Statistical analysis of the accelerated H2O ions above 1 keV: the comet 67P/Churyumov–Gerasimenko observed by the Rosetta spacecraft.

<p>The ESA/Rosetta spacecraft has studied the comet 67P/Churyumov-Gerasimenko for two years. Rosetta Plasma Consortium's Ion Composition Analyser (RPC/ICA) detected comet-origin water ions that are accelerated to > 100 eV.<span>  </span>Majority of them are interpreted as ordinary pick-up acceleration<span>  </span>by the solar wind electric field perpendicular to the magnetic field during low comet activity [1,2]. As the comet approaches the sun, a comet magnetosphere is formed, where solar winds cannot intrude.</p><p>However,  some water ions are accelerated to > 1 keV even in the magnetosphere [3]. Using RPC/ICA data during two years [4], we investigate the acceleration events > 1 keV where solar winds are not observed, and classify dispersion events with respect to the directions of the sun, the comet, and the magnetic field.<span>  </span>Majority of these water ions show reversed energy-angle dispersion. <span>Results of the investigation also show that these ions are flowing along the (enhanced) magnetic field, indicating that the parallel acceleration occurs in the magnetosphere.</span></p><p>In this meeting, we show a statistical analysis and discuss a possible acceleration mechanism.</p><p><strong>References</strong></p><p>[1] H. Nilsson et al., MNRAS 469, 252 (2017), doi:10.1093/mnras/stx1491</p><p>[2] G. Nicolau et al., MNRAS 469, 339 (2017), doi:10.1093/mnras/stx1621</p><p>[3] T. Kotani et al., EPSC, EPSC2020-576 (2020), https://doi.org/10.5194/epsc2020-576</p><p>[4] H. Nilsson et al., Space Sci. Rev., 128, 671 (2007), DOI: 10.1007/s11214-006-9031-z </p>