Enceladus produces plumes of water vapor and ice particles whose gaseous H₂O molecules dissociate into OH and O. The gas ejecta form a large toroidal planetary cloud colocated with and partially sourced by a similarly large torus of ice grain ejecta. Gas torus neutrals are ionized by charge exchange, solar ultraviolet, and electron impacts, producing the thermal water group ions, W⁺ (O⁺, OH⁺, H₂O⁺, and H₃O⁺), which become energized in Saturn's magnetosphere. We study the components of energetic (~96 keV) W⁺ using Cassini Charge‐Energy‐Mass Spectrometer (CHEMS) data from 78 near‐equatorial main ring current passes (dipole L = 7–16, ±10° in latitude) in 2004–2010. W⁺ fractional abundances are ~53% O⁺, ~22% OH⁺, ~22% H₂O⁺, and ~3% H₃O⁺, when averaged over L = 7–16, resulting in a mean water group mass of 16.7 amu. This large energetic O⁺ fractional abundance, over twice that observed for thermal O⁺ at L < 10, qualitatively agrees with the broad atomic O cloud observed by Cassini and predicted by some models. Fractional abundance ratios for O⁺/W⁺, OH⁺/W⁺, and H₂O⁺/W⁺ vary little over L = 7–21. Our observation of energetic H₂O⁺/W⁺ ≈ 22% out to L ~ 21 suggests that neutral H₂O spreads throughout the magnetosphere rather than being confined to a narrow torus centered on Enceladus' orbit. Although nearly constant at <2% for L > 13, H₃O⁺/W⁺ tends to increase significantly to ~4–5% at L ~ 7–8.

中文翻译：

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土星磁层中〜96 keV W +的组成

土卫二产生水蒸气和冰粒的羽状物，它们的气态H ₂ O分子分解成OH和O。气体喷出物形成一个巨大的环形行星云，与类似大的冰粒喷出物位于同一位置并部分由其提供。气体环形中性分子通过电荷交换，太阳紫外线和电子的撞击而离子化，产生热水基团离子W ⁺（O ⁺，OH ⁺，H ₂ O ⁺和H ₃ O ⁺），这些离子在土星的磁层中被激发。我们研究高能（〜96 keV）W ⁺的成分使用卡西尼充电能质谱仪（CHEMS）的数据，取自2004-2010年的78次近赤道主环电流通过（偶极子L  = 7–16，纬度为±10°）。当在L  = 7–16上求平均值时，W ^+的分数丰度为〜53％O ⁺，〜22％OH ⁺，〜22％H ₂ O ⁺和〜3％H ₃ O ⁺，从而得出平均水组质量16.7亩。这种较大的O ⁺分数丰度，是L处热O ^+的两倍 <10，在质量上与卡西尼观测到并由某些模型预测的宽原子O云一致。O ⁺ / W ⁺，OH ⁺ / W ⁺和H ₂ O ⁺ / W ^+的分数丰度比在L  = 7–21范围内变化不大。我们的高能H的观察₂ ö ⁺ / W ⁺  ≈22％出大号 〜21表明，中性ħ _2个ö散布于整个磁层，而不是被限制在一个狭窄的环形中心恩克拉多斯轨道。尽管对于L  > 13，H ₃ O ⁺几乎恒定在<2％/ W ⁺倾向于在以显著增加至〜4-5％大号 〜7-8。