Electron density dropout near Enceladus in the context of water‐vapor and water‐ice
Electron density dropout near Enceladus in the context of water‐vapor and water‐ice
复制标题
水蒸气和水冰背景下土卫二附近的电子密度下降
DOI：
10.1029/2008gl037108
复制
发表时间：
2009
影响因子：
5.2
通讯作者：
J. Waite
中科院分区：
文献类型：
--
作者：
W. Farrell;W. Kurth;D. Gurnett;R. E. Johnson;M. Kaiser;J. Wahlund;J. Waite
2008年3月12日，卡西尼号太空船与土卫二进行了一次近距离接触，距离土卫二不到52公里。航天器的轨道有意朝向南方，以与南极地区发出的强烈的水为主的羽流紧密对齐。在通过期间，卡西尼无线电和等离子体波系统（RPWS）检测到两个不同的无线电特征：1）与小水冰尘埃颗粒撞击相关的脉冲，2）在月球附近增强并显示频率急剧下降的上混合（UH）共振发射。UH发射的频率降低与电子密度意外地急剧下降有关，从1090 el/cm 3下降到20 el/cm 3以下，这发生在与月球最接近的一分钟时间尺度上。在这项工作中，我们考虑了一些情况来解释这种急剧的电子脱落，但推测冰粒的电子吸收是最有可能的过程。
On 12 March 2008, the Cassini spacecraft made a close encounter with the Saturnian moon Enceladus, passing within 52 km of the moon. The spacecraft trajectory was intentionally‐oriented in a southerly direction to create a close alignment with the intense water‐dominated plumes emitted from the south polar region. During the passage, the Cassini Radio and Plasma Wave System (RPWS) detected two distinct radio signatures: 1) Impulses associated with small water‐ice dust grain impacts and 2) an upper hybrid (UH) resonance emission that both intensified and displayed a sharp frequency decrease in the near‐vicinity of the moon. The frequency decrease of the UH emission is associated with an unexpectedly sharp decrease in electron density from ∼90 el/cm3 to below 20 el/cm3 that occurs on a time scale of a minute near the closest encounter with the moon. In this work, we consider a number of scenarios to explain this sharp electron dropout, but surmise that electron absorption by ice grains is the most likely process.