Suprathermal Magnetospheric Atomic and Molecular Heavy Ions at and Near Earth, Jupiter, and Saturn: Observations and Identification

We examine long‐term suprathermal, singly charged heavy ion composition measured at three planets using functionally identical charge‐energy‐mass ion spectrometers, one on Geotail, orbiting Earth at ~9–30 Re, the other on Cassini, in interplanetary space, during Jupiter flyby, and then in orbit around Saturn. O + , a principal suprathermal (~80–220 keV/e) heavy ion in each magnetosphere, derives primarily from outflowing ionospheric O + at Earth, but mostly from satellites and rings at Jupiter and Saturn. Comparable amounts of Iogenic O + and S + are present at Jupiter. Ions escaping the magnetospheres: O + and S + at Jupiter; C + , N + , O + , H 2 O + , 28 M + (possibly an aggregate of the molecular ions, MI, CO + , N 2 + , HCNH + , and/or C 2 H 4 + ), and O 2 + at Saturn; and N + , O + , N 2 + , NO + , O 2 + , and Fe + at Earth. Generally, escaped atomic ions (MI) at Earth and Saturn have similar (higher) ratios to O + compared to their magnetospheric ratios; Saturn's H 2 O + and Fe + ratios are lower. At Earth, after O + and N + , ionospheric origin N 2 + , NO + , and O 2 + (with proportions ~0.9:1.0:0.2) dominate magnetospheric heavy ions, consistent with recent high‐altitude/latitude ionospheric measurements and models; average ion count rates correlate positively with geomagnetic and solar activity. At ~27–33 amu/e, Earth's MIs dominate over lunar pickup ions (PUIs) in the magnetosphere; MIs are roughly comparable to lunar PUIs in the magnetosheath, and lunar PUIs dominate over MIs beyond Earth's bow shock. Lunar PUIs are detected at ~39–48 amu/e in the lobe and possibly in the plasma sheet at very low levels.