The sputtering of radiolytic O₂ in ion irradiated H₂O-ice

Charged particle bombardment alters the physical and chemical properties of extraterrestrial icy surfaces by simultaneously producing radiolytic products and sputtered material. To better understand these phenomena, we measure the total sputtering yield of H₂O-ice induced by 0.5–5 keV Ar⁺ at temperatures between 40 and 120 K, using microbalance gravimetry as our analytical tool. In addition, we also estimate the sputtered flux of radiolytic products formed during irradiation and in both cases find good agreement with comparable laboratory studies. At 120 K, we find that the O₂/H₂O sputtered ratio increases nearly linearly with the ion range suggesting that the ions are stopping at depths where O₂ is still efficiently being produced below the surface. Furthermore, we find that although theoretical models appear to over predict our O₂ sputtering yields by about a factor of three, we can make a small adjustment to this model, which improves the agreement between the model and the laboratory data significantly. This empirical adjustment may have implications for models of energetic processing that occurs on extraterrestrial icy surfaces, such as Europa, where low-energy ions are thought to be the primary source producing O₂ from sputtering of the surface H₂O-ice.