^1,2,3Yan Fan,^1,4Deze Liu,^1,5Shijie Li,⁶Xiangdong Li,³Shen Liu,¹Dehan Shen,⁷Qing-Zhu Yin
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.70175]
¹Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, China
²Xi’an Center, China Geological Survey, Xi’an, China
³State Key Laboratory of Continental Dynamics and Department of Geology, Northwest University, Xi’an, China
⁴Department of Earth Sciences, University of Oxford, Oxford, UK
⁵Chinese Academy of Sciences, Center for Excellence in Comparative Planetology, Hefei, China
⁶Environmental Engineering Unit, Department of Civil and Structural Engineering, The Hong Kong Polytechnic University,Kowloon, Hong Kong
⁷Department of Earth and Planetary Sciences, University of California at Davis, Davis, California, USA
Published by arrangement with John Wiley & Sons

This study assesses mercury (Hg) concentrations and their isotopic compositions in Antarctic chondrites, desert chondrites, and drilled samples from the Jilin chondrite (H5). Desert chondrites show mercury concentrations between 2.2 ng g−1 and 156.8 ng g−1, with δ202Hg ranging from −3.69‰ to 1.19‰. Δ199Hg and Δ201Hg vary from −0.23‰ to −0.02‰ and −0.2‰ to 0.02‰, respectively, showing a weak positive correlation among these parameters (slope 0.74 ± 0.24, R2 = 0.46). These Hg concentrations and isotopic composition data of desert chondrites indicate that Hg in desert chondrites has been altered due to terrestrial processes in addition to evaporation loss during its terrestrial residence period. Antarctic chondrites exhibit mercury concentrations from 8.0 ng g−1 to 3940.8 ng g−1, with δ202Hg from −2.51‰ to 1.16‰. Δ199Hg and Δ201Hg range from −0.83‰ to −0.05‰ and −0.71‰ to 0.10‰, with a significant correlation (slope 0.93 ± 0.15, R2 = 0.76), likely influenced by Antarctic snow that has experienced significant photochemical processes during atmospheric mercury depletion events (AMDEs) and has elevated mercury content (such as drifted snow). Jilin meteorite’s δ202Hg, Δ199Hg, and Δ201Hg vary between −3.74‰ to −1.79‰, −0.12‰ to 0.09‰, and −0.12‰ to −0.01‰, respectively. A weak positive correlation between Δ199Hg and Δ201Hg (slope 1.45 ± 0.28, R2 = 0.67) suggests localized Hg evaporation due to shock processes on the parent body; however, Hg isotopic heterogeneity from nebular or parent body processes cannot be excluded. Terrestrial weathering and shock events could alter Hg content and isotopic compositions in chondrites, challenging their use as accurate indicators of Hg’s cosmochemical behavior.

¹A. J. King,¹P. F. Schofield,¹J. Najorka,¹H. C. Bates,¹S. S. Russell,²T. J. McCoy,³T. J. Zega,^3,4,5H. C. Connolly Jr,³D. S. Lauretta
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70169]
¹Planetary Materials Group, Natural History Museum, London, UK
²National Museum of Natural History, Smithsonian Institution, Washington, DC, USA
³Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, USA
⁴Department of Geology, Rowan University, Glassboro, New Jersey, USA
⁵Department of Earth and Planetary Science, American Museum of Natural History, New York City, New York, USA
Published by arranegment with John Wiley & Sons

Samples returned by NASA’s OSIRIS-REx mission from the carbonaceous asteroid (101955) Bennu hold clues about conditions in the early solar system and the formation of planetary bodies. Initial investigation of Bennu samples found that they are rich in phyllosilicates and other secondary minerals formed during aqueous alteration of a larger parent body. To better understand the phyllosilicate minerals and constrain the extent and settings of alteration, we used X-ray powder diffraction (XRD) to characterize the mineralogy of homogenized aggregate (unsorted) samples and an angular particle from Bennu. We find that these samples consist of abundant (>80 vol%) phyllosilicates and few (≤2 vol%) precursor anhydrous silicates, in excellent agreement with remote observations of the global asteroid surface, and consistent with extensive aqueous alteration of Bennu’s parent body. The XRD patterns and modal mineralogy of the Bennu samples are similar to those of CI carbonaceous chondrites and particles returned from the carbonaceous asteroid (162173) Ryugu by JAXA’s Hayabusa2 mission, offering further support for the close genetic relationship among these materials suggested by other studies. Bennu’s phyllosilicates are dominated by a mixture of trioctahedral Mg-rich clay minerals that formed from alkaline fluids under high water to rock ratios and likely evolved in response to changes in temperature and/or fluid chemistry as alteration progressed. Based on the XRD characteristics of the phyllosilicates, the Bennu samples did not experience a peak temperature at or above ~300°C after aqueous alteration. Finally, we show that the interlayer space of the clay minerals potentially contains up to ~2 wt% water and does not host trapped organic species. The abundance of interlayer water in Bennu samples is notably higher than reported for Ryugu samples (<0.3 wt%), which we speculate is due to differences in either the timing at which the asteroids decoupled from the Main Belt or the sampling depths and/or mechanisms of the respective spacecraft.

¹A. J. Cavosie et al.(>10)
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70163]
¹Space Science and Technology Centre, School of Earth and Planetary Science, Curtin University, Perth, Western Australia, Australia
Publishesd by arrangement with John Wiley & Sons

The framework of the Impact Cratering Committee (ICC) of the Meteoritical Society was approved in 2020, with the first committee members appointed in 2023. The ICC has a mandate to (1) approve, maintain, and update a database of confirmed terrestrial meteorite impact structures, (2) define and regularly update the criteria used for identification of impact structures and their related deposits, and (3) evaluate new candidate sites for inclusion in the ICC database. Prior to certifying a list of confirmed impact structures, the ICC has compiled a list of all impact-diagnostic criteria that are currently considered as representing irrefutable or “gold standard” evidence that can be used independently to confirm whether or not a terrestrial geological structure has an impact origin. The ICC currently recognizes three categories of “gold standard” impact-diagnostic evidence: (1) Shock metamorphic features within rocks or minerals that on Earth have only been reported to occur in impactites, and whose formation conditions (high P–T) have been demonstrated through experiments to only form at conditions created during hypervelocity impacts; (2) meteorites that are spatially and chronologically associated with a site suspected of being an impact structure; and (3) geochemical elemental or isotopic detection of an extraterrestrial signature in melt rocks or breccias associated with a site suspected of being an impact structure. Other mineral and rock features have been reported from impact structures that are important to document, but they do not represent irrefutable or unambiguous evidence of impact. For this reason, we present two lists: The first list describes each impact-diagnostic criterion and provides recommendations for reporting protocols. The second list describes other features commonly reported from impact settings and the rationale for why these are not currently considered by the ICC to represent impact-diagnostic evidence. The ICC will provide a list of confirmed terrestrial impact structures in a subsequent publication and online. Updates to the list based on new discoveries and/or new understanding of impact-diagnostic criteria will be published online by the ICC.