¹Elin M. Morton,^1,4Harvey Pickard,²Frank Wombacher,¹Yihang Huang,³Emeliana Palk,¹Rayssa Martins,⁵Sven Kuthning,⁶Maria Schönbächler,¹Mark Rehkämper
The Astrophysical Journal 977, 53 Open Access Link to Article [DOI 10.3847/1538-4357/ad87ed]
¹Department of Earth Science & Engineering, Imperial College London, London SW7 2AZ, UK
²Institut für Geologie und Mineralogie, Universität zu Köln, Zülpicher Str. 49b, 50674 Köln, Germany
³School of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK
⁴National Environmental Isotope Facility, British Geological Survey, Keyworth, Nottingham, NG12 5GG, UK
⁵Geologischer Dienst NRW—Landesbetrieb, De-Greiff-Straße 195, 47803 Krefeld, Germany
⁶Department of Earth Sciences, ETH Zürich, Clausiusstrasse 25, 8092 Zürich, Switzerland

The origin of volatile depletion in the solar system remains a topic of intense debate. To further inform our understanding of the mechanisms involved, this study characterized the mass-dependent Zn, Cd, and Te isotope compositions and concentrations of a comprehensive suite of carbonaceous chondrites (CCs). In accord with previous studies, Zn and Te display covariations between light isotope enrichments and elemental depletions. Observed here for the first time, Cd shows a similar trend. These correlations are consistent with the interpretation that the primary volatile element budgets of CCs were established by mixing of a volatile-rich CI-like matrix and a volatile-depleted non-matrix endmember (NME) in the solar nebula. All three elements display minor isotopic variations in CI and CM chondrites, as a consequence of aqueous alteration at low temperatures. In contrast, Cd and Te isotope compositions and concentrations are highly variable in CV and CO (Cd) and CK chondrites (Te). This reflects mobilization of the elements during thermal metamorphism at distinct redox conditions. The data of this study show that the NME has Zn, Cd, and Te concentrations that are depleted to an identical level of 0.12 ± 0.03 × CI chondrites, and it is characterized by mass-dependent isotope compositions for all three elements that are fractionated to light isotope values relative to CIs by a similar extent. In conjunction with literature data, this suggests that the concentrations and isotope compositions of NME volatiles record the same depletion processes, and that the NME volatile inventory is likely hosted predominantly in chondrules.

¹Lauren E. McGraw,¹Cristina A. Thomas,²Tim A. Lister,³Becky J. Williams,⁴Andy S. Rivkin,⁵Bryan Holler,⁶Leslie A. Young
The Astrophysical Journal 977, L25 Open Access Link to Article [DOI 10.3847/2041-8213/ad9728]
¹Northern Arizona University, Flagstaff, AZ 86011, USA
²Las Cumbres Observatory, Goleta, CA 93117, USA
³University of Virginia, Charlottesville, VA 22904, USA
⁴JHU/APL, Laurel, MD 20146, USA
⁵Space Telescope Science Institute, Baltimore, MD 21218, USA
⁶Southwest Research Institute, Boulder, CO 80302, USA

Near-Earth object 2024 MK was discovered on 2024 June 16, less than 2 weeks before it made a sub-lunar-distance close approach. This close approach provided an ideal opportunity to determine how planetary encounters affect asteroid surfaces in preparation for the numerous missions to (99942) Apophis during its close approach in 2029. We collected spectroscopic data before and after its close approach to determine if planetary encounters induce spectral changes due to surface refreshing. We used NASA’s Infrared Telescope Facility’s (IRTF) near-infrared spectrometer SpeX prism mode (0.7–2.5 μm) to observe 2024 MK pre and postapproach. We also observed the asteroid before its close approach using Las Cumbres Observatory’s FLOYDS visible spectrometer and after its close approach using IRTF’s SpeX long-wavelength cross-dispersed short grating mode, resulting in full spectral coverage from 0.32 to 4.2 μm. 2024 MK is an S-type asteroid that is compositionally most analogous to an L-ordinary chondrite. Spectral analysis of the 3 μm region indicates no surficial water or hydroxide within the level of noise. Band parameter analysis of the pre and postapproach data shows the planetary encounter did not induce any significant spectral changes, suggesting that surface refreshing did not occur on a measurable scale. Similar studies of other targets at smaller encounter distances are required to determine if the lack of spectral changes on 2024 MK indicates it was not close enough to Earth to affect its surface or if the spectral similarity pre and postapproach instead indicates planetary encounters do not cause surface refreshing.