Losses of Radiation Belt Energetic Particles by Encounters With Four of the Inner Moons of Jupiter

Abstract

The major energy source of the Jovian system is derived from its fast rotation, and its major particle source is from volcanic activities from Io (Bolton et al., 2015). In addition to being plasma sources, large moons embedded within the Jovian magnetosphere can act as candidates responsible for losses of magnetospheric energetic particles as well (Paonessa & Cheng, 1985). The net effect of how moons affect radiation intensities in their environment is determined by the balance of loss processes (such as the moon absorption time scale) and sources (such as how fast new particles are provided by radial transport or local acceleration). Therefore, the moon absorption of radially diffusing energetic particles is recognized as an important physical process that needs to be considered when evaluating the particle dynamics in the Jovian magnetosphere (e.g.,

Pitch Angle Distribution of MeV Electrons in the Magnetosphere of Jupiter

“…The pitch angle dependency of the loss rate associated with moon absorption can create field‐aligned distributions (Long et al., 2022), as seen for energetic ions close to Jupiter (Roussos et al., 2022)…”

“…True field‐aligned auroral beams likely show the signature of high‐latitude auroral acceleration mechanisms. A scattered beam may however be the signature of one of the 4 following physical phenomena in the middle and outer magnetosphere of Jupiter: A scattered beam can be a true auroral beam which has been scattered over time by an unknown process at the M‐shell where the auroral beam was produced, or may have been scattered and accelerated during adiabatic inward radial transport The pitch angle dependency of the loss rate associated with moon absorption can create field‐aligned distributions (Long et al., 2022), as seen for energetic ions close to Jupiter (Roussos et al., 2022) The loss or cooling of energetic electrons due to interaction with equatorial neutral gas or cold plasma populations may also create energetic electron field‐aligned distributions (Clark et al., 2014), although physics‐based modeling indicates that these processes are likely negligible for energetic electrons in the Jovian magnetosphere (Nénon et al., 2017) Outward adiabatic radial transport with conservation of the two first adiabatic invariants of energetic electrons can create field‐aligned distributions (e.g., Rymer et al., 2008). …”

“…A scattered beam can be a true auroral beam which has been scattered over time by an unknown process at the M-shell where the auroral beam was produced, or may have been scattered and accelerated during adiabatic inward radial transport 2. The pitch angle dependency of the loss rate associated with moon absorption can create field-aligned distributions (Long et al, 2022), as seen for energetic ions close to Jupiter (Roussos et al, 2022) 3. The loss or cooling of energetic electrons due to interaction with equatorial neutral gas or cold plasma populations may also create energetic electron field-aligned distributions (Clark et al, 2014), although physics-based modeling indicates that these processes are likely negligible for energetic electrons in the Jovian magnetosphere (Nénon et al, 2017) 4.…”

Quantifying the Absorption Loss of Radiation Belt Energetic Particles by Saturn's Inner Moons

“…Based on the aforementioned studies, Long, Ni, et al. (2022) developed an improved moon absorption model, which has taken into account the multiple effects of different absorption mechanisms and is not limited to the small absorption probability approximation. Long, Ni, et al.…”

“…Long, Ni, et al. (2022) subsequently performed a quantitative analysis of the lifetimes of radiation belt particles due to encounters with the inner moons of Jupiter. However, the absorption loss of radiation belt energetic particles by Saturn's moons is still not fully understood.…”