Transport of Mass and Energy in Mercury's Plasma Sheet

Poh, Gangkai; Slavin, J. A.; Jia, Xianzhe; Sun, W.; Raines, J. M.; Imber, Suzanne M.; DiBraccio, G. A.; Gershman, D. J.

doi:10.1029/2018gl080601

Cited by 14 publications

(22 citation statements)

References 54 publications

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“…For Mercury, if one considered a proton density of ∼3 cm −3 (Gershman et al, ; Poh et al, ; Sun et al, ), and the relatively thin current sheet width in Mercury's tail near midnight is ∼2 R M where 1 R M ∼2,440 km (Poh et al, ; Rong et al, ; Sun et al, ), then the global dawn‐dusk extent is ∼37 d i , comparable to our 31 d i case studied here. While for Earth, the proton density in the plasma sheet is around an order of magnitude smaller than that at Mercury (Baumjohann et al, ; Huang & Frank, ; Sun et al, ), and the width of the relatively thin current sheet near midnight is ∼20 R E (Nakai et al, ; Zhang et al, ), corresponding to ∼300 d i .…”

Section: Summary and Discussion On The Dawn‐dusk Asymmetrysupporting

confidence: 72%

Three‐Dimensional Magnetic Reconnection With a Spatially Confined X‐Line Extent: Implications for Dipolarizing Flux Bundles and the Dawn‐Dusk Asymmetry

Liu

Hesse

et al. 2019

JGR Space Physics

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Using 3-D particle-in-cell simulations, we study magnetic reconnection with the X-line being spatially confined in the current direction. We include thick current layers to prevent reconnection at two ends of a thin current sheet that has a thickness on an ion inertial (d i ) scale. The reconnection rate and outflow speed drop significantly when the extent of the thin current sheet in the current direction is ≲ O(10d i ). When the thin current sheet extent is long enough, we find that it consists of two distinct regions; a suppressed reconnecting region (on the ion-drifting side) exists adjacent to the active region where reconnection proceeds normally as in a 2-D case with a typical fast rate value ≃ 0.1. The extent of this suppression region is ≃ O(10d i ), and it suppresses reconnection when the thin current sheet extent is comparable or shorter. The time scale of current sheet thinning toward fast reconnection can be translated into the spatial scale of this suppression region, because electron drifts inside the ion diffusion region transport the reconnected magnetic flux, which drives outflows and furthers the current sheet thinning, away from this region. This is a consequence of the Hall effect in 3-D. While the existence of this suppression region may explain the shortest possible azimuthal extent of dipolarizing flux bundles at Earth, it may also explain the dawn-dusk asymmetry observed at the magnetotail of Mercury, which has a global dawn-dusk extent much shorter than that of Earth.

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Section: Summary and Discussion On The Dawn‐dusk Asymmetrysupporting

confidence: 72%

Three‐Dimensional Magnetic Reconnection With a Spatially Confined X‐Line Extent: Implications for Dipolarizing Flux Bundles and the Dawn‐Dusk Asymmetry

Liu

Hesse

et al. 2019

JGR Space Physics

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“…Proton density and pressure shown in Figure 2 were derived from 1 min average distributions of protons under the assumption that they are isotropic and stationary Maxwellian distributions (Gershman et al, 2013;Raines et al, 2011Raines et al, , 2013. The proton moments derived from this method were applied in several studies on the plasma sheet dynamics (Gershman et al, 2014;Poh et al, 2018;Raines et al, 2011;Sun et al, 2017Sun et al, , 2018. The proton density distribution (Figure 2, left) shows clear dawn-dusk asymmetry with proton densities higher on the dawnside (∼6 to 8 amu/cc) than on the duskside (∼2 to 4 amu/cc).…”

Section: Proton Propertiesmentioning

confidence: 99%

Studying Dawn‐Dusk Asymmetries of Mercury's Magnetotail Using MHD‐EPIC Simulations

et al. 2019

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MESSENGER has observed a lot of dawn-dusk asymmetries in Mercury's magnetotail, such as the asymmetries of the cross-tail current sheet thickness and the occurrence of flux ropes, dipolarization events, and energetic electron injections. In order to obtain a global pictures of Mercury's magnetotail dynamics and the relationship between these asymmetries, we perform global simulations with the magnetohydrodynamics with embedded particle-in-cell (MHD-EPIC) model, where Mercury's magnetotail region is covered by a PIC code. Our simulations show that the dawnside current sheet is thicker, the plasma density is larger, and the electron pressure is higher than the duskside. Under a strong interplanetary magnetic field driver, the simulated reconnection sites prefer the dawnside. We also found the dipolarization events and the planetward electron jets are moving dawnward while they are moving toward the planet, so that almost all dipolarization events and high-speed plasma flows concentrate in the dawn sector. The simulation results are consistent with MESSENGER observations.

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“…In Mercury's plasma sheet, the loss cone of protons (

α < \arcsin \sqrt{\frac{B_{m a x}}{B_{e q}}}

) ranges from 0° to 20° (Poh et al, 2018). Protons within the loss cone would impact the planetary surface and being absorbed (hereinafter referred to as surface precipitation).…”

Section: Introductionmentioning

confidence: 99%

Proton Properties in Mercury's Magnetotail: A Statistical Study

Zhao

Zong

Slavin

et al. 2020

Geophysical Research Letters

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This study investigates the properties of protons in the magnetotail plasma sheet of Mercury. By superposing 5-year measurements from the MESSENGER spacecraft, we obtain the average energy spectrum of protons in the plasma sheet, which can be fitted nicely by the Gaussian-Kappa model. The proton density, pressure, and energy spectral index are found to be higher on the dawnside than on the duskside. The proton temperature shows a clearly outward radial gradient. The field-aligned density profile indicates that the protons in the outer plasma sheet move adiabatically. The pitch angle distribution reveals the reflected fluxes to be always less than the incident fluxes and indicates the loss of protons due to their impact on the planetary surface. Plain Language Summary Mercury has a miniature magnetosphere subject to intense solar wind forcing. This magnetosphere, among the smallest in the solar system, resembles the Earth's in many key respects. It is also an analog for other small and outside-driven magnetospheres, such as Ganymede's inside Jupiter's magnetosphere. Mercury does not have a significant atmosphere but a tenuous exosphere. Therefore, Mercury's magnetospheric ions are thought to come predominately from the solar wind, and only about 10% of the ions are of planetary origin. This study presents a statistical picture of the protons in Mercury's magnetotail plasma sheet measured by the Fast Imaging Plasma Spectrometer (FIPS) onboard MESSENGER spacecraft. Many parameters are obtained through a best fit procedure with a Gaussian-Kappa distribution. The proton number density, proton pressure, and spectral index show clear dawn-dusk asymmetric features. The results also suggest that the motion of the protons is adiabatic in the outer plasma sheet and non-adiabatic in the central plasma sheet. Furthermore, the loss feature of the protons is also revealed by their asymmetric pitch angle distributions.

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Transport of Mass and Energy in Mercury's Plasma Sheet

Cited by 14 publications

References 54 publications

Three‐Dimensional Magnetic Reconnection With a Spatially Confined X‐Line Extent: Implications for Dipolarizing Flux Bundles and the Dawn‐Dusk Asymmetry

Three‐Dimensional Magnetic Reconnection With a Spatially Confined X‐Line Extent: Implications for Dipolarizing Flux Bundles and the Dawn‐Dusk Asymmetry

Studying Dawn‐Dusk Asymmetries of Mercury's Magnetotail Using MHD‐EPIC Simulations

Proton Properties in Mercury's Magnetotail: A Statistical Study

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