Lorenz Roth^1,2,*,†, Joachim Saur^2,†, Kurt D. Retherford¹, Darrell F. Strobel^3,4, Paul D. Feldman⁴, Melissa A. McGrath⁵, Francis Nimmo⁶

¹Southwest Research Institute, San Antonio, TX, USA.
²Institute of Geophysics and Meteorology, University of Cologne, Germany.
³Department of Earth and Planetary Science, The Johns Hopkins University, Baltimore, MD, USA.
⁴Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD, USA.
⁵NASA Marshall Space Flight Center, Huntsville, AL, USA.
^† These authors contributed equally to this work.

In November and December 2012, the Hubble Space Telescope (HST) imaged Europa’s ultraviolet emissions in the search for vapor plume activity. We report statistically significant coincident surpluses of hydrogen Lyman-α and oxygen OI 130.4-nanometer emissions above the southern hemisphere in December 2012. These emissions were persistently found in the same area over the 7 hours of the observation, suggesting atmospheric inhomogeneity; they are consistent with two 200-km-high plumes of water vapor with line-of-sight column densities of about 1020 per square meter. Nondetection in November 2012 and in previous HST images from 1999 suggests varying plume activity that might depend on changing surface stresses based on Europa’s orbital phases. The plume was present when Europa was near apocenter and was not detected close to its pericenter, in agreement with tidal modeling predictions.

Reference
Roth L, Joachim Saur J, Retherford KD, Strobel DF, Feldman PD, McGrath MA and Nimmo F (2014) Transient Water Vapor at Europa’s South Pole. Science 343:171-174.
[doi:10.1126/science.1247051]
Reprinted with permission from AAAS

Link to Article