Ozone production by electron irradiation of regolith ice

Due to the lack of a dense atmosphere, the icy moons of Jupiter are directly exposed to a harsh radiation environment. Precipitating energetic particles contribute to the formation of the thin atmospheres of the moons and process the upper layer of their surfaces[1]. Radiolytically produced molecules can remain trapped in the ice. In particular, molecular oxygen and ozone have been observed in the surfaces of Ganymede[2] and other icy moons. We conducted laboratory experiments irradiating regolith pure water ice samples with electrons, simulating the processing of the icy moons’ surfaces. The ice regolith[3] was produced to closely emulate the physical properties expected on the surface of the Galilean icy moons, in terms of grain size (~67 μm) and temperature (90±5 K). Using a time-of-flight mass spectrometer similar to the Neutral and Ion Mass Spectrometer on board Jupiter Icy Moons Explorer, we analysed the species radiolytically produced and sputtered from the ice.We observed that ozone is produced in the ice regolith during 10 keV irradiations. Part of the produced ozone is stored in the ice. We give an estimate of the production of O3, with respect to the radiolytically produced O2. Preliminary results appear to show that ozone production depends on the grain size of the regolith ice.[1] Vorburger, Audrey, and Peter Wurz. "Europa’s ice-related atmosphere: the sputter contribution." Icarus 311 (2018): 135-145.[2] Noll, Keith S., et al. "Detection of ozone on Ganymede." Science 273.5273 (1996): 341-343.[3] Pommerol, Antoine, et al. "Experimenting with mixtures of water ice and dust as analogues for icy planetary material: recipes from the ice laboratory at the University of Bern." Space science reviews 215 (2019): 1-68.