  When mobilized, granular materials become charged as grains undergo
collisions and frictional interactions. On Earth, this process, known as
triboelectrification, has been recognized in volcanic plumes and sandstorms.
Yet, frictional charging almost certainly exists on other worlds, both in our
own Solar System (such as Mars, the Moon, and Venus) and exosolar planets.
Indeed, observations suggest that numerous planets in the galaxy are enshrouded
by optically-thick clouds or hazes. Triboelectric charging within these clouds
may contribute to global electric circuits of these worlds, providing
mechanisms to generate lightning, drive chemical processes in the atmospheres,
and, perhaps, influence habitability. In this work, we explore the frictional
electrification of potassium chloride and zinc sulfide, two substances proposed
to make up the clouds of giant exo-planets with >50x solar metallicities,
including the widely-studied super-Earth GJ 1214b, super-earth HD 97658b,
Neptune-sized GJ 436b, and hot- Jupiter WASP-31b. We find that both materials
become readily electrified when mobilized, attaining charge densities similar
to those found on volcanic ash particles. Thus, if these worlds do indeed host
collections of mineral particles in their atmospheres, these clouds are likely
electrified and may be capable of producing lightning or corona discharge.
