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+, H2O+, 28M+ (possibly an aggregate of the molecular ions, MI, CO+, N2+, HCNH+, and/or C2H4+), and O2+ at Saturn; and N+, O+, N2+, NO+, O2+, 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 H2O+ and Fe+ ratios are lower. At Earth, after O+ and N+, ionospheric origin N2+, NO+, and O2+ (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. Plain Language Summary Some of the air we breathe, a gas of ~78% N2 and ~21% O2 molecules, expands into the high‐altitude atmosphere, the thermosphere, and becomes ionized by sunlight and charged particles from space to become the ionosphere. Molecules can break up into their component atoms or combine with other ions to form other molecules. Some ionospheric ions flow out into space, mostly during geomagnetic disturbances, and are further energized. Magnetospheres, plasma bubbles filled with these energized particles, form around planets with magnetic fields, like the Earth whose magnetic field stands off the steady stream of ions and electrons from the Sun called the solar wind. Particles inside the bubbles can be planet or satellite origin, and outside the bubble, they are mostly Sun origin. However, some inside get out and some outside get in. Improved ion measurements from space give us information