| 摘要: | 土星上所謂的「環雨（Ring Rain）」現象的物理起源是來自帶電冰粒和/或水分子離子從環系統下降，這長期以來一直是一個難題。這是因為如果冰粒最初位於環平面上的圓形克卜勒軌道上，那麼從行星中心向北偏移且近乎是個磁偶極的磁場（Connerney et al.,1982）會對這些帶電塵埃產生南北不同的影響：會將環雨效應的墜落點限制在南半球。但是在卡西尼號任務大結局任務階段的塵埃測量卻檢測到北半球的塵埃的墜入（Hsu et al., 2018），這表明相應的塵埃粒子一定是從行星際流星體轟擊或是其他原因中獲得了垂直於環平面的顯著垂直速度（Ip et al.,2016 年）。也就是說，這些獲得了北上速度的塵埃粒子很大程度上就是北半球環雨的起源。但在過去的模擬結果中表明，獲得垂直北上速度的塵埃會因其各種不同條件（如：荷質比、垂直速度大小……等）而有包括但不僅限於北半球的落點（Liu and Ip, 2014）。在本篇中，我們將嘗試去模擬各種條件下的北上帶電塵埃的各種軌跡可能性，並分析討論這些塵埃對土星環雨以及土星大氣系統的影響。;The physical origin of the so-called "Ring Rain" phenomenon on Saturn comes from the falling of charged ice particles and/or water molecular ions from the ring system, which has been a problem for a long time. This is because if ice particles are initially located in a circular Kepler orbit on the plane of the ring, a magnetic field that is almost a magnetic dipole offset northward from the center of the planet (Connerney et al., 1982) will cause these charged dusts to have different results from northern and southern hemisphere: the falling point of the ring rain effect will be limited to the southern hemisphere. However, the dust measurement in the final stage of the Cassini mission detected the fall of dust in the northern hemisphere (Hsu et al., 2018), indicating that the corresponding dust particles must have been bombarded by interplanetary meteoroids or other reasons obtained a significant vertical velocity perpendicular to the ring plane (Ip et al., 2016). In other words, these dust particles that have obtained the northward velocity are largely the origin of the northern hemisphere′s ring rain. However, in the past simulation results (Liu and Ip, 2014), it has been shown that the dust that obtains the vertical northward velocity will include but not limited to the landing point in the northern hemisphere, due to various conditions (such as: charge-to-mass ratio, vertical velocity, etc). In this work, we will try to simulate the various trajectories of the northward charged dust under various conditions, and analyze and discuss the impact of these dust on Saturn′s ring rain and Saturn′s atmospheric system. |
