Coordinated neutron and X‐ray computed tomography of meteorites: Detection and distribution of hydrogen‐bearing materials

Abstract

The presence and distribution of hydrogen-bearing materials in meteorites are important constraints on processes in the early solar system, and the delivery of volatile constituents to growing planets. Here, we show that coordinated neutron and X-ray computed tomography, NXCT, can reveal the presence and distributions of hydrogenbearing materials in meteorites, and thus help constrain the presence and actions of water in the early solar system. NXCT is nearly nondestructive of meteorite samples. Neutron fluence in NXCT is approximately seven orders of magnitude less than in typical instrumental neutron activation analysis, and so produces little residual radioactivity and currently undetectable changes in isotope ratios. Heating during NXCT is minimal, but NXCT will overprint the record of cosmic ray exposure held in natural thermoluminescence. Two meteorites were examined. EET 87503 is a howardite, a regolith breccia inferred to be from the asteroid 4 Vesta, and contains fragments of eucrite basalt, diogenite pyroxenite, and H-rich carbonaceous chondrites. With NXCT, the chondrite fragments within the meteorite piece can be clearly located and characterized, in preparation for possible extraction and detailed analyses. Graves Nunataks (GRA) 06100 is a CR2 chondrite meteorite that contains abundant iron metal and H-bearing silicates from aqueous alteration. In NXCT, H-bearing altered material is clearly distinguished from metal, and its distribution in three dimensions is revealed as a constraint on the processes of alteration.

Combined Neutron and X‐Ray Tomography—A Versatile and Non‐Destructive Tool in Planetary Geosciences

“…In a recent study, Treiman et al. (2022) reported that their NCT study of a chondrite meteorite sample had a very limited effect (below uncertainty levels in the current analyses) on the isotopic systems of a set of isotopes, for example, Hf‐W, within the sample and that NCT caused negligible heating. However, they note that some high‐precision isotopic analyses could be affected and that both XCT and NCT will influence thermoluminescence and thus overprint the cosmic ray exposure records within meteorites (see Sears et al., 2016; Treiman et al., 2022).…”

“…(2022) reported that their NCT study of a chondrite meteorite sample had a very limited effect (below uncertainty levels in the current analyses) on the isotopic systems of a set of isotopes, for example, Hf‐W, within the sample and that NCT caused negligible heating. However, they note that some high‐precision isotopic analyses could be affected and that both XCT and NCT will influence thermoluminescence and thus overprint the cosmic ray exposure records within meteorites (see Sears et al., 2016; Treiman et al., 2022). Also, it remains unknown whether NCT has detectable effects on chemical structures (such as might be detectable by e.g., Raman spectroscopy) or on organic molecules of possible relevance in the search for organic markers of extraterrestrial life.…”

“…To visualize the tomography images of the different samples, and to enable segmentation and extraction of inclusions, software enabling simultaneous visualization of the 3D images from both modalities slice‐by‐slice and in a combined 3D rendering mode is important. Phase segmentation can be performed in the dual XCT/NCT images using a bivariate histogram (LaManna et al., 2020; Martell et al., 2022; Treiman et al., 2022), but in samples containing phases with overlapping attenuation values (grayscales), the option to segment manually will enable fine‐tuning of the segmentation. In this study, we used the Dragonfly® ORS software for data analysis.…”

“…Nevertheless, NCT has been used for non-destructive structural characterization of iron meteorites (Caporali et al, 2016;Peetermans et al, 2013) and chondrite meteorites (Kichanov et al, 2022). In addition, a few studies have used combined NCT and XCT to study various types of impactites and meteorites; these studies have provided insight into the distribution of hydrogen in Martian meteorites (Martell et al, 2022) and chondrite meteorites (Treiman et al, 2018(Treiman et al, , 2022, as well as petrographic characterization of terrestrial impactites (Fedrigo et al, 2018;Needham et al, 2020;Pakhnevich, 2016;Steen Duchnik et al, 2012).…”

“…Neutrons are particularly “sensitive” to certain PGEs such as iridium (Tengattini et al., 2021) and, unlike X‐rays, also to hydrogen and chlorine (Kardjilov et al., 2018). These elements are highly relevant within the field of planetary geology; iridium can be used to detect and confirm a meteoritic component within impactites (e.g., Koeberl et al., 2012), and the distribution of hydrogen in meteorites can shed light on aqueous processes on Solar System bodies and their driving forces in the early Solar System (e.g., Treiman et al., 2022). Furthermore, deciphering fluid pathways within meteorites can give insight into the source and timing of the fluids, as well as the degree of terrestrial weathering of recovered meteorites (Martell et al., 2022).…”