Hybrid code simulations of the solar wind interaction with Comet 19P/Borrelly
Hybrid code simulations of the solar wind interaction with Comet 19P/Borrelly
复制标题
太阳风与彗星 19P/Borrelly 相互作用的混合代码模拟
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发表时间：
2006
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通讯作者：
P. Delamere
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作者：
P. Delamere
1. 2001年9月22日“深空1号”（DS1）飞越19P/博雷利彗星期间，行星探测等离子体实验（PEPE）对该彗星的等离子体环境进行了详细观测。DS1相对于黄道面在彗星向阳面从北向南飞行，观测到所有等离子体边界（即首次和末次拾取离子、弓形激波、减速的太阳风）都向北偏移。这一令人惊讶的结果最初归因于DS1上的MICAS相机所观测到的从彗核向北偏约10°的、准直性良好的大型昼侧喷流。然而，施莱歇尔等人（2003年）的地基观测表明，相对于彗核 - 太阳连线存在一个对称的气体云。为了解决这一难题，我们进行了一系列混合等离子体模拟，以研究在1.36天文单位处较大的拾取离子回转半径（即与彗星障碍物的长度尺度相当）的影响。我们发现，当拾取离子回转半径与弓形激波的驻点距离相当或更小时（IMF约为4纳特），会产生与观测结果一致的最大不对称性。对于更大和更小的磁场强度，不对称程度会降低。
[1] Detailed observations of the plasma environment of Comet 19P/Borrelly were made by the Plasma Experiment for Planetary Exploration (PEPE) during the Deep Space 1 (DS1) flyby on 22 September 2001. DS1 flew from north to south relative to the plane of the ecliptic on the sunward side of the comet and all plasma boundaries (i.e., first and last pickup ions, bow shock, decelerated solar wind) were observed to be shifted northward. This surprising result was initially attributed to large well-collimated dayside jets directed ∼10° northward from the nucleus as observed by the DS1 MICAS camera. However, ground-based observations of Schleicher et al. (2003) indicate a symmetric gas cloud with respect to the comet-Sun line. In an attempt to resolve this conundrum, we have conducted a series of hybrid plasma simulations to investigate the effects of the large pickup ion gyroradius (i.e., comparable to the length scale of the cometary obstacle) at 1.36 AU. We find that that a maximum asymmetry, consistent with the observations, is generated when the pickup ion gyroradius is comparable to or less than the standoff distance of the bow shock (BIMF ∼ 4 nT). The degree of asymmetry is reduced for larger and smaller magnetic field strengths.