In‐situ observations of cometary pick‐up iIons ≥0.2 AU upstream of comet Halley: ICE observations
In‐situ observations of cometary pick‐up iIons ≥0.2 AU upstream of comet Halley: ICE observations
复制标题
哈雷彗星上游 ≥0.2 AU 彗星拾取离子的原位观测：ICE 观测
DOI：
--
复制
发表时间：
1986
期刊：
影响因子：
--
通讯作者：
B. Tsurutani
中科院分区：
文献类型：
--
作者：
K. Wenzel;T. Sanderson;I. Richardson;S. Cowley;R. Hynds;S. Bame;R. Zwickl;E. Smith;B. Tsurutani
1986年3月下旬，国际彗星探测器(ICE)上的EPAS仪器在最接近P/Hley彗星(上游28×106公里)时观察到高能离子的爆发式增强。增强显示出相当大的时间结构和高度各向异性的角分布，沿反太阳方向有很强的离子流动。离子强度受到不同太阳风速的调制(后者达到最大值约600公里S−1)，这是在冰川与P/贾科比尼-津纳彗星(G-Z)相遇期间，太阳风流中的重彗星离子被太阳风流中的加速所加速的情况。因此，我们得出结论，我们观察到哈雷彗星的重中性物产生的拾取离子(最有可能是≥，65keV的氧离子)。此时，拾取离子的区域从原子核延伸到超过0.2AU(∼35×106公里)，比在乔托和织女星相遇时观察到的距离至少远三倍。对高能离子的如此大距离的观测表明，在原子核周围的中性大气中，存在一个电离尺度长度为500-1000万公里的分量，这是由于S−1的相对较高的膨胀速度和/或电离时间尺度的几倍106秒造成的。
Burst-like enhancements of energetic ions were observed by the EPAS instrument on the International Cometary Explorer (ICE) during its closest approach to (28 × 106 km upstream of) Comet P/Halley, in late March 1986. The enhancements showed considerable temporal structure and highly anisotropic angular distributions, with strong ion streaming in the antisolar direction. The ion intensity was modulated by the varying solar wind speed (the latter reaching maxima of around 600 km s−1), as was found to be the case for heavy cometary ions accelerated by pick-up in the solar wind flow, during the ICE encounter with Comet P/Giacobini-Zinner (G-Z). We therefore conclude that we observed pick-up ions (most probably ≥ 65 keV oxygen ions) produced by heavy neutrals from Comet Halley. The region of pick-up ions extended to more than 0.2 AU (∼35 × 106 km) from the nucleus at this time, at least three times further than was observed during the Giotto and VEGA encounters. The observations of energetic ions at such large distances suggest the presence, in the neutral atmosphere surrounding the nucleus, of a component with an ionisation scale length of 5-10 million km, resulting from a relatively high expansion speed of a few km s−1 and/or an ionisation time scale of a few times 106s.