Jupiter’s moon Europa might harbor life in its vast water ocean below the thick ice crust. This deep subsurface habitat could potentially be investigated at locations of active outgassing, giving the question whether Europa is geologically active a crucial importance. Evidence for present-day activity yet remained elusive for decades.

In 2012, Hubble Space Telescope observations revealed localized hydrogen and oxygen emissions, refueling the idea that Europa is actively outgassing water vapor. Following this detection several studies derived the existence of water vapor plumes on various locations. These studies used a variety of methods from remote-sensing telescope observations (HST, Keck) to in-situ spacecraft magnetic field and plasma measurements. However, the final proof for the existence of active water plumes is still missing. I will review the different studies claiming evidence and explain why we still do not understand Europa’s plume activity.