¹S. De Angelis, ^1,2F. Furnari, ¹M. Ferrari, ¹E. La Francesca, ¹C. Carli, ¹G. Piccioni, ¹S. Rubino, ¹S. Stefani, ¹F. Tosi
Journal of Geophysical Research: Planets, 131, e2026JE009723 Link to Article [DOI: 10.1029/2026JE009723]
¹Institute for Space Astrophysics and Planetology—INAF‐IAPS, Rome, Italy
²Sapienza University of Rome, Rome, Italy
Published by arrangement with John Wiley & Sons

Hexahydrite (MgSO₄·6H₂O) is among the possible candidates of the hydrated salts composing the “non-icy” materials on the surface of Europa. However, given the conditions of extreme vacuum characterizing the surfaces of icy and other airless Solar System bodies, a crucial aspect is to determine the conditions of stability of such hydrated salts in a wide range of pressures from ambient to high vacuum. The effect of varying temperatures in conjunction with variable vacuum is another important aspect to be considered. Studying the stability field of such compounds is crucial to establish the conditions of their presence on icy moons. In this work, we conducted an infrared (1–12 μm) and Raman spectral study on hexahydrite samples from ambient pressure to high vacuum, at ambient and low temperatures. We observe two main effects occurring upon lowering the pressure at which the sample is exposed, that is (a) de-hydration of the sample and consequent (b) loss of crystallinity and increase of structural disorder of the material. While the de-hydration is clear from the notable modification of H₂O absorption bands in the near-infrared, the effect of loss of crystallinity is observable in the mid-IR spectral region and also confirmed by Raman analyses. The transition is marked by the progressive loss of fine structure in the 1.5 and 2 μm hydration bands and by the collapse of the ∼9 μm Reststrahlen peak. Our measurements provide important laboratory constraints concerning the stability conditions of such hydrated materials that should provide aid in interpretation of mission data.

^1,2Lilin Huang, ^3,4Yanxue Wu, ¹Riqiang Wen, ⁵Chunwen Huang, ¹Chunmei Li, ¹Jiangmin Ma
Journal of Geophysical Research: Planets, 131, e2026JE010002 Link to Article [DOI: 10.1029/2026JE010002]
¹Hezhou University, Hezhou, China
²Key Laboratory of Planetary Geological Evolution at Universities of Guangxi Province, Institute of Meteorites and Planetary Materials Research, Guilin University of Technology, Guilin, China
³State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Macau, China
⁴Analysis and Test Center, Guangdong University of Technology, Guangzhou, China
⁵Hezhou Information Network Center of Science and Technology, Hezhou, China
Published by arrangement with John Wiley & Sons

In this study, we report amorphous silica dendrites in three eucritic pyroxene grains from a howardite meteorite NWA 14701. These textures exhibit enhanced metasomatic features characterized by irregular or rounded amorphous silica containing numerous nanoscale ilmenite and chromian ulvöspinel inclusions distributed along both sides of fractures to form dendritic networks in the host pyroxene. These dendritic networks manifest as a discontinuous series of discrete, equant-shaped silica masses that project as embayments into the walls of the fractures. We propose that the formation mechanism of these amorphous silica dendrites was related to fluid-mediated alteration processes, as recorded by pyroxene decomposition to Fe–Ti–Cr oxides and amorphous silica along fractures. Such fluid preferentially leached and removed highly mobile cations (e.g., Mg, Ca, and Fe). Concomitantly, high field-strength elements (Cr and Ti) with extremely low mobility became passively enriched in situ due to their limited transportability within the fluid phase, subsequently crystallizing as ilmenite and chromian ulvöspinel at nanoscale dimensions. Meanwhile, the Si-O framework of the original host pyroxene, depleted in most interstitial cations, was preserved as a chemically inert amorphous silica framework. Our work suggests that the amorphous silica dendrites represent an unique type of secondary alteration texture on the HED parent asteroid that was previously undocumented, and they may also occur on other airless, differentiated planetary bodies.