Saturn's Innermost Radiation Belt Throughout and Inward of the D-Ring

P. Kollmann , E. Roussos , A. Kotova (1) , L. Regoli , D. G. Mitchell , J. Carbary , G. Clark , N. Krupp , C. Paranicas

1 IRAP - Institut de recherche en astrophysique et planétologie

Cassini discovered Saturn's innermost radiation belt during the end of its mission. The belt is populated with relativistic protons, probably up to the trapping limit of ≈20 GeV. It extends from Saturn's dense atmosphere into and throughout the D-ring. The A-C rings separate this belt entirely from the previously known radiation belts, suggesting that the innermost radiation belt is populated entirely via cosmic ray albedo neutron decay. We find that the proton pitch angle distributions are consistent with being shaped by losses to the D-ring and the upper atmosphere rather than, for example, wave-particle interactions. This supports that the main loss process of this new radiation belt is energy loss in neutral material, different from Saturn's other radiation belts. This property constrains the overall scale height of Saturn's exosphere to <700 km and the average D-ring water molecule column density to being about 1 order of magnitude below the Enceladus gas torus.

Mots clés: Saturn; radiation belt; CRAND; ring; exosphere; pitch angle

Domaines: Planète et Univers [physics]

P. Kollmann, E. Roussos, A. Kotova, L. Regoli, D. G. Mitchell, et al.. Saturn's Innermost Radiation Belt Throughout and Inward of the D-Ring. Geophysical Research Letters, 2018, 45, pp.10,912-10,920. ⟨10.1029/2018GL077954⟩. ⟨insu-03678173⟩