¹José A. P. M. Devienne,¹Thomas A. Berndt,²Wyn Williams,¹Shichu Chen
Journal of Geophysical Research (Planets) Link to Article [https://doi.org/10.1029/2023JE008268]
¹Department of Geophysics, School of Earth and Space Sciences, Peking University, Beijing, PR China
²School of GeoSciences, The University of Edinburgh, Edinburgh, UK
Published by arrangement with John Wiley & Sons

An increasing amount of evidence suggests that the tetrataenite-bearing cloudy zones (CZ) in iron and stony-iron meteorites can preserve magnetic records of ancient magnetic activity of their parent bodies over solar system timescales. Tetrataenite islands in the CZ are nanometer-sized (<200 nm) crystals that usually form through ordering from precursor taenite islands upon extremely slow cooling through 320°C. Recent micromagnetic models have shown that such precursor taenite islands form highly thermally stable single-domain (SD) or single-vortex states (SV). In this work we employ a 3D finite element multi-phase micromagnetic modeling to show that tetrataenite inherits the magnetic remanence of taenite precursor when it forms over underlying SD states. When taenite forms SV states, however, tetrataenite resets the precursor magnetization and records a new remanence through chemical ordering at 320°C. We further assess the thermal stability of tetrataenite islands. We show that in cases where tetrataenite inherits the domain states of its precursor taenite, the origin of the remanence can be up to ∼105 years older than previously thought in fast-cooled meteorites, and ∼1–≳6 Myr in slowly cooled meteorites. It indicates, therefore, that different regions across slowly cooled CZ record distinct stages of planetary formation.

¹E. Caminiti,²C. Lantz,³S. Besse,²R. Brunetto,⁴C. Carli,⁵L. Serrano,⁶N. Mari,²M. Vincendon,¹A. Doressoundiram
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2024.116191]
¹LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de paris, 5 place Jules Janssen, 92195 Meudon, France
²Institut d’Astrophysique Spatiale, Université Paris- Saclay, CNRS, 91400 Orsay, France
³European Space Agency (ESA), European Space Astronomy Centre (ESAC), Camino Bajo del Castillo s/n, Villanueva de la Cañada, 28692 Madrid, Spain
⁴IAPS-INAF, Via Fosso del Cavaliere, 100, 00133 Rome, Italy
⁵Independent researcher, 660001 Pereira, Colombia
⁶Department of Earth and Environmental Sciences, University of Pavia, 27100 Pavia, Italy
Copyright Elsevier

The surface of Mercury is subject to space weathering that complicates remote sensing data analysis. We present an experimental study performed on Mercury volcanic surface analogues to provide a better constraint on spectral alterations induced by solar wind. We used 20 keV He+ with fluences up to 5 × 1017 ions/cm2 to simulate ion irradiation reaching the surface. Terrestrial ultramafic lava already identified as good analogues for Mercury were used: a boninite, a basaltic komatiite and a komatiite. Spectra were acquired in the visible to mid-infrared (VMIR) wavelength range, between 0.4 and 16 μm. Spectral alterations induced by irradiation are observed. In the visible to near-infrared (VNIR) samples show an exponential darkening, a reddening and a flattening of spectra. Above a certain irradiation dose (1 × 1017 ions/cm2 in our conditions), the darkening reaches a plateau while the reddening and flattening do not show any definable trend. In the mid-infrared (MIR) we observe a shift of Reststrahlen bands towards longer wavelengths (≤0.42 μm). The Christiansen feature is shifted towards longer or shorter wavelengths according to the irradiation dose (≤0.2 μm). The spectral alteration is closely influenced by the composition. As Mercury’s surface is compositionally heterogeneous, the degree of spectral alteration varies on the planet and putatively participates in the heterogeneous spectral properties of the surface. This work provides ground-truth data for future ESA-JAXA-BepiColombo observations. The alteration of VMIR spectral features induced by ion irradiation simulated in the laboratory will be used for future SIMBIO-SYS (Spectrometer and Imaging for MPO BepiColombo Integrated Observatory SYStem) and MERTIS (Mercury Radiometer and Thermal Infrared Spectrometer) data analysis.