Following up on the Discovery of Water Vapor at Europa’s South Pole with HST

Friday, 19 December 2014: 11:20 AM
Lorenz Roth1,2, Kurt D Retherford1, Joachim Saur3, Darrell F Strobel4, Paul D Feldman4, Melissa A McGrath5, Francis Nimmo6, John R Spencer7, Cesare Grava1 and Aljona Bloecker3, (1)Southwest Research Institute San Antonio, San Antonio, TX, United States, (2)KTH Royal Institute of Technology, EES, Stockholm, Sweden, (3)University of Cologne, Cologne, Germany, (4)Johns Hopkins University, Baltimore, MD, United States, (5)NASA Marshall Space Flight Center, Huntsville, AL, United States, (6)University of California-Santa Cruz, Department of Earth and Planetary Sciences, Santa Cruz, CA, United States, (7)Southwest Research Institute, Boulder, CO, United States
We will present new Hubble Space Telescope (HST) observations of Europa’s UV aurora obtained within two campaigns in 2014 to follow up on the water vapor plume detection.

HST aurora images taken in 2012 have revealed coincident signals from atomic hydrogen and oxygen pointing to the existence of transient water vapor plumes near the south pole. The water vapor was detected only during one HST visit in December 2012 when Europa was near apocenter position and was speculated to be correlated with changing tidal stresses along Europa’s orbit. In a first follow-up campaign new aurora images were taken by HST early in 2014 with Europa near apocenter, but the initial detection was not confirmed. More HST aurora images will be obtained in the course of a larger Hubble observing campaign starting in November 2014. We will review all HST aurora imaging observations to date and discuss potential sources for varying plume activity and changing detectability by HST. In particular, we will examine various explanations for the non-detections in the early 2014 observations near apocenter.