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

Abstract

Mercury possesses a global dipole magnetic field with a similar polarity to Earth's dipole field, but the magnetic field intensity near Mercury's magnetic equatorial plane (∼200 nT) is much less than the strength of Earth's field (∼30,000 nT) (see Anderson et al., 2012). Mercury's magnetic field can hold off the constantly streaming solar wind with a subsolar magnetopause distance of around one thousand kilometers above the planet's surface

Observations of Mercury's Plasma Sheet Horn: Characterization and Contribution to Proton Precipitation

“…Using this method, the average estimated precipitation flux in orbit 3,795 is 2.9 × 10 7 cm −2 s −1 , and in orbit 3,807 is 4.8 × 10 7 cm −2 s −1 . These estimates are of the same order of magnitude as has been previously found for average proton precipitation in the northern dayside cusp (Raines et al, 2022), and about one order of magnitude less than the proton precipitation rate during active magnetopause reconnection intervals (Sun et al, 2022).…”

“…Because of the earlier‐mentioned recent finding that sodium may be more tightly bound to the surface than previously estimated (Morrissey et al., 2022), at least one widely used model does not anticipate that a highly variable process like ion sputtering (brought about by ion precipitation) could be a dominant source process for Mercury's more slowly varying exosphere (Killen et al., 2022), and that other processes like photon‐stimulated desorption (Cassidy et al., 2015) and micrometeoroid impacts (Cassidy et al., 2021; Jasinski et al., 2020) dominate. Notwithstanding that conclusion, recent analysis has also successfully shown that the cusp ion precipitation rate is well‐correlated with significant variability in the density of singly ionized sodium in Mercury's near space environment (Sun et al., 2022).…”

Solar-wind electron precipitation on weakly magnetized bodies: the planet Mercury

“…2b. This result support the common assumption of negligible EII for the Na exosphere [16,35]. Nevertheless, compared to photoionization, EII should not be considered a secondary process for the H, He, O and Mn exosphere.…”

Three-dimensional Global Hybrid Simulations of Flux Transfer Event Showers at Mercury

“…Flux transfer events (FTEs), a series of distinct bipolar perturbations in the magnetic field component normal to the planetary magnetopause, topologically connect the interplanetary and planetary magnetic fields in the magnetopause (Russell & Elphic 1978), and provide a channel for mass and energy from the solar wind to the planetary magnetosphere (Lockwood & Moen 1999;Paschmann et al 1982;Hasegawa et al 2006;Kuznetsova et al 2009;Tan et al 2011;Dong et al 2017;Sun et al 2022). It is generally believed that FTEs are essentially magnetic flux ropes formed in multiple X-line reconnection occurring in the magnetopause current sheet (Lee & Fu 1985;Zhong et al 2013;Fuselier et al 2018;Guo et al 2020).…”

“…During a typical FTE shower, each FTE has the duration of about 1-2 s, and the separation between two neighboring FTE centers is about 5-6 s (Sun et al 2020). An FTE shower can occur at the low-latitude dayside magnetopause when the IMF has a southward component, as well as at the high-latitude nightside magnetopause when the IMF has a northward component (Sun et al 2020;Zhong et al 2020;Sun et al 2022). Therefore, the properties of FTEs in Mercury's magnetopause are much different from those at Earth, where the duration of FTE ranges from about 1-2 minutes and the separation is about 8 minutes (Rijnbeek et al 1984).…”