A 3D MHD‐Particle Tracing Model of Na⁺ Energization on Mercury's Dayside

Abstract

Mercury has been a target of interest and study since the flybys by Mariner 10 in 1974 and 1975 and has been subject to intense subsequent study by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft (Solomon et al., 2007), which orbited Mercury from 2011 until early 2015. As many previous works have noted, Mercury occupies a unique place among the solar system's planets. It is situated closest to the Sun, in a plasma and magnetic environment that is an order of magnitude more intense than at Earth and more than 2 orders of magnitude more intense than Jupiter on average (Slavin & Holzer, 1981). As a result, although Mercury has an Earth-like intrinsic dipolar magnetic field and a magnetosphere that obeys the Dungey cycle, its response to external solar forcing is far more dynamic and rapid than is observed at Earth-the reconfiguration time of Mercury's magnetosphere is approximately 2 min, compared to approximately 1 h at Earth (Dungey, 1961;Siscoe et al., 1975;Slavin et al., 2009).At both Earth and Mercury, the planetary cusps are a key region of the dayside magnetosphere. The cusps of both planets are defined as the region at and above the planetary surface (at Mercury, with its lack of ionosphere) or atmosphere (at Earth) colocated with the foot points of field lines that have just undergone reconnection on the dayside (Cowley & Owen, 1989). These field lines convect through the cusp toward the magnetotail, carrying magnetic and plasma flux as they move (Dungey, 1961). Crucially, these field lines

MESSENGER Observations of Planetary Ion Enhancements at Mercury's Northern Magnetospheric Cusp During Flux Transfer Event Showers

“…This process could be similar to the pickup process of Na + test particles shown in Glass et al. ( 2021 ). Those authors suggested that the large‐scale magnetospheric convection electric field energized Na + test particles from very low altitudes on the dayside enough that they could gyrate through the magnetopause.…”

“…If they could reach high enough altitudes, they would then be accelerated by the convection electric field in the entry layer, which was driven by the potential drop associated with the dayside magnetopause reconnection since the magnetic field lines in the entry layer were newly opened by the magnetopause reconnection. This process could be similar to the pickup process of Na + test particles shown in Glass et al (2021). Those authors suggested that the large-scale magnetospheric convection electric field energized Na + test particles from very The Flux of Na + -group Ions Near Mercury's Surface Underneath the Cusp, Which Corresponds to the Pitch Angle-Energy Distribution in Figure 7 low altitudes on the dayside enough that they could gyrate through the magnetopause.…”

“…When the sputtered ions moving antiplanetward along the magnetic field lines, that is, outflowing, reach higher altitudes, they would be subject to centrifugal acceleration (Delcourt et al., 2012 ) and they would also encounter the solar wind convection electric field and be accelerated further (also see Glass et al., 2021 ; Raines et al., 2014 ). Once in the magnetosheath, they would move along the magnetopause and reach keV energies before passing through the cusp (at similar altitudes to our observations in Figures 1b and 3 ).…”

Modeling the Impact of a Strong X‐Class Solar Flare on the Planetary Ion Composition in Mercury's Magnetosphere

“…The test‐particle trajectory in Figure 3 seems to suggest that the Population 2 ions in Region A does not belong to the Type 0 or Type 1 ion populations described in Glass et al. (2021), but could be part of Type 3. Glass et al.…”

“…The test-particle trajectory in Figure 3 seems to suggest that the Population 2 ions in Region A does not belong to the Type 0 or Type 1 ion populations described in Glass et al (2021), but could be part of Type 3. Glass et al (2021) identified different types of Na + test-particle trajectories which could be responsible for the population of > 1 keV Na + ions observed in Mercury's northern magnetospheric cusp by FIPS (Raines et al, 2014). Type 0 ions pass through the magnetosheath before crossing the northern cusp, while Type 1 ions move directly into the northern cusp without passing through or coming near the magnetosheath boundary.…”