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

Abstract

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.Plain Language Summary Some of the air we breathe, a gas of~78% N 2 and~21% O 2 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 to help unravel both the outflowing particles' interactions on the way out and when and how ions escape or penetrate magnetospheres. Planets' satellites and rings also contribute ionized and neutral particles to the mix, making various determinations more difficult than others. Ions from solar wind and sunlight impacting Earth's satellite, the Moon, which spends most of its time outside Earth's magnetosphere, dominate ion composition at some masses and energies there while contributing little overall inside...

The Contribution of N+ Ions to Earth's Polar Wind

“…The 7iPWOM provides an updated view into the transport mechanisms behind the up‐flowing of the major heavy ion species. Observations from Supra‐Thermal Ion Composition Spectrometer (STICS) on board the Geotail indicates significant presence of N + and molecular ions in the magnetosphere, especially in the storm time (Christon et al., 2020); however, their transport is not quantified, nor understood, at this time. Therefore, knowledge of the differential transport and path of energization for the ionospheric heavy ions will help interpret observations and guide the development of instrumentation for future missions.…”

The Contribution of N+ ions to Earth's Polar Wind

“…The 7iPWOM provides an updated view into the transport mechanisms behind the up-flowing of the major heavy ion species. Observations from Supra-Thermal Ion Composition Spectrometer (STICS) on board the Geotail indicates significant presence of N + and molecular ions in the magnetosphere, especially in the storm time (Christon et al, 2020); however, their transport is not quantified, nor understood, at this time. Therefore, knowledge of the differential transport and path of energization for the ionospheric heavy ions will help interpret observations and guide the development of instrumentation for future missions.…”

Suprathermal Fe in the Earth's Plasma Environment: Cluster RAPID Observations

“…However, the reported abundances of isotopes other than Fe within this mass range are much lower in the regions of space relevant for the present study (Jarosewich, ; Manuel & Hwaung, ; von Steiger et al,, ). Molecular ions such as N , CO, NO, and O , sometimes found in the magnetosphere as a result of ion outflow (Christon, ; Yau et al, ) have atomic masses in the range 28–32 and should show outside the Fe interval in the E‐TOF map.…”

“…But also other, heavier ion species and even molecular ions are present in geospace. Molecular ions are predominantly of terrestrial origin (Dandouras et al, ; Christon, ; Yau et al, ), whereas the sources of other heavy ions and their relative contribution is still debated. In this paper, we present Cluster observations of iron (Fe), which has an atomic mass around 56 atomic mass units (AMU) in its most frequently occurring isotope.…”