  At the inner edge of a protoplanetary disk solids are illuminated by stellar
light. This illumination heats the solids and creates temperature gradients
along their surfaces. Interactions with ambient gas molecules lead to a radial
net gas flow. Every illuminated solid particle within the edge is an individual
small gas pump transporting gas inward. In total the inner edge can provide
local mass flow rates as high as $\dot{M} = 10^{-5} M_{\odot}$ yr$^{-1}$.
