Suprathermal electrons near the nucleus of comet 67P/Churyumov‐Gerasimenko at 3 AU: Model comparisons with Rosetta data
Suprathermal electrons near the nucleus of comet 67P/Churyumov‐Gerasimenko at 3 AU: Model comparisons with Rosetta data
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3 AU 处 67P/Churyumov-Gerasimenko 彗核附近的超热电子：与 Rosetta 数据的模型比较
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发表时间：
2016
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通讯作者：
N. L. Reedy
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作者：
H. Madanian;T. Cravens;A. Rahmati;R. Goldstein;J. Burch;A. Eriksson;N. Edberg;P. Henri;K. Mandt;G. Clark;M. Rubin;T. Broiles;N. L. Reedy
2014年底，Rosetta轨道器上的IES(离子与电子传感器)仪器对67P/Churyumov-Gerasimenko(67P)彗星核附近的彗发进行了观测，结果表明，电子通量远远超过太阳风电子通量。IES是Rosetta等离子体联盟的一部分。本文报道了彗星在日心距约3 AU时，原子核附近IES测量的电子能谱，以及超热电子的近似密度和平均能量。并与其他仪器测得的电子密度进行了比较。观测到的高电子密度(例如Ne ≈ 10-100 cm−3)肯定与主要由太阳辐射使彗星气体光致电离而产生的彗星离子密度增强有关；还有其他过程也有贡献。准中性要求电子密度和离子密度相同，在某些条件下，需要一个双极电场才能达到准中性。我们给出了一个太阳风拾取彗星离子的实验粒子模型和一个双流电子输运程序的结果，并用这些结果解释了IES数据。我们还估计了电子流体团压缩对电子能谱的影响。IES探测到的电子在彗星附近的能量有时可以高达100-200 eV，在这种情况下，热电子可以通过碰撞电离显著提高中性粒子的电离率。
Observations of the coma near the nucleus of comet 67P/Churyumov‐Gerasimenko (67P) made by the IES (Ion and Electron Sensor) instrument onboard the Rosetta Orbiter during late 2014 showed that electron fluxes greatly exceeded solar wind electron fluxes. The IES is part of the Rosetta Plasma Consortium. This paper reports on electron energy spectra measured by IES near the nucleus as well as approximate densities and average energies for the suprathermal electrons when the comet was at a heliocentric distance of about 3 AU. Comparisons are made with electron densities measured by other instruments. The high electron densities observed (e.g., ne ≈ 10–100 cm−3) must be associated with the cometary ion density enhancement created mainly by the photoionization of cometary gas by solar radiation; there are other processes that also contribute. Quasineutrality requires that the electron and ion densities be the same, and under certain conditions an ambipolar electric field is required to achieve quasi‐neutrality. We present the results of a test particle model of cometary ion pickup by the solar wind and a two‐stream electron transport code and use these results to interpret the IES data. We also estimate the effects on the electron spectrum of a compression of the electron fluid parcel. The electrons detected by IES can have energies as high as about 100–200 eV near the comet on some occasions, in which case the hot electrons can significantly enhance ionization rates of neutrals via impact ionization.