^1,2M. Germanà et al (>10)
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70190]
¹Dipartimento di Fisica e Astronomia, Universita degli Studi di Catania, Catania, Italy
²INAF-Osservatorio Astrofisico di Catania, Catania, Italy
Published by arrangement with John Wiley and Sons

Amorphous carbon (αC) is found in various extraterrestrial particles, including those thought to originate from the outer Solar System. αC can form through two main processes involving C-rich materials: exposure to energetic charged particles and thermal processing. Laboratory analyses can constrain the origin of αC in space, as it is not easily detectable through remote sensing. We here investigate the formation of αC on the icy surface of Trans-neptunian objects and Oort cloud comets throughout their exposure to energetic ions. We use organic refractory residues (ORRs), which are laboratory simulants of refractory organics in space, obtained from the irradiation (200 keV ions) of various icy mixtures (N2, CO, CH4, CH3OH). As formed ORRs were further irradiated at room temperature (αC-ORRs) and analyzed by Raman spectroscopy. Our as formed ORRs do not exhibit αC that is in turn detected in αC-ORRs. The carbonaceous structure of αC-ORRs shows high disorder and dependence on the initial icy composition. Nitrogen-bearing αC-ORRs exhibit structural properties similar to some extraterrestrial particles likely originating from icy outer bodies, whereas annealed αC-ORRs mimic materials that underwent different degrees of metamorphism. Our findings highlight how Raman characterization of αC in extraterrestrial samples serves as a strong analysis tool in providing insights into the evolution of different Solar System objects.

¹Aelita Girich,¹Addi Bischoff,¹Samuel Ebert,²Kazuhide Nagashima,¹Andreas Morlok,¹Harald Hiesinger,³Jasper Berndt
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70195]
¹Institut f€ur Planetologie, University of Münster, Münster, Germany
²University of Hawaii at Manoa, Honolulu, Hawaii, USA
³Institut f€ur Mineralogie, University of Münster, Münster, Germany
Published by arrangement with John Wiley & Sons

An unusual chondritic xenolith was found in two sequentially prepared thin sections of a sample from the Krymka (LL3.2) chondrite. The xenolith has a rounded, slightly deformed shape of about 5 mm in apparent diameter and is partially surrounded by a double rim made of an inner fine-grained silicate-rich rim and an outer sulfide-rich rim. The xenolithic inclusion is characterized by partially equilibrated mineral constituents, a recrystallized chondritic texture with relic chondrules, and a high abundance of CAIs (0.11 vol%). Within the core of the xenolith, olivine and low-Ca pyroxene are the most abundant mineral phases, and randomly analyzed grains by grid analysis revealed mean compositions of Fa9.8±5.5 and Fs7.2±4.4Wo2.9±2.2 for olivine and low-Ca pyroxene, respectively. Within the entire clast, a feldspar-normative mesostasis is embedding all constituents, indicating partial melting of the xenolith, probably during impact metamorphism. Thus, the xenolithic clast is very likely an impact melt rock. Infrared (IR) spectroscopic studies revealed the dominance of olivine and low-Ca pyroxene in the obtained spectra from the fine-grained silicate-rich rim of the xenolith. Oxygen isotope analyses by SIMS show that, in the three-oxygen isotope diagram, most individual olivine grains from the xenolith plot within the field of bulk ordinary chondrites and their chondrules, except for three olivines: Two grains from the xenolith’s core (Δ17O = −1.6 ± 0.5‰ and −2.4 ± 0.5‰) and one olivine from the rim (Δ17O = −6.5 ± 0.4‰) show significant 16O enrichments. The chondritic impact melt rock studied here clearly demonstrates that this xenolithic clast formed prior to the Krymka parent body accretion within another pre-existing chondritic parent body. While previous studies have discussed a potential late-stage accretion of large Krymka constituents, the components within the apparent first-generation parent body experienced thermal annealing, and, subsequently, the xenolith suffered partial melting due to a shock event that probably caused this fragment to be ejected from its first-generation parent body.