Electrodynamic currents in near-Mars space

Abstract

The interaction between the solar wind and Mars gives rise to interesting plasma processes in the vicinity of the planet. Since Mars does not possess an internal dynamo field like Earth, the solar wind and its magnetic field are encountering its ionosphere directly, depositing energy in it and creating an induced magnetosphere. While the interplanetary magnetic field (IMF) flows through the conductive ionosphere, currents are generated in order to deflect the IMF. These currents, reaching into the lower parts of the ionosphere, can drive ions to high altitudes, where they can be swiped away by the solar wind, contributing to the significant atmospheric losses the planet has gone through over the course of its lifetime. In this work we estimate, characterise these induced currents, and the influence Mars’s remnant crustal magnetism and the solar wind activity have on them.

We use magnetic field measurements around Mars, provided by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft over a long time period in a coordinate system defined by the solar wind velocity and magnetic field directions. Average maps of the magnetic field are created in a spherical grid and the current densities are calculated by applying the finite differences approximation of Ampere’s law. We also examine how the currents change if we exclude Mars’s south pole, which contains most of its crustal magnetic fields, and how the currents are affected by different solar wind dynamic pressure conditions.

Our results suggest current structures that are established at the boundaries of the induced magnetosphere and then close in the ionosphere, with significant asymmetries between northern-southern hemisphere, as well as the magnetic dawn and dusk regions. In the case without crustal magnetization the IMF reaches deeper in the ionosphere, interacting with denser parts of it. Our results for different solar wind dynamic pressures show the contraction of the induced magnetosphere when the solar wind is more energetic and stronger currents flowing closer to the planet, potentially contributing to the large scale transport of ions to the outer induced magnetosphere of Mars.

Results

• Final report

Example result: magnetic field (a) and current density vector components for low solar wind dynamic pressure (max 0.72 nPa) at 594 km.