Dr Penny Wozniakiewicz
Dr Penny Wozniakiewicz studied for an MSci in Planetary Sciences at University College London before moving to Imperial College London to complete her PhD. Between 2009 and 2013 she was a postdoctoral research associate, firstly at the Institute of Geophysics & Planetary Physics, Lawrence Livermore National Laboratory (LLNL) in California, USA and then in the School of Physical Sciences at the University of Kent. Penny went on to hold the Marie Curie International Incoming Fellowship in the Department of Earth Sciences at the Natural History Museum in London and remains a Visiting Research Associate there. Since 2015 she has been a Lecturer in Space Science at the University of Kent.
Dr Wozniakiewicz's research interests include:
- studying hypervelocity impacts in the laboratory
- studying surfaces returned from low Earth orbit
- investigating early solar system formation and evolution through the study of samples from comets and asteroids
- investigating new methods for collecting extraterrestrial dust on Earth.
She uses a variety of analytical equipment, having gained expertise in scanning and transmission electron microscopy and focused ion beam sample preparation techniques.
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.
Wozniakiewicz, P. (2017). Cosmic dust in space and on Earth. Astronomy and Geophysics [Online] 58. Available at: https://doi.org/10.1093/astrogeo/atx027.
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. Â© 2013. The American Astronomical Society. All rights reserved..
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.
Kearsley, A., Burchell, M., Price, M., Graham, G., Wozniakiewicz, P., Cole, M., Foster, N. and Teslich, N. (2009). Interpretation of Wild 2 dust fine structure: Comparison of Stardust aluminum foil craters to the three-dimensional shape of experimental impacts by artificial aggregate particles and meteorite powders. Meteoritics and Planetary Science [Online] 44:1489-1509. Available at: http://dx.doi.org/10.1111/j.1945-5100.2009.tb01188.x.New experimental results show that Stardust crater morphology is consistent with interpretation of many larger Wild 2 dust grains being aggregates, albeit most of low porosity and therefore relatively high density. The majority of large Stardust grains (i.e. those carrying most of the cometary dust mass) probably had density of 2.4 g cm-3 (similar to soda-lime glass used in earlier calibration experiments) or greater, and porosity of 25% or less, akin to consolidated carbonaceous chondrite meteorites, and much lower than the 80% suggested for fractal dust aggregates. Although better size calibration is required for interpretation of the very smallest impacting grains, we suggest that aggregates could have dense components dominated by Î¼-scale and smaller sub-grains. If porosity of the Wild 2 nucleus is high, with similar bulk density to other comets, much of the pore space may be at a scale of tens of micrometers, between coarser, denser grains. Successful demonstration of aggregate projectile impacts in the laboratory now opens the possibility of experiments to further constrain the conditions for creation of bulbous (Type C) tracks in aerogel, which we have observed in recent shots. We are also using mixed mineral aggregates to document differential survival of pristine composition and crystalline structure in diverse finegrained components of aggregate cometary dust analogues, impacted onto both foil and aerogel under Stardust encounter conditions. © The Meteoritical Society, 2009.
Wozniakiewicz, P., Kearsley, A., Burchell, M., Foster, N., Cole, M., Bland, P. and Russell, S. (2009). In situ analysis of residues resulting from laboratory impacts into aluminum 1100 foil: Implications for Stardust crater analyses. Meteoritics and Planetary Science [Online] 44:1541-1559. Available at: http://dx.doi.org/10.1111/j.1945-5100.2009.tb01191.x.The encounter between the Stardust spacecraft and particles from comet 81P/Wild 2 gave impacts at a relative velocity of 6.1 km s-1 and near perpendicular incidence to the collector surface. Such conditions are well within the performance limits of light gas gun laboratory simulations. For this study, two series of shots were conducted at the University of Kent, firing magnesium silicates (Mg end-member forsterite, enstatite, diopside and lizardite), followed by a suite of increasingly Ferich olivines (through to Fe end-member fayalite) into Stardust flight-spare foils. Preserved residues were analysed using scanning electron microscopy combined with energy dispersive X-ray analyses (SEM/EDX). X-ray count integrals show that mineral compositions remain distinct from one another after impact, although they do show increased scatter. However, there is a small but systematic increase in Mg relative to Si for all residues when compared to projectile compositions. While some changes in Mg:Si ay be due to complex analytical geometries in craters, there appears to be some preferential loss of Si. In practice, EDX analyses in craters on Stardust AI 1100 foil inevitably include contributions from Fe- and Si-rich alloy inclusions, leading to further scattering of element ratios. Such inclusions have complicated Mg:Fe data interpretation. Compositional heterogeneity in the synthetic olivine projectiles also introduces data spread. Nevertheless, even with the preceding caveats, we find that the main groups of mafic silicates can be easily and reliably distinguished in EDX analyses performed in rapid surveys of foil craters, enabling access to a valuable additional collection of cometary materials Â© The Meteoritical Society, 2009. Printed in USA.
Conference or workshop item
Duff, M., Lynn, K., Jones, K., Soundararajan, R., Bradley, J., Ishii, H., Aguiar, J. and Wozniakiewicz, P. (2010). Characterization of secondary phases and other defects in CdZnTe. In: Hard X-Ray, Gamma-Ray, and Neutron Detector Physics XII. U.S.: SPIE. Available at: http://dx.doi.org/10.1117/12.862379.Semiconducting CdZnTe or "CZT" crystals are very suitable for use as a room temperature-based gamma radiation spectrometer. During the last decade, modifications in growth methods for CZT have significantly improved the quality of the produced crystals however there are material features that can influence the performance of these materials as radiation detectors. For example, various structural heterogeneities within the CZT crystals, such as, pipes, voids, polycrystallinity, and secondary phases (SP) can have a negative impact on the detector performance. In this study, a CZT material was grown by the modified vertical Bridgman growth (MVB) method with zone leveled growth in the absence of excess Te in the melt. Numerous SP were imaged using transmission IR at a volume % of 0.002. Samples from this material were analyzed using various analytical techniques to evaluate its electrical properties, purity and detector performance as radiation spectrometers and to determine the morphology, dimension and elemental /structural composition of one of the SP in this material. This material was found to have a high resistivity and good radiation spectrometer performance. It had SPs that were rich in calcium (Ca), carbon (C) and oxygen (O) (possibly CaCO3) or only C and O that were 5 Î¼m or less in diameter. Â© 2010 Copyright SPIE - The International Society for Optical Engineering.
Foster, N., Wozniakiewicz, P., Kearsley, A., Burchell, M., Cole, M. and Bland, P. (2010). Investigating the ability of Stardust capture media to preserve collected particles intact. In: Physics and Astrophysics of Planetary Systems. Les Ulis, France: EDP Sciences, pp. 395-398. Available at: http://dx.doi.org/10.1051/eas/1041031.We briefly summarise our ongoing efforts to evaluate the success of cometary particle capture by NASA's Stardust mission. We demonstrate the use of a variety of analysis techniques to investigate the state of preservation in laboratory analogues of the Stardust encounter at 6.1 km s-1, using well characterised projectiles and flight grade foils and aerogel. © EAS, EDP Sciences, 2010.
Burchell, M., Foster, N., Kearsley, A. and Wozniakiewicz, P. (2009). Capture of cometary dust grains in impacts at 6.1 km s-1. In: Conference of the American Physical Society Topical Group on Shock Compression of Condensed Matter, 2009 APS SCCM. American IOP Institute of Physics, pp. 898-901. Available at: http://dx.doi.org/10.1063/1.3295289.The NASA Stardust mission to comet 81P/Wild 2 collected grains of cometary dust freshly ejected from the comet during a fly-by at a speed of 6.1 km s -1. These were captured on aluminum foils and in blocks of silica aerogel. The dust underwent a severe shock during capture. The nature of the shock process depends on the properties of the dust and the collecting media. On the aluminium, the shock process and impact damage is typical of that between high-density (or hard materials) at high velocity, resulting in craters lined with impactor residues. The peak shock pressures are estimated at 60-80 GPa. Two main crater types are seen, simple bowl shaped and multiple pit craters: these reflect the degree of consolidation of the original dust grain. Capture in the low density aerogel was via a more gradual slowing of the dust grains accompanied by a variety of effects on the grains (complete break up of weak grains vs. ablation of well consolidated grains). The relation between the structure of the dust grains and the resulting impact features in both collector materials is discussed. © 2009 American Institute of Physics.
Kearsley, A., Burchell, M., Price, M., Graham, G., Wozniakiewicz, P. and Cole, M. (2009). Micrometeoroid impacts on spacecraft: Can asteroidal and cometary dust be distinguished?. In: 5th European Conference on Space Debris. European Space Agency. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-77950846284&partnerID=40&md5=b443317edf0ca9a713f51a9485914763.Both cometary and asteroidal sources should contribute to the population of micrometeoroids (MM) reaching Earth [1,2], although there is debate as to their relative numbers. Small impact features on spacecraft surfaces returned from low Earth orbit (LEO) can provide sufficient evidence to distinguish some, but certainly not all, impacts from these dust sources. In this paper we review the difficulties in attributing a source to MM impactors.