Reference : Hubble Space Telescope observations of variation of the O I 135.6 nm/ O I 130.4 nm ra...
Scientific congresses and symposiums : Poster
Physical, chemical, mathematical & earth Sciences : Space science, astronomy & astrophysics
Hubble Space Telescope observations of variation of the O I 135.6 nm/ O I 130.4 nm ratio in Ganymede’s atmosphere
Molyneux, P. M. [University of Leicester > > > >]
Nichols, J. D. [University of Leicester > > > >]
Bannister, N. P. [University of Leicester > > > >]
Bunce, E. J. [University of Leicester > > > >]
Clarke, J. T. [Boston University > > > >]
Cowley, S. W. [University of Leicester > > > >]
Grodent, Denis mailto [Université de Liège > Département d'astrophys., géophysique et océanographie (AGO) > Labo de physique atmosphérique et planétaire (LPAP) >]
Milan, S. E. [University of Leicester > > > >]
Paty, C. [Georgia Institute of Technology > > > >]
Magnetospheres of the Outer Planets 2015
1-6 juin 2015
Georgia Tech
Atlanta, Georgia
[en] Ganymede ; HST ; atmosphere ; LiSRI
[en] We present new high-sensitivity HST/COS measurements of the atmospheric O I 135.6 nm/ O I 130.4 nm ratio at Ganymede, which we show exhibits significant spatial and temporal variability. Specifically, the ratios observed on Ganymede’s leading hemispheres vary between 2.14±0.03 and 2.67±0.02, while on the trailing hemisphere the ratios are observed to be between 0.98±0.02 and 1.53±0.03. These high-sensitivity observations increase the signal to noise of these measurements by an order of magnitude over previous HST/STIS observations of the same [1], thus confirming that the temporal variation suggested by these previous observations is real. The emissions are excited through electron-impact excitation of Ganymede’s oxygen atmosphere by electrons which are locally accelerated within its magnetosphere [2,3]. The variation in the ratio magnitude may be explained either by variations in the ratio of atomic to molecular oxygen in the atmosphere or by a change in the temperature of the electrons exciting the emissions. An increase in the proportion of molecular oxygen acts to increase the ratio, as does a cooler electron temperature.References
[1] Feldman, P. D., McGrath, M. A., Strobel, D. F., Moos, H. W., Retherford, K. D. and Wolven, B. C., HST/STIS ultraviolet imaging of polar aurora on Ganymede, Astrophys. J., Vol. 535, pp. 1085-1090, 2000.
[2] Hall, D. T., Feldman, P. D., McGrath, M. A. and Strobel, D. F., The far-ultraviolet oxygen airglow of Europa and Ganymede, Astrophys. J., Vol. 499, pp. 475-481, 1998.
[3] Eviatar, A., Strobel, D. F., Wolven, B. C., Feldman, P. D., McGrath, M. A. and Williams, D. J., Excitation of the Ganymede ultraviolet aurora, Astrophys. J., Vol. 555, pp. 1013-1019, 2001.
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