Ionizing atmospheres in collisions of grains

The ionization of atmospheres is important for a number of physical and chemical processes from earth to other planets to protoplanetary disks. As many atmospheres are particle ladden at times with frequent collisions, we study the microphysics of particle collisions on ionization. It is well known that due to tribocharging particles carry charges after a collision. However, this charge transfer is not restricted to the grain surfaces. Somewhat less obvious, the gas phase also becomes ionized along.

 

In laboratory experiments, we quantify the amount of ions produced in a collision of glass beads with 2.8 mm diameter. We extract the ions by applying an external electrostatic field and measuring the generated current. The ions are detected at all the pressures studied, i.e. from 0.3 mbar to 100 mbar. However, the ionization rate peaks at about 1 mbar. Scaled to individual bouncing collisions, charge as high as 1 pC of each polarity was detected (Hock et al. 2025). This implies collisions of grains can be a significant source of ions in various atmospheres. In view of these results, this process might be a significant source of ionization in certain parts of atmospheres.