Discovery of Suprathermal Fe+ in the Magnetospheres of Earth and Saturn

Friday, 19 December 2014
Stephen P Christon1, Douglas C Hamilton2, Donald G Mitchell3, John M C Plane4, Robert D DiFabio5, Stamatios M Krimigis3,6, Stuart R Nylund3 and Anthony Lui3, (1)Focused Analysis and Research, Columbia, MD, United States, (2)University of Maryland, College Park, MD, United States, (3)Applied Physics Laboratory Johns Hopkins, Laurel, MD, United States, (4)University of Leeds, University of Leeds, Leeds, LS2, United Kingdom, (5)University of Louisiana, Department of Physics, Lafayette, LA, United States, (6)Academy of Athens, Office of Space Research and Technology, Athens, Greece
We compare measurements from two similar ion spectrometers to report on the first observations of suprathermal Fe+ in the magnetospheres of Earth and Saturn at tens to hundreds of keV/e. Geotail/EPIC/STICS has measured ions at Earth since late-1992 and Cassini/MIMI/CHEMS has measured ions at Saturn since mid-2004. The 56 amu/e singly-charged Fe+ ions are rare in both magnetospheres and easily identified in long-term averages. At Earth, the long-term averages also reveal N+, O+, N2+, and NO+ ions, which, to our knowledge, likely only originate in Earth's lower ionosphere and escape primarily during disturbed geomagnetic intervals. At Saturn, the Fe+ displays a distinct spatial variation and may originate from either of two possible sources - ionospheric escape as at Earth and/or meteoric materials embedded in Saturn's main rings. We will compare and contrast aspects of the observations at the two planets.