Tribocharged solids in protoplanetary discs: internal and external discharge time-scales

Abstract

Particles regularly tribocharge in collisions. Here, we study how long charges can persist on such particles in the environment of a protoplanetary disk. We did set up three complementary experiments to quantify discharge timescales. We first directly measure the time dependency of charge on triboelectrically charged objects. For this aspect we performed two long time experiments under different environmental conditions. We find that charge persists on the tribocharged bodies on timescales between minutes to years. Discharge might be mediated by external ions or internally, by conduction. To constrain the latter, we also determined the specific electric resistance of dust samples as simulants for dust aggregates in protoplanetary disks. In this third experiment, we see an increase in resistivity at decreasing ambient pressure up to the limit of the instrument. These findings are consistent with the assumption that water on all relevant surfaces including dust grains within the pore space of aggregates is the main driver of discharge. Under disk conditions charge might persist for weeks to years. This leaves net charged isolated grains in dense parts of the midplane of protoplanetary disks charged in between collisions.