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Cassini CAPS identification of pickup ion compositions at Rhea

Desai, R. T. and Taylor, S. A. and Regoli, L. H. and Coates, A. J. and Nordheim, T. A. and Cordiner, M. A. and Teolis, B. D. and Thomsen, M. F. and Johnson, R. E. and Jones, G. H. and Cowee, M. M. and Waite, J. H. (2018) Cassini CAPS identification of pickup ion compositions at Rhea. Geophysical Research Letters, 45 (4). pp. 1704-1712. ISSN 0094-8276. doi:10.1002/2017GL076588.

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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−, C_2H-, 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 CO_2 exosphere and surprisingly low O_2 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.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Desai, R. T.0000-0002-2015-4053
Taylor, S. A.0000-0001-5213-7947
Regoli, L. H.0000-0002-7628-1510
Coates, A. J.0000-0002-6185-3125
Nordheim, T. A.0000-0001-5888-4636
Cordiner, M. A.0000-0001-8233-2436
Teolis, B. D.0000-0001-8386-6413
Thomsen, M. F.0000-0003-0140-9265
Jones, G. H.0000-0002-5859-1136
Cowee, M. M.0000-0003-3117-4030
Waite, J. H.0000-0002-1978-1025
Additional Information:© 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. Received 29 NOV 2017; Accepted 24 JAN 2018; Accepted article online 30 JAN 2018; Published online 19 FEB 2018. R. T. D. acknowledges STFC Studentship 1429777. A. J. C. and G. H. J. acknowledge support from the STFC consolidated grants to UCL‐MSSL ST/K000977/1 and ST/N000722/1. The Cassini CAPS data used are available on the Planetary Database System (PDS) or upon reasonable request.
Funding AgencyGrant Number
Science and Technology Facilities Council (STFC)1429777
Science and Technology Facilities Council (STFC)ST/K000977/1
Science and Technology Facilities Council (STFC)ST/N000722/1
Subject Keywords:Rhea; exosphere; icy satellites; pickup ions; plasma interactions
Issue or Number:4
Record Number:CaltechAUTHORS:20180221-095333999
Persistent URL:
Official Citation:Desai, R. T., Taylor, S. A., Regoli, L. H., Coates, A. J., Nordheim, T. A., Cordiner, M. A.,…Waite, J. H. (2018). Cassini CAPS identification of pickup ion compositions at Rhea. Geophysical Research Letters, 45, 1704–1712.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:84901
Deposited By: Tony Diaz
Deposited On:22 Feb 2018 18:17
Last Modified:15 Nov 2021 20:23

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