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International audience; Silicates are ubiquitous in space. They dominate the surfaces of the inner rocky planets (Mercury in the case of the Solar System), the Moon, and asteroids, forming the major part of the non-volatile material. The physical and chemical properties of the rocky surfaces are determined not only by their initial composition but also by the processes occurring on them. Here we discuss one of these processes; irradiation by energetic cosmic particles that induces many effects among which structural changes and sputtering, the latter contributing to the formation of exospheres. In the current work we report the results of experiments conducted on anorthite, jadeite and nepheline silicates that have been irradiated with energetic heavy ions with the aim to better understand the interaction of galactic cosmic rays, solar wind, and solar energetic particles with planetary and small body surfaces. The sputtering effects induced by energetic (MeV/u) multicharged heavy ions (e.g., 105 Rh and 140 Ba) were analyzed by the PDMS-TOF-SIMS technique (plasma desorption mass spectrometry-time-of-flight secondary ion mass spectrometry). Positive and negative secondary ionic species are identified: Na + , K + , Al + , Ca + , SiO2-. Ejection of (SiO2)nand (AlSi)Omcluster series are also observed. Less frequent, negative ion yields are one order of magnitude less than positive ones, or greater, which is the case for nepheline, with 0.671 ions impact-1 for positive and 0.126 ions impact-1 for negative ions. The results concerning ejection of ionic species show, for instance, that the Na + /K + ratio is ~2.5, which is in very good agreement with that observed in the Hermean exosphere found to be ~2.3.

Cosmic rays, solar wind and solar energetic particles induce changes in the physical structure and chemical composition of frozen volatiles on the surface solar system outer objects, such as satellites of giant planets, centaurs and Kuiper-belt objects (e.g., Johnson 1990, Strazzulla et al. 2003, Urso et al. 2020). Such energetic particles can be responsible for the formation of C-rich refractory materials that determine the appearance of red slopes in the visible and near-infrared spectra of small bodies (e.g., Brunetto et al. 2006, Brown et al. 2011). Laboratory experiments performed to simulate the irradiation of frozen surfaces in space show that energetic ions or electrons (keV-MeV) determine the formation of new species, not present in the original samples (e.g., Rothard et al. 2017). The subsequent warm-up of processed mixtures causes both the sublimation of volatile compounds and an increase in the molecular diffusion and reactivity. As a consequence, the chemical complexity increases and organic refractory residues are formed. Residues are thought to be representative of the refractory materials on the surface of outer bodies as well as of cometary materials and a possible precursor of the soluble organic matter (SOM) found in meteorites (e.g., Strazzulla & Johnson 1991, Munoz-Caro & Schutte 2003, Brunetto et al. 2006, Danger et al. 2013, Baratta et al 2015, Urso et al. 2017, Poston et al. 2018}. We present recent laboratory experiments to produce and characterize organic refractory residues produced after ion irradiation of frozen volatiles. Water, methanol and ammonia mixtures in ratios 1:1:1 and 3:1:1 are deposited at 15 K and exposed to 40 keV H+ by means of the INGMAR setup (Urso et al. 2020). After irradiation, mixtures are warmed up with a constant heating rate and organic refractory residues are formed at 300 K. Throughout the experiment, we monitor the sample evolution by means of in-situ infrared transmission spectroscopy (4000-700 cm-1, 2.5-13.3 µm). After warmup, organic refractory residues are recovered from the irradiation chamber and are further characterized through ex-situ Very High Resolution Mass Spectrometry. The combination of both techniques allows to shed light on the composition of irradiated frozen volatiles and of residues. We also search for specific molecules by means of tandem Mass Spectrometry/High Resolution Mass Spectrometry. Furthermore, we compare the chemical composition of our samples with that of organic refractory residues produced after UV photolysis of volatile mixtures. Our results give information on the effects induced by different experimental parameters (dose, mixture ratio) on the composition of organic refractory materials. In particular, we investigate the effects of increasing irradiation dose in the elemental abundance and in the Double Bond Equivalent (DBE) of residues. We also give the timescales necessary to observe in solar system outer objects the effects revealed in laboratory experiments, and we discuss the role of the various sources of processing (cosmic rays, solar wind, solar energetic particles) in determining changes in the chemical composition of frozen surfaces in space. Our work supports the interpretation of space mission data and astronomical observations of comets and solar system outer objects as well as of star-forming regions in the Interstellar medium, where cosmic rays bombard icy grain mantles and thus play a role in the synthesis of complex organic molecules in the early stage of star-formation. Acknowledgements This work is supported by the CNES-France. INGMAR (IAS-CSNSM, Orsay) is funded by the French Programme National de Planétologie (PNP), Faculté des Sciences d'Orsay, Université Paris-Sud (Attractivité 2012), French National Research Agency ANR (contract ANR-11-BS56-0026, OGRESSE), P2IO LabEx (ANR-10-LABX-0038) in the framework Investissements d'Avenir (ANR-11-IDEX-0003-01). We thank the support from RAHIIA SSOM (ANR-16-CE29-0015). R.G.U. thanks the CNES postdoctoral program. References:Baratta, G. A., Chaput, D., Cottin, H., et al. 2015, Planetary and Space Science, 211 Brunetto, R., Barucci, M. A., Dotto, E., Strazzulla, G. 2006, ApJ, 644, 646 Brown, M. E. Schaller, E. L., Fraser, W. C. 2011, ApJ Letters, 739, L60 Danger, G., Orthous-Daunay, F. R., de Marcellus, P., et al. 2013, GeoCoA, 118, 184 Johnson, R. E., 1990, Energetic charged-particle interactions with atmospheres and surfaces Munoz Caro, G. M., Schutte, W. A. 2003, A&A, 412, 121 Poston, M. J., Mahjoub, A., Ehlmann, B. L., et al. 2018, ApJ, 856, 124 Rothard, H., Domaracka, A., Boduch, P. et al. 2017, Journal of Physics B, 50, 062011 Strazzulla, G., & Johnson, R. E. 1991, Irradiation Effects on Comets and Cometary Debris, Comets in the post-Halley era (Dordrecht: Springer Netherlands) Strazzulla, G., Cooper, J. F., Christina, E. R., Johnson, R. E., 2003, Comptes Rendus Physique, 4, 7, 791 Urso, R. G., Scirè, C., Baratta, G. A., et al. 2017, PCCP, 19, 21759 Urso, R. G. Baklouti, D., Djouadi, Z., Pinilla-Alonso, N., Brunetto, R. 2020, ApJ Letters, 894, 1, L3