Event Title

An Overview of Mercury’s Plasma and Magnetic Field Environment

Location

Yosemite National Park

Start Date

2-13-2014 9:10 AM

End Date

2-13-2014 9:40 AM

Description

MESSEGNER plasma and magnetic field measurements in Mercury’s magnetosphere are reviewed and comparisons are drawn with Earth. The magnetosphere created by the solar wind interaction with Mercury’s dipolar spin-axis aligned magnetic field resembles that of Earth in many respects. The magnetic field intensities and plasma densities and temperatures are all higher at Mercury due to the increased solar wind pressures in the inner solar system. Magnetospheric plasma at Mercury appears to be primarily of solar wind origin, but with 10% Na+ due to solar EUV ionization of exospheric Na. The low plasma β (i.e., ratio of plasma thermal to magnetic pressure) magnetosheath at Mercury results in strong plasma depletion layers adjacent to the magnetopause. In this environment magnetopause reconnection does not exhibit the “half-wave rectifier” response to interplanetary magnetic direction (i.e. low latitude reconnection is only observed at large magnetic shear angles) found at Earth. The comparable magnetic field intensities on the two sides of the magnetopause current layer support reconnection for all non-zero shear angles with plasma β as the primary parameter controlling the rate. Flux transfer events (FTEs) are observed at most magnetopause crossings, often in “showers” with FTEs being encountered every ~ 10 s for several minutes. Unlike at Earth where FTEs account for only order 1% of the magnetic flux driving the Dungey cycle, the contribution of FTEs at Mercury appears nearly comparable to that of steady magnetopause reconnection at a single X-line. Mercury’s magnetotail sometimes displays similar loading/unloading to that observed at Earth during isolated substorms. The primary difference is that the Dungey cycle-time at Mercury is ~ 2 – 3 min as compared to ~ 1 hr at Earth. Mercury’s magnetosphere can also exhibit Earth-like steady magnetospheric convection with quasi-periodic plasmoid ejection down the tail and dipolarizations closer to the planet. Mercury’s highly resistive crust inhibits strong, long duration coupling via field aligned currents, but its large, highly conducting iron core supports strong “inductive” coupling. The currents induced in the outermost layers of the core by increased solar wind pressure, such as during coronal mass ejections and high-speed streams, are observed to decrease the compressibility of Mercury’s dayside magnetosphere. The effects of this inductive magnetosphere – core coupling on other aspects of magnetospheric dynamics at Mercury remain to be determined.

Streaming Media

This document is currently not available here.

Share

COinS
 
Feb 13th, 9:10 AM Feb 13th, 9:40 AM

An Overview of Mercury’s Plasma and Magnetic Field Environment

Yosemite National Park

MESSEGNER plasma and magnetic field measurements in Mercury’s magnetosphere are reviewed and comparisons are drawn with Earth. The magnetosphere created by the solar wind interaction with Mercury’s dipolar spin-axis aligned magnetic field resembles that of Earth in many respects. The magnetic field intensities and plasma densities and temperatures are all higher at Mercury due to the increased solar wind pressures in the inner solar system. Magnetospheric plasma at Mercury appears to be primarily of solar wind origin, but with 10% Na+ due to solar EUV ionization of exospheric Na. The low plasma β (i.e., ratio of plasma thermal to magnetic pressure) magnetosheath at Mercury results in strong plasma depletion layers adjacent to the magnetopause. In this environment magnetopause reconnection does not exhibit the “half-wave rectifier” response to interplanetary magnetic direction (i.e. low latitude reconnection is only observed at large magnetic shear angles) found at Earth. The comparable magnetic field intensities on the two sides of the magnetopause current layer support reconnection for all non-zero shear angles with plasma β as the primary parameter controlling the rate. Flux transfer events (FTEs) are observed at most magnetopause crossings, often in “showers” with FTEs being encountered every ~ 10 s for several minutes. Unlike at Earth where FTEs account for only order 1% of the magnetic flux driving the Dungey cycle, the contribution of FTEs at Mercury appears nearly comparable to that of steady magnetopause reconnection at a single X-line. Mercury’s magnetotail sometimes displays similar loading/unloading to that observed at Earth during isolated substorms. The primary difference is that the Dungey cycle-time at Mercury is ~ 2 – 3 min as compared to ~ 1 hr at Earth. Mercury’s magnetosphere can also exhibit Earth-like steady magnetospheric convection with quasi-periodic plasmoid ejection down the tail and dipolarizations closer to the planet. Mercury’s highly resistive crust inhibits strong, long duration coupling via field aligned currents, but its large, highly conducting iron core supports strong “inductive” coupling. The currents induced in the outermost layers of the core by increased solar wind pressure, such as during coronal mass ejections and high-speed streams, are observed to decrease the compressibility of Mercury’s dayside magnetosphere. The effects of this inductive magnetosphere – core coupling on other aspects of magnetospheric dynamics at Mercury remain to be determined.