Cassini CAPS identification of pickup ion compositions at Rhea
File(s)
Published version
Author(s)
Type
Journal Article
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 urn:x-wiley:grl:media:grl56939:grl56939-math-0001 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−, urn:x-wiley:grl:media:grl56939:grl56939-math-0002, urn:x-wiley:grl:media:grl56939:grl56939-math-0003, 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.
Date Issued
2018-02-28
Date Acceptance
2018-01-24
Citation
Geophysical Research Letters, 2018, 45 (4), pp.1704-1712
ISSN
0094-8276
Publisher
Wiley
Start Page
1704
End Page
1712
Journal / Book Title
Geophysical Research Letters
Volume
45
Issue
4
Copyright Statement
©2018. The Authors. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
License URL
Identifier
http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000427564300001&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=1ba7043ffcc86c417c072aa74d649202
Subjects
Science & Technology
Physical Sciences
Geosciences, Multidisciplinary
Geology
Rhea
exosphere
icy satellites
pickup ions
plasma interactions
CARBON-DIOXIDE ATMOSPHERE
SATURNS MAGNETOSPHERE
VIMS
SATELLITES
EUROPA
PLASMA
DIONE
SPACE
MODEL
Publication Status
Published
Date Publish Online
2018-01-30