SOLAR-WIND ELECTRONS AS TRACERS OF THE MARTIAN MAGNETOTAIL TOPOLOGY

Simultaneous measurements of electrons and magnetic field ate used to study the topology of the Martian magnetosphere. Halo solar wind elect rons streaming along magnetic field lines replicate variations of the B-x component, thus tracing the interplanetary magnetic field draping in most parts of the Martian tail. This suggests that the magnetic fie ld observed near the equatorial plane of Mars is mainly induced. Howev er, there are regions where this perfect tracing is violated. This cou ld be considered as evidence for an intrinsic planetary field. An alte rnative interpretation involves the relationship between these regions and ionospheric holes.