1M. Broussard,1M. Neuman,1B. L. Jolliff,1P. Koefoed,1R. L. Korotev,2R. V. Morris,3K. C. Welten,1K. Wang
Journal of Geophysical Research (Planets)(in Press) Open Access Link to Article [https://doi.org/10.1029/2024JE008371]
1Department of Earth, Environmental, and Planetary Sciences and the McDonnell Center for the Space Sciences,
Washington University in St. Louis, St. Louis, MO, USA
2ARES NASA Johnson Space Center, Houston, TX, USA
3Space Sciences Laboratory, University of California, Berkeley, CA, USA
Published by arrangement with John Wiley & Sons
Space weathering alters the surface materials of airless planetary bodies; however, the effects on moderately volatile elements in the lunar regolith are not well constrained. For the first time, we provide depth profiles for stable K and Fe isotopes in a continuous lunar regolith core, Apollo 17 double drive tube 73001/2. The top of the core is enriched in heavy K isotopes (δ41K = 3.48 ± 0.05‰) with a significant trend toward lighter K isotopes to a depth of 7 cm; while the lower 44 cm has only slight variation with an average δ41K value of 0.15 ± 0.05‰. Iron, which is more refractory, shows only minor variation; the δ56Fe value at the top of the core is 0.16 ± 0.02‰ while the average bottom 44 cm is 0.11 ± 0.03‰. The isotopic fractionation in the top 7 cm of the core, especially the K isotopes, correlates with soil maturity as measured by ferromagnetic resonance. Kinetic fractionation from volatilization by micrometeoroid impacts is modeled in the double drive tube 73001/2 using Rayleigh fractionation and can explain the observed K and Fe isotopic fractionation. Effects from cosmogenic 41K (from decay of 41Ca) were calculated and found to be negligible in 73001/2. In future sample return missions, researchers can use heavy K isotope signatures as tracers of space weathering effects.
Day: May 2, 2025
Spectro-photometry of Phobos simulants, II: Effects of porosity and texture
1,2Antonin Wargnier et al. (>10)
Icarus (in Press) Open Access Link to Article [https://doi.org/10.1016/j.icarus.2025.116611]
1LIRA, Observatoire de Paris, Université PSL, Sorbonne Université, Université de Paris-Cité, CY Cergy Paris Université, CNRS, 5 place Jules Janssen, Meudon, 92195, France
2LATMOS, CNRS, Université Versailles St-Quentin, Université Paris-Saclay, Sorbonne Université, 11 Bvd d’Alembert, Guyancourt, F-78280, France
Copyright Elsevier
Surface porosity and texture has been found to be an important property for small bodies. Some asteroids and comets can exhibit an extremely high surface porosity in the first millimeter layer. This layer may be produced by various processes and maintained by the lack of an atmosphere. However, the influence of porosity on the spectro-photometric properties of small body surfaces is not yet fully understood.
In this study, we looked into the effect of the texture on the spectro-photometric properties of Phobos regolith spectroscopic simulants. Macro- and micro-porosity were created by mixing the simulants with ultra-pure water, producing ice-dust particles, and then sublimating the water. The sublimation of the water ice enabled the production of porous and rough powdered simulants with significant micro- and macro-porosity associated with macro-roughness. The reflectance spectroscopic properties in the visible and near-infrared (0.5–4.2 μm) demonstrate a brightening of the porous samples in comparison to the compact ones. One simulant exhibits a bluing of the spectral slope after increasing porosity, which is likely linked to the presence of expandable phyllosilicates. In the mid-infrared range, a contrast increase of the 10 μm emissivity-related plateau due to silicates is observed. This spectral feature is typically observed as a 10 μm emissivity plateau on some asteroids, making the mid-infrared region important for assessing mineralogy and surface texture.
Photometry reveals a modification of the phase reddening behavior between the compact powder and the sublimation residue for both simulants. However, the observed behavior is different between the simulants, suggesting that the phase reddening may be dependent on the composition of the simulants. The phase curves of the sublimation residues exhibit a higher contribution of forward scattering. The derivation of the Hapke parameters indicates an increase in roughness for the porous sample, but no significant modification of the opposition effect. The modifications of the spectrophotometric properties observed in this experiment are definitely due to the textural changes obtained after sublimation, which depend on the initial composition of the simulants.
This study aims to provide new insights into the understanding of porosity by using two Phobos simulants in the context of the upcoming JAXA/Martian Moons eXploration mission. We suggest that the Phobos blue unit may be due to the presence of a highly porous layer, rather than only to space-weathering processes, as often postulated.
Cosmochemistry Papers 