Magnetic fields and plasmas in the inner heliosphere: Helios results

Abstract

The magnetic ÿeld of Mercury and the structure and dynamics of Mercury's magnetosphere, which will be studied by the spacecraft orbiting Mercury, are strongly in uenced by the interaction of the solar wind with Mercury. In order to understand the internal magnetic ÿeld, it will be necessary to correct the observations of the external ÿeld for the distortions produced by the solar wind. Understanding of the solar wind interaction with Mercury is essential for understanding the structure and dynamics of the magnetosphere and phenomena such as magnetic storms. Helios 1 and 2 made a number of passes in the region traversed by the orbit of Mercury, and each pass provided a sample of the solar wind environment of Mercury. This paper reviews the plasma and magnetic ÿeld observations from Helios that provide a general basis for interpreting the observations of Mercury that will be made by orbiting spacecraft. The variables that govern the structure and dynamics of the magnetospheres of Mercury and Earth are approximately 5 -10 times larger at Mercury than at Earth. Thus, the solar wind interaction with Mercury will be much stronger than the interaction with Earth. Moreover, the solar wind at Mercury is probably more variable than that at Earth. There is a clear need for measurements of the solar wind during the approach of spacecraft to Mercury and while they are in orbit around Mercury.

Plasma Sources in Planetary Magnetospheres: Mercury

“…Mercury's orbit than at any other planet of the solar system [Burlaga, 2001] Proton temperature was much lower than the average at Earth, 2 MK versus 30-56 201 MK, respectively. Plasma beta, the ratio of magnetic to plasma pressure, was also 202 found to be lower and more steady at ~2 in Mercury's central plasma sheet.…”

Plasma Sources in Planetary Magnetospheres: Mercury

“…Mercury's orbit than at any other planet of the solar system [Burlaga, 2001] with those at Earth (0.2-0.5 cm -3 ) during similarly quiet magnetospheric conditions. 200…”

A modelling approach to infer the solar wind dynamic pressure from magnetic field observations inside Mercury’s magnetosphere

“…a few seconds flux transfer events (Slavin et al 2012b) and plasmoids (Slavin et al 2012a;DiBraccio et al 2015)) indicate that the magnetosphere of Mercury is highly dynamic, sensitive, and responsive to the solar wind plasma and IMF variations, much more than any other magnetized planet in the solar system (Burlaga 2001;Slavin et al 2008Slavin et al , 2009). Solar wind variations contribute considerably to altering the structure of Mercury's magnetosphere (e.g.…”