^1,2Daisuke Nakashima, ^2,3,4Jon M. Friedrich, ^2,5Ulrich Ott
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2025.06.016]
¹Department of Earth and Planetary Material Sciences, Faculty of Science, Tohoku University, Aoba, Sendai, Miyagi 980-8578, Japan
²Max-Planck Institute for Chemistry, Hahn-Meitner-Weg, 1, D-55128 Mainz, Germany
³Department of Chemistry and Biochemistry, Fordham University, 441 East Fordham Road, Bronx, NY 10458, USA
⁴Department of Earth and Planetary Sciences, American Museum of Natural History, 200 Central Park West, New York, NY 10024, USA
⁵HUN-REN Institute for Nuclear Research, Bem tér 18/c, 4026 Debrecen, Hungary
Copyright Elsevier

Noble gas isotopes and trace element abundances in five Ca-Al-rich inclusions (CAIs) from two CV3 chondrites (Allende and Axtell) were analyzed. The noble gases consist of spallogenic, radiogenic, fission, and trapped components. The old U/Th-4He ages of the CAIs (4.0 – 5.4 Ga) suggest no significant loss of radiogenic 4He and, by inference, no significant disturbance of the initial (244Pu/238U) ratios, (244Pu/238U)0, which are derived using concentrations of 244Pu-fission 136Xe. The abundances of rare earth elements and U in the CAIs suggest variable formation temperatures, which is reflected in variable (Pr/238U)0 ratios. The (244Pu/238U)0 ratios of the CAIs are variable from 0.0103 ± 0.0010 to 0.0419 ± 0.0031, which correlate with the (Pr/238U)0 ratios. The correlation suggests Pu-Pr-U fractionation during CAI formation. From the intersection between the correlation line and the calculated early Solar System Pr/238U ratio of 9.27, the 244Pu/238U ratio before Pu-Pr-U fractionation in the CAI formation region is calculated as 0.0108 ± 0.0051, which is similar to those derived using other Solar System materials such as chondrites, achondrites, chondrules, and terrestrial zircons. We thus suggest that the initial 244Pu/238U ratio has been spatially homogeneous in the inner part of the early solar nebula including the innermost solar nebula, where CAIs formed.
We also used our Xe isotope data to search for the possible presence of Xe-G, a characteristic feature of presolar silicon carbide, which has previously been reported for the CAI Curious Marie (Pravdivtseva et al., 2020). Following the same approach as those authors, we find no evidence of Xe-G in our CAIs except for possibly one (All-4). We identified a correlation, during stepped gas release, in the Curious Marie data from the literature between 130Xe-G and radiogenic 129Xe, which is surprising and not apparent in All-4. However, the exact amount of Xe-G in Curious Marie (and the very presence in All-4) sensitively depend on the applied component resolution scheme. We infer that the abundance of Xe-G in Curious Marie is about twice that previously reported and that All-4 contains Xe-HL, the characteristic Xe component of presolar nanodiamonds. While we cannot rule out the presence of presolar SiC noble gas components at a lower level than found in CAI Curious Marie as a general feature of fine-grained CAIs, Curious Marie appears to be a special case.

^1,2Laurence A. J. Garvie,³László Trif,⁴Christian G. Hoover
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.70000]
¹Buseck Center for Meteorite Studies, Arizona State University, Tempe, Arizona, USA
²School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, USA
³Institute of Materials and Environmental Chemistry, HUN-REN Research Center for Natural Sciences, Budapest, Hungary
⁴School of Sustainable Engineering and the Built Environment, Ira A. Fulton Schools of Engineering, Arizona State University, Tempe, Arizona, USA
Published by arrangement with John Wiley & Sons

Meteorites arriving on Earth possess indigenous organic, isotopic, mineralogic, and magnetic properties that reveal conditions and processes from their formation. However, these properties can rapidly change when exposed to the Earth’s environment. Asteroids, which formed nearly 4.5 billion years ago, inhabit the ultrahigh vacuum of interplanetary space, with a pressure of around 1.3 × 10−11 Pa, equivalent to only a few tens of atoms per cubic centimeter. Fragments of these asteroids, which land on Earth as meteorites, immediately adsorb atmospheric gases into their pore spaces, which can subsequently adsorb into and onto the minerals. In this study, we show that adsorption of atmospheric water can significantly increase the mass of the smectite-rich Tarda (C2-ung) meteorite, with mass gains reaching around 30 wt% at 100% relative humidity (RH) and between 5 and 10 wt% under typical laboratory conditions (up to ~50% RH). In contrast, the serpentine-rich Aguas Zarcas meteorite gains approximately 11 wt% at 100% RH and around 2 wt% at ~50% RH. This water adsorption leads to observable mass fluctuations in clay-rich carbonaceous chondrites (CCs), especially those with high smectite content, which undergo a “breathing-like” process. This process involves the uptake and release of water, influenced by atmospheric humidity. Although this mass change is reversible in the short term, prolonged “breathing” can alter the mineral composition and physical properties of these materials, complicating our understanding of their origins and evolution. For instance, gypsum forms in Tarda after 10 min of exposure to 100% RH at room temperature, while the Aguas Zarcas meteorite forms significant gypsum within 24 h under similar conditions. In addition, mass changes for Tarda are measured with thermal gravimetry in a He atmosphere, by heating the sample at 100°C in a high vacuum, and after curation under an ultradry atmosphere. These experiments show that samples exposed to the atmosphere rapidly adsorb significant water that is not removed by curation under dry N2. Our findings indicate that this “breathing” process can profoundly and rapidly affect the properties of astromaterials, including samples returned from asteroids Ryugu and Bennu. Maintaining these materials in a stable, low-humidity environment can help prevent such changes and preserve their indigenous properties.