^1,2G.Poggiali,³S.Iannini Lelarge, ²J.R.Brucato, ¹M.A.Barucci, ^3,4M.Masotta ,²M.A.Corazzi, ²T.Fornaro, ⁵A.J.Brown, ⁶L.Mandon, ⁷N.Randazzo
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115449]
¹LESIA-Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, 5 place Jules Janssen, 92190 Meudon, France
²INAF-Astrophysical Observatory of Arcetri, Firenze, Italy
³Department of Earth Science, University of Pisa, Pisa, Italy
⁴CISUP, Centro per l’Integrazione della Strumentazione Università di Pisa, Pisa, Italy
⁵Plancius Research, Severna Park, MD 21146, USA
⁶Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
¹Earth and Atmospheric Sciences, University of Alberta, Alberta, Canada
Copyright Elsevier

Identification of water in our Solar System is a key point to understanding the formation and evolution of planetary bodies as well as for astrobiological studies. Scientists identified hydrated minerals as a prime source of H2O in our Solar System. Minerals such as clays, serpentines and other phyllosilicates were discovered by orbiter and lander spacecraft and ground observations on a large variety of rocky surfaces from Mars to small asteroids using InfraRed (IR) spectroscopy as primary technique. It has already been observed that in the presence of large amounts of hydrated minerals in mixtures with anhydrous minerals, the IR spectra can be dominated by the features of hydrated minerals. However, it is still poorly studied how the IR spectra change in presence of different grain size of the two components.

The goal of this study was to investigate the infrared spectroscopic features of anhydrous mineral spectra in presence of low amounts of small grain size hydrated hyperfine particles. We prepared several mixtures using 1 wt% and 5 wt% of very small grain size (< 10 μm) hydrated minerals and 95 wt% and 99 wt% of larger grain size (200–500 μm) anhydrous minerals. We measured the IR reflectance spectrum of these mixtures in the range 8000–400 cm−1 (1.25–25 μm). Results presented here show how the presence of a very limited amount of hydrated minerals with grain size one order of magnitude smaller than the anhydrous component is sufficient to change the IR spectrum, especially in the Near-InfraRed (NIR) region where some of the major hydrated features manifest. On the contrary, the Mid-InfraRed (MIR) part of the spectrum (also identified as thermal infrared) is definitely less affected and anhydrous mineral features continue to be dominant with slight modifications. This result is of pivotal importance for correctly interpreting the IR reflectance observations of planetary bodies such as Mars or asteroids where a mixing of anhydrous and hydrated minerals can be observed. The presence of strong spectroscopic features due to hydrated minerals can be misinterpreted as a large abundance of this material instead of a spectroscopic effect.

^1,2Alessandro Bragagni,¹Frank Wombacher,^1,3Maria Kirchenbaur,^1,4Ninja Braukmüller,¹Carsten Münker
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2023.01.014]
¹Institut für Geologie und Mineralogie, Universität zu Köln, Zülpicher Str. 49b, 50674 Köln, Germany
²Dipartimento di Scienze della Terra, Università degli studi di Firenze, via La Pira 4, 50121 Firenze, Italy
³Institut für Mineralogie, Leibniz Universität Hannover, Callinstraße 3, 30167 Hannover, Germany
⁴Institut für Geologische Wissenschaften, Freie Universität, Malteserstr. 74-100, 12249, Berlin, Germany
Copyright Elsevier

Tin has ten stable isotopes, providing the opportunity to investigate and discriminate nucleosynthetic isotope anomalies from mass-dependent and mass-independent isotope fractionation. Novel protocols for chemical separation (based on TBP-resin) and MC-ICP-MS analyses are reported here for high precision Sn isotope measurements on terrestrial rocks and chondrites. Relative to the Sn reference standard (NIST SRM 3161a), terrestrial basalts and chondrites show isotope patterns that are consistent with mass-dependent and mass-independent isotope fractionation processes as well as with 115Sn radiogenic ingrowth from 115In.

Two different mass-independent isotope effects are identified, namely the nuclear volume (or nuclear field shift) and the magnetic isotope effect. The magnetic isotope effect dominates in the two measured ordinary chondrites, while repeated analyses of the carbonaceous chondrite Murchison (CM2) display a pattern consistent with a nuclear volume effect. Terrestrial basalts show patterns that are compatible with a mixture of nuclear volume and magnetic isotope effects. The ultimate origin of the isotope fractionation is unclear but a fractionation induced during sample preparation seems unlikely because different groups of chondrites show distinctly different patterns, hence pointing towards natural geo/cosmochemical processes. Only the carbonaceous chondrite Murchison (CM2) shows a Sn isotope pattern similar to what expected for nucleosynthetic variations. However, this pattern is better reproduced by nuclear volume effects. Thus, after considering mass-independent and mass-dependent effects, we find no evidence of residual nucleosynthetic anomalies, in agreement with observations for most other elements with similar half-mass condensation temperatures.

Most chondrites show a deficit in 115Sn/120Sn (typically −150 to −200 ppm) relative to terrestrial samples, with the exception of one ordinary chondrite that displays an excess of about +250 ppm. The 115Sn/120Sn data correlate with In/Sn, being consistent with the β− decay of 115In over the age of the solar system. This represents the first evidence of the 115In-115Sn decay system in natural samples. The radiogenic 115Sn signature of the BSE derives from a suprachondritic In/SnBSE, which reflects preferential partitioning of Sn into the Earth’s core.