¹Matthias van Ginneken,²Vinciane Debaille,³Sophie Decrée,⁴Steven Goderis,⁵Alan B. Woodland,¹Penelope Wozniakiewicz,³Marleen De Ceukelaire,³Thierry Leduc,³Philippe Claeys
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.13818]
¹Centre for Astrophysics and Planetary Science, School of Physical Sciences, Ingram Building, University of Kent, Canterbury, CT2 7NH UK
²Laboratoire G-Time, Université Libre de Bruxelles, Brussels, BE1050 Belgium
³Geological Survey of Belgium, Royal Belgian Institute of Natural Sciences, rue Vautier 29, Brussels, BE1000 Belgium
⁴Analytical, Environmental, and Geochemistry, Vrije Universiteit Brussel, Pleinlaan 2, Brussels, BE1050 Belgium
⁵Institut für Geowissenschaften, Goethe-Universität Frankfurt, Altenhöferallee 1, Frankfurt am Main, D-60438 Germany
Published by arrangement with John Wiley & Sons

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.

¹J.-Y.Chaufray,¹F.Leblanc,¹A.I.E.Werner,¹R.Modolo,²S.Aizawa
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115081]
¹LATMOS-IPSL, CNRS, Sorbonne-Université, Paris-Saclay, Paris, France
²IRAP, CNRS, Toulouse, France
Copyright Elsevier

We simulate the seasonal variations of the Mg 285.3 nm and Ca 422.7 nm brightness and compared our results to the MESSENGER/MASCS observations at dawn. Our results are consistent with the previous studies of Ca while for Mg we used another seasonal variation for the g -value (excitation frequency) at 285.3 nm. We find that both emissions are well reproduced from micrometeoroid impacts when the true anomaly angle (TAA) of Mercury is larger than 80°. For true anomaly angle lower than 80°, an additional source is needed to reproduce the Ca observations in agreement with previous studies, and possibly the Mg observations. We compare several solar spectra (observed or modeled) to study the Mg g-value and found that the seasonal variation of the g-value peaking near TAA = 60° used by previous studies to analyse the MESSENGER observations of Mg may be due to an artefact not present in the solar spectrum. The observed seasonal variations of the Mg brightness are better reproduced without this artefact. However, observations of the solar spectrum near 285.3 nm at a spectral resolution of ~20 mA would be needed to better estimate the seasonal variations of the Mg excitation frequencies and then to better understand the possible differences in the source of these two species in the exosphere of Mercury.