「すいせい」によるハレー彗星紫外 (L_yα) 観測

概要

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The Ultraviolet Imager aboard Suisei, the first Japanese interplanetary spacecraft, successfully ended ist mission by continuously observing the Ly α intensities of comet Halley. The major findings obtained from these observations are as follows : 1) Strong short-term variation of the Ly α intensities of comet Halley; Such a rapid variation was quite unexpected in the knowledge of the past Ly α observations of comet. In relation to this variation, an accurate determination of the rotation period of this comet was attempted (52.9 hours). 2) The first measurement of the Ly α intensities from within a thick hydrogen cloud of comet. While the intensity distribution as a function of the distance from the nucleus approximately follows that predicted by the Haser model, it is also compatible with the jet repetition model. 3) Existence of a fine structure in the above photometry data, which possibly represents local enhancements of the atomic hydrogen density. 4) Brightness variation within one rotational period was pursued, producing an outburst occurrence diagram. The rapid variation of the Ly α intensities as observed suggests that in an outburst event there must be involved a small amount of hydrogen-containing molecules whose photodissociation lifetimes are quite short. 5) The observed images are brighter (overally twice) than those expected from the nominal model by IACC/WG.
宇宙航空研究開発機構の論文