ray fluorescence analysis of six Stardust interstellar candidates measured with the Advanced Photon Source 2-ID-D microprobe. Meteoritics and Planetary Science [Online] 49:1626-1644. Available at: http://doi.org/10.1111/maps.12144.
    The NASA Stardust spacecraft exposed an aerogel collector to the interstellar dust passing through the solar system. We performed X-ray fluorescence element mapping and abundance measurements, for elements 19 ? Z ? 30, on six “interstellar candidates,” potential interstellar impacts identified by Stardust@Home and extracted for analyses in picokeystones. One, I1044,3,33, showed no element hot-spots within the designated search area. However, we identified a nearby surface feature, consistent with the impact of a weak, high-speed particle having an approximately chondritic (CI) element abundance pattern, except for factor-of-ten enrichments in K and Zn and an S depletion. This hot-spot, containing approximately 10 fg of Fe, corresponds to an approximately 350 nm chondritic particle, small enough to be missed by Stardust@Home, indicating that other techniques may be necessary to identify all interstellar candidates. Only one interstellar candidate, I1004,1,2, showed a track. The terminal particle has large enrichments in S, Ti, Cr, Mn, Ni, Cu, and Zn relative to Fe-normalized CI values. It has high Al/Fe, but does not match the Ni/Fe range measured for samples of Al-deck material from the Stardust sample return capsule, which was within the field-of-view of the interstellar collector. A third interstellar candidate, I1075,1,25, showed an Al-rich surface feature that has a composition generally consistent with the Al-deck material, suggesting that it is a secondary particle. The other three interstellar candidates, I1001,1,16, I1001,2,17, and I1044,2,32, showed no impact features or tracks, but allowed assessment of submicron contamination in this aerogel, including Fe hot-spots having CI-like Ni/Fe ratios, complicating the search for CI-like interstellar/interplanetary dust.
  • Postberg, F., Hillier, J., Armes, S., Bugiel, S., Butterworth, A., Dupin, D., Fielding, L., Fujii, S., Gainsforth, Z., Grün, E., Li, Y., Srama, R., Sterken, V., Stodolna, J., Trieloff, M., Westphal, A., Achilles, C., Allen, C., Ansari, A., Bajt, S., Bassim, N., Bastien, R., Bechtel, H., Borg, J., Brenker, F., Bridges, J., Brownlee, D., Burchell, M., Burghammer, M., Changela, H., Cloetens, P., Davis, A., Doll, R., Floss, C., Flynn, G., Frank, D., Heck, P., Hoppe, P., Huss, G., Huth, J., Kearsley, A., King, A., Lai, B., Leitner, J., Lemelle, L., Leonard, A., Leroux, H., Lettieri, R., Marchant, W., Nittler, L., Ogliore, R., Ong, W., Price, M., Sandford, S., Tressaras, J., Schmitz, S., Schoonjans, T., Schreiber, K., Silversmit, G., Simionovici, A., Solé, V., Stadermann, F., Stephan, T., Stroud, R., Sutton, S., Tsou, P., Tsuchiyama, A., Tyliczszak, T., Vekemans, B., Vincze, L., Zevin, D. and Zolensky, M. (2014). Stardust Interstellar Preliminary Examination IX: High-speed interstellar dust analog capture in Stardust flight-spare aerogel. Meteoritics and Planetary Science [Online] 49:1666-1679. Available at: http://doi.org/10.1111/maps.12173.
    The NASA Stardust mission used silica aerogel slabs to slowly decelerate and capture impinging cosmic dust particles for return to Earth. During this process, impact tracks are generated along the trajectory of the particle into the aerogel. It is believed that the morphology and dimensions of these tracks, together with the state of captured grains at track termini, may be linked to the size, velocity, and density of the impacting cosmic dust grain. Here, we present the results of laboratory hypervelocity impact experiments, during which cosmic dust analog particles (diameters of between 0.2 and 0.4 ?m), composed of olivine, orthopyroxene, or an organic polymer, were accelerated onto Stardust flight-spare low-density (approximately 0.01 g cm?3) silica aerogel. The impact velocities (3–21 km s?1) were chosen to simulate the range of velocities expected during Stardust's interstellar dust (ISD) collection phases. Track lengths and widths, together with the success of particle capture, are analyzed as functions of impact velocity and particle composition, density, and size. Captured terminal particles from low-density organic projectiles become undetectable at lower velocities than those from similarly sized, denser mineral particles, which are still detectable (although substantially altered by the impact process) at 15 km s?1. The survival of these terminal particles, together with the track dimensions obtained during low impact speed capture of small grains in the laboratory, indicates that two of the three best Stardust candidate extraterrestrial grains were actually captured at speeds much lower than predicted. Track length and diameters are, in general, more sensitive to impact velocities than previously expected, which makes tracks of particles with diameters of 0.4 ?m and below hard to identify at low capture speeds (<10 km s?1). Therefore, although captured intact, the majority of the interstellar dust grains returned to Earth by Stardust remain to be found.
  • Westphal, A., Anderson, D., Butterworth, A., Frank, D., Lettieri, R., Marchant, W., Von Korff, J., Zevin, D., Ardizzone, A., Campanile, A., Capraro, M., Courtney, K., Criswell, M., Crumpler, D., Cwik, R., Gray, F., Hudson, B., Imada, G., Karr, J., Wah, L., Mazzucato, M., Motta, P., Rigamonti, C., Spencer, R., Woodrough, S., Santoni, I., Sperry, G., Terry, J., Wordsworth, N., Yahnke, T., Allen, C., Ansari, A., Bajt, S., Bastien, R., Bassim, N., Bechtel, H., Borg, J., Brenker, F., Bridges, J., Brownlee, D., Burchell, M., Burghammer, M., Changela, H., Cloetens, P., Davis, A., Doll, R., Floss, C., Flynn, G., Gainsforth, Z., Grün, E., Heck, P., Hillier, J., Hoppe, P., Huth, J., Hvide, B., Kearsley, A., King, A., Lai, B., Leitner, J., Lemelle, L., Leroux, H., Leonard, A., Nittler, L., Ogliore, R., Ong, W., Postberg, F., Price, M., Sandford, S., Tresseras, J., Schmitz, S., Schoonjans, T., Silversmit, G., Simionovici, A., Solé, V., Srama, R., Stephan, T., Sterken, V., Stodolna, J., Stroud, R., Sutton, S., Trieloff, M., Tsou, P., Tsuchiyama, A., Tyliszczak, T., Vekemans, B., Vincze, L. and Zolensky, M. (2014). Stardust Interstellar Preliminary Examination I: Identification of tracks in aerogel. Meteoritics and Planetary Science [Online] 49:1509-1521. Available at: http://doi.org/10.1111/maps.12168.
    Here, we report the identification of 69 tracks in approximately 250 cm2 of aerogel collectors of the Stardust Interstellar Dust Collector. We identified these tracks through Stardust@home, a distributed internet-based virtual microscope and search engine, in which > 30,000 amateur scientists collectively performed >9 × 107 searches on approximately 106 fields of view. Using calibration images, we measured individual detection efficiency, and found that the individual detection efficiency for tracks > 2.5 ?m in diameter was >0.6, and was >0.75 for tracks >3 ?m in diameter. Because most fields of view were searched >30 times, 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. The actual 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, the detection efficiency of these tracks was lower than detection efficiency of calibrations presented in training, testing, and ongoing calibration. Nevertheless, as calibration images based 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 of identification of tracks of hypervelocity projectiles captured in aerogel.
  • Simionovici, A., Lemelle, L., Cloetens, P., Solé, V., Tresseras, J., Butterworth, A., Westphal, A., Gainsforth, Z., Stodolna, J., Allen, C., Anderson, D., Ansari, A., Bajt, S., Bassim, N., Bastien, R., Bechtel, H., Borg, J., Brenker, F., Bridges, J., Brownlee, D., Burchell, M., Burghammer, M., Changela, H., Davis, A., Doll, R., Floss, C., Flynn, G., Frank, D., Grün, E., Heck, P., Hillier, J., Hoppe, P., Hudson, B., Huth, J., Hvide, B., Kearsley, A., King, A., Lai, B., Leitner, J., Leonard, A., Leroux, H., Lettieri, R., Marchant, W., Nittler, L., Ogliore, R., Ong, W., Postberg, F., Price, M., Sandford, S., Schmitz, S., Schoonjans, T., Silversmit, G., Srama, R., Stadermann, F., Stephan, T., Sterken, V., Stroud, R., Sutton, S., Trieloff, M., Tsou, P., Tsuchiyama, A., Tyliszczak, T., Vekemans, B., Vincze, L., Von Korff, J., Wordsworth, N., Zevin, D. and Zolensky, M. (2014). Stardust Interstellar Preliminary Examination VI: Quantitative elemental analysis by synchrotron X-ray fluorescence nanoimaging of eight impact features in aerogel. Meteoritics and Planetary Science [Online] 49:1612-1625. Available at: http://doi.org/10.1111/maps.12208.
    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.
  • Brenker, F., Westphal, A., Vincze, L., Burghammer, M., Schmitz, S., Schoonjans, T., Silversmit, G., Vekemans, B., Allen, C., Anderson, D., Ansari, A., Bajt, S., Bastien, R., Bassim, N., Bechtel, H., Borg, J., Bridges, J., Brownlee, D., Burchell, M., Butterworth, A., Changela, H., Cloetens, P., Davis, A., Doll, R., Floss, C., Flynn, G., Fougeray, P., Frank, D., Gainsforth, Z., Grün, E., Heck, P., Hillier, J., Hoppe, P., Hudson, B., Huth, J., Hvide, B., Kearsley, A., King, A., Lai, B., Leitner, J., Lemelle, L., Leroux, H., Leonard, A., Lettieri, R., Marchant, W., Nittler, L., Ogliore, R., Ong, W., Postberg, F., Price, M., Sandford, S., Tresseras, J., Simionovici, A., Solé, V., Srama, R., Stadermann, F., Stephan, T., Sterken, V., Stodolna, J., Stroud, R., Sutton, S., Trieloff, M., Tsou, P., Tsuchiyama, A., Tyliszczak, T., Von Korff, J., Wordsworth, N., Zevin, D. and Zolensky, M. (2014). Stardust Interstellar Preliminary Examination V: XRF analyses of interstellar dust candidates at ESRF ID13. Meteoritics and Planetary Science [Online] 49:1594-1611. Available at: http://doi.org/10.1111/maps.12206.
    Here, we report analyses by synchrotron X-ray fluorescence microscopy of the elemental composition of eight candidate impact features extracted from the Stardust Interstellar Dust Collector (SIDC). Six of the features were unambiguous tracks, and two were crater-like features. Five of the tracks are so-called “midnight” tracks—that is, they had trajectories consistent with an origin either in the interstellar dust stream or as secondaries from impacts on the Sample Return Capsule (SRC). In a companion paper reporting synchrotron X-ray diffraction analyses of ISPE candidates, we show that two of these particles contain natural crystalline materials: the terminal particle of track 30 contains olivine and spinel, and the terminal particle of track 34 contains olivine. Here, we show that the terminal particle of track 30, Orion, shows elemental abundances, normalized to Fe, that are close to CI values, and a complex, fine-grained structure. The terminal particle of track 34, Hylabrook, shows abundances that deviate strongly from CI, but shows little fine structure and is nearly homogenous. The terminal particles of other midnight tracks, 29 and 37, had heavy element abundances below detection threshold. A third, track 28, showed a composition inconsistent with an extraterrestrial origin, but also inconsistent with known spacecraft materials. A sixth track, with a trajectory consistent with secondary ejecta from an impact on one of the spacecraft solar panels, contains abundant Ce and Zn. This is consistent with the known composition of the glass covering the solar panel. Neither crater-like feature is likely to be associated with extraterrestrial materials. We also analyzed blank aerogel samples to characterize background and variability between aerogel tiles. We found significant differences in contamination levels and compositions, emphasizing the need for local background subtraction for accurate quantification.
  • Butterworth, A., Westphal, A., Tyliszczak, T., Gainsforth, Z., Stodolna, J., Frank, D., Allen, C., Anderson, D., Ansari, A., Bajt, S., Bastien, R., Bassim, N., Bechtel, H., Borg, J., Brenker, F., Bridges, J., Brownlee, D., Burchell, M., Burghammer, M., Changela, H., Cloetens, P., Davis, A., Doll, R., Floss, C., Flynn, G., Grün, E., Heck, P., Hillier, J., Hoppe, P., Hudson, B., Huth, J., Hvide, B., Kearsley, A., King, A., Lai, B., Leitner, J., Lemelle, L., Leroux, H., Leonard, A., Lettieri, R., Marchant, W., Nittler, L., Ogliore, R., Ong, W., Postberg, F., Price, M., Sandford, S., Sans? Tresseras, J., Schmitz, S., Schoonjans, T., Silversmit, G., Simionovici, A., Solé, V., Srama, R., Stadermann, F., Stephan, T., Sterken, V., Stroud, R., Sutton, S., Trieloff, M., Tsou, P., Tsuchiyama, A., Vekemans, B., Vincze, L., Von Korff, J., Wordsworth, N., Zevin, D. and Zolensky, M. (2014). Stardust Interstellar Preliminary Examination IV: Scanning transmission X-ray microscopy analyses of impact features in the Stardust Interstellar Dust Collector. Meteoritics and Planetary Science [Online] 49:1562-1593. Available at: http://doi.org/10.1111/maps.12220.
    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.
  • Li, Y., Bugiel, S., Trieloff, M., Hillier, J., Postberg, F., Price, M., Shu, A., Fiege, K., Fielding, L., Armes, S., Wu, Y., Grün, E. and Srama, R. (2014). Morphology of craters generated by hypervelocity impacts of micron-sized polypyrrole-coated olivine particles. Meteoritics & Planetary Science [Online] 49:1375-1387. Available at: http://doi.org/10.1111/maps.12338.
    To understand the process of cosmic dust particle impacts and translate crater morphology on smoothed metallic surfaces to dust properties, correct calibration of the experimental impact data is needed. This article presents the results of studies of crater morphology generated by impacts using micron-sized polypyrrole (PPy)-coated olivine particles. The particles were accelerated by an electrostatic dust accelerator to high speeds before they impacted onto polished aluminum targets. The projectile diameter and velocity ranges were 0.3–1.2 ?m and 3–7 km s?1. After impact, stereopair images of the craters were taken using scanning electron microscope and 3-D reconstructions made to provide diameter and depth measurements. In this study, not just the dimensions of crater diameters and depths, but also the shape and dimensions of crater lips were analyzed. The craters created by the coated olivine projectiles are shown to have complicated shapes believed to be due to the nonspherical shape of the projectiles.
  • Westphal, A., Stroud, R., Bechtel, H., Brenker, F., Butterworth, A., Flynn, G., Frank, D., Gainsforth, Z., Hillier, J., Postberg, F., Simionovici, A., Sterken, V., Allen, C., Anderson, D., Ansari, A., Bajt, S., Bastien, R., Bassim, N., Bridges, J., Brownlee, D., Burchell, M., Burghammer, M., Changela, H., Cloetens, P., Davis, A., Doll, R., Floss, C., Grün, E., Heck, P., Hoppe, P., Hudson, B., Huth, J., Kearsley, A., King, A., Lai, B., Leitner, J., Lemelle, L., Leonard, A., Leroux, H., Lettieri, R., Marchant, W., Nittler, L., Ogliore, R., Jia Ong, W., Price, M., Sandford, S., Sans Tresseras, J., Schmitz, S., Schoonjans, T., Schreiber, K., Silversmit, G., Solé, V., Srama, R., Stadermann, F., Stephan, T., Stodolna, J., Sutton, S., Trieloff, M., Tsou, P., Tyliszczak, T., Vekemans, B., Vincze, L., Von Korff, J., Wordsworth, N., Zevin, D. and Zolensky, M. (2014). Coordinated Microanalyses of Seven Particles of Probable Interstellar Origin from the Stardust Mission. Microscopy and Microanalysis [Online] 20:1692-1693. Available at: http://doi.org/10.1017/S1431927614010198.
  • Burchell, M., Bowden, S., Cole, M., Price, M. and Parnell, J. (2014). Survival of Organic Materials in Hypervelocity Impacts of Ice on Sand, Ice, and Water in the Laboratory. Astrobiology [Online] 14:473-485. Available at: http://dx.doi.org/10.1089/ast.2013.1007.
    The survival of organic molecules in shock impact events has been investigated in the laboratory. A frozen mixture of anthracene and stearic acid, solvated in dimethylsulfoxide (DMSO), was fired in a two-stage light gas gun at speeds of ?2 and ?4?km s?1 at targets that included water ice, water, and sand. This involved shock pressures in the range of 2–12 GPa. It was found that the projectile materials were present in elevated quantities in the targets after impact and in some cases in the crater ejecta as well. For DMSO impacting water at 1.9?km s?1 and 45° incidence, we quantify the surviving fraction after impact as 0.44±0.05. This demonstrates successful transfer of organic compounds from projectile to target in high-speed impacts. The range of impact speeds used covers that involved in impacts of terrestrial meteorites on the Moon, as well as impacts in the outer Solar System on icy bodies such as Pluto. The results provide laboratory evidence that suggests that exogenous delivery of complex organic molecules from icy impactors is a viable source of such material on target bodies.
  • Sterken, V., Westphal, A., Altobelli, N., Grün, E., Hillier, J., Postberg, F., Srama, R., Allen, C., Anderson, D., Ansari, A., Bajt, S., Bastien, R., Bassim, N., Bechtel, H., Borg, J., Brenker, F., Bridges, J., Brownlee, D., Burchell, M., Burghammer, M., Butterworth, A., Changela, H., Cloetens, P., Davis, A., Doll, R., Floss, C., Flynn, G., Frank, D., Gainsforth, Z., Heck, P., Hoppe, P., Hudson, B., Huth, J., Hvide, B., Kearsley, A., King, A., Lai, B., Leitner, J., Lemelle, L., Leroux, H., Leonard, A., Lettieri, R., Marchant, W., Nittler, L., Ogliore, R., Ong, W., Price, M., Sandford, S., Tresseras, J., Schmitz, S., Schoonjans, T., Silversmit, G., Simionovici, A., Solé, V., Stephan, T., Stodolna, J., Stroud, R., Sutton, S., Trieloff, M., Tsou, P., Tsuchiyama, A., Tyliszczak, T., Vekemans, B., Vincze, L., Korff, J., Wordsworth, N., Zevin, D. and Zolensky, M. (2014). Stardust Interstellar Preliminary Examination X: Impact speeds and directions of interstellar grains on the Stardust dust collector. Meteoritics & Planetary Science [Online] 49:1680-1697. Available at: http://dx.doi.org/10.1111/maps.12219.
    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 (<10 km s?1) for particles with the ratio of the solar radiation pressure force to the solar gravitational force ? > 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 g cm?3, 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.
  • Lennox, R., Price, M., Jamieson, W., Jura, M., Daoud-Aladine, A., Murray, C., Tang, C. and Arnold, D. (2014). Strain driven structural phase transformations in dysprosium doped BiFeO3 ceramics. Journal of Materials Chemistry C [Online] 2:3345-3360. Available at: http://dx.doi.org/10.1039/c3tc32345e.
    A detailed powder neutron and synchrotron diffraction study coupled with a complementary Raman spectroscopy study of the addition of Dy3+ into BiFeO3 ceramics is reported here. It can be seen that the addition of Dy3+ destabilises the polar R3c symmetry due to chemical strain effects arising from the large size mismatch between the two A-site cations (Dy3+ and Bi3+). This results in a lowering of the symmetry to a polar Cc model and in the range 0.05 ? x ? 0.30 in Bi1?xDyxFeO3 competition develops between the strained polar Cc and non-polar Pnma symmetries with the Cc model becoming increasingly strained until approximately x = 0.12 at which point the Pnma model becomes favoured. However, phase co-existence between the Cc and Pnma phases persists to x = 0.25. Preliminary magnetic measurements also suggest weak ferromagnetic character which increases in magnitude with increasing Dy3+ content. Preliminary electrical measurements suggest that whilst Bi0.95Dy0.05FeO3 is most likely polar; Bi0.70Dy0.30FeO3 shows relaxor-type behaviour.
  • Burchell, M., McDermott, K., Price, M. and Yolland, L. (2014). Survival of fossils under extreme shocks induced by hypervelocity impacts. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences [Online] 372:20130190. Available at: http://dx.doi.org/10.1098/rsta.2013.0190.
    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.
  • Price, M., Ramkissoon, N., McMahon, S., Miljkovi?, K., Parnell, J., Wozniakiewicz, P., Kearsley, A., Blamey, N., Cole, M. and Burchell, M. (2014). Limits on methane release and generation via hypervelocity impact of Martian analogue materials. International Journal of Astrobiology [Online] 13:132-140. Available at: http://dx.doi.org/10.1017/S1473550413000384.
    The quantity of methane in Mars' atmosphere, and the potential mechanism(s) responsible for its production, are still unknown. In order to test viable, abiotic, methangenic processes, we experimentally investigated two possible impact mechanisms for generating methane. In the first suite of experiments, basaltic rocks were impacted at 5 km s?1 and the quantity of gases (CH4, H2, He, N2, O2, Ar and CO2) released by the impacts was measured. In the second suite of experiments, a mixture of water ice, CO2 ice and anhydrous olivine grains was impacted to see if the shock induced rapid serpentinization of the olivine, and thus production of methane. The results of both suites of experiments demonstrate that impacts (at scales achievable in the laboratory) do not give rise to detectably enhanced quantities of methane release above background levels. Supporting hydrocode modelling was also performed to gain insight into the pressures and temperatures occurring during the impact events.
  • Westphal, A., Stroud, R., Bechtel, H., Brenker, F., Butterworth, A., Flynn, G., Frank, D., Gainsforth, Z., Hillier, J., Postberg, F., Simionovici, A., Sterken, V., Nittler, L., Allen, C., Anderson, D., Ansari, A., Bajt, S., Bastien, R., Bassim, N., Bridges, J., Brownlee, D., Burchell, M., Burghammer, M., Changela, H., Cloetens, P., Davis, A., Doll, R., Floss, C., Grun, E., Heck, P., Hoppe, P., Hudson, B., Huth, J., Kearsley, A., King, A., Lai, B., Leitner, J., Lemelle, L., Leonard, A., Leroux, H., Lettieri, R., Marchant, W., Ogliore, R., Ong, W., Price, M., Sandford, S., Tresseras, J., Schmitz, S., Schoonjans, T., Schreiber, K., Silversmit, G., Sole, V., Srama, R., Stadermann, F., Stephan, T., Stodolna, J., Sutton, S., Trieloff, M., Tsou, P., Tyliszczak, T., Vekemans, B., Vincze, L., Von Korff, J., Wordsworth, N., Zevin, D. and Zolensky, M. (2014). Evidence for interstellar origin of seven dust particles collected by the Stardust spacecraft. Science [Online] 345:786-791. Available at: http://dx.doi.org/10.1126/science.1252496.
    Seven particles captured by the Stardust Interstellar Dust Collector and returned to Earth for laboratory analysis have features consistent with an origin in the contemporary interstellar dust stream. More than 50 spacecraft debris particles were also identified. The interstellar dust candidates are readily distinguished from debris impacts on the basis of elemental composition and/or impact trajectory. The seven candidate interstellar particles are diverse in elemental composition, crystal structure, and size. The presence of crystalline grains and multiple iron-bearing phases, including sulfide, in some particles indicates that individual interstellar particles diverge from any one representative model of interstellar dust inferred from astronomical observations and theory.
  • Westphal, A., Bechtel, H., Brenker, F., Butterworth, A., Flynn, G., Frank, D., Gainsforth, Z., Hillier, J., Postberg, F., Simionovici, A., Sterken, V., Stroud, R., Allen, C., Anderson, D., Ansari, A., Bajt, S., Bastien, R., Bassim, N., Borg, J., Bridges, J., Brownlee, D., Burchell, M., Burghammer, M., Changela, H., Cloetens, P., Davis, A., Doll, R., Floss, C., Grün, E., Heck, P., Hoppe, P., Hudson, B., Huth, J., Hvide, B., Kearsley, A., King, A., Lai, B., Leitner, J., Lemelle, L., Leroux, H., Leonard, A., Lettieri, R., Marchant, W., Nittler, L., Ogliore, R., Ong, W., Price, M., Sandford, S., Tresseras, J., Schmitz, S., Schoonjans, T., Silversmit, G., Solé, V., Srama, R., Stadermann, F., Stephan, T., Stodolna, J., Sutton, S., Trieloff, M., Tsou, P., Tsuchiyama, A., Tyliszczak, T., Vekemans, B., Vincze, L., Von Korff, J., Wordsworth, N., Zevin, D. and Zolensky, M. (2014). Final reports of the Stardust Interstellar Preliminary Examination. Meteoritics & Planetary Science [Online] 49:1720-1733. Available at: http://dx.doi.org/10.1111/maps.12221.
  • Wozniakiewicz, P., Bradley, J., Ishii, H., Price, M. and Brownlee, D. (2013). Pre-accretional sorting of grains in the outer solar nebula. Astrophysical Journal [Online] 779. Available at: http://dx.doi.org/10.1088/0004-637X/779/2/164.
    Despite their micrometer-scale dimensions and nanogram masses, chondritic porous interplanetary dust particles (CP IDPs) are an important class of extraterrestrial material since their properties are consistent with a cometary origin and they show no evidence of significant post-accretional parent body alteration. Consequently, they can provide information about grain accretion in the comet-forming region of the outer solar nebula. We have previously reported our comparative study of the sizes and size distributions of crystalline silicate and sulfide grains in CP IDPs, in which we found these components exhibit a size-density relationship consistent with having been sorted together prior to accretion. Here we extend our data set and include GEMS (glass with embedded metal and sulfide), the most abundant amorphous silicate phase observed in CP IDPs. We find that while the silicate and sulfide sorting trend previously observed is maintained, the GEMS size data do not exhibit any clear relationship to these crystalline components. Therefore, GEMS do not appear to have been sorted with the silicate and sulfide crystals. The disparate sorting trends observed in GEMS and the crystalline grains in CP IDPs present an interesting challenge for modeling early transport and accretion processes. They may indicate that several sorting mechanisms operated on these CP IDP components, or alternatively, they may simply be a reflection of different source environments. © 2013. The American Astronomical Society. All rights reserved..
  • Gainsforth, Z., Brenker, F., Simionovici, A., Schmitz, S., Burghammer, M., Butterworth, A., Cloetens, P., Lemelle, L., Tresserras, J., Schoonjans, T., Silversmit, G., Solé, V., Vekemans, B., Vincze, L., Westphal, A., Allen, C., Anderson, D., Ansari, A., Bajt, S., Bastien, R., Bassim, N., Bechtel, H., Borg, J., Bridges, J., Brownlee, D., Burchell, M., Changela, H., Davis, A., Doll, R., Floss, C., Flynn, G., Fougeray, P., Frank, D., Grün, E., Heck, P., Hillier, J., Hoppe, P., Hudson, B., Huth, J., Hvide, B., Kearsley, A., King, A., Lai, B., Leitner, J., Leroux, H., Leonard, A., Lettieri, R., Marchant, W., Nittler, L., Ogliore, R., Ong, W., Postberg, F., Price, M., Sandford, S., Srama, R., Stephan, T., Sterken, V., Stodolna, J., Stroud, R., Sutton, S., Trieloff, M., Tsou, P., Tsuchiyama, A., Tyliszczak, T., Von Korff, J., Zevin, D. and Zolensky, M. (2013). Stardust Interstellar Preliminary Examination VIII: Identification of crystalline material in two interstellar candidates. Meteoritics & Planetary Science [Online] 49:1645-1665. Available at: http://doi.org/10.1111/maps.12148.
    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 µm in size with internal strain fields up to 0.3%. The unit cell dimensions were a = 4.85 ± 0.08 Å, b = 10.34 ± 0.16 Å, c = 6.08 ± 0.13 Å (2?). The second particle, I1043,1,30 (Orion), contained an olivine grain ? 2 µm in length and >500 nm in width. It was polycrystalline with both mosaiced domains varying over ? 20math formula and additional unoriented domains, and contained internal strain fields < 1%. The unit cell dimensions of the olivine were a = 4.76 ± 0.05 Å, b = 10.23 ± 0.10 Å, c = 5.99 ± 0.06 Å (2?), which limited the olivine to a forsteritic composition math formula (2?). Orion also contained abundant spinel nanocrystals of unknown composition, but unit cell dimension a = 8.06 ± 0.08 Å (2?). 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.
  • Bechtel, H., Flynn, G., Allen, C., Anderson, D., Ansari, A., Bajt, S., Bastien, R., Bassim, N., Borg, J., Brenker, F., Bridges, J., Brownlee, D., Burchell, M., Burghammer, M., Butterworth, A., Changela, H., Cloetens, P., Davis, A., Doll, R., Floss, C., Frank, D., Gainsforth, Z., Grün, E., Heck, P., Hillier, J., Hoppe, P., Hudson, B., Huth, J., Hvide, B., Kearsley, A., King, A., Lai, B., Leitner, J., Lemelle, L., Leroux, H., Leonard, A., Lettieri, R., Marchant, W., Nittler, L., Ogliore, R., Ong, W., Postberg, F., Price, M., Sandford, S., Tresseras, J., Schmitz, S., Schoonjans, T., Silversmit, G., Simionovici, A., Solé, V., Srama, R., Stadermann, F., Stephan, T., Sterken, V., Stodolna, J., Stroud, R., Sutton, S., Trieloff, M., Tsou, P., Tsuchiyama, A., Tyliszczak, T., Vekemans, B., Vincze, L., Von Korff, J., Westphal, A., Wordsworth, N., Zevin, D. and Zolensky, M. (2013). Stardust Interstellar Preliminary Examination III: Infrared spectroscopic analysis of interstellar dust candidates. Meteoritics & Planetary Science [Online] 49:1548-1561. Available at: http://doi.org/10.1111/maps.12125.
    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.
  • Fendyke, S., Price, M. and Burchell, M. (2013). Hydrocode modelling of hypervelocity impacts on ice. Advances in Space Research [Online] 52:705-714. Available at: http://dx.doi.org/10.1016/j.asr.2013.04.010.
    Experimental data are now widely available for the size of craters resulting from hypervelocity impacts of millimetre scale projectiles onto water ice targets. At such size scales the bowl shaped crater formed in ductile materials, or in larger scale impacts, is here surrounded by a large spallation zone due to the brittle nature of the ice. Modelling of these impacts therefore has to take account of this spallation. Here we used the iSALE2 hydrocode to simulate such impacts and compared the results to experimental data. We found that it was possible to reproduce the experimental data over a range of speeds (1–7 km s−1) for aluminium and copper projectiles. Initially, to reproduce the large spallation regions around the craters it was assumed that above a certain degree of damage, material was removed by spallation. However this simple one-parameter model failed to model the crater depth adequately. Accordingly, to obtain the best agreement of the simulations with the experimental data, a two-step ice strength was introduced, whereby above a critical amount of damage (0.95), the yield strength reduced from 1 MPa (intact) to 70 kPa (damaged). As a result, experimental data for crater depth and diameter and the results of the simulations agree to within 6% for diameter and 5% for depth over the impact energy range used in the experiments (1–240 J).
  • Loft, K., Price, M., Cole, M. and Burchell, M. (2013). Impacts into metals targets at velocities greater than 1 km s?1: A new online resource for the hypervelocity impact community and an illustration of the geometric change of debris cloud impact patterns with impact velocity. International Journal of Impact Engineering [Online] 56:47-60. Available at: http://dx.doi.org/10.1016/j.ijimpeng.2012.07.007.
    We announce the creation of a new online archive containing high resolution images, and measurements of over 200 metal plates impacted with a variety of projectiles at velocities between 1 and 8.5 km s?1. This archive is being made freely accessible for use by the shock physics and hypervelocity impact research communities.

    During the course of this archival work, it was discovered that debris cloud impact patterns from nylon projectiles form distinct geometric patterns, and that these patterns seem to fall into a distinct group depending on the projectile impact velocity. Complementary hydrocode modelling (using Ansys' AUTODYN) has been performed to try to recreate the patterns, but was not entirely successful, indicating that there is some physics that is not simulated within the hydrocode.
  • Wozniakiewicz, P., Bradley, J., Ishii, H., Brownlee, D., Kearsley, A., Burchell, M. and Price, M. (2013). Erratum: Grain sorting in cometary dust from the outer solar nebula (The Astrophysical Journal Letters (2012) 760 (L23)). Astrophysical Journal Letters [Online] 764:L18-L18. Available at: http://dx.doi.org/10.1088/2041-8205/764/1/L18.
  • Price, M., Kearsley, A. and Burchell, M. (2013). Validation of the Preston–Tonks–Wallace strength model at strain rates approaching ?1011 s?1 for Al-1100, tantalum and copper using hypervelocity impact crater morphologies. International Journal of Impact Engineering [Online] 52:1-10. Available at: http://dx.doi.org/10.1016/j.ijimpeng.2012.09.001.
    Data from hypervelocity impact experiments shows that the size of an impact crater is a non-linear function of the projectile diameter for micrometre-scale and smaller sized impactors. This non-linearity is thought to arise due to the strain rate hardening of the target materials at the ultra-high strain rates experienced during the impact event (approaching 1010 s?1). Here we investigate this ultra-high strain regime using a combination of experimental and simulated results. The experimental work involved samples of monodisperse silica and sodalime glass spheres with diameters between 500 nm and 22 ?m which were fired onto aluminium 1100 alloy, high purity (99.5+%) tantalum and copper targets at a velocity of ca. 6 km s?1 using a light gas gun. Precise measurements of the resulting crater diameters were made using scanning electron microscopy (with a resolution of a few tens of nanometers). We also ran hydrocode simulations of the impact events using ANSYS’ AUTODYN to compare the modelled results against the experimental data. The Preston–Tonks–Wallace (PTW) constitutive model was used in the hydrocode as it specifically deals with loading events at very high strain rates. Comparison is also made with results obtained using the Steinberg-Guinan strength model which is also applicable at high strain rates.

    The results demonstrate that current literature values for the PTW model need refining in order to accurately model micrometre-scale (and below), hypervelocity impact events. We present updated model parameters for Al, Cu and Ta and thus show that impact craters give an indirect measurement of the yield strength of a material at strain rates approaching 1011 s?1.
  • Foster, N., Wozniakiewicz, P., Price, M., Kearsley, A. and Burchell, M. (2013). Identification by Raman spectroscopy of Mg–Fe content of olivine samples after impact at 6kms?1 onto aluminium foil and aerogel: In the laboratory and in Wild-2 cometary samples. Geochimica Et Cosmochimica Acta [Online] 121:1-14. Available at: http://dx.doi.org/10.1016/j.gca.2013.07.022.
  • Morris, A., Price, M. and Burchell, M. (2013). IS THE LARGE CRATER ON THE ASTEROID (2867) STEINS REALLY AN IMPACT CRATER?. Astrophysical Journal [Online] 774:L11. Available at: http://dx.doi.org/10.1088/2041-8205/774/1/L11.
    The large crater on the asteroid (2867) Steins attracted much attention when it was first observed by the Rosetta spacecraft in 2008. Initially, it was widely thought to be unusually large compared to the size of the asteroid. It was quickly realized that this was not the case and there are other examples of similar (or larger) craters on small bodies in the same size range; however, it is still widely accepted that it is a crater arising from an impact onto the body which occurred after its formation. The asteroid (2867) Steins also has an equatorial bulge, usually considered to have arisen from redistribution of mass due to spin-up of the body caused by the YORP effect. Conversely, it is shown here that, based on catastrophic disruption experiments in laboratory impact studies, a similarly shaped body to the asteroid Steins can arise from the break-up of a parent in a catastrophic disruption event; this includes the presence of a large crater-like feature and equatorial bulge. This suggests that the large crater-like feature on Steins may not be a crater from a subsequent impact, but may have arisen directly from the fragmentation process of a larger, catastrophically disrupted parent.
  • Price, M., Solscheid, C., Burchell, M., Jossé, L., Adamek, N. and Cole, M. (2013). Survival of yeast spores in hypervelocity impact events up to velocities of 7.4kms?1. Icarus [Online] 222:263-272. Available at: http://dx.doi.org/10.1016/j.icarus.2012.10.035.
  • Martins, Z., Price, M., Goldman, N., Sephton, M. and Burchell, M. (2013). Shock synthesis of amino acids from impacting cometary and icy planet surface analogues. Nature Geoscience [Online] 6:1045-1049. Available at: http://dx.doi.org/10.1038/NGEO1930.
    Comets are known to harbour simple ices and the organic precursors of the building blocks of proteins—amino acids—that are essential to life. Indeed, glycine, the simplest amino acid, was recently confirmed to be present on comet 81P/Wild-2 from samples returned by NASA’s Stardust spacecraft. Impacts of icy bodies (such as comets) onto rocky surfaces, and, equally, impacts of rocky bodies onto icy surfaces (such as the jovian and saturnian satellites), could have been responsible for the manufacture of these complex organic molecules through a process of shock synthesis. Here we present laboratory experiments in which we shocked ice mixtures analogous to those found in a comet with a steel projectile fired at high velocities in a light gas gun to test whether amino acids could be produced. We found that the hypervelocity impact shock of a typical comet ice mixture produced several amino acids after hydrolysis. These include equal amounts of D- and L-alanine, and the non-protein amino acids ?-aminoisobutyric acid and isovaline as well as their precursors. Our findings suggest a pathway for the synthetic production of the components of proteins within our Solar System, and thus a potential pathway towards life through icy impacts.
  • Stroud, R., Allen, C., Ansari, A., Anderson, D., Bajt, S., Bassim, N., Bastien, R., Bechtel, H., Borg, J., Brenker, F., Bridges, J., Brownlee, D., Burchell, M., Burghammer, M., Butterworth, A., Changela, H., Cloetens, P., Davis, A., Doll, R., Floss, C., Flynn, G., Frank, D., Gainsforth, Z., Grün, E., Heck, P., Hillier, J., Hoppe, P., Huth, J., Hvide, B., Kearsley, A., King, A., Kotula, P., Lai, B., Leitner, J., Lemelle, L., Leroux, H., Leonard, A., Lettieri, R., Marchant, W., Nittler, L., Ogliore, R., Ong, W., Postberg, F., Price, M., Sandford, S., Tresseras, J., Schmitz, S., Schoonjans, T., Schreiber, K., Silversmit, G., Simionovici, A., Solé, V., Srama, R., Stephan, T., Sterken, V., Stodolna, J., Sutton, S., Trieloff, M., Tsou, P., Tsuchiyama, A., Tyliszczak, T., Vekemans, B., Vincze, L., Westphal, A., Von Korff, J., Zevin, D. and Zolensky, M. (2013). Stardust Interstellar Preliminary Examination XI: Identification and elemental analysis of impact craters on Al foils from the Stardust Interstellar Dust Collector. Meteoritics & Planetary Science [Online] 49:1698-1719. Available at: http://dx.doi.org/10.1111/maps.12136.
  • Avanaki, M., Podoleanu, A., Price, M., Corr, S. and Hojjatoleslami, S. (2013). Two applications of solid phantoms in performance assessment of optical coherence tomography systems. Applied Optics [Online] 52:7054-7061. Available at: http://www.dx.doi.org/10.1364/AO.52.007054.
    Virtual tissues (phantoms) are widely used for performance evaluation of imaging systems. Specific design of the phantom is necessary for the correct assessment of a system's parameters. In an effort to reduce the amount of time and energy spent making application-oriented phantoms, we describe procedures to make epoxy-resin solid phantoms based on Mie scattering theory, with two different scatterers: polystyrene and gold microspheres. The phantoms are specifically designed to be used in two applications: (a) the gold microspheres solid phantoms are used to estimate the point-spread function (PSF) of an optical coherence tomography (OCT) system, and (b) the polystyrene solid phantom are used to evaluate the performance of an OCT-images optical properties extraction (OPE) algorithm. Phantoms with differing combination of materials have been tested to achieve the most suitable combination for producing an accurate PSF for application (a) and a valid evaluation/parameter optimization of the algorithm in application (b). An en face time-domain dynamic focus OCT is used for imaging. © 2013 Optical Society of America.
  • Frank, D., Westphal, A., Zolensky, M., Gainsforth, Z., Butterworth, A., Bastien, R., Allen, C., Anderson, D., Ansari, A., Bajt, S., Bassim, N., Bechtel, H., Borg, J., Brenker, F., Bridges, J., Brownlee, D., Burchell, M., Burghammer, M., Changela, H., Cloetens, P., Davis, A., Doll, R., Floss, C., Flynn, G., Grün, E., Heck, P., Hillier, J., Hoppe, P., Hudson, B., Huth, J., Hvide, B., Kearsley, A., King, A., Lai, B., Leitner, J., Lemelle, L., Leroux, H., Leonard, A., Lettieri, R., Marchant, W., Nittler, L., Ogliore, R., Ong, W., Postberg, F., Price, M., Sandford, S., Tresseras, J., Schmitz, S., Schoonjans, T., Silversmit, G., Simionovici, A., Solé, V., Srama, R., Stephan, T., Sterken, V., Stodolna, J., Stroud, R., Sutton, S., Trieloff, M., Tsou, P., Tsuchiyama, A., Tyliszczak, T., Vekemans, B., Vincze, L., Korff, J., Wordsworth, N. and Zevin, D. (2013). Stardust Interstellar Preliminary Examination II: Curating the interstellar dust collector, picokeystones, and sources of impact tracks. Meteoritics & Planetary Science [Online] 49:1522-1547. Available at: http://doi.org/10.1111/maps.12147.
    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 ?-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.
  • Wozniakiewicz, P., Bradley, J., Ishii, H., Brownlee, D., Kearsley, A., Burchell, M. and Price, M. (2012). Grain sorting in cometry dust from the outer solar nebula. Astrophysical Journal [Online] 760:L23. Available at: http://dx.doi.org/10.1088/2041-8205/760/2/L23.
    Most young stars are surrounded by a disk of gas and dust. Close to the hot stars, amorphous dust grains from the parent molecular cloud are reprocessed into crystals that are then distributed throughout the accretion disk. In some disks, there is a reduction in crystalline grain size with heliocentric distance from the star. We investigated crystalline grain size distributions in chondritic porous (CP) interplanetary dust particles (IDPs) believed to be from small, icy bodies that accreted in outer regions of the solar nebula. The grains are Mg-rich silicates and Fe-rich sulfides, the two most abundant minerals in CP IDPs. We find that they are predominantly <0.25 ?m in radius with a mean grain size that varies from one CP IDP to another. We report a size-density relationship between the silicates and sulfides. A similar size-density relationship between much larger silicate and sulfide grains in meteorites from the asteroid belt is ascribed to aerodynamic sorting. Since the silicate and sulfide grains in CP IDPs are theoretically too small for aerodynamic sorting, their size-density relationship may be due to another process capable of sorting small grains.
  • Wozniakiewicz, P., Kearsley, A., Ishii, H., Burchell, M., Bradley, J., Teslick, N., Cole, M. and Price, M. (2012). The origin of crystalline residues in Stardust Al foils: Surviving cometary dust or crystallized impact melts?. Meteoritics & Planetary Science [Online] 47:660-670. Available at: http://dx.doi.org/10.1111/j.1945-5100.2011.01328.x.
    Samples returned by the Stardust mission from comet 81P/Wild 2 provide an unequaled opportunity to investigate cometary formation and evolution. Crystalline silicates have been identified in impact craters in Stardust Al foil, yet their origin is ambiguous. They may be original cometary components, or they may have grown from melt generated by impact. We have now studied experimental impacts of the calcium silicate mineral wollastonite, using scanning and transmission electron microscopy to document the relationship between impact feature shape and crystal lattice orientation in impact residue. Wollastonite can have a characteristic acicular habit, forming crater shapes that indicate crystal orientation upon impact. From extracted impact residue, we determined the lattice orientation of crystalline material for comparison with the whole particle orientation. We assume that crystallization from melt, without surviving seed nuclei, should result in randomly oriented crystallite growth, with no preferred direction for individual crystals. However, we find that the majority of crystalline material in the residue retains b-axis orientation parallel to the long axis of the crater form. This, together with impact parameter calculations and lack of Al incorporation by the residue (suggesting melting did not occur), indicates that these crystals and, by analogy, the majority of Al-free crystalline silicates in Stardust foil, are surviving remnants of the impactor. Furthermore, amorphous wollastonite residue probably did not form via melting and subsequent quenching, but instead by high-pressure amorphization or degradation of unquenchable phases. Finally, one crystal studied appears to be a new high-pressure/temperature polymorph of CaSiO3, indicating that such polymorphs may be observed in Stardust residues in craters.

Book section

  • Avanaki, M., Podoleanu, A., Price, M., Corr, S., Khoshki, R. and Hojjatoleslami, S. (2012). Phantoms for performance assessment of optical coherence tomography systems. In: Optical Diagnostics and Sensing XII: Toward Point-of-Care Diagnostics; And Design and Performance Validation of Phantoms Used in Conjunction With Optical Measurement of Tissue IV. SPIE. Available at: http://dx.doi.org/10.1117/12.912086.
    In this paper, we describe the procedures to make epoxy resin and agarose phantoms designed using Mie scattering calculations. The phantoms are constructed to be used in the estimation of point spread function (PSF) of an optical coherence tomography (OCT) and evaluation of optical properties extraction (OPE) algorithm.

Conference or workshop item

  • Alesbrook, L., Wozniakiewicz, P. and Price, M. (2019). Simulating the Atmospheric Entry of Micrometeorites Using a Two Stage Light Gas Gun. In: Lunar and Planetary Science Conference.
    We present our work on the use of A Light Gas Gun to simulate atmospheric entry of micrometeorites.

Thesis

  • Wickham-Eade, J. (2017). Fragmentation of Carbon-Bearing Projectiles and the Effects on Their Raman Spectra Due to Hypervelocity Impacts.
    The term hypervelocity refers to something that is travelling at speeds in excess of a few km/s. Impacts within the Solar System generally occur at these speeds, hence they are referred to as Hypervelocity Impacts.

    Typical impact speeds in the Solar System depends on their location. Within the main asteroid belt, the average impact speed is generally considered to be 5 km/s. Moving to impacts on Earth, the Moon and Mars, an asteroid average impact speed is approximately 22, 19 and 9 km/s respectively. Move to the outer Solar System and the average impact speed on Pluto is thought to be approximately 2 km/s

    Generally, research into hypervelocity impacts looks into cratering and the ejecta from these craters. However, the fate of the projectile is relatively neglected. Hence, this topic was explored in this thesis. To achieve this, experiments were performed using the University of Kent's two-stage light gas gun.

    Along with a mechanical effect on the projectile material, the propagating shock wave can cause effects on the molecular structure. This can be investigated using Raman Spectroscopy, which is an inelastic scattering effect resulting from the laser light interaction with the molecules of the sample. By comparing a before and after spectrum of an impacted material, it is possible to determine the effects of shock pressure.

    An important biomarker is carbon. The Raman spectra of carbon often contain a D (disorder) and G (graphite/order) band. The amplitude and area ratios of these two bands denote the structural organisation of the carbon-bearing materials. Impacting these materials can affect the Raman spectra. Changes in the spectra can reflect the effect shock pressures have had on the molecular structure of the material.

    Firstly, the mechanical effect of a hypervelocity impact was investigated for basalt and shale. The materials were filed into 1.5 mm cubes. These cubes were then fired into water at speeds up to 6.13 km/s (peak shock pressure of 30.9 GPa). The water was then filtered through a 0.1 um filter membrane and a scanning electron microscope used to image the entire filter paper. ImageJ was then used to analyse the fragments. From this, information on the morphology, cumulative fragment size distribution, survival percentage and the energy density at the catastrophic disruption threshold are obtained. Catastrophic disruption is where the shock wave of an impact is sufficiently intense that the largest fragment is equal to or less than 50% of the original mass of the body (exactly 50% is the threshold limit). Over 400,000 fragments were measured per shot, providing fragment sizes down to 10^-3 of the original projectile size. When excluding the partially disrupted projectiles (impacts not sufficient enough to surpass the catastrophic disruption threshold limit), the average semi-minor to semi-major axis ratio (b/a) for basalt and shale were 0.58 +/- 0.16 and 0.59 +/- 0.14 respectively. This suggests that the difference in morphology does not have an effect on this ratio at higher impact speeds. From the results an estimate of percentage survival at Pluto, the Moon, in the asteroid belt and on Mars is 76 +/- 11 %, 39 +/- 8 %, 17 +/- 5 % and 10 +/- 4 % respectively. It was found that for basalt and shale the catastrophic disruption energy density was (24.0 +/- 2.1) x 10^4 and (9.4 +/- 5.0) x 10^4 J/kg respectively.

    The work then moved on to investigating the effect of the shock upon the fragments of the projectile. An additional material (graphite) was used with basalt and shale. The materials were shot using the same method used to investigate the mechanical effect of the hypervelocity impact. Pre-shot the projectile was mapped using a 532 nm laser in a Raman spectrometer. These spectra were then compared to the spectra of 40 separate randomly chosen fragments in each shot. From this, it is possible to determine the shock pressure effects of the impact. Although no trends were identified positive shifts were observed for the D band peak position for basalt and shale, the G band peak position of basalt experienced a positive shift while graphite experienced both a positive and negative shift. Additionally, the G band width for basalt and shale experienced an absolute narrowing of 12.2% and 8.1% respectively, while graphite exhibited an absolute broadening of 17.6%. Overall, all the materials displayed an increased structural disorder after impact, as suggested by plotting the Raman spectra R1 and R2 values. These are ratios of the D and G band amplitudes (R1) and the bands' areas (R2). Furthermore, it was found from this work that there is a possibility of misinterpreting a sample when attempting to determine whether it is biotic carbon if from a shocked environment.

    The samples were also subjected to static pressure up to a maximum pressure of 3.59 GPa using a diamond anvil cell, and heating/cooling (temperature range 173 to 773 K) using a Linkam temperature stage. This was done in order to ascertain the effects of flash heating upon Raman spectra during hypervelocity impacts. It was found that the effects of temperature are mostly opposite to the effect of shock and static pressure on a carbon Raman spectrum. Increasing static pressure led to the G band peak position for shale and graphite shifting a total of 19.2 and 15.0 cm^-1, at 3.48 and 3.23 GPa respectively. In contrast, for shale and graphite the D and G band peak position were shifted to lower wavenumbers at high temperature (>300 K), and to higher wavenumbers at low temperature (
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