Ultraviolet observation of Enceladus' plume in transit across Saturn, compared to Europa

Abstract Saturn's moon Enceladus is known to have a water vapor plume erupting from fissures across its south polar region. The plume was detectable in an observation of Enceladus transiting Saturn by Cassini's Ultraviolet Imaging Spectrograph (UVIS), but only at 1216 A (Lyman alpha). Jupiter's moon Europa also may have multiple water vapor plumes, detected via similar ultraviolet observations of Europa transiting Jupiter (after being discovered via emission features) by Hubble Space Telescope. Comparison of the UVIS Enceladus transit observation to published Europa transit results reveals that Europa's plumes have very different properties than Enceladus' plume using the same observational technique. For example, the mass of water expelled is two orders of magnitude less at Enceladus compared to Europa.