Complicated and Strongly Variable Subsolar Magnetosphere of Mars

Dayside magnetosphere of Mars is a thin layer between the magnetosheath and the ionosphere. The Mars Atmosphere and Volatile Evolution Mission (MAVEN) spacecraft provided, for the first time, high temporal and spatial resolution measurements enabling to study the structure of the dayside magnetosphere.

Analysis of Maven measurements at SZA ~ 70o of Mars showed that the structure and properties of the dayside magnetosphere strongly depend on the location in MSE coordinate system. At "high magnetic latitudes" (small angle relative to direction of the motional electric field vector -1/c Vsw x B where Vsw is the solar wind velocity vector) the energy of magnetospheric heavy ions is usually ~ 10-100 eV. Plume plasma often dominates in magnetosphere. Magnetic barrier is strong and spans through internal magnetosheath and magnetosphere. At "equatorial latitudes", where motional electric field is nearly horizontal, the main features are irregular structure of magnetic field in barrier and in magnetosphere, magnetospheric plasma is not steady and often consists of decreasing energy structures. At "low magnetic latitudes" where motional electric field is directed Mars-ward the magnetic barrier is weak and magnetospheric plasma has smooth structure and energy ~ 10-20 eV.

The model and observations of dayside magnetosphere suggest that it forms from narrow slab of incoming magnetic flux tubes at subsolar region and move along the planet to the terminator continue to pick-up heavy planetary ions. This is in agreement with observation of the heavy ions flow at the flank of the magnetosphere moving parallel to magnetosphere boundary that is marked by the current layer and by the change of ion composition.

Observations of the subsolar part of magnetosphere show very strong variability of the plasma and magnetic properties. There are several properties of the magnetosphere near subsolar point very different from what is observed at the magnetospheric flank. There are quite a few cases when the magnetosphere almost disappeared or is quite thin and filed by heated ionospheric layer. In many cases magnetospheric population has properties suggesting that ionosphere is the main supply of magnetosphere. Sometime the hot and dense ionospheric "islands" are observed outside apparent magnetopause suggesting separated ionospheric bubbles or waves on the ionopause surface. Description and comparison of two regions of magnetosphere is given.