Processing of 72-K water-rich ices by keV and MeV oxygen ions: implications for the Saturnian moon Enceladus. Issue 2 (21st April 2020)

• Record Type: Journal Article
• Authors: Rachid, M G; Pilling, S; Rocha, W R M; Agnihotri, A; Rothard, H; Boduch, P
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 494:Issue 2(2020)
• Page Start: 2396
• Page End: 2409
• Publication Date: 2020-04-21
• Subjects: astrochemistry -- methods: laboratory: molecular -- methods: laboratory: solid state -- techniques: spectroscopic; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/staa778
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: The processing of H2 O:CO2 :CH4 (10:1:1) and H2 O:CO2 :CH4 :NH3 (10:1:1:1) ices at 72 K by oxygen ions was studied in an attempt to simulate the physicochemical effects induced by energetic ions on the surface of Enceladus (or similar cold surfaces in the outer Solar System). The experiments were carried out at the Grand Accélérateur National d'Ions Lourds (GANIL) in Caen/France. The samples were irradiated with 15.7-MeV O 5+ at the IRRadiation SUD (IRRSUD) beamline and with 108-keV O 6+ at the Accélérateurs pour les Recherches avec les Ions de Basses Energies (ARIBE) beamline. The frozen samples were monitored by Fourier Transform Infrared Spectroscopy (FTIR) spectroscopy (4000–650 cm −1, 2.5–15.4 μm, at 1 cm −1 resolution). The identified molecular species formed during irradiation were CO, OCN −, CH3 OH, HCN, CN −, H2 CO3, HNCO, HCO and CO3 . The effective formation cross-sections for the synthesis of new species and the effective molecular destruction cross-sections of the parent species in the experiments with MeV ions were found to be of the order of 10 −14 –10 −13 cm 2 . For the keV ion experiments, these values were of the order of 10 −16 –10 −15 cm 2 . The fluence at which the sample reaches chemical equilibrium and the molecular abundances in this region (equilibrium branching ratios) were estimated. These experiments suggest that the chemical inventory on the surface of Enceladus can be influenced by the incidence of charged particles on to the moon's surface.