TY - JOUR
T1 - An assessment and test of Enceladus as an important source of Saturn's ring atmosphere and ionosphere
AU - Tseng, Wei Ling
AU - Ip, Wing Huen
N1 - Funding Information:
We thank Prof. R.E. Johnson and his student, M.K. Elrod for useful discussions. This work is supported by a grant from NASA’s Planetary Atmosphere’s Program and by a NASA Cassini Data Analysis Grant . This is also partially supported by Taiwan NSC 97-2111-M-008-018-MY3 and NSC 97-2112-M-008-018-MY3 .
PY - 2011/3
Y1 - 2011/3
N2 - The existence of an oxygen exosphere and ionosphere in Saturn's main ring region has been confirmed by the Saturn Orbital Insertion (SOI) observations of the Cassini spacecraft. Through the ion-molecule collisions, the ring atmosphere could serve as a source of O2+ ions throughout Saturn's magnetosphere. If photolysis of ice in the main rings is the dominant source of O2, then the complex structure of the ring atmosphere/ionosphere and the injection rate of neutral O2 will be subject to modulation by the seasonal variation of Saturn along its orbit (Tseng, Wei-Ling, Ip, W.-H., Johnson, R.E., Cassidy, T.A., Erlod, M.K. [2010]. Icarus 206, 382-389). In addition, the radio and plasma wave science (RPWS) instrument onboard Cassini found that a large amount of the Enceladus-originated water-group plasma would be deposited on the outer edge of the A ring (Farrell, W.M., Kaiser, M.L., Gurnett, D.A., Kurth, W.S., Persoon, A.M., Wahlund, J.E., Canu, P. [2008]. Geophys. Res. Lett. 35, L02203). A large amount of Enceladus' plume neutrals (water-group neutrals) would collide with the main rings through collisional interaction with the ambient neutrals and plasma ions (Jurac, S., Richardson, J.D. [2007]. Geophys. Res. Lett. 34, L08102; Cassidy, T.A., Johnson, R.E. [2010]. Icarus, in press). These absorbed ions and neutrals could be recycled to neutral oxygen molecules via grain-surface chemistry to contribute the ring oxygen atmosphere. In this work, we have examined the mass budget of the ring oxygen atmosphere of Saturn taking into account such an " exogenic" source. The maximum O2 source rate from recycling of Enceladus-originated plasma and neutrals is probably comparable or higher to the one from photolytic decomposition of ices. In the above case, the neutral O2 source rate would be independent of the solar insolation angle. Therefore, even at Saturn's Equinox, the extended oxygen atmosphere still could be an important supplier of oxygen ions in the saturnian magnetosphere. We have performed several studies for different recycling source rates from Enceladus. These predictions need further the Cassini Plasma Spectrometer (CAPS) and the Magnetospheric Imaging Instrument (MIMI) observations to be verified in future.
AB - The existence of an oxygen exosphere and ionosphere in Saturn's main ring region has been confirmed by the Saturn Orbital Insertion (SOI) observations of the Cassini spacecraft. Through the ion-molecule collisions, the ring atmosphere could serve as a source of O2+ ions throughout Saturn's magnetosphere. If photolysis of ice in the main rings is the dominant source of O2, then the complex structure of the ring atmosphere/ionosphere and the injection rate of neutral O2 will be subject to modulation by the seasonal variation of Saturn along its orbit (Tseng, Wei-Ling, Ip, W.-H., Johnson, R.E., Cassidy, T.A., Erlod, M.K. [2010]. Icarus 206, 382-389). In addition, the radio and plasma wave science (RPWS) instrument onboard Cassini found that a large amount of the Enceladus-originated water-group plasma would be deposited on the outer edge of the A ring (Farrell, W.M., Kaiser, M.L., Gurnett, D.A., Kurth, W.S., Persoon, A.M., Wahlund, J.E., Canu, P. [2008]. Geophys. Res. Lett. 35, L02203). A large amount of Enceladus' plume neutrals (water-group neutrals) would collide with the main rings through collisional interaction with the ambient neutrals and plasma ions (Jurac, S., Richardson, J.D. [2007]. Geophys. Res. Lett. 34, L08102; Cassidy, T.A., Johnson, R.E. [2010]. Icarus, in press). These absorbed ions and neutrals could be recycled to neutral oxygen molecules via grain-surface chemistry to contribute the ring oxygen atmosphere. In this work, we have examined the mass budget of the ring oxygen atmosphere of Saturn taking into account such an " exogenic" source. The maximum O2 source rate from recycling of Enceladus-originated plasma and neutrals is probably comparable or higher to the one from photolytic decomposition of ices. In the above case, the neutral O2 source rate would be independent of the solar insolation angle. Therefore, even at Saturn's Equinox, the extended oxygen atmosphere still could be an important supplier of oxygen ions in the saturnian magnetosphere. We have performed several studies for different recycling source rates from Enceladus. These predictions need further the Cassini Plasma Spectrometer (CAPS) and the Magnetospheric Imaging Instrument (MIMI) observations to be verified in future.
KW - Enceladus
KW - Magnetospheres
KW - Rings
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U2 - 10.1016/j.icarus.2010.12.003
DO - 10.1016/j.icarus.2010.12.003
M3 - Article
AN - SCOPUS:79952008442
SN - 0019-1035
VL - 212
SP - 294
EP - 299
JO - Icarus
JF - Icarus
IS - 1
ER -