Hubble Space Telescope discovery of water vapor at Jupiter’s moon Europa

With its subsurface water ocean and relatively young icy surface Europa is among the top candidates in the search for habitable environments in our Solar System. Existence of water vapor plumes on Europa has long been speculated and might provide accessibility of the potentially habitable subsurface liquid reservoirs.  Images of auroral emissions obtained in December 2012 by the Hubble Space Telescope (HST) revealed coincident signals from hydrogen and oxygen pointing to the existence of transient water vapor near the moon’s south pole. The water vapor was proposed to originate from plume activity correlated with Europa’s orbital position through tidal stress variations. Follow-up observations taken in 2014 with Europa at the same orbital positions could not confirm the initial detection. Europa’s water vapor aurora is now targeted within a large HST observing campaign with 23 observations between November 2014 and May 2015 in order to understand and characterize Europa’s plume activity. If confirmed, the plumes will have a significant impact on the planning of NASA’s future mission to Europa.