Oxygen Ions Observed Near Saturn's A Ring
J. H. Waite, Jr.,1
T. E. Cravens,2*
W.-H. Ip,3
W. T. Kasprzak,4
J. G. Luhmann,5
R. L. McNutt,6
H. B. Niemann,4
R. V. Yelle,7
I. Mueller-Wodarg,8
S. A. Ledvina,5
S. Scherer1
Ions were detected in the vicinity of Saturn's A ring by the Ion and Neutral Mass Spectrometer (INMS) instrument onboard the Cassini Orbiter during the spacecraft's passage over the rings. The INMS saw signatures of molecular and atomic oxygen ions and of protons, thus demonstrating the existence of an ionosphere associated with the A ring. A likely explanation for these ions is photoionization by solar ultraviolet radiation of neutral O2 molecules associated with a tenuous ring atmosphere. INMS neutral measurements made during the ring encounter are dominated by a background signal.
1 Department of Atmospheric, Oceanic, and Space Physics, University of Michigan, Ann Arbor, MI 48109, USA.
2 Department of Physics and Astronomy, University of Kansas, Lawrence, KS 66045, USA.
3 Institute of Astronomy, National Central University, Chung-Li 32054, Taiwan.
4 NASA Goddard Spaceflight Center, Greenbelt, MD 20771, USA.
5 Space Science Laboratory, University of California, Berkeley, CA 94720, USA.
6 Applied Physics Laboratory, Johns Hopkins University, Laurel, MD 20723, USA.
7 Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA.
8 Space and Atmospheric Physics Group, Imperial College, London SW7 2BW, UK.
* To whom correspondence should be addressed. E-mail: cravens{at}ku.edu
