¹C. R. Fisher,¹M. C. Price,¹M. J. Burchell
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13729]
¹Centre for Astrophysics and Planetary Science, School of Physical Sciences, University of Kent, Canterbury, Kent, CT2 7NH UK
Published ba arrangement with John Wiley & Sons

The plumes naturally erupting from the icy satellite Enceladus were sampled by the Cassini spacecraft in high-speed fly-bys, which gave evidence of salt. This raises the question of how salt behaves under high-speed impact, and how it can best be sampled in future missions to such plumes. We present the results of 35 impacts onto aluminum targets by a variety of salts (NaCl, NaHCO3, MgSO4, and MgSO4·7H2O) at speeds from 0.26 to 7.3 km s−1. Using SEM-EDX, identifiable projectile residue was found in craters at all speeds. It was possible to distinguish NaCl and NaHCO3 from each other, and from the magnesium sulfates, but not to separate the hydrous from anhydrous magnesium sulfates. Raman spectroscopy on the magnesium sulfates and NaHCO3 residues failed to find a signal at low impact speeds (<0.5 km s−1) where there was insufficient projectile material deposited at the impact sites. At intermediate speeds (0.5 to 2–3 km s−1), identifiable Raman spectra were found in the impact craters, but not at higher impact speeds, indicating a loss of structure during the high speed impacts. Thus, intact capture of identifiable salt residues on solid metal surfaces requires impact speeds between 0.75 and 2 km s−1.

¹Jinia Sikdar,^1,2Vinai K. Rai
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13722]
¹Physical Research Laboratory, Ahmedabad, 380009 India
²School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, 85287 USA
Published by arrangement with John Wiley & Sons

Magnesium, a major mineral-forming element of the inner solar system, is partitioned between the silicate and the unique sulfidic phases (niningerite, MgS) of enstatite chondrites (ECs) owing to the formation of EC under exceptionally reducing conditions. In this study, we have carried out mineralogical characterization of the distinct Mg- and Si-bearing phases of unequilibrated ECs (EH3). To evaluate the Mg isotope variations in such reduced planetary bodies, we have analyzed the Mg isotope composition of several enstatitic silicate phases, matrices (composed of mixed proportions of silicate and sulfidic phases), and bulk meteorite fractions micro milled from three EH3 chondrites. We found that the stable Mg isotope composition (expressed as δ25Mg) of the microphase separates of EH3 chondrites ranged from −0.216 ± 0.014‰ to −0.094 ± 0.014‰. Despite the dispersion in Mg isotope values, the average δ25Mg of the silicate fractions of the studied EH3 chondrites was similar to its matrix and bulk meteorite fractions. Mass-dependent Mg isotope fractionation was evinced among the phase separates of EH3 chondrites with the slope of the fractionation line on a δ25Mg versus δ26Mg plot being closer to kinetic fractionation trend. Experimental and theoretical considerations hint that Mg isotope exchange between the silicate and sulfide phases might have generated the observed Mg isotope variations among the microphase separates of EH3 chondrites. Based on our Mg isotope data, in combination with the Si isotope composition obtained in the same aliquot of silicate–matrix fractions of EH3 chondrites and its subsolar Al/Si ratio, we suggest that the high abundance of Si in EC (due to the partitioning of Si among diverse silicates, silica, and metallic phases) and the loss of Mg and refractory components from EC-forming regions could explain the lower Mg/Si ratio of EC compared to that of ordinary and carbonaceous chondrites.

¹S.T.M. Peters,^1,2M.B. Fischer,¹A. Pack,³K. Szilas,⁴P.W.U. Appel,⁵C. Münker,⁶L. Dallai,⁵C.S. Marien
Geochemical Perspectives Letters (in Press) Link to Article [doi: 10.7185/geochemlet.2120]
¹Georg-August-Universität Göttingen, Geowissenschaftliches Zentrum, Goldschmidtstraße 1, 37077 Göttingen, Germany
²Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
³University of Copenhagen, Department of Geosciences and Natural Resource Management, Øster Voldgade 10, 1350 København K, Denmark
⁴Geological Survey of Denmark and Greenland, Øster Voldgade 10, 1350 København K, Denmark
⁵Universität zu Köln, Institut für Geologie und Mineralogie, Zülpicher Str. 49b, 50674 Köln, Germany
⁶CNR-Istituto di Geoscienze e Georisorse, Via Moruzzi 1, 56124 Pisa, Italy

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