HUBBLE SPACE TELESCOPE/ADVANCED CAMERA FOR SURVEYS OBSERVATIONS OF EUROPA'S ATMOSPHERIC ULTRAVIOLET EMISSION AT EASTERN ELONGATION
- Institute of Geophysics and Meteorology, University of Cologne, Cologne (Germany)
- Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD (United States)
- Department of Earth and Planetary Sciences, University of California, Santa Cruz, CA (United States)
- Southwest Research Institute, San Antonio, TX (United States)
- NASA Marshall Space Flight Center, Huntsville, AL (United States)
- Laboratory for Planetary and Atmospheric Physics, University of Liege, Liege (Belgium)
We report results of a Hubble Space Telescope (HST) campaign with the Advanced Camera for Surveys to observe Europa at eastern elongation, i.e., Europa's leading side, on 2008 June 29. With five consecutive HST orbits, we constrain Europa's atmospheric O I 1304 A and O I 1356 A emissions using the prism PR130L. The total emissions of both oxygen multiplets range between 132 {+-} 14 and 226 {+-} 14 Rayleigh. An additional systematic error with values on the same order as the statistical errors may be due to uncertainties in modeling the reflected light from Europa's surface. The total emission also shows a clear dependence of Europa's position with respect to Jupiter's magnetospheric plasma sheet. We derive a lower limit for the O{sub 2} column density of 6 x 10{sup 18} m{sup -2}. Previous observations of Europa's atmosphere with the Space Telescope Imaging Spectrograph in 1999 of Europa's trailing side show an enigmatic surplus of radiation on the anti-Jovian side within the disk of Europa. With emission from a radially symmetric atmosphere as a reference, we searched for an anti-Jovian versus sub-Jovian asymmetry with respect to the central meridian on the leading side and found none. Likewise, we searched for departures from a radially symmetric atmospheric emission and found an emission surplus centered around 90 deg. west longitude, for which plausible mechanisms exist. Previous work about the possibility of plumes on Europa due to tidally driven shear heating found longitudes with strongest local strain rates which might be consistent with the longitudes of maximum UV emissions. Alternatively, asymmetries in Europa's UV emission can also be caused by inhomogeneous surface properties, an optically thick atmospheric contribution of atomic oxygen, and/or by Europa's complex plasma interaction with Jupiter's magnetosphere.
- OSTI ID:
- 21584864
- Journal Information:
- Astrophysical Journal, Vol. 738, Issue 2; Other Information: DOI: 10.1088/0004-637X/738/2/153; Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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