Solar wind charge exchange in cometary atmospheres III. Results from the Rosetta mission to comet 67P/Churyumov-Gerasimenko
Cyril Simon Wedlund, Etienne Behar, Hans Nilsson, Markku Alho, Esa Kallio, Herbert Gunell, Dennis Bodewits, Kevin Heritier, Marina Galand, Arnaud Beth, Martin R… 展开作者
Cyril Simon Wedlund, Etienne Behar, Hans Nilsson, Markku Alho, Esa Kallio, Herbert Gunell, Dennis Bodewits, Kevin Heritier, Marina Galand, Arnaud Beth, Martin Rubin, Kathrin Altwegg, Martin Volwerk, Guillaume Gronoff, Ronnie Hoekstra
备注：
15 pages, 10 figures. ERRATUM included: The original article showed figures with incorrect neutral density products (Figs. 3, 5A, and 6) and ENA predictions (Figs. 9 and 10). These are now all corrected in the present version. Because this mistake was made for figures only, results and conclusions remain unchanged except for a few quoted dates in Sect. 4.4
Solar wind charge-changing reactions are of paramount importance to the physico-chemistry of the atmosphere of a comet. The ESA/Rosetta mission to comet 67P/Churyumov-Gerasimenko (67P) provides a unique opportunity to study charge-changing processes in situ. To understand the role of these reactions in the evolution of the solar wind plasma, and interpret the complex in-situ measurements made by Rosetta, numerical or analytical models are necessary. We use an extended analytical formalism describing solar wind charge-changing processes at comets along solar wind streamlines. The model is driven by solar wind ion measurements from the Rosetta Plasma Consortium-Ion Composition Analyzer (RPC-ICA) and neutral density observations from the Rosetta Spectrometer for Ion and Neutral Analysis-Comet Pressure Sensor (ROSINA-COPS), as well as charge-changing cross sections of hydrogen and helium particles in a water gas. A mission-wide overview of charge-changing efficiencies at comet 67P is presented. Electron capture cross sections dominate and favor the production of He and H energetic neutral atoms, with fluxes expected to rival those of H+ and He2+ ions. Neutral outgassing rates are retrieved from local RPC-ICA flux measurements, and match ROSINA's estimates very well. From the model, we find that solar wind charge exchange is unable to fully explain the magnitude of the sharp drop of solar wind ion fluxes observed by Rosetta for heliocentric distances below 2.5 AU. This is likely because the model does not take into account the relative ion dynamics and, to a lesser extent, ignore the formation of bow shock-like structures upstream of the nucleus. This work also shows that the ionization by solar EUV radiation and energetic electrons dominates the source of cometary ions, although solar wind contributions may be significant during isolated events.
我们目前的罗塞塔观测彗星67 P/Churyumov-Gerasimenko在日冕物质抛射（CME）的影响。CME于2015年10月5日至6日撞击，当时罗塞塔距离彗星核\textcolor{black}{and 1.4 AU from the Sun}约800公里。撞击后，等离子体环境被压缩到太阳风离子的水平，几天前在1500公里处没有看到，现在到达罗塞塔。响应于压缩，超热电子的通量增加了5-10倍，背景磁场强度增加了$\sim$ 2.5倍。等离子体密度增加了10倍，达到600 cm $^{-3}$，这是由于粒子碰撞电离、电荷交换和等离子体环境的绝热压缩的增加。我们还观察到前所未有的大磁场尖峰在800公里，达到200 nT以上，这是解释为磁通量绳。我们认为，这些可能是形成的磁重联过程中的昏迷的磁场在整个CME改变极性，或作为一个结果，强烈的剪切造成开尔文-亥姆霍兹不稳定性的等离子体流。由于\textcolor{black}{limited orbit of Rosetta}，我们无法观察到在CME撞击期间是否发生尾部断开，这可以根据以前对其他CME彗星相互作用的远程观测来预期。
The $^{16}$O/$^{18}$O ratio in Water in the Coma of Comet 67P / Churyumov-Gerasimenko measured with the Rosetta / ROSINA Double-Focusing Mass Spectrometer
The dust-to-gas ratio, size distribution, and dust fall-back fraction of comet 67P/Churyumov-Gerasimenko: Inferences from linking the optical and dynamical properties of the inner comae
Limitations in the determination of surface emission distributions on comets through modelling of observational data -- A case study based on Rosetta observations
