The Suisei probe made a closest approach of 151,000km to comet Halley at 13 : 06 UT on 8 March 1986,and during the enocounter Suisei passed through a strong interaction region, where the solar-wind flow was severely perturbed by picked-up ions of cometary origin. Plasma-flow observation shows a characteristic pattern of the flow around the comet as an obstacle. The pickup shells of water-group ions and protons of cometary origin were clearly identified in the phase-space distribution. It is interesting to note that the shell is incompletely filled (by 50-70% of the filling factor). Field-line draping around the comet was observed within 2×10^5km of the Halley's nucleus, where magnetic-field directions are derived from the symmetry axes of the ion-pickup shells. Other ions, such as CO^+ (and/or N_2^+) and CH^+ (and/or C^+), were also identified from energy per charge spectrum near the closest approach. Flow turbulence was observed as short-term (period of ≲2min) fluctuations of the anisotropy direction in the outer cometosheath (2-4.5×10^5km from the nucleus), while the flow was found to be laminar near the closest approach (1.5-2×10^5km from the nucleus). An abrupt change of the plasma parameter was detected around 4.5×10^5km away from the nucleus, representing the bow-shock crossing. The mass-loading effect was observed at a distance of up to ∿1×10^6km. Spatial distribution of density of water-group ions (identified up to 4×10^6km from the nucleus) is also presented.
「すいせい」で観測されたハレー彗星と太陽風の相互作用
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