¹Court, R. W., ¹Tan, J.
¹Impacts and Astromaterials Research Centre, Department of Earth Science and Engineering, Imperial College, London, UK

Ablation of micrometeoroids during atmospheric entry yields volatile gases such as water, carbon dioxide, and sulfur dioxide, capable of altering atmospheric chemistry and hence the climate and habitability of the planetary surface. While laboratory experiments have revealed the yields of these gases during laboratory simulations of ablation, the reactions responsible for the generation of these gases have remained unclear, with a typical assumption being that species simply undergo thermal decomposition without engaging in more complex chemistry. Here, pyrolysis–Fourier transform infrared spectroscopy reveals that mixtures of meteorite-relevant materials undergo secondary reactions during simulated ablation, with organic matter capable of taking part in carbothermic reduction of iron oxides and sulfates, resulting in yields of volatile gases that differ from those predicted by simple thermal decomposition. Sulfates are most susceptible to carbothermic reduction, producing greater yields of sulfur dioxide and carbon dioxide at lower temperatures than would be expected from simple thermal decomposition, even when mixed with meteoritically relevant abundances of low-reactivity Type IV kerogen. Iron oxides were less susceptible, with elevated yields of water, carbon dioxide, and carbon monoxide only occurring when mixed with high abundances of more reactive Type III kerogen. We use these insights to reinterpret previous ablation simulation experiments and to predict the reactions capable of occurring during ablation of carbonaceous micrometeoroids in atmospheres of different compositions.

Reference
Court RW, Tan J (2016) Insights into secondary reactions occurring during atmospheric ablation of micrometeoroids. Meteoritics & Planetary Science (in Press)
Link to Article [doi: 10.1111/maps.12652]
Published by arrangement with John Wiley & Sons

¹Thompson, M. S., ¹Zega, T. J., ¹Becerra, P., ¹Keane, J. T., ¹Byrne, S.
¹Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, USA

We report measurements of the oxidation state of Fe nanoparticles within lunar soils that experienced varied degrees of space weathering. We measured >100 particles from immature, submature, and mature lunar samples using electron energy-loss spectroscopy (EELS) coupled to an aberration-corrected transmission electron microscope. The EELS measurements show that the nanoparticles are composed of a mixture of Fe0, Fe2+, and Fe3+ oxidation states, and exhibit a trend of increasing oxidation state with higher maturity. We hypothesize that the oxidation is driven by the diffusion of O atoms to the surface of the Fe nanoparticles from the oxygen-rich matrix that surrounds them. The oxidation state of Fe in the nanoparticles has an effect on modeled reflectance properties of lunar soil. These results are relevant to remote sensing data for the Moon and to the remote determination of relative soil maturities for various regions of the lunar surface.

Reference
Thompson MS, Zega TJ, Becerra P, Keane JT, Byrne S (2016) The oxidation state of nanophase Fe particles in lunar soil: Implications for space weathering. Meteoritics & Planetary Science (in Press)
Link to Article [doi: 10.1111/maps.12646]
Published by arrangement with John Wiley & Sons

¹T. J. Barrett, ¹J. J. Barnes, ^1,2R. Tartèse, ²M. Anand, ¹I. A. Franchi, ¹R. C. Greenwood, ^1,2B. L. A. Charlier, ^1,3M. M. Grady
¹Planetary and Space Sciences, The Open University, Milton Keynes, UK
²Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, Muséum National d’Histoire Naturelle, Sorbonne Universités, CNRS, UPMC & IRD, Paris, France
³Department of Earth Sciences, Natural History Museum, London, UK

Volatile elements play a key role in the dynamics of planetary evolution. Extensive work has been carried out to determine the abundance, distribution, and source(s) of volatiles in planetary bodies such as the Earth, Moon, and Mars. A recent study showed that the water in apatite from eucrites has similar hydrogen isotopic compositions compared to water in terrestrial rocks and carbonaceous chondrites, suggesting that water accreted very early in the inner solar system given the ancient crystallization ages (~4.5 Ga) of eucrites. Here, the measurements of water (reported as equivalent H2O abundances) and the hydrogen isotopic composition (δD) of apatite from five basaltic eucrites and one cumulate eucrite are reported. Apatite H2O abundances range from ~30 to ~3500 ppm and are associated with a weighted average δD value of −34 ± 67‰. No systematic variations or correlations are observed in H2O abundance or δD value with eucrite geochemical trend or metamorphic grade. These results extend the range of previously published hydrogen isotope data for eucrites and confirm the striking homogeneity in the H-isotopic composition of water in eucrites, which is consistent with a common source for water in the inner solar system.

Reference
Barrett TJ, Barnes JJ, Tartèse R, Anand M, Franchi IA, Greenwood RC, Charlier BLA, Grady MM (2016) The abundance and isotopic composition of water in eucrites. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12649]
Published by arrangement with John Wiley & Sons

¹Kathryn H. Harriss, ¹M.J.Burchell
¹School of Physical Sciences, University of Kent, Canterbury, Kent, UK

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

Reference
Harriss KH, Burchell MJ (2016) A study of the observed shift in the peak position of olivine Raman spectra as a result of shock induced by hypervelocity impacts. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12660]
Published by arrangement with John Wiley & Sons

¹Benjamin J. Farcy, ^2,3Juliane Gross, ⁴Paul Carpenter, ¹Jacob Hicks, ¹Justin Filiberto
¹Carbondale, Parkinson Lab, Geology Department, Southern Illinois University, Carbondale, Illinois, USA
²Department of Earth and Planetary Sciences, Rutgers University, Piscataway, New Jersey, USA
³Department of Earth and Planetary Sciences, American Museum of Natural History, New York, New York, USA
⁴Department of Earth and Planetary Sciences, Washington University, St. Louis, Missouri, USA

Martian magmas are thought to be rich in chlorine compared with their terrestrial counterparts. Here, we experimentally investigate the effect of chlorine on liquidus depression and near-liquidus crystallization of olivine-phyric shergottite NWA 6234 and compare these results with previous experimental results on the effect of chlorine on near-liquidus crystallization of the surface basalts Humphrey and Fastball. Previous experimental results showed that the change in liquidus temperature is dependent on the bulk composition of the basalt. The effect of chlorine on liquidus depression is greater for lower SiO2 and higher Al2O3 magmas than for higher SiO2 and lower Al2O3 magmas. The bulk composition for this study has lower Al2O3 and higher FeO contents than previous work; therefore, we provide additional constraints on the effect of the bulk composition on the influence of chlorine on near-liquidus crystallization. High pressure and temperature crystallization experiments were performed at 1 GPa on a synthetic basalt, of the bulk composition of NWA 6234, with 0–4 wt% Cl added to the sample as AgCl. The results are consistent with previous notions that with increasing wt% Cl in the melt, the crystallization temperature decreases. Importantly, our results have a liquidus depression ∆T (°C) from added chlorine that is consistent with the difference in bulk composition and suggest a dependence on both the bulk Al2O3 and FeO content. Our results suggest that the addition of chlorine to the Martian mantle may lower magma genesis temperatures and potentially aid in the petrogenesis of Martian magmas.

Reference
Farcy BJ, Gross J, Carpenter P, Hicks J, Filiberto J (2016) Effect of chlorine on near-liquidus crystallization of olivine-phyric shergottite NWA 6234 at 1 GPa: Implication for volatile-induced melting of the Martian mantle. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12662]
Published by arrangement with John Wiley & Sons