Analogues of enigmatic L-types: The effect of space weathering on CV, CO, CK, and CL chondrites

L-type asteroids are rare asteroids located throughout the Main Belt. They are unique among the minor bodies as their spectral appearance in the visible-near-infrared (VisNIR) is thought to be dominated by calciumaluminium-rich inclusions (CAIs): agglomerates of minerals found in chondritic meteorites that contain the first solids that condensed in the solar nebula 1, 2. A primary mineral phase in CAI is the aluminium oxide spinel (MgAl2O4), which presents an absorption feature at 2m when enriched in iron due to thermal metamorphism. This absorption feature is observed in L-types, suggesting an enrichment of refractory inclusions in these bodies 3. Therefore, the parent bodies of L-types might have formed at an early time and within a region of the protoplanetary nebula with a high concentration of CAI. If this is the case, the significance of L-type asteroids as tracers of planetary compositional and dynamical evolution cannot be overstated. The key question is: How rich in refractory inclusions are L-type asteroids?Sunshine et al. (2008) concluded that some L-types contain between 22%-39% of FeO-rich CAI 4, an order of magnitude larger than what has been observed in the meteorite collection (1mm in diameter) CAI rich in iron-bearing spinel in a section of CV Allende via scanning-electron microscopy, analogous to the inclusion expected on the asteroidal surfaces. For all samples (chondrites and CAI), we have concluded a dense spectral characterisation over a large wavelength range (VisNIR as described above and mid-infrared spectra at Synchrotron SOLEIL, Saint-Aubin), which is to be followed-up by ion irradiation using the INGMAR experiment (IAS ICJLab, Orsay) to simulate space weathering by the solar wind 12. We aim to acquire VisNIR spectra during the irradiation process at different dosages of ion implementation, capturing different degrees of space weathering. After irradiation, we aim to repeat the spectral characterisation executed before to capture and quantify spectral changes relevant for the interpretation of asteroidal spectral, including the common VisNIR range but also the mid-infrared range, now more accessible to remote-sensing observations than previously thanks to NASA JWST (e.g. 13).The irradiation and post-irradiation characterisation are scheduled to be concluded by July 2024. We will present first results of the irradiation experiments and further on-going efforts to describe the response of the samples to irradiation and phase-angle variations, crucial for the interpretation of remote-sensing observations of asteroids. Ultimately, the results obtained in this study will guide us in further constraining the nature of L-type asteroids by determining the closest analogue material within the meteorite collection and by aiding the interpretation of new spectra of L-type asteroids acquired in an on-going observational campaign with ESO's VLT/X-SHOOTER as part of this project.1 The Loongana (CL) group is a recent addition to the taxonomy of chondrites 9.References:1 Amelin, Y., et al. (2002), Science, 297, 16782 Piralla, M., et al. (2023), Icarus, 394, 1154273 Burbine, T. H., et al. (1991), BAAS, 23, 11424 Sunshine, J. M., et al. (2008), Science, 320, 5145 Scott, E. R. D. A. N. Krot (2014), In Meteor. and Cosmoch. Proc., 1, 656 Devogle, M., et al. (2018), Icarus, 304, 317 Mahlke, M., et al. (2023), AA, 676, A948 Lantz, C., et al. (2017), Icarus, 285, 43-579 Metzler, K., et al. (2021), GCA, 304, 1-3110 Potin, S., et al. (2018), Applied Optics, 57:8279, 201811 Beck, P., et al. (2021), Icarus, 354, 11406612 Brunetto, R., et al., (2014), Icarus, 237:278-292, 7 201413 De Kleer, K., et al. (2024), LPSC Abstract, 3040Acknowledgements: This work was supported by the Programme National dePlantologie (PNP) of CNRS-INSU co-funded by CNES.