Analysis of dayside magnetosphere of Mars: High mass loading case as observed on MAVEN spacecraft

MAVEN spacecraft provides new opportunities for analysis of Martian environment and physical process in near-Mars space. One of interesting regions of near-Mars space is the Martian magnetosphere that is formed from mass-loaded magnetic flux tubes. There is quite detailed knowledge of the night-side magnetosphere of Mars, however the number of publications on the dayside magnetosphere are quite limited. We analyze the plasma and magnetic structure and properties of Martian magnetosphere at strong mass-loading conditions as observed on MAVEN at Mars at the solar-zenith angle of ∼80° on January 4, 2015. This strong mass loading of upstream flow was apparently associated with plume ions ejected from upper part of Martian magnetosphere by the solar wind motional electric field. The magnetosphere is defined by two current layers separating it from the magnetosheath at higher altitudes and from ionosphere plasma at lower altitudes. It is characterized by dominance of planetary ions which number density increases by two orders of magnitude from upper boundary to lower one. There is approximate equipartition between magnetic, ion thermal and kinetic energies through magnetosphere. The data suggest that the boundary of the magnetosphere is in pressure equilibrium with magnetosheath flow. The total energy of ion flow above (in the magnetosheath) and below (in the region of accelerated ionospheric ions) magnetosphere exceeds the magnetic energy. The upper boundary of magnetosphere was located at the place where the ratio of heavy ions and protons number densities reached ∼0.4. Within magnetosphere this ratio continued to rise and increased by about 2 orders of magnitude at the inner boundary of magnetosphere. The heavy ion number density profile within magnetosphere suggests that it was formed by the solar wind magnetic flux tubes that reached Mars in a narrow region near the subsolar point, and then drifted around Mars to the terminator region, mass-loaded by UV-ionized upper atmosphere neutrals during this drift.