Gas Phase Ions in Protoplanetary Disks from Collisions of Solids

Ionization is important for magnetohydrodynamics and chemistry in protoplanetary disks but known ionization sources are often weak along the midplane. We present, for the first time, data from a laboratory experiment, where we measure ions from colliding mm-basalt grains emitted into the surrounding gas phase. This positive detection implies that very basic collisions in early phases of planet formation are sources of ionization. The midplane of protoplanetary disks might be ionized despite the lack of intense radiation sources.