Top: schematic simulation setup for studying the track of a sulfur ion at 20 MeV. Only a section of the track in the vicinity of the surface is simulated. The energy deposited by the swift ion is given to the atoms as local temperature increase (purple region). Insets show several of the most abundant ions and molecules originally present in the ice mixture – H₂O, O₂, Na, Cl, SO₄, SO₂ and H₂ S – according to Table 1. Bottom: snapshot of the expanding track volume at a time of 0.5 ps after track formation. The width of the snapshot corresponds to 202 Å. The color represents the local temperature varying between cyan (101 K, corresponding to the surface temperature of Europa) and purple (>373 K).