Cosmic ion bombardment of the icy moons of Jupiter

Abstract

A large number of experiments have been performed in many laboratories in the world with the aim to investigate the physico-chemical effects induced by fast ions irradiating astrophysical relevant materials. The laboratory in Catania (Italy) has given a contribution to some experimental works. In this paper I review the results of two class of experiments performed by the Catania group, namely implantation of reactive (H +, C +, N +, O + and S +) ions in ices and the ion irradiation induced synthesis of molecules at the interface between water ice and carbonaceous or sulfurous solid materials. The results, discussed in the light of some questions concerning the surfaces of the Galilean moons, contribute to understand whether minor molecular species (CO 2, SO 2, H 2SO 4, etc.) observed on those objects are endogenic i.e. native from the satellite or are produced by exogenic processes, such as ion implantation. The results indicate that: – C-ion implantation is not the dominant formation mechanism of CO 2 on Europa, Ganimede and Callisto. – Implantation of sulfur ions into water ice produces hydrated sulfuric acid with high efficiency such to give a very important contribution to the sulfur cycle on the surface of Europa and other satellites. – Implantation of protons into carbon dioxide produces some species containing the projectile (H 2CO 3, and O–H in poly-water). – Implantation of protons into sulfur dioxide produces SO 3, polymers, and O 3 but not H–S bonds. – Water ice has been deposited on refractory carbonaceous materials: a general finding is the formation of a noteworthy quantity of CO 2. We suggest that this is the primary mechanism to explain the presence of carbon dioxide on the surfaces of the Galilean satellites. – Water ice has been deposited on refractory sulfurous materials originating from SO 2 or H 2S irradiation. No evidence for an efficient synthesis of SO 2 has been found.