Ring Shadowing Effects on Saturn's Ionosphere: Implications for Ring Opacity and Plasma Transport

Lina Hadid (1) , M. W. Morooka (1) , J.‐ E. Wahlund (1) , L. Moore (2) , T. E. Cravens (3) , M. M. Hedman (4) , N. J. T. Edberg (1) , E. Vigren (1) , J. H. Waite Jr. (5) , R. Perryman (5) , W. S. Kurth (6) , W. M. Farrell (7) , A. I. Eriksson (1)

1 IRF - Swedish Institute of Space Physics [Uppsala / Kiruna]
2 CSP - Center for Space Physics [Boston]
3 Department of Physics and Astronomy [Lawrence, Kansas]
4 University of Idaho [Moscow, USA]
5 Space Science and Engineering Division [San Antonio]
6 University of Iowa [Iowa City]
7 GSFC - NASA Goddard Space Flight Center

We present new results obtained by the Radio and Plasma Wave Science Langmuir probe on board Cassini during the Grand Finale. The total direct current sampled by the Langmuir probe at negative bias voltage is used to study the effect of the ring shadows on the structure of the Kronian topside ionosphere. The D and C rings and the Cassini Division are confirmed to be optically thin to extreme ultraviolet solar radiation. However, different responses from the opaque A and B rings are observed. The edges of the A ring shadow are shown to match the A ring boundaries, unlike the B ring, which indicates variable responses to the B ring shadow. We show that the variable responses are due to the ionospheric plasma, more precisely to the longer chemical lifetime of H+ compared to H2+ and H3+ suggesting that the plasma is transported from the sunlit region to the shadowed one in the ionosphere.

Domaines: Planétologie et astrophysique de la terre [astro-ph.EP]; Physique des plasmas [physics.plasm-ph]

Lina Hadid, M. W. Morooka, J.‐ E. Wahlund, L. Moore, T. E. Cravens, et al.. Ring Shadowing Effects on Saturn's Ionosphere: Implications for Ring Opacity and Plasma Transport. Geophysical Research Letters, 2018, 45 (19), pp.10,084-10,092. ⟨10.1029/2018GL079150⟩. ⟨hal-02640853⟩