(a): Density profile of the O₂ exospheric species on Europa, in the Sun-subsolar point direction, as estimated with the EGEON model (Plainaki et al. 2012, 2013), accounting for the release-yield revisions (see Milillo et al. 2015; Plainaki et al. 2015). Different configurations correspond to different orbital phases hence to different orientations between plasma impact direction and illumination. (b) Ion density profiles at Europa. The dominant component, O₂⁺, the H₂⁺ population, water group ions (e.g. O⁺, OH⁺ and H₂O⁺) and the Na⁺, SO₂⁺ and CO₂⁺ trace species are considered. The flow speed (black line) of the plasma as it is mass loaded and eventually stops below the altitude of ~40 km (ionopause), is also shown (right ordinate axis). From Sittler et al. (2013).