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HST/ACS Observations of Europa's Atmospheric UV Emission at Eastern Elongation | Joachim Saur
; Paul D. Feldman
; Lorenz Roth
; Francis Nimmo
; Darrell F. Strobel
; Kurt D. Retherford
; Melissa A. McGrath
; Nico Schilling
; Jean-Claude Gérard
; Denis Grodent
; | Date: |
7 Jun 2011 | Abstract: | 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 ion{O}{1} 1304 A and ion{O}{1} 1356 A
emissions using the prism PR130L. The total emissions of both oxygen multiplets
range between 132 $pm$ 14 and 226 $pm$ 14 Rayleigh. An additional systematic
error with values on the same order as the statistical errors may be due to
uncertainties in modelling 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$_2$
column density of 6 $ imes$ 10$^{18}$ m$^{-2}$. Previous observations of
Europa’s atmosphere with STIS 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 vs 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 degree 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, inhomogeneous solar illuminations, and/or by
Europa’s complex plasma interaction with Jupiter’s magnetosphere. | Source: | arXiv, 1106.1409 | Services: | Forum | Review | PDF | Favorites |
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