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

AbstractOlivine, (Mg, Fe)2[SiO4], is a common mineral in extraterrestrial materials, whose Mg–Fe content varies from the end-members Forsterite (Mg2SiO4: denoted ‘Fo’) to Fayalite (Fe2SiO4: denoted ‘Fa’), together with minor quantities of Ca, Cr, Mn and Ni. Olivine is readily identified by Raman spectroscopy, and the Mg–Fe content can be obtained by precise measurements of the position of the two strongest Raman peaks. Here we show that this is not only true for pristine and highly crystalline olivine, but also for grains which have undergone high pressure shock processing during hypervelocity impact. We demonstrate that there are subtle changes to the Raman spectra in grains impacted at 6.1kms−1 onto aluminium foil and into low density aerogel. We quantify these changes, and also show that if no correction is made for the impact effects, the Fe:Mg molar ratio of the olivine can be significantly misinterpreted. This study was stimulated by NASA’s Stardust mission to comet 81P/Wild-2, since freshly ejected cometary dust particles were collected (via impact) onto aluminium foil and into aerogel cells at 6.1kms−1 and these samples are being investigated with Raman spectroscopy. We identify the residue in one Stardust impact crater on aluminium foil as arising from an olivine with a composition of Fo97–100

Space Dust and Debris Near the Earth

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

Simulating the Atmospheric Entry of Micrometeorites Using a Two Stage Light Gas Gun

We present our work on the use of A Light Gas Gun to simulate atmospheric entry of micrometeorites

The grain size distribution of matrix in primitive chondrites

The matrix of primitive chondrites is composed of submicron crystals embedded in amorphous silicates. These grains are thought to be the remains of relatively unprocessed dust from the inner regions of the protoplanetary disk. The matrix of primitive meteorites is often compared to chondritic porous interplanetary dust particles (CP‐IDPs) which are believed to be of cometary origin, having accreted in the outermost regions of the solar nebula. Crystalline grains in CP‐IDPs show evidence of a size–density relationship between the silicates and sulfides suggesting that these components experienced sorting prior to accretion. Here, we investigate whether such evidence of sorting is also present in the matrix constituents of primitive chondrites. We report findings from our study of grain size distributions of discrete silicate and opaque (sulfide and metal) grains within the matrix of the primitive meteorites Acfer 094 (C2‐ung.), ALHA77307 (CO3), MIL 07687 (C3‐ung.), and QUE 99177 (CR2). Mean radii of matrix silicate grains range from 103 nm in QUE 99177 to 2018 nm in MIL 07687. The opaque grains show a wider variation, with average radii ranging from 15 nm in QUE 99177 to 219 nm in MIL07687. Our results indicate that, in contrast to CP‐IDPs, the size distribution of matrix components of these primitive meteorites cannot be explained by aerodynamic sorting that took place prior to accretion. We conclude that any evidence of sorting is likely to have been lost due to a greater variety and degree of processing experienced on these primitive chondrites than on cometary parent bodies

Synthesis of Autofluorescent Phenanthrene Microparticles via Emulsification: A Useful Synthetic Mimic for Polycyclic Aromatic Hydrocarbon-Based Cosmic Dust

Phenanthrene is the simplest example of a polycyclic aromatic hydrocarbon (PAH). Herein, we exploit its relatively low melting point (101 °C) to prepare microparticles from molten phenanthrene droplets by conducting high-shear homogenization in a 3:1 water/ethylene glycol mixture at 105 °C using poly(N-vinylpyrrolidone) as a non-ionic polymeric emulsifier. Scanning electron microscopy studies confirm that this protocol produces polydisperse phenanthrene microparticles with a spherical morphology: laser diffraction studies indicate a volume-average diameter of 25 ± 21 μm. Such projectiles are fired into an aluminum foil target at 1.87 km s−1 using a two-stage light gas gun. Interestingly, the autofluorescence exhibited by phenanthrene aids analysis of the resulting impact craters. More specifically, it enables assessment of the spatial distribution of any surviving phenanthrene in the vicinity of each crater. Furthermore, these phenanthrene microparticles can be coated with an ultrathin overlayer of polypyrrole, which reduces their autofluorescence. In principle, such core−shell microparticles should be useful for assessing the extent of thermal ablation that is likely to occur when they are fired into aerogel targets. Accordingly, polypyrrole-coated microparticles were fired into an aerogel target at 2.07 km s−1. Intact microparticles were identified at the end of carrot tracks and their relatively weak autofluorescence suggests that thermal ablation during aerogel capture did not completely remove the polypyrrole overlayer. Thus, these new core−shell microparticles appear to be useful model projectiles for assessing the extent of thermal processing that can occur in such experiments, which have implications for the capture of intact PAH-based dust grains originating from cometary tails or from plumes emanating from icy satellites (e.g., Enceladus) in future space missions

Artificial weathering of an ordinary chondrite: Recommendations for the curation of Antarctic meteorites

Meteorites are prone to errestrial weathering not only after their fall on the Earth’s surface but also during storage in museum collections. To study the susceptibility of this material to weathering, weathering experiments were carried out on polished sections of the H5 chondrite Asuka 10177. The experiments consisted of four 100-days cycles during which temperature and humidity varied on a twelve hours basis. The first alteration cycle consisted of changing the temperature from 15 to 25 °C; the second cycle consisted of modifying both humidity and temperature from 35 to 45% and 15 to 25 °C, respectively; the third cycle consisted of varying the humidity level from 40 to 60%; and the fourth cycle maintained a fixed high humidity of 80%. Weathering products resulting from the experiments were identified and characterized using scanning electron microscopy–energy dispersive spectroscopy and Raman spectroscopy. Such products were not observed at the microscopic scale after the first cycle of alteration. Conversely, products typical of the corrosion of meteoritic FeNi metal were observed during scanning electron microscope surveys after all subsequent cycles. Important increases in the distribution of weathering products on the samples were observed after cycles 2 and 4 but not after cycle 3, suggesting that the combination of temperature and humidity fluctuations or high humidity (>60%) alone is most detrimental to chondritic samples. Chemistry of the weathering products revealed a high degree of FeNi metal corrosion with a limited contribution of troilite corrosion. No clear evidence of mafic silicate alteration was observed after all cycles, suggesting that postretrieval alteration remains limited to FeNi metal and to a lesser extent to troilite

The identification of airbursts in the past: insights from the BIT-58 layer

Airbursts are estimated to be the most frequent type of destructive impact events. Yet, confirmation of these events is elusive, resulting in a major gap in the impact record of Earth. The recent discovery of igneous chondritic spherules produced during a new type of touchdown airburst 430 thousand years (kyr) ago over Antarctica, in which a projectile vapor jet interacts with the Antarctic ice sheet, provided the first trace of such an impact in the geological record. In terms of petrology and geochemistry, particles constituting the BIT-58 dust horizon, which was found in surface ice at near Allan Hills in Antarctica, are almost identical to those produced 430 kyr ago. We demonstrate here that BIT-58 particles were indeed formed during a touchdown event between 2.3 and 2.7 million years (Myr) ago. This represents the oldest record of an airburst on Earth identified to date. Slight geochemical differences with 430 kyr old airburst spherules provide additional constraints on spherule condensation in large airburst plumes. Finding confirmation of airbursts in the paleorecord can provide insight into the frequency of the most hazardous impacts and, thus, has implications for planetary defence

Palladium-coated kapton for use on dust detectors in low earth orbit: Performance under hypervelocity impact and atomic oxygen exposure

Observation of dust and debris in the near Earth environment is a field of great commercial and scientific interest, vital to maximising the operational and commercial life-cycle of satellites and reducing risk to increasing numbers of astronauts in Low Earth Orbit (LEO). To this end, monitoring and assessment of the flux of particles is of paramount importance to the space industry and wider socio-economic interests that depend upon data products/services from orbital infrastructure. We have designed a passive space dust detector to investigate the dust environment in LEO—the Orbital Dust Impact Experiment (ODIE). ODIE is designed for deployment in LEO for ~1 year, whereupon it would be returned to Earth for analysis of impact features generated by dust particles. The design emphasises the ability to distinguish between the orbital debris (OD) relating to human space activity and the naturally occurring micrometeoroid (MM) population at millimetre to submillimetre scales. ODIE is comprised of multiple Kapton foils, which have shown great potential to effectively preserve details of the impacting particles’ size and chemistry, with residue chemistry being used to interpret an origin (OD vs. MM). LEO is a harsh environment—the highly erosive effects of atomic oxygen damage Kapton foil—requiring the use of a protective coating. Common coatings available for Kapton (e.g., Al, SiO2, etc.) are problematic for subsequent analysis and interpretation of OD vs. MM origin, being a common elemental component of MM or OD, or having X-ray emission peaks overlapping with those of elements used to distinguish MM from OD. We thus propose palladium coatings as an alternative for this application. Here we report on the performance of palladium as a protective coating for a Kapton-based passive dust detector when exposed to atomic oxygen and impact. When subjected to impact, we observe that thicker coatings suffer delamination such that a coating of <50 nm is recommended. Analysis of atomic oxygen exposed samples shows a thin 10 nm coating of palladium significantly reduces the mass loss of Kapton, while coatings of 25 nm and over perform as well as or better than other commonly used coating

Synthesis of phenanthrene/pyrene hybrid microparticles: useful synthetic mimics for polycyclic aromatic hydrocarbon-based cosmic dust

Polycyclic aromatic hydrocarbons (PAHs) are found throughout the interstellar medium and are important markers for the evolution of galaxies and both star and planet formation. They are also widely regarded as a major source of carbon, which has implications in the search for extraterrestrial life. Herein we construct a melting point phase diagram for a series of phenanthrene/pyrene binary mixtures to identify the eutectic composition (75 mol % phenanthrene) and its melting point (83 °C). The molten oil obtained on heating this eutectic composition to 90 °C in aqueous solution is homogenized in the presence of a water-soluble polymeric emulsifier. On cooling to 20 °C, polydisperse spherical phenanthrene/pyrene hybrid microparticles are obtained. Varying the stirring rate and emulsifier type enables the mean microparticle diameter to be adjusted from 11 to 279 μm. Importantly, the phenanthrene content of individual microparticles remains constant during processing, as expected for the eutectic composition. These new hybrid microparticles form impact craters and undergo partial fragmentation when fired into a metal target at 1 km s–1 using a light gas gun. When fired into an aerogel target at the same speed, microparticles are located at the ends of characteristic “carrot tracks”. Autofluorescence is observed in both types of experiments, which at first sight suggests minimal degradation. However, Raman microscopy analysis of the aerogel-captured microparticles indicates prominent pyrene signals but no trace of the more volatile phenanthrene component. Such differential ablation during aerogel capture is expected to inform the in situ analysis of PAH-rich cosmic dust in future space missions

Next generation protein-based materials capture and preserve projectiles from supersonic impacts

Extreme energy dissipating materials are essential for a range of applications. The military and police force require ballistic armour to ensure the safety of their personnel, while the aerospace industry requires materials that enable the capture, preservation and study of hypervelocity projectiles. However, current industry standards display at least one inherent limitation. To resolve these limitations we have turned to nature, utilising proteins that have evolved over millennia to enable effective energy dissipation. Specifically, a recombinant form of the mechanosensitive protein talin was incorporated into a monomeric unit and crosslinked, resulting in the production of the first reported example of a talin shock absorbing material (TSAM). When subjected to 1.5 km/s supersonic shots, TSAMs were shown not only to absorb the impact, but to capture/preserve the projectile, making TSAMs the first reported protein material to achieve this