Experimental Measurements of Electric and Magnetic Fields in Simulated Dust Storms.

Mars is the only planet in our solar system with an atmosphere for which there have been no observations of lightning. Despite this, it is expected to occur, with the planet known to have dust devils, which due to triboelectrification become charged. Terrestrially, dust storms generate electric fields of around 100 kV/m and there have been recordings of magnetic fields in the region of 0.4 nT. On Earth, the electric fields are not sufficient to cause breakdown. If dust devils generate similar fields on Mars, the field strength will exceed the breakdown field strength of approximately 20 kV/m, thus discharges can be expected – although these may not take the form of terrestrial discharges. The Kazachok surface platform of ExoMars 2022 will deliver the MAIGRET instrument (consisting of a search coil magnetometer, electric field antenna, and a flux gate magnetometer), which will put the capability to measure electric and magnetic fields onto Mars. To better understand the dust devils on Mars, and to aid with the interpretation of returned data from ExoMars, a series of experiments are planned to investigate the magnetic fields from charged dust.

In 2003 Krauss et al performed experiments to determine the necessary conditions for sufficient tribocharging to cause breakdown in a Mars-like atmosphere by first mixing dust to simulate wind speed, and then by dropping dust vertically at a range of pressures. Based upon Krauss’s work, two experiments will be performed with an electric field mill (CS110) and the engineering model of the MAIGRET search coil and thus two hypotheses will be tested. These are, firstly, that the vertical separation of charge is responsible for the electric field, and, secondly, that the spiralling motion of the charged particles is responsible for the magnetic field. The planned vertical drop and horizontal mixing experiments isolate these components of motion, allowing the predictions to be tested.