Ion sputtering and surface erosion at Europa

New results from the energetic particle detector (EPD) experiment on the Galileo mission are used to update the ion sputtering rate at Europa. It is found that the resultant gas emission rates are 5.7×10²⁷ O₂ s^-1 and 9.5×10²⁷ H₂O s^-1 in total if the maximum self-sputtering effect of the exospheric pickup ions is taken into consideration. This means that the surface number density of O₂ molecules could be as much as 1.8×10⁹ cm^-3 and the average column density is 3.4×10¹⁵ O₂ molecules cm^-2. The corresponding ion production rate is on the order of 1.3×10²⁷ ions s^-1 probably leading to a plasma density of about 2000 ions cm^-3 in the ionospheric wake region. The magnetospheric particle bombardment effect is also effective in redistributed mass across Europa's surface. The maximum mass redistribution rate can be estimated to be ≈80 m per 100 Myrs with the associated net erosion rate ≈20 m/100 Myrs. At the same time, mass resurfacing rate by liquid water or out-gassing could reach similar magnitude.