Desai, RT;
Taylor, SA;
Regoli, LH;
Coates, AJ;
Nordheim, TA;
Cordiner, MA;
Teolis, BD;
... Waite, JH; + view all
(2018)
Cassini CAPS Identification of Pickup Ion Compositions at Rhea.
Geophysical Research Letters
, 45
(4)
pp. 1704-1712.
10.1002/2017GL076588.
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Abstract
Saturn's largest icy moon, Rhea, hosts a tenuous surface‐sputtered exosphere composed primarily of molecular oxygen and carbon dioxide. In this Letter, we examine Cassini Plasma Spectrometer velocity space distributions near Rhea and confirm that Cassini detected nongyrotropic fluxes of outflowing CO_{2}^{+} during both the R1 and R1.5 encounters. Accounting for this nongyrotropy, we show that these possess comparable along‐track densities of ∼2 × 10⁻³ cm⁻³. Negatively charged pickup ions, also detected during R1, are surprisingly shown as consistent with mass 26 ± 3 u which we suggest are carbon‐based compounds, such as CN⁻, C₂H⁻, C_{2}^{-}, or HCO⁻, sputtered from carbonaceous material on the moon's surface. The negative ions are calculated to possess along‐track densities of ∼5 × 10⁻⁴ cm⁻³ and are suggested to derive from exogenic compounds, a finding consistent with the existence of Rhea's dynamic CO₂ exosphere and surprisingly low O₂ sputtering yields. These pickup ions provide important context for understanding the exospheric and surface ice composition of Rhea and of other icy moons which exhibit similar characteristics.
Type: | Article |
---|---|
Title: | Cassini CAPS Identification of Pickup Ion Compositions at Rhea |
Open access status: | An open access version is available from UCL Discovery |
DOI: | 10.1002/2017GL076588 |
Publisher version: | http://dx.doi.org/10.1002/2017GL076588 |
Language: | English |
Additional information: | © 2018. The Authors. This is an open access article under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/). |
Keywords: | Rhea, exosphere, icy satellites, pickup ions, plasma interactions |
UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics |
URI: | https://discovery.ucl.ac.uk/id/eprint/10044328 |
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