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

Despite no direct observations of lightning on Mars, it is expected to occur. The planet is known to have large dust storms - which are believed to generate electric and magnetic fields. Magnetic fields are also expected in dust storms on Earth, though measurements are extremely limited. Understanding of electric and magnetic fields of this prevalent feature of the Martian landscape is vital to understanding and developing missions of Mars.

Two hypotheses were postulated. Firstly, 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. An experimental apparatus was designed to isolate the vertical and horizontal components of the motion in a dust storm in the lab with Martian analogue material by dropping or rotating the particulates respectively. In this rig electric fields are measured using a field mill (CS110) and magnetic fields with a search coil magnetometer (LEMI 133, the engineering model from the postponed ExoMars22 mission). The rig is carefully screened from background electrical and magnetic fields.

The equipment is currently being commissioned, and in the vertical separation mode, particulates such as polystyrene and glass beads were dropped onto a Faraday cup. By determination of the capacitance of the tank, the voltage signal can be converted into charge. In addition to this, the signals from the Faraday cup and field mill can be visualised across the time profile of a given drop. In the horizontal motion mode, the particulate is mixed with a paddle, akin to an ice-cream machine, to entrain the dust in a vortex. Results from these lab-based experiments are presented here.