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Poster (Scientific congresses and symposiums)
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.; Nichols, J. D.; Bannister, N. P. et al.
2015Magnetospheres of the Outer Planets 2015
 

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Keywords :
Ganymede; HST; atmosphere; LiSRI
Abstract :
[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.
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
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, Stanley W.H.;  University of Leicester
Grodent, Denis  ;  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
Language :
English
Title :
Hubble Space Telescope observations of variation of the O I 135.6 nm/ O I 130.4 nm ratio in Ganymede’s atmosphere
Publication date :
June 2015
Event name :
Magnetospheres of the Outer Planets 2015
Event organizer :
Georgia Tech
Event place :
Atlanta, Georgia, United States
Event date :
1-6 juin 2015
Audience :
International
Additional URL :
Available on ORBi :
since 18 June 2015

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