Measurements of a.c. magnetic fields and currents in the Hermean magnetosphere

Due to the lack of a dense resistive ionosphere and to the slow rate of planetary rotation, the plasma trapped inside the Hermean magnetosphere is unlikely to corotate. Therefore unlike other magnetized planets, a large convection electric field should prevail close to Mercury. In the absence of collisions, even at low altitudes, kinetic processes such as wave-particle interactions are likely to play a very important role. Some of these processes are discussed in a companion paper by Blomberg (Planet. Space Sci., 45, 143–148, 1997). Here, the ULF part of the spectrum is focused on. The magnetosphere of Mercury evolves over very short times and small spatial scales. Therefore small-scale fluctuating currents involving Alfvén waves are expected to develop and to exert a control on the magnetospheric dynamics. In view of this, it is important to be able to measure a.c. magnetic fields and possibly a.c. currents. Technical solutions to carry out these measurements will also be briefly described.